The ALICE collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity $|y|<0.8$ and transverse momentum $1<p_{\mathrm{T}}<10$ GeV/$c$, in pp collisions at $\sqrt{s} = $ 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD calculations agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, $\sigma_{\mathrm{b} \rightarrow \mathrm{e}} = 3.47\pm0.40(\mathrm{stat})^{+1.12}_{-1.33}(\mathrm{sys})\pm0.07(\mathrm{norm}) \mu$b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) predictions to obtain the total b$\bar{\mathrm{b}}$ production cross section, $\sigma_{\mathrm{b\bar{b}}} = 130\pm15.1(\mathrm{stat})^{+42.1}_{-49.8}(\mathrm{sys})^{+3.4}_{-3.1}(\mathrm{extr})\pm2.5(\mathrm{norm})\pm4.4(\mathrm{BR}) \mu$b.
Azimuthal correlation distribution between heavy-flavour decay electrons and charged hadrons, scaled by the number of electrons in minimum bias triggered events in the electron transverse momentum range 1.5-2.5 GeV/$c$.
Azimuthal correlation distribution between heavy-flavour decay electrons and charged hadrons, scaled by the number of electrons in minimum bias triggered events in the electron transverse momentum range 1.5-2.5 GeV/c.
Azimuthal correlation distribution between heavy-flavour decay electrons and charged hadrons, scaled by the number of electrons in EMCal triggered events in the electron transverse momentum range 4.5-6 GeV/$c$.
The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range $1 < p_{\rm T} < 8$ Gev/$c$ with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy $\sqrt{s} = 7$ TeV using an integrated luminosity of 2.2 nb$^{-1}$. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs.
Double differential cross section for charm and beauty electron production as a function of transverse momentum. The systematic error does not include the error on the Luminosity (3.5%).
Double differential cross section for charm and beauty electron production as a function of transverse momentum. The systematic error does not include the error on the Luminosity (3.5%).
Cross sections for the production of a Z boson in association with jets in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 8 TeV are measured using a data sample collected by the CMS experiment at the LHC corresponding to 19.6 inverse femtobarns. Differential cross sections are presented as functions of up to three observables that describe the jet kinematics and the jet activity. Correlations between the azimuthal directions and the rapidities of the jets and the Z boson are studied in detail. The predictions of a number of multileg generators with leading or next-to-leading order accuracy are compared with the measurements. The comparison shows the importance of including multi-parton contributions in the matrix elements and the improvement in the predictions when next-to-leading order terms are included.
The cross section for Z($\rightarrow\ell\ell$) + jets production measured as a function of the exclusive jet multiplicity, $N_{\text{jets}}$, and breakdown of the relative uncertainty.
Bin-to-bin correlation in the the cross section for Z($\rightarrow\ell\ell$) + jets production measured as a function of the exclusive jet multiplicity, $N_{\text{jets}}$.
The cross section for Z($\rightarrow\ell\ell$) + jets production measured as a function of the 1$^\text{st}$ jet $p_{\text{T}}$, $p_{\text{T}}(\text{j}_1)$, and breakdown of the relative uncertainty.
We report the first observations of the first harmonic (directed flow, v_1), and the fourth harmonic (v_4), in the azimuthal distribution of particles with respect to the reaction plane in Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Both measurements were done taking advantage of the large elliptic flow (v_2) generated at RHIC. From the correlation of v_2 with v_1 it is determined that v_2 is positive, or {\it in-plane}. The integrated v_4 is about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8) harmonics upper limits on the magnitudes are reported.
$v_1$ of charged particles as a function of pseudorapidity for 10-70% centrality. Non-flow systematic uncertainties are approximately 20%.
$v_2$ with respect to the second harmonic event plane as a function of $p_T$ for the minimum bias Au+Au collisions. Background from secondary particles is expected to be less than 15%. Non-flow systematic uncertainties are approximately 20%. Fluctuations in initial geometry can lead to an effect of about a factor of 1.2 to 1.5.
$v_4$ with respect to the second harmonic event plane as a function of $p_T$ for the minimum bias Au+Au collisions. Background from secondary particles is expected to be less than 15%. Non-flow systematic uncertainties are approximately 20%. Fluctuations in initial geometry can lead to an effect of about a factor of 1.2 to 1.5.
We report on the observed differences in production rates of strange and multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp interactions at the same energy. The strange baryon yields in Au+Au collisions, then scaled down by the number of participating nucleons, are enhanced relative to those measured in pp reactions. The enhancement observed increases with the strangeness content of the baryon, and increases for all strange baryons with collision centrality. The enhancement is qualitatively similar to that observed at lower collision energy sqrts =17.3 GeV. The previous observations are for the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange baryons even exceed binary scaling from pp yields.
Midrapidity E(i) as a function of $<N_{part}>$ for $\Lambda$, $\bar{\Lambda}$ ($|y| < 1.0$), $\Xi^{-}$, $\bar{\Xi}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature. Grand Canonical Model arrows(values in brackets), for $\Lambda$ E(2.6) and T(165 MeV) for $\bar{\Lambda}$ E(2.2) and T(170 MeV), for $\Xi$ E(10.7) and T(165 MeV), for anti-$\Xi$ E(7.5) and T(170 MeV).
Midrapidity E(i) as a function of $<N_{part}>$ for $\Omega^{-}+\bar{\Omega}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
Midrapidity E(i) as a function of $<N_{part}>$ for inclusive $p$ ($|y| < 0.5$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
The STAR Collaboration at RHIC presents a systematic study of high transverse momentum charged di-hadron correlations at small azimuthal pair separation \dphino, in d+Au and central Au+Au collisions at $\rts = 200$ GeV. Significant correlated yield for pairs with large longitudinal separation \deta is observed in central Au+Au, in contrast to d+Au collisions. The associated yield distribution in \detano$\times$\dphi can be decomposed into a narrow jet-like peak at small angular separation which has a similar shape to that found in d+Au collisions, and a component which is narrow in \dphi and \textcolor{black}{depends only weakly on} $\deta$, the 'ridge'. Using two systematically independent analyses, \textcolor{black}{finite ridge yield} is found to persist for trigger $\pt > 6$ \GeVc, indicating that it is correlated with jet production. The transverse momentum spectrum of hadrons comprising the ridge is found to be similar to that of bulk particle production in the measured range ($2 < \pt < 4 \GeVc$).
FIG. $2: \quad Y_{\text {slice }}(\Delta \eta ; \delta=0.3)$ (Eq. 5 ) for central Au+Au collisions, $2 \mathrm{GeV} / \mathrm{c}<p_{t}^{a s s o c}<p_{t}^{t r i g}$, and various $p_{t}^{t r i g}$ vs. $\Delta \eta$; the shaded bands represents the systematic uncertainties due to $v_{2}$ (not shown for $6<p_{t}^{\text {trig }}<10 \mathrm{GeV} / \mathrm{c}$ ). The solid and dashed lines represents a constant or linear fit to $1<|\Delta \eta|$ $<1.8$; only shown for $3<p_{t}^{t r i g}<4 \mathrm{GeV} / c$ (see text). Some data points are displaced horizontally for clarity.
FIG. 3. Left panel: width of Gaussian fit to jet-like peak for Eq. (6) $(\Delta \eta$ width, circles) and Eq. (7) $(\Delta \phi$ width, triangles) ; $ 2 \mathrm{GeV}/c<p_{t}^{\text{assoc}}<p_{t}^{\text {trig }}$, as a function of $p_{t}^{\text {trig }},$ for central $\mathrm{Au}+$ Au collisions (filled symbols) and $d+$ Au collisions (open symbols). Some data points are displaced horizontally for clarity. Right panel: the distributions of Eqs. (6) and (7) for $4<p_{t}^{\text {trig }}<5 \mathrm{GeV} / c$ and $2 \mathrm{GeV} / c<p_{t}^{\text {assoc }}<p_{t}^{\text {trig }}$.
FIG. 3. Left panel: width of Gaussian fit to jet-like peak for Eq. (6) $(\Delta \eta$ width, circles) and Eq. (7) $(\Delta \phi$ width, triangles) ; $ 2 \mathrm{GeV}/c<p_{t}^{\text{assoc}}<p_{t}^{\text {trig }}$, as a function of $p_{t}^{\text {trig }},$ for central $\mathrm{Au}+$ Au collisions (filled symbols) and $d+$ Au collisions (open symbols). Some data points are displaced horizontally for clarity. Right panel: the distributions of Eqs. (6) and (7) for $4<p_{t}^{\text {trig }}<5 \mathrm{GeV} / c$ and $2 \mathrm{GeV} / c<p_{t}^{\text {assoc }}<p_{t}^{\text {trig }}$.
The STAR collaboration at RHIC reports measurements of the inclusive yield of non-photonic electrons, which arise dominantly from semi-leptonic decays of heavy flavor mesons, over a broad range of transverse momenta ($1.2 < \pt < 10$ \gevc) in \pp, \dAu, and \AuAu collisions at \sqrtsNN = 200 GeV. The non-photonic electron yield exhibits unexpectedly large suppression in central \AuAu collisions at high \pt, suggesting substantial heavy quark energy loss at RHIC. The centrality and \pt dependences of the suppression provide constraints on theoretical models of suppression.
Non photonic electron yield in P+P collisions versus PT To obtain a differential cross-section in mb/(GeV2), multiply listed data by 30 Note that, in addition to the statistical and systematical errors, there is a normalization error on the value, given in the second column.
Non photonic electron yield in P+P collisions versus $p_{T}$. To obtain a differential cross-section in mb/(GeV$^2$), multiply listed data by 30.
Non photonic electron yield in minimum bias D+AU collisions versus PT To obtain a differential cross-section in mb/(GeV2), multiply listed data by 30 Note that, in addition to the statistical and systematical errors, there is a normalization error on the value, given in the second column.
We present results on the system size dependence of high transverse momentum di-hadron correlations at $\sqrt{s_{NN}}$ = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation ($\Delta\phi\sim0$, $\Delta\eta\sim0$) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
Di-hadron correlations in $\Delta\phi$ for small $|\Delta\eta|$ ($|\Delta\eta|<0.7$) and large ($0.7<|\Delta\eta|<1.7$), scaled to match small $|\Delta\eta|$ at large $\Delta\phi$.
Subtracted distributions for di-hadron correlations in $\Delta\phi$ for small $|\Delta\eta|$ ($|\Delta\eta|<0.7$) minus large ($0.7<|\Delta\eta|<1.7$), scaled to match small $|\Delta\eta|$ at large $\Delta\phi$.
Subtracted distributions for di-hadron correlations in $\Delta\eta$.
Forward-backward multiplicity correlation strengths have been measured for the first time with the STAR detector for Au+Au and $\textit{p+p}$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. Strong short and long range correlations are seen in central (0-10%) Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in 40-50% Au+Au collisions. The results are in agreement with predictions from the Dual Parton and Color Glass Condensate models.
FB Correlation strength for Au+Au at different centralities and p+p reactions as a function of $\Delta\eta$.
Backward-forward dispersion, $D_{bf}^{2}$ and forward-forward dispersion $D_{bf}^{2}$ for Au+Au 0-10% centrality and p+p reactions as a function of $\Delta\eta$.
We report the first three-particle coincidence measurement in pseudorapidity ($\Delta\eta$) between a high transverse momentum ($p_{\perp}$) trigger particle and two lower $p_{\perp}$ associated particles within azimuth $\mid$$\Delta\phi$$\mid$$<$0.7 in $\sqrt{{\it s}_{NN}}$ = 200 GeV $d$+Au and Au+Au collisions. Charge ordering properties are exploited to separate the jet-like component and the ridge (long-range $\Delta\eta$ correlation). The results indicate that the particles from the ridge are uncorrelated in $\Delta\eta$ not only with the trigger particle but also between themselves event-by-event. In addition, the production of the ridge appears to be uncorrelated to the presence of the narrow jet-like component.
Correlated hadron distribution in ∆φ(|η|<1 with a high-p⊥trigger particle in 0-12% Au+Au collisions for 3<p(t)⊥<10 GeV/cand 1<p(a)⊥<3GeV/c. The ZYA1-normalized flow background is shown by the curve.
Correlated hadron distribution ∆η(|∆φ|<0.7) with a high-p⊥ trigger particle in 0-12% Au+Au collisions for 3<p(t)⊥<10 GeV/c and 1<p(a)⊥<3GeV/c. The ∆η distributions are background subtracted and corrected for ∆η acceptance and are for like and unlike-sign pairs separately. The curves in are Gaussian fits. Errors are statistical.
Background-subtracted charge-independent (AAT ) correlated hadron pair density in minimum bias d+Au collisions for 3<p(t)⊥<10 GeV/cand 1<p(a)⊥<3 GeV/c. The results are for near-side correlated hadrons within |∆φ1,2|<0.7, and corrected for the 3-particle ∆η-∆η acceptance. Statistical errors at (∆η1,∆η2)∼(0,0)are approximately 0.033 for d+Au respectively.
We report charged-particle pair correlation analyses in the space of Delta -phi (azimuth) and Delta -eta (pseudo-rapidity), for central Au + Au collisions at sqrt{s_{NN}} = 200 GeV in the STAR detector. The analysis involves unlike-sign charge pairs and like-sign charge pairs, which are transformed into charge-dependent (CD) signals and charge-independent (CI) signals. We present detailed parameterizations of the data. A model featuring dense gluonic hot spots as first proposed by van Hove predicts that the observables under investigation would have sensitivity to such a substructure should it occur, and the model also motivates selection of transverse momenta in the range 0.8 < p_t < 2.0$ GeV/c. Both CD and CI correlations of high statistical significance are observed and possible interpretations are discussed.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 1: a) left side: The $\Delta\phi$ - $\Delta\eta$ correlation data for unlike-sign charge particle pairs from the Star central trigger dataset shown in a 2-dimensional (2-D) perspective plot. The particle tracks have 0.8 GeV/c < $p_t$ < 2.0 GeV/c and |$\eta$| < 1.0. The structure that looks like tiles on a roof is due to the readout boundary effects of the 12 sector TPC. b) right side: The similar correlation data for like-sign charge particle pairs is shown.
FIG. 2: a) left side: The correlation data for the ratio of the histograms of same-event-pairs to mixed-event-pairs for unlike-sign charged pairs, shown in a two-dimensional (2-D) perspective plot $\Delta\phi$ - $\Delta\eta$. The plot was normalized to a mean of 1. b) right side: The similar correlation data for like-sign charge pairs.
Identified charged particle spectra of $\pi^{\pm}$, $K^{\pm}$, $p$ and $\pbar$ at mid-rapidity ($|y|<0.1$) measured by the $\dedx$ method in the STAR-TPC are reported for $pp$ and d+Au collisions at $\snn = 200$ GeV and for Au+Au collisions at 62.4 GeV, 130 GeV, and 200 GeV. ... [Shortened for arXiv list. Full abstract in manuscript.]
Uncorrected charged particle multiplicity distribution measured in the TPC in $|\eta| < 0.5$ for Au+Au collisions at 62.4 GeV and 200 GeV. The shaded regions indicate the centrality bins used in the analysis. The 200 GeV data are scaled by a factor 5 for clarity.
Uncorrected charged particle multiplicity distribution measured in the TPC in $|\eta| < 0.5$ for Au+Au collisions at 62.4 GeV and 200 GeV. The shaded regions indicate the centrality bins used in the analysis. The 200 GeV data are scaled by a factor 5 for clarity.
Uncorrected charged particle multiplicity distribution measured in the E-FTPC (Au-direction) within $−3.8 < |\eta| < −2.8$ in d+Au collisions at 200 GeV. The shaded regions indicate the centrality bins used in the analysis.
We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.
(a) Inclusive differential cross section for p+p -> jet +X at sqrt(s) = 200 GeV versus jet pT for a jet cone radius of 0.4. The symbols show MB (open squares) and HT (filled circles) data from the years 2003 and 2004 combined. The horizontal bars indicate the ranges of the pT intervals. The curve shows a NLO calculation. (b) Comparison of theory and data. The band indicates the experimental systematic uncertainty. The upper (lower) dashed line indicates the relative change of the NLO calculation when it is evaluated at &mu = pT/2 (&mu = 2pT).
(a) Inclusive differential cross section for p+p -> jet +X at sqrt(s) = 200 GeV versus jet pT for a jet cone radius of 0.4. The symbols show MB (open squares) and HT (filled circles) data from the years 2003 and 2004 combined. The horizontal bars indicate the ranges of the pT intervals. The curve shows a NLO calculation. (b) Comparison of theory and data. The band indicates the experimental systematic uncertainty. The upper (lower) dashed line indicates the relative change of the NLO calculation when it is evaluated at &mu = pT/2 (&mu = 2pT).
The longitudinal double-spin asymmetry ALL in p+p-> jet +X at sqrt(s) = 200 GeV versus jet pT. The uncertainties on the data points are statistical. The gray band indicates the systematic uncertainty from the beam polarization measurement, and the hatched band the total systematic uncertainty. The curves show predictions based on deep-inelastic scattering parametrizations of gluon polarization.
Nuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons - composed of an antiproton, antineutron, and antilambda hyperon - produced by colliding gold nuclei at high energy. Our analysis yields 70 +- 17 antihypertritons and 157 +- 30 hypertritons. The measured yields of hypertriton (antihypertriton) and helium3 (antihelium3) are similar, suggesting an equilibrium in coordinate and momentum space populations of up, down, and strange quarks and antiquarks, unlike the pattern observed at lower collision energies. The production and properties of antinuclei, and nuclei containing strange quarks, have implications spanning nuclear/particle physics, astrophysics, and cosmology.
(A, B) show the invariant mass distribution of the daughter 3He + π. The open circles represent the signal candidate distributions, while the solid black lines are background distributions. The blue dashed lines are signal (Gaussian) plus background (double exponential) combined fit.
(A, B) show the invariant mass distribution of the daughter 3He + π. The open circles represent the signal candidate distributions, while the solid black lines are background distributions. The blue dashed lines are signal (Gaussian) plus background (double exponential) combined fit. A (B) shows the 3ΛH (3Λ¯H) candidate distributions.
The 3ΛH (solid squares) and Λ (open circles) yield distributions versus cτ. The solid lines represent the cτ fits. The inset depicts the $\chi^2$ distribution of the best 3ΛH cτ fit. The error bars represent the statistical uncertaintiesonly.
Pion-kaon correlation functions are constructed from central Au+Au data taken at $\sqrt{s_{NN}} = 130$ GeV. The results suggest that pions and kaons are not emitted at the same average space-time point. Space-momentum correlations, i.e. transverse flow, lead to a space-time emission asymmetry of pions and kaons that is consistent with the data. This result provides new independent evidence that the system created at RHIC undergoes a collective transverse expansion.
Pion-kaon correlation functions and ratios of correlation functions. Errors are statistical only.
Pion-kaon correlation functions and ratios of correlation functions. Errors are statistical only.
Pion-kaon correlation functions and ratios of correlation functions. Errors are statistical only.
We present STAR measurements of the azimuthal anisotropy parameter $v_2$ for pions, kaons, protons, $\Lambda$, $\bar{\Lambda}$, $\Xi+\bar{\Xi}$, and $\Omega + \bar{\Omega}$, along with $v_4$ for pions, kaons, protons, and $\Lambda + \bar{\Lambda}$ at mid-rapidity for Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV. The $v_2(p_T)$ values for all hadron species at 62.4 GeV are similar to those observed in 130 and 200 GeV collisions. For observed kinematic ranges, $v_2$ values at 62.4, 130, and 200 GeV are as little as 10%--15% larger than those in Pb+Pb collisions at $\sqrt{s_{_{NN}}}=17.3$ GeV. At intermediate transverse momentum ($p_T$ from 1.5--5 GeV/c), the 62.4 GeV $v_2(p_T)$ and $v_4(p_T)$ values are consistent with the quark-number scaling first observed at 200 GeV. A four-particle cumulant analysis is used to assess the non-flow contributions to pions and protons and some indications are found for a smaller non-flow contribution to protons than pions. Baryon $v_2$ is larger than anti-baryon $v_2$ at 62.4 and 200 GeV perhaps indicating either that the initial spatial net-baryon distribution is anisotropic, that the mechanism leading to transport of baryon number from beam- to mid-rapidity enhances $v_2$, or that anti-baryon and baryon annihilation is larger in the in-plane direction.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
Minimum-bias (0–80% of the collision cross section) v2(pT ) for identified hadrons at |η| < 1 from Au+Au collisions at √sNN = 62.4 GeV. To facilitate comparisons between panels, v2 values for inclusive charged hadrons are displayed in each panel. The error bars on the data points represent statistical uncertainties. Systematic uncertainties for the identified particles are shown as shaded bands around v2 = 0.
Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for pp, d+Au, and Au+Au collisions at 200 GeV by the STAR experiment. The acoplanarities in pp and d+Au indicate initial state kT broadening. Larger acoplanarity is observed in Au+Au collisions. The central Au+Au data show an additional effect signaling conical emission of correlated charged hadrons.
FIG. 1: (a) Raw two-particle correlation signal $Y_2$ (red), background $aB_{inc}F_2$ (solid histogram), and background systematic uncertainty from a (dashed histograms). (b) Background-subtracted two-particle correlation $\hat{Y}_2$ (red), and systematic uncertainties due to a (dashed histograms) and flow (blue histograms). (c) Raw three-particle correlation $Y_3$. (d) $ba^2Y_{inc}^2$ . (e) Sum of trig-corr-bkgd and trigger flow. Data are from 12% central Au+Au collisions. Statistical errors in (a,b) are smaller than the point size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
FIG. 1: (a) Raw two-particle correlation signal $Y_2$ (red), background $aB_{inc}F_2$ (solid histogram), and background systematic uncertainty from a (dashed histograms). (b) Background-subtracted two-particle correlation $\hat{Y}_2$ (red), and systematic uncertainties due to a (dashed histograms) and flow (blue histograms). (c) Raw three-particle correlation $Y_3$. (d) $ba^2Y_{inc}^2$ . (e) Sum of trig-corr-bkgd and trigger flow. Data are from 12% central Au+Au collisions. Statistical errors in (a,b) are smaller than the point size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
FIG. 1: (a) Raw two-particle correlation signal $Y_2$ (red), background $aB_{inc}F_2$ (solid histogram), and background systematic uncertainty from a (dashed histograms). (b) Background-subtracted two-particle correlation $\hat{Y}_2$ (red), and systematic uncertainties due to a (dashed histograms) and flow (blue histograms). (c) Raw three-particle correlation $Y_3$. (d) $ba^2Y_{inc}^2$ . (e) Sum of trig-corr-bkgd and trigger flow. Data are from 12% central Au+Au collisions. Statistical errors in (a,b) are smaller than the point size.
We report measurements of transverse momentum $p_t$ spectra for ten event multiplicity classes of p-p collisions at $\sqrt{s} = 200$ GeV. By analyzing the multiplicity dependence we find that the spectrum shape can be decomposed into a part with amplitude proportional to multiplicity and described by a L\'evy distribution on transverse mass $m_t$, and a part with amplitude proportional to multiplicity squared and described by a gaussian distribution on transverse rapidity $y_t$. The functional forms of the two parts are nearly independent of event multiplicity. The two parts can be identified with the soft and hard components of a two-component model of p-p collisions. This analysis then provides the first isolation of the hard component of the $p_t$ spectrum as a distribution of simple form on $y_t$.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 1: Corrected and normalized charged-particle spectra on transverse momentum $p_t$ (left) and transverse rapidity $y_t$ (right) for 10 event multiplicity classes, displaced upward by successive factors 40 relative to $\hat{n}_{ch}$ = 1 at bottom. Solid curves represent reference function $n_s/n_{ch} · S_0(y_t)$ (cf.Sec. IV C). Dotted curves are spline fits to guide the eye.
FIG. 2. Left: Relative residuals from power-law fits to $p_{t}$ spectra in Fig. 1. The hatched band represents the expected statistical errors for STAR data. Right: Exponents $n$ from power-law fits to data (solid points) and to corresponding twocomponent fixed-model functions (open circles, see Sec. VI) compared to the two-component fixed-model Lévy exponent $12.8 \pm 0.15$ (hatched band). NOTE 1: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty. NOTE 2: The "data_stat" uncertainty corresponds to the expected statistical error (hatched band).
Transverse momentum spectra of charged pions, kaons, and protons are measured in proton-proton collisions at sqrt(s) = 13 TeV with the CMS detector at the LHC. The particles, identified via their energy loss in the silicon tracker, are measured in the transverse momentum range of pt ~ 0.1-1.7 GeV and rapidities abs(y) < 1. The pt spectra and integrated yields are compared to previous results at smaller sqrt(s) and to predictions of Monte Carlo event generators. The average pt increases with particle mass and charged particle multiplicity of the event. Comparisons with previous CMS results at sqrt(s) = 0.9, 2.76, and 7 TeV show that the average pt and the ratios of hadron yields feature very similar dependences on the particle multiplicity in the event, independently of the center-of-mass energy of the pp collision.
Measured transverse momentum distributions of identified charged hadrons (PI+, K+ and P) at a centre-of-mass energy of 13 TeV.
Measured transverse momentum distributions of identified charged hadrons (PI+, K+ and P) at a centre-of-mass energy of 13 TeV.
Measured transverse momentum distributions of identified charged hadrons (PI-, K- and PBAR) at a centre-of-mass energy of 13 TeV.
We present the first large-acceptance measurement of event-wise mean transverse momentum mean p_t fluctuations for Au-Au collisions at nucleon-nucleon center-of-momentum collision energy sqrt{s_{NN}} = 130 GeV. The observed non-statistical mean p_t fluctuations substantially exceed in magnitude fluctuations expected from the finite number of particles produced in a typical collision. The r.m.s. fractional width excess of the event-wise mean p_t distribution is 13.7 +/- 0.1(stat) +/- 1.3(syst)% relative to a statistical reference, for the 15% most-central collisions and for charged hadrons within pseudorapidity range |eta|<1, 2pi azimuth and 0.15 < p_t < 2 GeV/c. The width excess varies smoothly but non-monotonically with collision centrality, and does not display rapid changes with centrality which might indicate the presence of critical fluctuations. The reported mean p_t fluctuation excess is qualitatively larger than those observed at lower energies and differs markedly from theoretical expectations. Contributions to mean p_t mean fluctuations from semi-hard parton scattering in the initial state and dissipation in the bulk colored medium are discussed.
Event frequency distribution on $\sqrt{n}(\langle p_t\rangle - \hat{p}_t)/\sigma\hat{p}_t$ for 80% of primary charged hadrons in $|\eta|$ < 1 for 183k central events
Difference in upper panel between data and gamma reference
Centrality dependences of the measured charge independent (CI) and charge dependent (CD) difference factors $\Delta\sigma_{p_t:n}$ plus the corresponding values extrapolated to 100% tracking efficiency. Statistical errors $\pm$ 0.5 MeV/c; systematic errors are $\pm$ 9%. Difference factors extrapolated to 100% tracking efficiency and no secondary particle contamination. Uncertainties are $\pm$ 12%.
We have searched for strangelets in a triggered sample of 61 million central (top 4%) Au+Au collisions at $\sNN = 200 $GeV near beam rapidities at the STAR detector. We have sensitivity to metastable strangelets with lifetimes of order $\geq 0.1 ns$, in contrast to limits over ten times longer in AGS studies and longer still at the SPS. Upper limits of a few 10^{-6} to 10^{-7} per central Au+Au collision are set for strangelets with mass ${}^{>}_{\sim}30$ GeV/c^{2}.
Upper limit for neutral (Z=0) and charged (Z=5) strangelet as a function of mass.
Upper limit for charged (Z=1) strangelet as a function of lifetime.
The longitudinal spin transfer, $D_{LL}$, from high energy polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons has been measured for the first time in proton-proton collisions at $\sqrt{s} = 200 \mathrm{GeV}$ with the STAR detector at RHIC. The measurements cover pseudorapidity, $\eta$, in the range $|\eta| < 1.2$ and transverse momenta, $p_\mathrm{T}$, up to $4 \mathrm{GeV}/c$. The longitudinal spin transfer is found to be $D_{LL}= -0.03\pm 0.13(\mathrm{stat}) \pm 0.04(\mathrm{syst})$ for inclusive $\Lambda$ and $D_{LL} = -0.12 \pm 0.08(\mathrm{stat}) \pm 0.03(\mathrm{syst})$ for inclusive $\bar{\Lambda}$ hyperons with $<\eta> = 0.5$ and $<p_\mathrm{T}> = 3.7 \mathrm{GeV}/c$. The dependence on $\eta$ and $p_\mathrm{T}$ is presented.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The spin transfer $D_{LL}$ to (a) $\Lambda$ and (b) $\bar{\Lambda}$ hyperons produced at positive pseudorapidity with respect to the polarized proton beam from $MB$, $JP$, and $HT$ data versus hyperon transverse momenta $p_{T}$. The sizes of the statistical and systematic uncertainties are indicated by the vertical bars and bands, respectively. For clarity, the HT data points have been shifted slightly in $p_{T}$. The dotted vertical lines indicate the $p_{T}$ intervals in the analysis of HT and JP data.
The pseudorapidity asymmetry and centrality dependence of charged hadron spectra in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV are presented. The charged particle density at mid-rapidity, its pseudorapidity asymmetry and centrality dependence are reasonably reproduced by a Multi-Phase Transport model, by HIJING, and by the latest calculations in a saturation model. Ratios of transverse momentum spectra between backward and forward pseudorapidity are above unity for \pT below 5 GeV/$c$. The ratio of central to peripheral spectra in d+Au collisions shows enhancement at 2 $<$ \pT $<$ 6 GeV/$c$, with a larger effect at backward rapidity than forward rapidity. Our measurements are in qualitative agreement with gluon saturation and in contrast to calculations based on incoherent multiple partonic scatterings.
The p$_T$ spectra of charged hadrons for various centrality classes.
The pseudorapidity dependence of charged particle densities for various centrality classes.
The ratio of charged hadron spectra in the backward rapidity to forward rapidity region for minimum bias and ZDC-d neutron-tagged events.
We report on the first measurement of elliptic flow $v_2(p_T)$ of multi-strange baryons $\Xi+\bar{Xi}$ and $\Omega+\bar{Omega} in heavy-ion collisions. In minimum bias Au+Au collisions at sqrt(s_NN) = 200 GeV, a significant amount of elliptic flow, comparable to other non-strange baryons, is observed for multi-strange baryons which are expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions. The $p_T$ dependence of $v_2$ of the multi-strange baryons confirms the number of constituent quark scaling previously observed for lighter hadrons. These results support the idea that a substantial fraction of the observed collective motion is developed at the early partonic stage in ultra-relativistic nuclear collisions at RHIC.
$\Xi^{-} + \Xi^{+}$ invariant mass distribution from minimum bias (0–80%) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
$\Omega^{-} + \Omega^{+}$ invariant mass distribution from minimum bias (0–80%) Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Azimuthal distributions with respect to the event plane of the $\Xi^{-} + \Xi^{+}$ and $\Omega^{-} + \Omega^{+}$ raw yields.
We present the directed flow ($v_1$) measured in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 62.4 GeV in the mid-pseudorapidity region $|\eta|<1.3$ and in the forward pseudorapidity region $2.5 < |\eta| < 4.0$. The results are obtained using the three-particle cumulant method, the event plane method with mixed harmonics, and for the first time at the Relativistic Heavy Ion Collider (RHIC), the standard method with the event plane reconstructed from spectator neutrons. Results from all three methods are in good agreement. Over the pseudorapidity range studied, charged particle directed flow is in the direction opposite to that of fragmentation neutrons.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
Directed flow of charged particles as a function of pseudorapidity, for centrality 10%-70%.
The system created in non-central relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Due to spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of Lambda and anti-Lambda hyperon global polarization measurements in Au+Au collisions at sqrt{s_NN}=62.4 GeV and 200 GeV performed with the STAR detector at RHIC. The observed global polarization of Lambda and anti-Lambda hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P_{Lambda,anti-Lambda}| <= 0.02, is compared to the theoretical values discussed recently in the literature.
(Color online) Invariant mass distribution for the $\Lambda$ (filled circles) and $\overline{\Lambda}$ (open squares) candidates after the quality cuts for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%).
(Color online) Global polarization of $\Lambda$–hyperons as a function of $\Lambda$ transverse momentum $p^{\Lambda}_{t}$. Filled circles show the results for Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV (centrality region 20-70%) and open squares indicate the results for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%). Only statistical uncertainties are shown.
(Color online) Global polarization of $\Lambda$–hyperons as a function of $\Lambda$ pseudorapidity $\eta^{\Lambda}$. Filled circles show the results for Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV (centrality region 20-70%). A constant line fit to these data points yields $P_{\Lambda}=(2.8\pm 9.6)\times 10^{-3}$ with $\chi^{2}/ndf=6.5/10$. Open squares show the results for Au+Au collisions at $\sqrt{s_{NN}}$=62.4 GeV (centrality region 0-80%). A constant line fit gives $P_{\Lambda}=(1.9\pm 8.0)\times 10^{-3}$ with $\chi^{2}/ndf=14.3/10$. Only statistical uncertainties are shown.
Charged-particle spectra associated with direct photon ($\gamma_{dir} $) and $\pi^0$ are measured in $p$+$p$ and Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$ GeV with the STAR detector at RHIC. A hower-shape analysis is used to partially discriminate between $\gamma_{dir}$ and $\pi^0$. Assuming no associated charged particles in the $\gamma_{dir}$ direction (near side) and small contribution from fragmentation photons ($\gamma_{frag}$), the associated charged-particle yields opposite to $\gamma_{dir}$ (away side) are extracted. At mid-rapidity ($|\eta|<0.9$) in central Au+Au collisions, charged-particle yields associated with $\gamma_{dir}$ and $\pi^0$ at high transverse momentum ($8< p_{T}^{trig}<16$ GeV/$c$) are suppressed by a factor of 3-5 compared with $p$ + $p$ collisions. The observed suppression of the associated charged particles, in the kinematic range $|\eta|<1$ and $3< p_{T}^{assoc} < 16$ GeV/$c$, is similar for $\gamma_{dir}$ and $\pi^0$, and independent of the $\gamma_{dir}$ energy within uncertainties. These measurements indicate that the parton energy loss, in the covered kinematic range, is insensitive to the parton path length.
The $z_{T}$ dependence of $\pi^{0}-h^{\pm}$ near side and away-side associated particle yields. The errors denoted 'syst' are systematic errors correlated in $z_{T}$. The errors denoted 'syst uncorr' are point-to-point systematic errors.
The $z_{T}$ dependence of away-side associated-particle yields for $\pi^{0}-h^{\pm}$ triggers and $\gamma_{dir}$ triggers. The errors denoted 'syst' are systematic errors correlated in $z_{T}$. The errors denoted 'syst uncorr' are point-to-point systematic errors.
The $z_{T}$ dependence $I_{AA}$ for $\pi^{0}-h^{\pm}$ triggers and $\gamma_{dir}$ triggers. The errors denoted 'syst' are systematic errors correlated in $z_{T}$. The errors denoted 'syst uncorr' are point-to-point systematic errors.
First measurements of charge-independent correlations on angular difference variables $\eta_1 - \eta_2$ (pseudorapidity) and $\phi_1 - \phi_2$ (azimuth) are presented for primary charged hadrons with transverse momentum $0.15 \leq p_t \leq 2$ GeV/$c$ and $|\eta| \leq 1.3$ from Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Strong charge-independent angular correlations are observed associated with jet-like structures and elliptic flow. The width of the jet-like peak on $\eta_1 - \eta_2$ increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. New methods of jet analysis introduced here provide evidence for nonperturbative QCD medium effects in heavy ion collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for most-central collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for mid-central collisions.
Two-particle CI joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for mid-peripheral collisions.
We present the first measurements of charge-dependent correlations on angular difference variables $\eta_1 - \eta_2$ (pseudorapidity) and $\phi_1 - \phi_2$ (azimuth) for primary charged hadrons with transverse momentum $0.15 \leq p_t \leq 2$ GeV/$c$ and $|\eta| \leq 1.3$ from Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV. We observe correlation structures not predicted by theory but consistent with evolution of hadron emission geometry with increasing centrality from one-dimensional fragmentation of color strings along the beam direction to an at least two-dimensional hadronization geometry along the beam and azimuth directions of a hadron-opaque bulk medium.
Normalized LS pair-number ratios $\widehat{r} [X(p_{t1}),X(p_{t2})]-1$ for collisions in centrality class (a) (most-central) in $(\eta_{1},\eta_{2})$.
Normalized LS pair-number ratios $\widehat{r} [X(p_{t1}),X(p_{t2})]-1$ for collisions in centrality class (a) (most-central) in $(\phi_{1},\phi_{2})$.
Two-particle CD joint autocorrelations $\widehat{N}(\widehat{r}-1)$ on $(\eta_{\Delta}, \phi_{\Delta})$ for most-central collisions.
We report the first measurement of the opening angle distribution between pairs of jets produced in high-energy collisions of transversely polarized protons. The measurement probes (Sivers) correlations between the transverse spin orientation of a proton and the transverse momentum directions of its partons. With both beams polarized, the wide pseudorapidity ($-1 \leq \eta \leq +2$) coverage for jets permits separation of Sivers functions for the valence and sea regions. The resulting asymmetries are all consistent with zero and considerably smaller than Sivers effects observed in semi-inclusive deep inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the new results with the sizable transverse spin effects seen in SIDIS and forward hadron production in pp collisions.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
Measured and calculated asymmetries vs. di-jet pseudorapidity sum for $+\hat{z}$ (left) and $−\hat{z}$ (right) beams. (a,b): Fraction of the calculated di-jet cross section with a quark (gluon) from the $+\hat{z}$ $(−\hat{z})$ beam. (c,d): Unweighted asymmetries compared with pQCD calculations [20] (histograms) for two models of quark Sivers functions fitted to SIDIS results [8]. (e,f): Asymmetries for $|\sin\zeta|$-weighted yields, compared with calculations [20, 21] based on twist-3 quark-gluon correlations. Vertical (horizontal) bars on the data indicate statistical uncertainties (bin widths). The systematic error bands exclude a $\pm12\%$ beam polarization normalization uncertainty.
We report the measurements of $\Sigma (1385)$ and $\Lambda (1520)$ production in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR collaboration. The yields and the $p_{T}$ spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central $Au+Au$ collisions. Our results indicate that there may be a time-span between chemical and thermal freeze-out during which elastic hadronic interactions occur.
The transverse mass spectra for $\Sigma^{∗}$ and $\Lambda^{∗}$ in p+p and in central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Statistical and systematical errors are included.
Resonance to stable particle ratios for p + p and Au + Au collisions. The ratios are normalized to unity in p + p and compared to thermal and UrQMD model predictions for central Au + Au [8, 12]. Statistical and systematic uncertainties are included in the error bars. (In the paper figure, K*/K dNCh/dy axis is shifted +30 for visual purposes to seperate the error bar contributions.)
We present first measurements of the pseudorapidity and azimuth $(\eta,\phi)$ bin-size dependence of event-wise mean transverse momentum $<p_{t} >$ fluctuations for Au-Au collisions at $\sqrt{s_{NN}} = 200$ GeV. We invert that dependence to obtain $p_t$ autocorrelations on differences $(\eta_\Delta,\phi_\Delta)$ interpreted to represent velocity/temperature distributions on ($\eta,\phi$). The general form of the autocorrelations suggests that the basic correlation mechanism is parton fragmentation. The autocorrelations vary strongly with collision centrality, which suggests that fragmentation is strongly modified by a dissipative medium in the more central
Correlation amplitudes $B_{1}, B_{2}, B_{3}$ as well as positive-peak widths for pseudorapidity ($\sigma_{\eta_{1}}$) and azimuth ($\sigma_{\phi_{1}}$), plotted on mean participant path length $\nu$.
Correlations in the hadron distributions produced in relativistic Au+Au collisions are studied in the discrete wavelet expansion method. The analysis is performed in the space of pseudorapidity (|eta| < 1) and azimuth (full 2 pi) in bins of transverse momentum (p_t) from 0.14 < p_t < 2.1 GeV/c. In peripheral Au+Au collisions a correlation structure ascribed to mini-jet fragmentation is observed. It evolves with collision centrality and p_t in a way not seen before which suggests strong dissipation of minijet fragmentation in the longitudinally-expanding medium.
Normalized dynamic texture for fineness scale m = 0
Normalized dynamic texture for fineness scale m = 1
Normalized dynamic texture for fineness scale m = 0
We present results for two-particle transverse momentum correlations, <dpt,i dpt,j>, as a function of event centrality for Au+Au collisions at sqrt(sNN) = 20, 62, 130, and 200 GeV at the Relativistic Heavy Ion Collider. We observe correlations decreasing with centrality that are similar at all four incident energies. The correlations multiplied by the multiplicity density increase with incident energy and the centrality dependence may show evidence of processes such as thermalization, minijet production, or the saturation of transverse flow. The square root of the correlations divided by the event-wise average transverse momentum per event shows little or no beam energy dependence and generally agrees with previous measurements at the Super Proton Synchrotron.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 20 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 62 GeV for the 5% most central collisions.
Average transverse momentum per event for Au+Au at $\sqrt{s_{NN}}$ = 130 GeV for the 5% most central collisions.
We present the first study of the energy dependence of $p_t$ angular correlations inferred from event-wise mean transverse momentum $<p_{t} >$ fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure suggests that the principal source of $p_t$ correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related $<p_{t}>$ fluctuations near 10 GeV.
Per-particle fluctuation dependence on pseudorapidity scale $\delta\eta$ in central collisions.
Per-particle fluctuation dependence on pseudorapidity scale $\delta\eta$ in central collisions.
Centrality dependence of $<p_t>$ fluctuations in the STAR acceptance for four energies. $\nu$ is the mean participant path length (please consult text).
We measure directed flow ($v_1$) for charged particles in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}} =$ 200 GeV and 62.4 GeV, as a function of pseudorapidity ($\eta$), transverse momentum ($p_t$) and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all existing models, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to different collision systems, and investigate possible explanations for the observed sign change in $v_1(p_t)$.
Charged particle $v_1(\eta)$ for 0-5 % centrality in Au+Au collisions at 200 GeV.
$<P_x>/<P_t>$ of charged particles as a function of pseudorapidity, for centrality 0-5% in Au+Au collisions at 200 GeV.
Charged particle $v_1(\eta)$ for 5-40 % centrality in Au+Au collisions at 200 GeV.
Normalized differential cross sections for top quark pair production are measured in the dilepton (e$^+$e$^-$, $\mu^+\mu^-$, and $\mu^\mp$e$^\pm$) decay channels in proton-proton collisions at a center-of-mass energy of 13 TeV. The measurements are performed with data corresponding to an integrated luminosity of 2.1 fb$^{-1}$ using the CMS detector at the LHC. The cross sections are measured differentially as a function of the kinematic properties of the leptons, jets from bottom quark hadronization, top quarks, and top quark pairs at the particle and parton levels. The results are compared to several Monte Carlo generators that implement calculations up to next-to-leading order in perturbative quantum chromodynamics interfaced with parton showering, and also to fixed-order theoretical calculations of top quark pair production up to next-to-next-to-leading order.
Normalized differential ttbar cross sections with statistical and systematic uncertainties at the particle level as a function of pt(lepton).
Normalized differential ttbar cross sections with statistical and systematic uncertainties at the particle level as a function of pt(jet).
Normalized differential ttbar cross sections with statistical and systematic uncertainties at the particle level as a function of pt(top).
We report on the rapidity and centrality dependence of proton and anti-proton transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as measured by the STAR experiment at RHIC. Our results are from the rapidity and transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons and anti-protons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y|<0.5. Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton(anti-proton) yields and transverse mass distributions the possibility of pre-hadronic collective expansion may have to be taken into account.
$p$ differential yield. Systematic uncertainties are $\pm$10%.
$\bar{p}$ differential yield. Systematic uncertainties are $\pm$10%.
Rapidity distribution of $p$. Combined statitiscal uncertainty and systematic uncertainty from PID contramination. Systematic uncertainties from the track reconstruction efficiency are $\pm$25%.
Measurements of two-particle correlations on transverse momentum $p_t$ for Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV are presented. Significant large-momentum-scale correlations are observed for charged primary hadrons with $0.15 \leq p_t \leq 2$ GeV/$c$ and pseudorapidity $|\eta| \leq 1.3$. Such correlations were not observed in a similar study at lower energy and are not predicted by theoretical collision models. Their direct relation to mean-$p_t$ fluctuations measured in the same angular acceptance is demonstrated. Positive correlations are observed for pairs of particles which have large $p_t$ values while negative correlations occur for pairs in which one particle has large $p_t$ and the other has much lower $p_t$. The correlation amplitudes per final state particle increase with collision centrality. The observed correlations are consistent with a scenario in which the transverse momentum of hadrons associated with initial-stage semi-hard parton scattering is dissipated by the medium to lower $p_t$.
Symmetrized pair-density net ratios $\widehat{r} [X(p_{t1}),X(p_{t2})]-1$ for all nonidentified charged primary particles for most-central Au-Au collision events at $\sqrt{s_{NN}}=130$ GeV.
Symmetrized pair-density net ratios $\widehat{r}[X(p_{t1}),X(p_{t2})]-1$ for all nonidentified charged primary particles for mid-central Au-Au collision events at $\sqrt{s_{NN}}=130$ GeV.
Symmetrized pair-density net ratios $\widehat{r}[X(p_{t1}),X(p_{t2})]-1$ for all nonidentified charged primary particles for mid-peripheral Au-Au collision events at $\sqrt{s_{NN}}=130$ GeV.
We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < \eta < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for \sqrt{s_NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of \eta - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 2. (Color online.) Event-by-event photon multiplicity distributions (solid circles) for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=62.4$ and $200 \mathrm{GeV} .$ The distributions for top $0-5 \%$ central $\mathrm{Au}+$ Au collisions and top $0-10 \%$ central $\mathrm{Cu}+\mathrm{Cu}$ collisions are also shown (open circles). The photon multiplicity distributions for central collisions are observed to be Gaussian (solid line). Only statistical errors are shown. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
The transverse mass spectra and mid-rapidity yields for $\Xi$s and $\Omega$s plus their anti-particles are presented. The 10% most central collision yields suggest that the amount of multi-strange particles produced per produced charged hadron increases from SPS to RHIC energies. A hydrodynamically inspired model fit to the spectra, which assumes a thermalized source, seems to indicate that these multi-strange particles experience a significant transverse flow effect, but are emitted when the system is hotter and the flow is smaller than values obtained from a combined fit to $\pi$, K, p and $\Lambda$s.
$m_T$ spectra of $\Xi^-$ and $\bar{\Xi}^+$ for 0-10% centrality. Errors listed here are the quadrature sum of statistical and point-to-point systematic uncertainties. There is an additional overall $m_T$-independent systematic uncertainty of 10%.
$m_T$ spectra of $\Xi^-$ and $\bar{\Xi}^+$ for 10-25% centrality. Errors listed here are the quadrature sum of statistical and point-to-point systematic uncertainties. There is an additional overall $m_T$-independent systematic uncertainty of 10%.
$m_T$ spectra of $\Xi^-$ and $\bar{\Xi}^+$ for 25-75% centrality. Errors listed here are the quadrature sum of statistical and point-to-point systematic uncertainties. There is an additional overall $m_T$-independent systematic uncertainty of 10%.
We present the first spin alignment measurements for the $K^{*0}(892)$ and $\phi(1020)$ vector mesons produced at mid-rapidity with transverse momenta up to 5 GeV/c at $\sqrt{s_{NN}}$ = 200 GeV at RHIC. The diagonal spin density matrix elements with respect to the reaction plane in Au+Au collisions are $\rho_{00}$ = 0.32 $\pm$ 0.04 (stat) $\pm$ 0.09 (syst) for the $K^{*0}$ ($0.8<p_T<5.0$ GeV/c) and $\rho_{00}$ = 0.34 $\pm$ 0.02 (stat) $\pm$ 0.03 (syst) for the $\phi$ ($0.4<p_T<5.0$ GeV/c), and are constant with transverse momentum and collision centrality. The data are consistent with the unpolarized expectation of 1/3 and thus no evidence is found for the transfer of the orbital angular momentum of the colliding system to the vector meson spins. Spin alignments for $K^{*0}$ and $\phi$ in Au+Au collisions were also measured with respect to the particle's production plane. The $\phi$ result, $\rho_{00}$ = 0.41 $\pm$ 0.02 (stat) $\pm$ 0.04 (syst), is consistent with that in p+p collisions, $\rho_{00}$ = 0.39 $\pm$ 0.03 (stat) $\pm$ 0.06 (syst), also measured in this work. The measurements thus constrain the possible size of polarization phenomena in the production dynamics of vector mesons.
The spin-density matrix elements $\rho_{00}$ with respect to the reaction plane in midcentral $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV versus $p_{T}$ of the vector meson. The sizes of the statistical uncertainties are indicated by error bars, and the systematic uncertainties by caps. The $K^{∗0}$ data points have been shifted slightly in $p_{T}$ for clarity. The dashed horizontal line indicates the unpolarized expectation $\rho_{00}=1/3$. The bands and continuous horizontal lines show predictions discussed in the text.
The dependence of $\rho_{00}$ with respect to the reaction plane on the number of participants at midrapidity in $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV. The sizes of the statistical uncertainties are indicated by error bars and the systematic uncertainties by caps. The $\phi$ data for $p_{T} > 2$ GeV/$c$ and the $K^{∗0}$ data points have been shifted slightly in $\langle N_{\scriptsize{\mbox{part}}}\rangle$ for clarity. The dashed horizontal line indicates the unpolarized expectation $\rho_{00}=1/3$.
The spin-density matrix elements $\rho_{00}$ with respect to the production plane in midcentral $Au+Au$ and $p+p$ collisions at $\sqrt{s_{NN}}=200$ GeV versus $p_{T}$ of the vector meson. The sizes of the statistical uncertainties are indicated by error bars and the systematic uncertainties by caps. The $K^{*0}$ and the $\phi$ $p+p$ data points have been shifted slightly in $p_{T}$ for clarity. The dashed horizontal line indicates the unpolarized expectation $\rho_{00}=1/3$.
We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.
Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.
Midrapidity $(|y| < 0.5)$ transverse momentum spectra of $\phi$ mesons for various collision centrality classes for $Cu+Cu$ collisions at $\sqrt{s_{NN}}=62.4$ and 200 GeV. To study the system size dependence, comparison of $40-50\%$ $Au+Au$ spectra to $10-20\%$ $Cu+Cu$ spectra at 200 GeV, and $40-60\%$ $Au+Au$ spectra to $20-30\%$ $Cu+Cu$ spectra at 62.4 GeV are shown. These centralities for the two colliding systems have similar $\langle N_{\scriptsize{\mbox{part}}}\rangle$ values as outlined in Table 2. The errors represent the statistical and systematic errors added in quadrature. They are found to be within the symbol size. The spectra are fitted to a Levy function discussed in the text.
Upper panels. $N_{\scriptsize{\mbox{part}}}$ scaled ($R^{N_{\scriptsize{\mbox{part}}}}_{AA}$) nuclear modification factors as a function of $p_{T}$ of $\phi$ mesons for $0-10\%$ and $20-30\%$ $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV. Lower panel. Same as above for $N_{\scriptsize{\mbox{bin}}}$ scaled ($R^{N_{\scriptsize{\mbox{bin}}}}_{AA}$) nuclear modification factor. The error bars represent the statistical and systematic errors added in quadrature. The shaded band in upper panel around 1 at $p_{T}=4.5-5.5$ GeV/$c$ in the right side reflects the uncertainty in $N_{\scriptsize{\mbox{part}}}$ and that on the lower panel for $N_{\scriptsize{\mbox{bin}}}$ calculation for central $Au+Au$ collisions. The respective uncertainties for central $Cu+Cu$ collisions are of similar order.
Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au+Au collisions at $\sqrt{s_{_{NN}}}$= 200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au+Au collisions to those in $p+p$ at the same energy. Elliptic anisotropy, $v_2$, is found to reach its maximum at $p_t \sim 3$ GeV/c, then decrease slowly and remain significant up to $p_t\approx 7$ -- 10 GeV/c. Stronger suppression is found in the back-to-back high-$p_t$ particle correlations for particles emitted out-of-plane compared to those emitted in-plane. The centrality dependence of $v_2$ at intermediate $p_t$ is compared to simple models based on jet quenching.
Azimuthal correlations in Au+Au col- lisions (squares) as a function of centrality (peripheral to cen- tral from left to right) compared to minimum bias azimuthal correlations in p + p collisions (circles). Errors are statistical only.
$v_{2}$ of charged particles as a function of transverse momentum from the two-particle cumu- lant method (triangles) and four-particle cumulant method (stars). Open circles show the 2-particle correlation results after subtracting the correlations measured in p + p collisions. Only statistical errors are shown.
Upper panel, Azimuthal distributions of associated particles for trigger particles in-plane (squares) and out-of-plane (triangles) for Au+Au collisions at centrality 20-60%. Open symbols are reflections of solid symbols around $\Delta \phi$ = 0 and $\Delta \phi$ = $\pi$. Elliptic flow contribution is shown by dashed lines. Lower panel, Distributions after substracting elliptic flow, and the corresponding measurement in p + p collisions (histogram).
We report a new STAR measurement of the longitudinal double-spin asymmetry A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit of polarized deep-inelastic scattering measurements.
(a) The raw detected jet yield in data (points) compared with the STAR Monte Carlo simulations. (b) Correlation between the reconstructed jet transverse momenta at the particle and detector levels. The points indicate the means and the vertical error bars show the r.m.s. widths of the associated particle jet distributions within the detector jet bins. The dashed line represents the condition when the particle and detector jet $p_{T}$ values are equal.
(a) The raw detected jet yield in data (points) compared with the STAR Monte Carlo simulations. (b) Correlation between the reconstructed jet transverse momenta at the particle and detector levels. The points indicate the means and the vertical error bars show the r.m.s. widths of the associated particle jet distributions within the detector jet bins. The dashed line represents the condition when the particle and detector jet $p_{T}$ values are equal.
Longitudinal double-spin asymmetry $A_{LL}$ for inclusive jet production at $\sqrt{s_{NN}}$ = 200 GeV versus jet $p_{T}$. The points show results for particle jets with statistical error bars, while the curves show predictions for NLO parton jets from one global analysis [14]. The gray boxes indicate the systematic uncertainties on the measured $A_{LL}$ values (vertical) and in the corrections to the measured jet $p_{T}$ and the conversion between particle jet and NLO parton jet $p_{T}$ (horizontal).
We report results for $K/\pi$ fluctuations from Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. Our results for $K/\pi$ fluctuations in central collisions show little dependence on the incident energies studied and are on the same order as results observed by NA49 at the Super Proton Synchrotron in central Pb+Pb collisions at $\sqrt{s_{NN}}$ = 12.3 and 17.3 GeV. We also report results for the collision centrality dependence of $K/\pi$ fluctuations as well as results for $K^{+}/\pi^{+}$, $K^{-}/\pi^{-}$, $K^{+}/\pi^{-}$, and $K^{-}/\pi^{+}$ fluctuations. We observe that the $K/\pi$ fluctuations scale with the multiplicity density, $dN/d\eta$, rather than the number of participating nucleons.
(Color online) The event-by-event $K/\pi$ ratio for 200 GeV Au+Au central collisions (0-5%) compared with the same quantity calculated from mixed events. The inset shows the ratio of the distribution from real events to that from mixed events. The errors shown are statistical.
(Color online) The event-by-event $K/\pi$ ratio for 200 GeV Au+Au central collisions (0-5%) compared with the same quantity calculated from mixed events. The inset shows the ratio of the distribution from real events to that from mixed events. The errors shown are statistical.
(Color online) Measured dynamical $K/\pi$ fluctuations in terms of σdyn for central collisions (0 - 5%) of 19.6, 62.4, 130, and 200 GeV Au+Au compared with the central collisions (0 - 3.5%) of Pb+Pb from NA49 [7] and the statistical hadronization (SH) model of Ref. [14]. The solid line represents the relationship of the incident energy dependence of $\sigma_{dyn}$ in central collisions to the collision centrality dependence of $\nu_{dyn,K\pi}$ at higher energies. Both statistical (vertical line with horizontal bar) and systematic (no vertical line) error bars are shown for the experimental data.
We present measurements of net charge fluctuations in $Au + Au$ collisions at $\sqrt{s_{NN}} = $ 19.6, 62.4, 130, and 200 GeV, $Cu + Cu$ collisions at $\sqrt{s_{NN}} = $ 62.4, 200 GeV, and $p + p$ collisions at $\sqrt{s} = $ 200 GeV using the dynamical net charge fluctuations measure $\nu_{+-{\rm,dyn}}$. We observe that the dynamical fluctuations are non-zero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate $1/N_{ch}$ scaling, but display approximate $1/N_{part}$ scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation.
(Color online) Dynamical net charge fluctuations, $\nu_{+−,dyn}$, of particles produced within pseudorapidity $|\eta|$ < 0.5, as function of the number of participating nucleons.
(Color online) Corrected values of dynamical net charge fluctuations ($\nu^{corr}_{+−,dyn}$) as a function of $\sqrt{s_{NN}}$. See text for details.
(Color online) Dynamical net charge fluctuations, $\nu_{+−,dyn}$, of particles produced with pseudorapidity $|\eta|$ < 0.5 scaled by (a) the multiplicity, $dN_{ch}/d\eta$. The dashed line corresponds to charge conservation effect and the solid line to the prediction for a resonance gas, (b) the number of participants, and (c) the number of binary collisions.
Measurements of the production of forward high-energy pi0 mesons from transversely polarized proton collisions at \sqrt{s}=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x_F below about 0.3, and becomes positive and large at higher x_F, similar to the trend in data at \sqrt{s}<=20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p_T>1 GeV/c at a polarized proton collider.
Inclusive $\pi^{0}$ production cross section versus leading $\pi^{0}$ energy ($E_{\pi}$). The average transverse momentum ($\langle p_{T}\rangle$) is correlated with $E_{\pi}$, as the PFPD was at a fixed pseudorapidity ($\eta$). The inner error bars are statistical, and are smaller than the symbols for most points. The outer error bars combine these with the $E_{\pi}$-dependent systematic errors. The curves are NLO pQCD calculations evaluated at $\eta=3.8$ [29-31].
Analyzing powers versus Feynman $x$ ($x_{F}$). The average transverse momentum ($\langle p_{T}\rangle$) is correlated with $x_{F}$. The solid points are for identified $\pi^{0}$ mesons. The open points are for the total energy ($E_{\scriptsize{\mbox{tot}}}$), shifted by $x_{F}+0.01$. The inner error bars are statistical, and the outer combine these with the point-to-point systematic errors. The curves are from pQCD models evaluated at $p_{T}=1.5$ GeV/c [14-17]. The $A_{N}$ values are proportional to $A^{\scriptsize{\mbox{CNI}}}_{N}$, assumed to be 0.013 at 100 GeV.
We determine rapidity asymmetry in the production of charged pions, protons and anti-protons for large transverse momentum (pT) for d+Au collisions at \sqrt s_NN = 200 GeV. The identified hadrons are measured in the rapidity regions |y| < 0.5 and 0.5 < |y| < 1.0 for the pT range 2.5 < pT < 10 GeV/c. We observe significant rapidity asymmetry for charged pion and proton+anti-proton production in both rapidity regions. The asymmetry is larger for 0.5 < |y| < 1.0 than for |y|< 0.5 and is almost independent of particle type. The measurements are compared to various model predictions employing multiple scattering, energy loss, nuclear shadowing, saturation effects, and recombination, and also to a phenomenological parton model. We find that asymmetries are sensitive to model parameters and show model-preference. The rapidity dependence of \pi^{-}/\pi^{+} and \bar{p}/p ratios in peripheral d+Au and forward neutron-tagged events are used to study the contributions of valence quarks and gluons to particle production at high pT. The results are compared to calculations based on NLO pQCD and other measurements of quark fragmentation functions.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
High transverse-momentum spectra ($p_{T} > 2.5$ GeV/c) of charged pions, protons, and antiprotons for the rapidity regions $|y| < 0.5$ (solid symbols) and $0.5 < |y| < 1.0$ (open symbols) for $d+Au$ collisions and various event centrality classes at $\sqrt{s_{NN}}=200$ GeV.
We study the energy dependence of the transverse momentum (pT) spectra for charged pions, protons and anti-protons for Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV. Data are presented at mid-rapidity (|y| < 0.5) for 0.2 < pT < 12 GeV/c. In the intermediate pT region (2 < pT < 6 GeV/c), the nuclear modification factor is higher at 62.4 GeV than at 200 GeV, while at higher pT (pT >7 GeV/c) the modification is similar for both energies. The p/pi+ and pbar/pi- ratios for central collisions at \sqrt{s_NN} = 62.4 GeV peak at pT ~ 2 GeV/c. In the pT range where recombination is expected to dominate, the p/pi+ ratios at 62.4 GeV are larger than at 200 GeV, while the pbar/pi- ratios are smaller. For pT > 2 GeV/c, the pbar/pi- ratios at the two beam energies are independent of pT and centrality indicating that the dependence of the pbar/pi- ratio on pT does not change between 62.4 and 200 GeV. These findings challenge various models incorporating jet quenching and/or constituent quark coalescence.
Midrapidity (|y| < 0.5) transverse momentum spectra for pions, protons, anti-protons for various event centrality classes for Au+Au at sqrt(sNN) = 62.4 GeV. Also shown to study the energy dependence are the central 0-12% pion, proton, anti-proton spectra for Au+Au at sqrt(sNN) = 200 GeV.
The insets show pi−/pi+ ratios at sqrt(sNN) = 62.4 GeV and anti-proton/proton ratios at sqrt(sNN) = 62.4 (0-10%) and 200 GeV (0-12%).
The minimum bias data shown here were extracted from the figures by xyscan. Hence, the dataset is not full (especially in the lower pT range where it is hard to distinguish points), and the statistical errors shown here are an upper limit of the statistical uncertainty based on the marker sizes.
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