Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 79 (2009) 024906, 2009.
Inspire Record 791177 DOI 10.17182/hepdata.98972

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.

10 data tables

(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.

More…

System-size independence of directed flow at the Relativistic Heavy-Ion Collider

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 101 (2008) 252301, 2008.
Inspire Record 790350 DOI 10.17182/hepdata.102949

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 $v_1(p_t)$.

11 data tables

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.

More…

Indications of Conical Emission of Charged Hadrons at RHIC

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 102 (2009) 052302, 2009.
Inspire Record 785050 DOI 10.17182/hepdata.102085

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.

14 data tables

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.

More…

Spin alignment measurements of the $K^{*0}(892)$ and $\phi(1020)$ vector mesons in heavy ion collisions at $\sqrt{s}_{NN} = 200$ GeV

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 77 (2008) 061902, 2008.
Inspire Record 777248 DOI 10.17182/hepdata.101350

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.

3 data tables

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 $\rho_{00}=1/3$.


Hadronic resonance production in $d$+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV at RHIC

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 78 (2008) 044906, 2008.
Inspire Record 776722 DOI 10.17182/hepdata.97116

We present the first measurements of the $\rho(770)^0$, $K^*$(892), $\Delta$(1232)$^{++}$, $\Sigma$(1385), and $\Lambda$(1520) resonances in $d$+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV, reconstructed via their hadronic decay channels using the STAR detector at RHIC. The masses and widths of these resonances are studied as a function of transverse momentum ($p_T$). We observe that the resonance spectra follow a generalized scaling law with the transverse mass ($m_T$). The $<p_T>$ of resonances in minimum bias collisions is compared to the $<p_T>$ of $\pi$, $K$, and $\bar{p}$. The $\rho^0/\pi^-$, $K^*/K^-$, $\Delta^{++}/p$, $\Sigma(1385)/\Lambda$, and $\Lambda(1520)/\Lambda$ ratios in $d$+Au collisions are compared to the measurements in minimum bias $p+p$ interactions, where we observe that both measurements are comparable. The nuclear modification factors ($R_{dAu}$) of the $\rho^0$, $K^*$, and $\Sigma^*$ scale with the number of binary collisions ($N_{bin}$) for $p_T >$ 1.2 GeV/$c$.

93 data tables

rho0 reconstruction efficiency times detector acceptance as a function of the invariant mass for minimum bias d+Au. The error shown is due to the available statistics in the simulation.

K*0 reconstruction efficiency times detector acceptance as a function of pT for minimum bias d+Au and three different centralities.

K*+- reconstruction efficiency times detector acceptance as a function of pT for minimum bias d+Au and three different centralities.

More…

Forward Neutral Pion Transverse Single Spin Asymmetries in p+p Collisions at \sqrt{s}=200 GeV

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 101 (2008) 222001, 2008.
Inspire Record 777766 DOI 10.17182/hepdata.97117

We report precision measurements of the Feynman-x dependence, and first measurements of the transverse momentum dependence, of transverse single spin asymmetries for the production of \pi^0 mesons from polarized proton collisions at \sqrt{s}=200 GeV. The x_F dependence of the results are in fair agreement with perturbative QCD model calculations that identify orbital motion of quarks and gluons within the proton as the origin of the spin effects. Results for the p_T dependence at fixed x_F are not consistent with pQCD-based calculations.

12 data tables

Analyzing powers A_N(x_F) in x_F bins at < eta > =3.7 and x_F > 0.

Analyzing powers A_N(x_F) in x_F bins at < eta > =3.3 and x_F > 0.

Analyzing powers A_N(-x_F) in x_F bins at < eta > =3.7 and x_F < 0.

More…

Centrality dependence of charged hadron and strange hadron elliptic flow from sqrt(s_NN) = 200 GeV Au+Au collisions

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 77 (2008) 054901, 2008.
Inspire Record 777954 DOI 10.17182/hepdata.96906

We present STAR results on the elliptic flow v_2 of charged hadrons, strange and multi-strange particles from sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC. The detailed study of the centrality dependence of v_2 over a broad transverse momentum range is presented. Comparison of different analysis methods are made in order to estimate systematic uncertainties. In order to discuss the non-flow effect, we have performed the first analysis of v_2 with the Lee-Yang Zero method for K_s^0 and Lambda. In the relatively low p_T region, p_T <= 2 GeV/c, a scaling with m_T - m is observed for identified hadrons in each centrality bin studied. However, we do not observe v_2(p_T) scaled by the participant eccentricity to be independent of centrality. At higher p_T, 2 GeV/c <= p_T <= 6 GeV/c, v_2 scales with quark number for all hadrons studied. For the multi-strange hadron Omega, which does not suffer appreciable hadronic interactions, the values of v_2 are consistent with both m_T -m scaling at low p_T and number-of-quark scaling at intermediate p_T. As a function of collision centrality, an increase of p_T-integrated v_2 scaled by the participant eccentricity has been observed, indicating a stronger collective flow in more central Au+Au collisions.

28 data tables

$v_{2}(\eta)$ for charged hadrons, $0.15 < p_{T} < 2.0$ GeV/c, centrality $10-40\%$, from $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV.

$v_{2}$ as a function of $p_{T}$ for charged hadrons with $|\eta| < 1.0$ in 10–40$%$ $Au+Au$ collisions, at $\sqrt{s_{NN}} = 200$ GeV, from the Event Plane method (open circles).

$v_{2}$ as a function of $p_{T}$ for charged hadrons with $|\eta| < 1.0$ in 10–40$%$ $Au+Au$ collisions, at $\sqrt{s_{NN}} = 200$ GeV, from the 4-particle cumulant method (solid squares).

More…

rho^0 Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions with STAR

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 77 (2008) 034910, 2008.
Inspire Record 771169 DOI 10.17182/hepdata.98962

Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR collaboration presents a measurement of rho^0 and direct pi^+pi^- photoproduction in ultra-peripheral relativistic heavy ion collisions at sqrt(s_{NN})=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of sigma(AuAu) -> Au^*Au^*rho^0 = 530 pm 19 (stat.) pm 57 (syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The rho^0 transverse momentum spectrum (p_{T}^2) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus/ we find sigma_{inc}/sigma_{coh} = 0.29 pm 0.03 (stat.) pm 0.08 (syst.). The ratio of direct pi^+pi^- to rho^0 production is comparable to that observed in gamma p collisions at HERA, and appears to be independent of photon energy. Finally, the measured rho^0 spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.

10 data tables

ZDC spectra obtained with the minimum bias sample after the $\rho^{0}$ selection cuts are applied, and fit with three Gaussians. The east ZDC is shown on the left and the west ZDC is shown on the right. The ratio of numbers of candidates in the West ZDC of 1n:2n:3n is 1: 0.48 $\pm$ 0.03: 0.42 $\pm$ 0.03, while in the East ZDC, we find 1n:2n:3n is 1: 0.46 $\pm$ 0.03: 0.42 $\pm$ 0.03.

ZDC spectra obtained with the minimum bias sample after the $\rho^{0}$ selection cuts are applied, and fit with three Gaussians. The east ZDC is shown on the left and the west ZDC is shown on the right. The ratio of numbers of candidates in the West ZDC of 1n:2n:3n is 1: 0.48 $\pm$ 0.03: 0.42 $\pm$ 0.03, while in the East ZDC, we find 1n:2n:3n is 1: 0.46 $\pm$ 0.03: 0.42 $\pm$ 0.03.

The invariant mass distribution for the coherently produced $\rho^{0}$ candidates from the minimum bias sample with the cut on the $\rho^{0}$ transverse momentum $p_{T}$ < 150 MeV/c. The hatched area is the contribution from the combinatorial background. The solid line corresponds to Eq. 3 which encompasses the Breit-Wigner (dashed), the mass independent contribution from the direct $\pi^{+}\pi^{-}$ production (dash-dotted), and the interference term(dotted).

More…

Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.Lett. 100 (2008) 232003, 2008.
Inspire Record 763822 DOI 10.17182/hepdata.98970

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.

5 data tables

(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).

More…

Forward $\ensuremath{\Lambda}$ Production and Nuclear Stopping Power in $d$ + Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV

The STAR collaboration Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; et al.
Phys.Rev.C 76 (2007) 064904, 2007.
Inspire Record 752244 DOI 10.17182/hepdata.98961

We report the measurement of Lamda and Anti-Lamda yields and inverse slope parameters in d + Au collisions at sqrt(s_NN) = 200 GeV at forward and backward rapidities (y = +- 2.75), using data from the STAR forward time projection chambers. The contributions of different processes to baryon transport and particle production are probed exploiting the inherent asymmetry of the d + Au system. Comparisons to model calculations show that the baryon transport on the deuteron side is consistent with multiple collisions of the deuteron nucleons with gold participants. On the gold side HIJING based models do not describe the measured particle yields while models with initial state nuclear effects and/or hadronic rescattering do. The Multi-Chain Model can provide a good description of the net baryon density in d + Au collisions at RHIC, and the derived parameters of the model agree with those from nuclear collisions at lower energies.

18 data tables

(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.

(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.

(Color online) a) Invariant mass distribution of $\Lambda$ candidates on the deuteron side with estimated $K_{s}^{0}$ background distribution, b) and c) show the background subtracted $\Lambda$ and $\overline{\Lambda}$ invariant mass distributions. The widths of the peaks are due to the limited momentum resolution of the detectors, and are reproduced by simulations.

More…