The process $e^+e^- \to K^+K^-\pi^+\pi^-$ has been studied in the center-of-mass energy range from 1500 to 2000\,MeV using a data sample of 23 pb$^{-1}$ collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider. Using about 24000 selected events, the $e^+e^- \to K^+K^-\pi^+\pi^-$ cross section has been measured with a systematic uncertainty decreasing from 11.7\% at 1500-1600\,MeV to 6.1\% above 1800\,MeV. A preliminary study of $K^+K^-\pi^+\pi^-$ production dynamics has been performed.
Center-of-mass energy, integrated luminosity, number of four-track events, number of three-track events, detection efficiency, radiative correction and Born cross section of the process $e^{+}e^{-} \to K^{+} K^{-} \pi^{+} \pi^{-}$. Errors are statistical only.
Cross sections and decay distribution moments are presented for the reaction p p → Δ ++ Δ ++ at 3.6 GeV/ c , and compared with previously published data at 9.1 and 12 GeV/ c . With the aid of the quark model, we have isolated the natural and unnatural parity exchange contributions and shown them to accord with expectations based on simple Regge-pole exchanges.
DOUBLE RESONANCE PRODUCTION IS 62 +- 2 PCT OF CHANNEL.
The $e^+ e^- \to K^0_{S}K^0_{L}$ cross section has been measured in the center-of-mass energy range 1004--1060 MeV at 25 energy points using $6.1 \times 10^5$ events with $K^0_{S}\to \pi^+\pi^-$ decay. The analysis is based on 5.9 pb$^{-1}$ of an integrated luminosity collected with the CMD-3 detector at the VEPP-2000 $e^+ e^-$ collider. To obtain $\phi(1020)$ meson parameters the measured cross section is approximated according to the Vector Meson Dominance model as a sum of the $\rho, \omega, \phi$-like amplitudes and their excitations. This is the most precise measurement of the $e^+ e^- \to K^0_{S}K^0_{L}$ cross section with a 1.8\% systematic uncertainty.
Measurements of the differential cross-section and the transverse single-spin asymmetry, A_N, vs. x_F for pi0 and eta mesons are reported for 0.4 < x_F < 0.75 at an average pseudorapidity of 3.68. A data sample of approximately 6.3 pb^{-1} was analyzed, which was recorded during p+p collisions at sqrt{s} = 200 GeV by the STAR experiment at RHIC. The average transverse beam polarization was 56%. The cross-section for pi0 is consistent with a perturbative QCD prediction, and the eta/pi0 cross-section ratio agrees with previous mid-rapidity measurements. For 0.55 < x_F < 0.75, A_N for eta (0.210 +- 0.056) is 2.2 standard deviations larger than A_N for pi0 (0.081 +- 0.016).
Differential production cross-sections for $\pi^0$ and $\eta$ at average pseudorapidity of 3.68. Also shown are the previously published STAR results for similar kinematics [21] and a NLO pQCD calculation of the π0 cross-section [32]. The error band represents the uncertainty in the calculation due to scale variations.
The $\eta$ to $\pi^0$ cross-section ratio is shown in the bottom panel. The error bars indicate the total statistical and systematic uncertainties.
We present the measurement of non-photonic electron production at high transverse momentum ($p_T > $ 2.5 GeV/$c$) in $p$ + $p$ collisions at $\sqrt{s}$ = 200 GeV using data recorded during 2005 and 2008 by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The measured cross-sections from the two runs are consistent with each other despite a large difference in photonic background levels due to different detector configurations. We compare the measured non-photonic electron cross-sections with previously published RHIC data and pQCD calculations. Using the relative contributions of B and D mesons to non-photonic electrons, we determine the integrated cross sections of electrons ($\frac{e^++e^-}{2}$) at 3 GeV/$c < p_T <~$10 GeV/$c$ from bottom and charm meson decays to be ${d\sigma_{(B\to e)+(B\to D \to e)} \over dy_e}|_{y_e=0}$ = 4.0$\pm0.5$({\rm stat.})$\pm1.1$({\rm syst.}) nb and ${d\sigma_{D\to e} \over dy_e}|_{y_e=0}$ = 6.2$\pm0.7$({\rm stat.})$\pm1.5$({\rm syst.}) nb, respectively.
The electron pair invariant mass distributions for electrons at $2.5 < p_{T} < 3.0$ GeV/c
The electron pair invariant mass distributions for electrons at $8 < p_{T} < 10$ GeV/c
The simulated electron pair invariant mass distributions for electrons at $2.5 < p_{T} < 3$ GeV/c
We report measurements of charmed-hadron ($D^{0}$, $D^{*}$) production cross sections at mid-rapidity in $p$ + $p$ collisions at a center-of-mass energy of 200 GeV by the STAR experiment. Charmed hadrons were reconstructed via the hadronic decays $D^{0}\rightarrow K^{-}\pi^{+}$, $D^{*+}\rightarrow D^{0}\pi^{+}\rightarrow K^{-}\pi^{+}\pi^{+}$ and their charge conjugates, covering the $p_T$ range of 0.6$-$2.0 GeV/$c$ and 2.0$-$6.0 GeV/$c$ for $D^{0}$ and $D^{*+}$, respectively. From this analysis, the charm-pair production cross section at mid-rapidity is $d\sigma/dy|_{y=0}^{c\bar{c}}$ = 170 $\pm$ 45 (stat.) $^{+38}_{-59}$ (sys.) $\mu$b. The extracted charm-pair cross section is compared to perturbative QCD calculations. The transverse momentum differential cross section is found to be consistent with the upper bound of a Fixed-Order Next-to-Leading Logarithm calculation.
$c\bar{c}$ production cross section as inferred from D$^0$ and D$^\star$ production in p+p collisions at $\sqrt{s} = 200$ GeV at $|\eta| < 1$ compared with FONLL calculations. The D$^0$ and D$^\star$ data points were divided by the charm quark fragmentation ratios 0.565 ($c \rightarrow$ D$^0$) and 0.224 ($c \rightarrow$ D$^{\star +}$) [34], respectively, to convert to the $c\bar{c}$ production cross section.
We present results on strange and multi-strange particle production in Au+Au collisions at $\sqrt{s_{NN}}=62.4$ GeV as measured with the STAR detector at RHIC. Mid-rapidity transverse momentum spectra and integrated yields of $K^{0}_{S}$, $\Lambda$, $\Xi$, $\Omega$ and their anti-particles are presented for different centrality classes. The particle yields and ratios follow a smooth energy dependence. Chemical freeze-out parameters, temperature, baryon chemical potential and strangeness saturation factor obtained from the particle yields are presented. Intermediate transverse momentum ($p_T$) phenomena are discussed based on the ratio of the measured baryon-to-meson spectra and nuclear modification factor. The centrality dependence of various measurements presented show a similar behavior as seen in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.
Strange particle production yields at mid-rapidity in central Au+Au and Pb+Pb collisions versus the center of mass energy √sNN. The top panel shows results for K0S and Λ. The AGS values are from E896 [1] (centrality 0 − 5 %). The SPS values are from NA49 [20] (centrality 0 − 7 %) and the RHIC values are from STAR [4, 15] (centrality 0 − 5 %). For the multi-strange baryons Ξ and Ω (bottom panel), the SPS results are from NA57 [2] (centrality 0 − 11 %) and the RHIC values are from STAR [15, 21] (centrality 0 − 20 %).
Strange particle production yields at mid-rapidity in central Au+Au and Pb+Pb collisions versus the center of mass energy √sNN. The top panel shows results for K0S and Λ. The AGS values are from E896 [1] (centrality 0 − 5 %). The SPS values are from NA49 [20] (centrality 0 − 7 %) and the RHIC values are from STAR [4, 15] (centrality 0 − 5 %). For the multi-strange baryons Ξ and Ω (bottom panel), the SPS results are from NA57 [2] (centrality 0 − 11 %) and the RHIC values are from STAR [15, 21] (centrality 0 − 20 %).
Temperature and baryon chemical potential obtained from thermal model fits as a function of √sNN (see Ref. [22]). The dashed lines correspond to the parametrizations given in Ref. [22]. The solid stars show the result for √sNN=62.4 and 200 GeV.
We report the first measurement of the parity violating single-spin asymmetries for midrapidity decay positrons and electrons from $W^{+}$ and $W^{-}$ boson production in longitudinally polarized proton-proton collisions at $\sqrt{s}=500 $GeV by the STAR experiment at RHIC. The measured asymmetries, $A^{W^+}_{L}=-0.27\pm 0.10\/({\rm stat.})\pm 0.02\/({\rm syst.}) \pm 0.03\/({\rm norm.})$ and $A^{W^-}_{L}=0.14\pm 0.19\/({\rm stat.})\pm 0.02 \/({\rm syst.})\pm 0.01\/({\rm norm.})$, are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized DIS measurements.
$E^e_T$ for W+ (bottom) and W− (top) events showing the candidate histograms in black, the full background estimates in blue and the signal distributions in yellow.
$E^e_T$ for W+ (bottom) and W− (top) events showing the candidate histograms in black, the full background estimates in blue and the signal distributions in yellow.
Longitudinal single-spin asymmetry, AL, for W± events as a function of the leptonic pseudorapidity, $\eta_e$, for 25 < $E^e_T$ < 50 GeV in comparison to theory predictions
The contribution of $B$ meson decays to non-photonic electrons, which are mainly produced by the semi-leptonic decays of heavy flavor mesons, in $p+p$ collisions at $\sqrt{s} =$ 200 GeV has been measured using azimuthal correlations between non-photonic electrons and hadrons. The extracted $B$ decay contribution is approximately 50% at a transverse momentum of $p_{T} \geq 5$ GeV/$c$. These measurements constrain the nuclear modification factor for electrons from $B$ and $D$ meson decays. The result indicates that $B$ meson production in heavy ion collisions is also suppressed at high $p_{T}$.
Distributions of the azimuthal angle between nonphotonic electrons and charged hadrons normalized per nonphotonic electron trigger. The trigger electron has (top) $2.5 < p_{T} < 3.5$ GeV/$c$ and (bottom) $5.5 < p_{T} < 6.5$ GeV/$c$. The curves represent PYTHIA calculations for $D$ (dotted curve) and $B$ (dashed curve) decays. The fit result is shown as the black solid curve.
(a) Background-subtracted invariant mass distribution of $K$ pairs requiring at least one nonphotonic electron trigger in the event. The solid line is a Gaussian fit to the data near the peak region. (b) Distribution of the azimuthal angle between nonphotonic electron (positron) trigger particles and $D^{0}$ ($\bar{D}^{0}$). The solid (dashed) line is a fit of the correlation function from PYTHIA (MC$@$NLO) simulations to the data points.
Transverse momentum dependence of the relative contribution from $B$ mesons ($r_{B}$) to the nonphotonic electron yields. Error bars are statistical and brackets are systematic uncertainties. The solid curve is the FONLL calculation [14]. Theoretical uncertainties are indicated by the dashed curves.
We report measurements of Upsilon meson production in p+p, d+Au, and Au+Au collisions using the STAR detector at RHIC. We compare the Upsilon yield to the measured cross section in p+p collisions in order to quantify any modifications of the yield in cold nuclear matter using d+Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p+p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Upsilon(1S+2S+3S) in the rapidity range |y|<1 in d+Au collisions of R_dAu = 0.79 +/- 0.24 (stat.) +/- 0.03 (sys.) +/- 0.10 (pp sys.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au+Au collisions, we measure a nuclear modification factor of R_AA=0.49 +/- 0.1 (stat.) +/- 0.02 (sys.) +/- 0.06 (pp sys.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Upsilon mesons in Au+Au collisions. The additional suppression in Au+Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark-Gluon Plasma. However, understanding the suppression seen in d+Au is still needed before any definitive statements about the nature of the suppression in Au+Au can be made.
Comparison of our d+Au measurements to the pA measurements from E772. Ratio of $\Upsilon$ production in pA to pp scaled by mass number as a function of mass number. Shown are the 1S and 2S+3S $\Upsilon$ measurements from E772 and our 1S measurement.
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