We report transverse momentum ($p_{T} \leq15$ GeV/$c$) spectra of $\pi^{\pm}$, $K^{\pm}$, $p$, $\bar{p}$, $K_{S}^{0}$, and $\rho^{0}$ at mid-rapidity in p+p and Au+Au collisions at $\sqrt{s_{_{NN}}}$ ...= 200 GeV. Perturbative QCD calculations are consistent with $\pi^{\pm}$ spectra in p+p collisions but do not reproduce $K$ and $p(\bar{p})$ spectra. The observed decreasing antiparticle-to-particle ratios with increasing $p_T$ provide experimental evidence for varying quark and gluon jet contributions to high-$p_T$ hadron yields. The relative hadron abundances in Au+Au at $p_{T}{}^{>}_{\sim}8$ GeV/$c$ are measured to be similar to the p+p results, despite the expected Casimir effect for parton energy loss.
The STAR experiment was primarily designed to detect signals of a possible phase transition in nuclear matter. Its layout, typical for a collider experiment, contains a large Time Projection Chamber ...(TPC) in a solenoid magnet, a set of four layers of combined silicon strip and silicon drift detectors for secondary vertex reconstruction, plus other detectors. In this presentation, we will report on recent global and individual detector element alignment as well as drift velocity calibration work performed on this STAR inner silicon tracking system. We will show how attention to details positively impacts the physics capabilities of STAR and explain the iterative procedure conducted to reach such results in low, medium and high track density and detector occupancy.
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 sqrts = 500 GeV by the STAR experiment at RHIC. The measured asymmetries, A(L)(W+) = -0.27 ± 0.10(stat.) ± 0.02(syst.) ± 0.03(norm.) and A(L)(W-) = 0.14 ± 0.19(stat.) ± 0.02(syst.) ± 0.01(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 deep-inelastic scattering measurements.
The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at √s=200 GeV has been measured using ...azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of pT≥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 pT.
We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au+Au collisions at sNN=200 GeV using the STAR ...detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage −1.3,1.3. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.
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 pT even under the extreme case for the ratio of B to D contributions to non-photonic electrons.
We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at 200 GeV using the STAR detector ...at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage -1.3, 1.3. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.
OO/C++ reconstruction model based on GEANT3 Fine, V.E.; Fisyak, Y.V.; Nevski, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2003, Volume:
502, Issue:
2
Journal Article
Peer reviewed
An OO reconstruction model providing access to a GEANT3 geometry has been developed within the ROOT framework. The model includes classes to store GEANT3 simulated detector response (digits) and ...tools supporting navigation from digits to the geometry and vice versa.
Charged-particle spectra associated with direct photon ({gamma}{sub dir}) and {pi}{sup 0} are measured in p+p and Au+Au collisions at center-of-mass energy {radical}(s{sub N{sub N}})=200 GeV with the ...STAR detector at the Relativistic Heavy Ion Collider. A shower-shape analysis is used to partially discriminate between {gamma}{sub dir} and {pi}{sup 0}. Assuming no associated charged particles in the {gamma}{sub dir} direction (near side) and small contribution from fragmentation photons ({gamma}{sub frag}), the associated charged-particle yields opposite to {gamma}{sub dir} (away side) are extracted. In central Au+Au collisions, the charged-particle yields at midrapidity (|{eta}|<1) and high transverse momentum (3<p{sub T}{sup assoc}<16 GeV/c) associated with {gamma}{sub dir} and {pi}{sup 0} (|{eta}|<0.9, 8<p{sub T}{sup 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 is similar for {gamma}{sub dir} and {pi}{sup 0} and independent of the {gamma}{sub dir} energy within uncertainties. These measurements indicate that, in the kinematic range covered and within our current experimental uncertainties, the parton energy loss shows no sensitivity to the parton initial energy, path length, or color charge.
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