arXiv subjects

S. Gliske

Publications and source records attributed to S. Gliske.

At least 37 records · Page 2Linked to original sources

arXiv2014

Beam-Energy Dependence of Directed Flow of Protons, Antiprotons and Pions in Au+Au Collisions

Rapidity-odd directed flow($v_1$) measurements for charged pions, protons and antiprotons near mid-rapidity ($y=0$) are reported in $\sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV Au + Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). At intermediate impact parameters, the proton and net-proton slope parameter $dv_1/dy|_{y=0}$ shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton $dv_1/dy|_{y=0}$ changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.

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arXiv2014

Beam energy dependent two-pion interferometry and the freeze-out eccentricity of pions in heavy ion collisions at STAR

We present results of analyses of two-pion interferometry in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV measured in the STAR detector as part of the RHIC Beam Energy Scan program. The extracted correlation lengths (HBT radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality, and transverse mass ($m_{T}$) of the particles. The azimuthal analysis allows extraction of the eccentricity of the entire fireball at kinetic freeze-out. The energy dependence of this observable is expected to be sensitive to changes in the equation of state. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The eccentricity shows a monotonic decrease with beam energy that is qualitatively consistent with the trend from all model predictions and quantitatively consistent with a hadronic transport model.

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arXiv2014

Beam-helicity asymmetry in associated electroproduction of real photons $ep \to eγπN$ in the $Δ$-resonance region

The beam-helicity asymmetry in associated electroproduction of real photons, $ep\to eγπN$, in the $Δ$(1232)-resonance region is measured using the longitudinally polarized HERA positron beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels, $ep\to eγπ^0 p$ and $ep\to eγπ^+ n$, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.

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arXiv2013

Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions at sqrt{s} = 200 GeV

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range 0.8 < η < 2.0 in polarized proton-proton collisions at sqrt{s} = 200 GeV are presented. Neutral pions were detected using the endcap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of 5 < p_T < 16 GeV/c and is found to be within the scale uncertainty of a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry, A_LL, is measured in the same pseudorapidity range. This quantity is sensitive to the gluonic contribution to the proton spin, Δg(x), at low Bjorken-x (down to x approx 0.01), where it is less constrained by measurements at central pseudorapidity. The measured A_LL is consistent with model predictions. The parity-violating asymmetry, A_L, is also measured and found to be consistent with zero. The transverse single-spin asymmetry, A_N, is measured within a previously unexplored kinematic range in Feynman-x and p_T. Such measurements may aid our understanding of the on-set and kinematic dependence of the large asymmetries observed at more forward pseudorapidity (η approx 3) and their underlying mechanisms. The A_N results presented are consistent with a twist-3 model prediction of a small asymmetry within the present kinematic range.

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arXiv2013

Transverse target single-spin asymmetry in inclusive electroproduction of charged pions and kaons

Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the HERMES experiment. The asymmetries were studied as a function of the azimuthal angle $ψ$ about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum relative to the direction of the incident beam, and the Feynman variable $x_F$. The $\sin(ψ)$ amplitudes are positive for positive pions and kaons, slightly negative for negative pions and consistent with zero for negative kaons, with particular transverse-momentum but weak $x_F$ dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer.

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arXiv2013

Energy Dependence of Moments of Net-proton Multiplicity Distributions at RHIC

We report the beam energy (\sqrt s_{NN} = 7.7 - 200 GeV) and collision centrality dependence of the mean (M), standard deviation (σ), skewness (S), and kurtosis (κ) of the net-proton multiplicity distributions in Au+Au collisions. The measurements are carried out by the STAR experiment at midrapidity (|y| < 0.5) and within the transverse momentum range 0.4 < pT < 0.8 GeV/c in the first phase of the Beam Energy Scan program at the Relativistic Heavy Ion Collider. These measurements are important for understanding the Quantum Chromodynamic (QCD) phase diagram. The products of the moments, Sσand κσ^{2}, are sensitive to the correlation length of the hot and dense medium created in the collisions and are related to the ratios of baryon number susceptibilities of corresponding orders. The products of moments are found to have values significantly below the Skellam expectation and close to expectations based on independent proton and anti-proton production. The measurements are compared to a transport model calculation to understand the effect of acceptance and baryon number conservation, and also to a hadron resonance gas model.

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arXiv2013

Forward Neutral Pion Cross Section and Spin Asymmetry Measurements at STAR

The STAR endcap electromagnetic calorimeter (EEMC) was designed to allow measurement of cross sections and spin observables in the forward direction, $1 < η< 2$ and with the full azimuth. Using the EEMC to measure double longitudinal spin asymmetries in photonic channels---such as inclusive neutral pions, prompt photon, and prompt photon + jet---allows access to $ΔG$ within a low Bjorken-$x$ region ($0.01 < x < 0.33$ at $\sqrt{s}=200$) where $ΔG$ is poorly constrained. Additionally, transverse spin asymmetries, shown to be zero at $η$ near zero and as large as 10\% at $η$ near 4, occupy a previously unmeasured region in the 3D pseudorapidity, transverse momentum, and $x$-Feynman phase space when measured with the EEMC. The neutral pion cross section measurement verifies that the signal of interest can be properly reconstructed and isolated from the background. Pion reconstruction techniques in the STAR EEMC will be discussed and preliminary cross-section and transverse single spin asymmetry measurements presented.

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arXiv2013

Dihadron production in semi-inclusive DIS from transversely polarized protons

Transverse Momentum Dependent (TMD) dihadron production, including vector meson production, allows access to various TMD distribution and fragmentation functions. Dihadron production is complementary to single hadron semi-inclusive DIS measurements, pairing the same distribution functions with different fragmentation functions. While dihadrons present unique measurement opportunities, the TMD dihadron cross section is significantly more complex than that for single hadron production, due to the polarization in the final state. Various theoretical advances, which further clarify the complexity, will be highlighted. The HERMES analysis of the transverse target moments of the TMD dihadron cross section allows the first test of a particular prediction of the Lund/Artru string fragmentation model, specifically that the favored Collins fragmentation function has opposite sign in single hadron production versus vector meson production. The status and results of this analysis will be discussed and an extension of the Lund/Artru model for disfavored fragmentation will also be presented.

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arXiv2013

Third Harmonic Flow of Charged Particles in Au+Au Collisions at sqrtsNN = 200 GeV

We report measurements of the third harmonic coefficient of the azimuthal anisotropy, v_3, known as triangular flow. The analysis is for charged particles in Au+Au collisions at sqrtsNN = 200 GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. Two-particle correlations as a function of their pseudorapidity separation are fit with narrow and wide Gaussians. Measurements of triangular flow are extracted from the wide Gaussian, from two-particle cumulants with a pseudorapidity gap, and also from event plane analysis methods with a large pseudorapidity gap between the particles and the event plane. These results are reported as a function of transverse momentum and centrality. A large dependence on the pseudorapidity gap is found. Results are compared with other experiments and model calculations.

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arXiv2013

Measurement of the virtual-photon asymmetry A2 and the spin-structure function g2 of the proton

A measurement of the virtual-photon asymmetry A_2(x,Q^2) and of the spin-structure function g_2(x,Q^2) of the proton are presented for the kinematic range 0.004 < x < 0.9 and 0.18 GeV^2 < Q^2 < 20 GeV^2. The data were collected by the HERMES experiment at the HERA storage ring at DESY while studying inclusive deep-inelastic scattering of 27.6 GeV longitudinally polarized leptons off a transversely polarized hydrogen gas target. The results are consistent with previous experimental data from CERN and SLAC. For the x-range covered, the measured integral of g_2(x) converges to the null result of the Burkhardt-Cottingham sum rule. The x^2 moment of the twist-3 contribution to g_2(x) is found to be compatible with zero.

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arXiv2013

Multiplicities of charged pions and kaons from semi-inclusive deep-inelastic scattering by the proton and the deuteron

Multiplicities in semi-inclusive deep-inelastic scattering are presented for each charge state of π^\pm and K^\pm mesons. The data were collected by the HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron beams incident on a hydrogen or deuterium gas target. The results are presented as a function of the kinematic quantities x_B, Q^2, z, and P_h\perp. They represent a unique data set for identified hadrons that will significantly enhance our understanding of the fragmentation of quarks into final-state hadrons in deep-inelastic scattering.

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arXiv2013

Single Spin Asymmetry $A_N$ in Polarized Proton-Proton Elastic Scattering at $\sqrt{s}=200$ GeV

We report a high precision measurement of the transverse single spin asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant 0.035$ $\GeVcSq$, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of $A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.

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arXiv2013

Azimuthal distributions of charged hadrons, pions, and kaons produced in deep-inelastic scattering off unpolarized protons and deuterons

The azimuthal cosϕ and cos2ϕ modulations of the distribution of hadrons produced in unpolarized semi-inclusive deep-inelastic scattering of electrons and positrons off hydrogen and deuterium targets have been measured in the HERMES experiment. For the first time these modulations were determined in a four-dimensional kinematic space for positively and negatively charged pions and kaons separately, as well as for unidentified hadrons. These azimuthal dependences are sensitive to the transverse motion and polarization of the quarks within the nucleon via, e.g., the Cahn, Boer-Mulders and Collins effects.

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arXiv2013

Elliptic flow of identified hadrons in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7--62.4 GeV

Measurements of the elliptic flow, $v_{2}$, of identified hadrons ($π^{\pm}$, $K^{\pm}$, $K_{s}^{0}$, $p$, $\bar{p}$, $ϕ$, $Λ$, $\barΛ$, $Ξ^{-}$, $\barΞ^{+}$, $Ω^{-}$, $\barΩ^{+}$) in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV are presented. The measurements were done at mid-rapidity using the Time Projection Chamber and the Time-of-Flight detectors of the STAR experiment during the Beam Energy Scan program at RHIC. A significant difference in the $v_{2}$ values for particles and the corresponding anti-particles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, $\sqrt{s_{NN}}$ (or increasing baryon chemical potential, $μ_{B}$) and is larger for the baryons as compared to the mesons. This implies that particles and anti-particles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of $v_{2}$ that was observed at $\sqrt{s_{NN}}=$ 200 GeV. However, for the group of particles NCQ scaling at $(m_{T}-m_{0})/n_{q}>$ 0.4 GeV/$c^{2}$ is not violated within $\pm$10%. The $v_{2}$ values for $ϕ$ mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured $p_{T}$ values.

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arXiv2013

Observation of an energy-dependent difference in elliptic flow between particles and anti-particles in relativistic heavy ion collisions

Elliptic flow ($v_{2}$) values for identified particles at mid-rapidity in Au+Au collisions, measured by the STAR experiment in the Beam Energy Scan at RHIC at $\sqrt{s_{NN}}=$ 7.7--62.4 GeV, are presented. A beam-energy dependent difference of the values of $v_{2}$ between particles and corresponding anti-particles was observed. The difference increases with decreasing beam energy and is larger for baryons compared to mesons. This implies that, at lower energies, particles and anti-particles are not consistent with the universal number-of-constituent-quark (NCQ) scaling of $v_{2}$ that was observed at $\sqrt{s_{NN}}=$ 200 GeV.

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arXiv2012

Beam-helicity asymmetry arising from deeply virtual Compton scattering measured with kinematically complete event reconstruction

The beam-helicity asymmetry in exclusive electroproduction of real photons by the longitudinally polarized HERA positron beam scattering off an unpolarized hydrogen target is measured at HERMES. The asymmetry arises from deeply virtual Compton scattering and its interference with the Bethe--Heitler process. Azimuthal amplitudes of the beam-helicity asymmetry are extracted from a data sample consisting of $ep\rightarrow epγ$ events with detection of all particles in the final state including the recoiling proton. The installation of a recoil detector, while reducing the acceptance of the experiment, allows the elimination of background from $ep\rightarrow eNπγ$ events, which was estimated to contribute an average of about 12% to the signal in previous HERMES publications. The removal of this background from the present data sample is shown to increase the magnitude of the leading asymmetry amplitude by 0.054 +/- 0.016 to -0.328 +/- 0.027 (stat.) +/- 0.045 (syst.).

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arXiv2012

Measurements of $D^{0}$ and $D^{*}$ Production in $p$ + $p$ Collisions at $\sqrt{s}$ = 200 GeV

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 $D^{0}\rightarrow K^{-}π^{+}$, $D^{*+}\rightarrow D^{0}π^{+}\rightarrow K^{-}π^{+}π^{+}$ 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 $dσ/dy|_{y=0}^{c\bar{c}}$ = 170 $\pm$ 45 (stat.) $^{+38}_{-59}$ (sys.) $μ$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.

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arXiv2012

Di-electron spectrum at mid-rapidity in $p+p$ collisions at $\sqrt{s} = 200$ GeV

We report on mid-rapidity mass spectrum of di-electrons and cross sections of pseudoscalar and vector mesons via $e^{+}e^{-}$ decays, from $\sqrt{s} = 200$ GeV $p+p$ collisions, measured by the large acceptance experiment STAR at RHIC. The ratio of the di-electron continuum to the combinatorial background is larger than 10% over the entire mass range. Simulations of di-electrons from light-meson decays and heavy-flavor decays (charmonium and open charm correlation) are found to describe the data. The extracted $ω\rightarrow e^{+}e^{-}$ invariant yields are consistent with previous measurements. The mid-rapidity yields ($dN/dy$) of $ϕ$ and $J/ψ$ are extracted through their di-electron decay channels and are consistent with the previous measurements of $ϕ\rightarrow K^{+}K^{-}$ and $J/ψ\rightarrow e^{+}e^{-}$. Our results suggest a new upper limit of the branching ratio of the $η\rightarrow e^{+}e^{-}$ of $1.7\times10^{-5}$ at 90% confidence level.

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