arXiv subjects

Z. Chajecki

Publications and source records attributed to Z. Chajecki.

44 records · Page 3Linked to original sources

arXiv2010

K*0 production in Cu+Cu and Au+Au collisions at \sqrt{s_NN} = 62.4 GeV and 200 GeV

We report on K*0 production at mid-rapidity in Au+Au and Cu+Cu collisions at \sqrt{s_{NN}} = 62.4 and 200 GeV collected by the Solenoid Tracker at RHIC (STAR) detector. The K*0 is reconstructed via the hadronic decays K*0 \to K+ pi- and \bar{K*0} \to K-pi+. Transverse momentum, pT, spectra are measured over a range of pT extending from 0.2 GeV/c to 5 GeV/c. The center of mass energy and system size dependence of the rapidity density, dN/dy, and the average transverse momentum, , are presented. The measured N(K*0)/N(K) and N(ϕ)/N(K*0) ratios favor the dominance of re-scattering of decay daughters of K*0 over the hadronic regeneration for the K*0 production. In the intermediate pT region (2.0 < pT < 4.0 GeV/c), the elliptic flow parameter, v2, and the nuclear modification factor, RCP, agree with the expectations from the quark coalescence model of particle production.

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arXiv2010

Upsilon cross section in p+p collisions at sqrt(s) = 200 GeV

We report on a measurement of the Upsilon(1S+2S+3S) -> e+e- cross section at midrapidity in p+p collisions at sqrt(s)=200 GeV. We find the cross section to be 114 +/- 38 (stat.) +23,-24 (syst.) pb. Perturbative QCD calculations at next-to-leading order in the Color Evaporation Model are in agreement with our measurement, while calculations in the Color Singlet Model underestimate it by 2 sigma. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of Upsilon data to RHIC energies. The dielectron continuum in the invariant mass range near the Upsilon is also studied to obtain a combined cross section of Drell-Yan plus (b b-bar) -> e+e-.

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arXiv2009

Pion Interferometry in Au+Au and Cu+Cu Collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 and 200 GeV

We present a systematic analysis of two-pion interferometry in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 GeV and Cu+Cu collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 and 200 GeV using the STAR detector at RHIC. The multiplicity and transverse momentum dependences of the extracted correlation lengths (radii) are studied. The scaling with charged particle multiplicity of the apparent system volume at final interaction is studied for the RHIC energy domain. The multiplicity scaling of the measured correlation radii is found to be independent of colliding system and collision energy.

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arXiv2008

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

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 $ν_{+-{\rm,dyn}}$. 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.

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arXiv2006

Strange baryon resonance production in $\sqrt{s_{NN}} = 200$ GeV $p+p$ and $Au+Au$ collisions

We report the measurements of $Σ(1385)$ and $Λ(1520)$ 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.

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arXiv2005

Pion Interferemetry from p+p to Au+Au in STAR

The geometric substructure of the particle-emitting source has been characterized via two-particle interferometry by the STAR collaboration for all energies and colliding systems at RHIC. We present systematic studies of charged pion interferometry. The collective nature of the source is revealed through the $m_T$ dependence of HBT radii for all particle types. Preliminary results suggest a scaling in the pion HBT radii with overall system size, as central Au+Au collisions are compared to peripheral collisions as well as with Cu+Cu and even with d+Au and p+p collisions, naively suggesting comparable flow strength in all systems. To probe this issue in greater detail, multidimensional correlation functions are studied using a spherical decomposition method. This allows clear identification of source anisotropy and, for the light systems, the presence of significant long-range non-femtoscopic correlations.

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arXiv2005

Identical Particle Correlations in STAR

Preliminary results of identical-particle correlations probing the geometric substructure of the particle-emitting source at RHIC are presented. An $m_T$-independent scaling of pion HBT radii from large (central Au+Au) to small (p+p) collision systems naively suggests comparable flow strength in all of them. Multidimensional correlation functions are studied in detail using a spherical decomposition method. In the light systems, the presence of significant long-range non-femtoscopic correlations complicates the extraction of HBT radii.

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arXiv2005

AA versus pp and dA: A puzzling scaling in HBT@RHIC

A nontrivial space-time structure of the hot system created at RHIC is the defining aspect of the physics of relativistic heavy ion collisions. Femtoscopy through pion intensity interferometry provides direct access to the dynamic geometric substructure of the freeze-out stage, and appears to confirm source evolution via collective flow. Since flow is usually considered to be a bulk phenomenon, it is surpring to find a simple scaling in preliminary HBT radii from p+p, d+Au and Au+Au collisions. Investigating the light system data in detail, we discuss a new way to visualize the ``fine structure'' of 3D correlation functions and the potential importance of long range correlations.

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