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Paul Sorensen

Publications and source records attributed to Paul Sorensen.

30 records · Page 2Linked to original sources
arXiv2010

Implications of space-momentum correlations and geometric fluctuations in heavy-ion collisions

The standard picture of heavy-ion collisions includes a collective expansion. If the initial energy density in the collisions is lumpy, then a collective expansion can convert that spatial lumpiness into correlations between final-state particles. Correlations measurements in heavy-ion collisions show several prominent features not present in proton-proton collisions. I argue that many features of these correlations are related to the transference of over-densities from the initial overlap region into momentum-space during the quark gluon plasma phase of the expansion. I show results from a toy Monte-Carlo to illustrate the consequences of lumpy initial conditions and a collective expansion.

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arXiv2009

Elliptic Flow: A Study of Space-Momentum Correlations In Relativistic Nuclear Collisions

Here I review measurements of v2, the second component in a Fourier decomposition of the azimuthal dependence of particle production relative to the reaction plane in heavy-ion collisions. v2 is an observable central to the interpretation of the subsequent expansion of heavy-ion collisions. Its large value indicates significant space-momentum correlations, consistent with the rapid expansion of a strongly interacting Quark Gluon Plasma. Data is reviewed for collision energies from sqrt[sNN] = 2 to 200 GeV. Scaling observations and comparisons to hydrodynamic models are discussed.

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arXiv2008

Interpreting Near-side Correlations

Recent data from heavy ion collisions at RHIC show strong near-side correlations extending over several units of rapidity. This ridge-like correlation exhibits an abrupt onset with collision centrality. In this talk, I argue that the centrality and beam-energy dependence of these near-angle correlations could provide access to information about the Quark Gluon Plasma phase boundary and the Equation of State of nuclear matter. A beam-energy-scan at RHIC will better reveal the true source of these correlations and should be a high priority at RHIC.

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arXiv2008

Searching for Superhorizon Fluctuations in Heavy-Ion Collisions

In this talk I discuss novel explanations for the azimuthal correlations observed in heavy-ion collisions. I review some ideas about correlations and the evolution of heavy-ion collisions. Some aspects of the correlations observed in heavy-ion collisions may be indicitive of the suppression of super-horizon fluctuations.

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arXiv2008

Coalescence Models For Hadron Formation From Quark Gluon Plasma

We review hadron formation from a deconfined quark gluon plasma (QGP) via coalescence or recombination of quarks and gluons. We discuss the abundant experimental evidence for coalescence from the Relativistic Heavy Ion Collider (RHIC) and compare the various coalescence models advocated in the literature. We comment on the underlying assumptions and remaining challenges as well as the merits of the models. We conclude with a discussion of some recent developments in the field.

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arXiv2007

Elliptic flow fluctuations in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV

Please note that after these results were reported at Quark Matter 2006 and posted on the preprint server it was found that what is reported here as \textit{elliptic flow fluctuations}, should rather be taken as an upper limit on the fluctuations. Further analysis has shown that fitting the multiplicity dependence of the q-distribution does not enable one to disentangle non-flow and fluctuations. The data from the q-vector distrubution does not, therefore, exclude the case of zero fluctuations. The remainder of these proceedings we leave as they were originally reported.

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arXiv2007

Evidence from Identified Particles for Active Quark and Gluon Degrees of Freedom

Measurements of intermediate pT (1.5 < pT < 5.0 GeV/c) identified particle distributions in heavy ion collisions at SPS and RHIC energies display striking dependencies on the number of constituent quarks in the corresponding hadron. One finds that elliptic flow at intermediate pT follows a constituent quark scaling law as predicted by models of hadron formation through coalescence. In addition, baryon production is also found to increase with event multiplicity much faster than meson production. The rate of increase is similar for all baryons, and seemingly independent of mass. This indicates that the number of constituent quarks determines the multiplicity dependence of identified hadron production at intermediate pT. We review these measurements and interpret the experimental findings.

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arXiv2007

RHIC Critical Point Search: Assessing STAR's Capabilities

In this report we discuss the capabilities and limitations of the STAR detector to search for signatures of the QCD critical point in a low energy scan at RHIC. We find that a RHIC low energy scan will cover a broad region of interest in the nuclear matter phase diagram and that the STAR detector -- a detector designed to measure the quantities that will be of interest in this search -- will provide new observables and improve on previous measurements in this energy range.

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arXiv2006

Particle dependence of elliptic flow in Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV

The elliptic flow parameter ($v_2$) for $K_S^0$ and $Λ+\barΛ$ has been measured at mid-rapidity in Au + Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV by the STAR collaboration. The $v_2$ values for both $K_S^{0}$ and $Λ+\barΛ$ saturate at moderate $p_T$, deviating from the hydrodynamic behavior observed in the lower $p_T$ region. The saturated $v_2$ values and the $p_T$ scales where the deviation begins are particle dependent. The particle-type dependence of $v_2$ shows features expected from the hadronization of a partonic ellipsoid by coalescence of co-moving quarks. These results will be discussed in relation to the nuclear modification factor ($R_{CP}$) which has also been measured for $K_S^0$ and $Λ+\barΛ$ by the STAR collaboration.

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arXiv2004

Identified particle measurements at RHIC: elucidating hadronization mechanisms for bulk partonic matter

Measurements of identified particle momentum spectra at center of mass energy 200 GeV are reviewed. Emphasis is placed on the azimuthal dependence and the centrality dependence of hadron yields at intermediate transverse momentum (1.5 < p_T < 5 GeV/c). The first measurements of the fourth harmonic term (v_4) in the azimuthal variation of identified particle yields are shown. The recombination mechanism of hadron formation provides a consistent description of the dependence of these measurements on particle-type.

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arXiv2002

Azimuthal anisotropy of K^0_S and Lambda production at mid-rapidity from Au+Au collisions at root s_NN = 130 GeV

We report STAR results on the azimuthal anisotropy parameter v2 for strange particles K0S and Lambda at midrapidity in Au+Au collisions at /s_NN = 130 GeV at RHIC. The value of v2 as a function of transverse momentum pt and collision centrality is presented for both particles and compared to model calculations. A strong pt dependence in v2 is observed up to pt ~2.0 GeV/c where v2 begins to saturate.

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