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Rolf P Scharenberg Purdue University

Long-Range Forward-Backward Correlations and the formation of Partonic matter in Au-Au collisions at √s nn = 200 GeV. Rolf P Scharenberg Purdue University. Motivation. The investigation of high energy nucleus-nucleus collisions provides

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Rolf P Scharenberg Purdue University

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  1. Long-Range Forward-Backward Correlations and the formation of Partonic matter in Au-Au collisions at √s nn = 200 GeV Rolf P Scharenberg Purdue University

  2. Motivation • The investigation of high energy nucleus-nucleus collisions provides • an important tool to study the properties of hot and dense matter. The • motivation is drawn from lattice QCD numerical simulations, which • predict a transition from hadronic matter to a system of deconfined • quarks and gluons (QGP) at high temperature[1]. • With the large number of particles produced in heavy ion collisions • it has now become feasible to study fluctuations in forward-backward • multiplicity correlations on an event-by-event basis. Long range • pseudorapidity correlations are a unique signature for multiple • parton-parton interactions and the formation of dense gluon-quark • matter. 1. F. Karsch et al., Nucl. Phys. B605 579, (2001).

  3. Multiparticle production at high energies is can be described in terms of color strings stretched between the projectile and target. These strings hadronize to produce the observed particles. The # of strings grow with energy and the # of participating nucleons. Interaction between the strings must be considered. This problem acquires even more importance considering that, at very high energies, collisions of heavy nuclei at RHIC may produce many strings that can fill a volume. The interaction of the strings (multiple parton-parton scattering) in the volume is expected to subsequently evolve into a quark-gluon-plasma (QGP).

  4. <nf nb> - <nf > <nb> b = <nf 2> - <nf >2 F-B Correlations The multiplicities nf andnb , of the produced charged particles form the forward and backward correlation : < nb > (nf) = a + b nf Where < nb > is the mean backward multiplicity at a fixed forward multiplicity nfand a and b are constants. The coefficients a and b are determined by minimizing < [nb -(a+ b nf )]2> ( Linear Regression) = = Correlation Strength

  5. Fluctuation in # of inelastic collisions F-B Correlations • A gap about midrapidity will reduce the effect of short-range • correlations due to clusters, jets etc. • Dual Parton Model (DPM) assumes short-range correlations are confined to individual strings. • A. Capella et al., Phys. Rep. 236, 225(1994). • A. Capella and A. Krzywicki , Phys. Rev. D184,120(1978). • Long-range correlations are due to superposition of a fluctuating number of strings. short-range

  6. High Energy F-B Correlations Low Energy Strings Long Range Long Range Short + Long Range Backward nb Forward nf η - η1 η1 η2 - η2 0 STAR TPC coverage -1.0 < η < 1.0 Rapidity Gap Rapidity Interval

  7. F-B Correlations Analysis • Au+Au and p+p at 200 GeV. • 2. For Au+Au, eight centrality bins as defined by STAR charged particle reference multiplicity: • 0-10%, 10-20%, …, 70-80%. • |η| < 0.5 • 0.1 < pt < 1.0 GeV, • 3. Backward and forward intervals are 0.2 units in η. Intervals are separated by an increasing gap about midrapidty from 0 to 1.6. In case of A-A collisions the major source of non-dynamical fluctuations are due to the finite centrality bin width.

  8. STAR PreliminarySTAR Preliminary <nf> <nb> Nch Nch • STAR PreliminarySTAR Preliminary <nf*nf> <nf*nb> Nch Nch F-B Correlations • Calculate <nf>, <nb>, <nf>2, and <nf*nb> as functions of STAR reference multiplicity Nch.

  9. Calculating Dispersion • Previous quantities now expressed as function of Nch, eg. • Use to calculate respective dispersions as function of Nch,

  10. Preliminary 0-10% central Au+Au collisions The measured correlation strength b is nearly constant for all the gaps. We know that the SRC peaks at at =0 and the SRC decays as exp-(1-2) /  with  ~ 1. A second component (LRC) is present

  11. Preliminary

  12. 0-10% central Au+Au The SRC part from total correlation strength has been subtracted by scaling up the pp value to the =0 value Preliminary The LRC grows with the increasing pseudorapidity gap

  13. Preliminary Growth of LRC with centrality The LRC has become very weak by 30-40% centrality.

  14. Preliminary Comparison with models HIJING: (SRC) PSM: (SRC+LRC) PSM is the Parton String Model which is based on the Dual Parton Model

  15. PSM - fluctuating strings where the average multiplicities of in the forward and backward regions is given by and respectively in each elementary inelastic collision. The fluctuation in the number of elementary inelastic collisions is given by In the PSM the LRC originates from multiple partonic interactions The Color Glass Condensate (CGC) provides a theoretical QCD based description of multiple string interactions . The CGC argues for the existence of a LRC in rapidity, similar to those predicted in DPM. Recently, long range forward-backward multiplicity correlations have been discussed in the framework of the CGC and predict the growth of the LRC with the centrality of the collision .

  16. LRC summary This is the first measurement of the long-range correlation strength (LRC) in ultra relativistic nucleus-nucleus collisions. Both the DPM and CGC argue that the long range correlations are due to multiple parton-parton interactions. This indicates that dense partonic matter (gluon-quark matter) has been formed in mid-central and central Au+Au collisions at √sNN = 200 GeV. = 200 GeV.

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