1. Terence Tarnowsky Long-Range Multiplicity Correlations in Au+Au at Terence J Tarnowsky Purdue University for the STAR Collaboration 22nd Winter Workshop on Nuclear Dynamics San Diego, CA March 12-18, 2006

2. Terence TarnowskyWWND, 3/12/06, La Jolla, CA2 Outline I. Motivation II. Color Strings/Soft Particle Production Models III. F-B Multiplicity Correlations IV. Results V. Summary

3. Terence Tarnowsky3 Study of correlations among particles produced in different rapidity regions helps to understand the mechanisms of particle production. Many experiments show strong positive short-range correlations, indicating clustering of particles over a region of ~ 1 unit in rapidity. Production of particles in the central rapidity region dominated at all energies by these short-range correlations. Longer range correlations are observed in h-h interactions only at high energies. It has been suggested that the long-range correlations might be much stronger in h-A and A-A interactions, compared to h-h scattering at the same energy. Strong, long-range correlations are an indication of multiple inelastic collisions [1,2]. Motivation 1. Dual Parton Model (DPM): A. Capella et al., Phys. Rep. 236, 225 (1994). 2. A. Capella and A. Krzywicki, Phys. Rev. D184,120(1978).

4. Terence TarnowskyWWND, 3/12/06, La Jolla, CA4 Color Strings At low energies, valence quarks of nucleons form strings that then hadronize  wounded nucleon model. At high energies, contribution of sea quarks and gluons becomes dominant. –Additional color strings formed. –Multiple inelastic parton scattering.

5. Terence TarnowskyWWND, 3/12/06, La Jolla, CA5 Color Strings Created in nuclear collisions. Considered effective sources w/ fixed transverse area, r T ≈ 0.2 fm At large string density: Strings overlap. Clusters formed. Study of cluster dynamics allows calculation of physical observables. A.Capella, et al. Phys. Report. 236,225(1994) M.A.Braun and C.Pajares. Nucl. Phys. B390,542(1993)

6. Terence TarnowskyWWND, 3/12/06, La Jolla, CA6 Dual Parton Model (DPM) Model describing soft hadronic particle processes. Particle production proceeds via a Schwinger-type mechanism, –Strings hadronize to produce quark-antiquark pairs. DPM assumes that all strings hadronize independently. A. Capella et al., Phys. Rep. 236, 225 (1994).

7. Terence Tarnowsky7 The independence of string fragmentation in models such as DPM is considered a strong assumption. Since the average number of strings increases with energy: Simple mechanism of multiparticle production becomes invalid. Overlapping strings could merge into “ropes” or fuse, leading to F-B correlations very different from the ones predicted in independent string models. When strings fuse w/o producing long-range correlations, a decrease of F-B correlations compared to independent string picture is expected [1,2,3]. 1.N. S. Amelin, N. Armesto, M.A.Braun, E. G. Ferrerio and C. Pajares Phys. Rev. Lett. 73, 2813(1994). 2. N. Armesto, M.A.Braun, E. G. Ferrerio and C. Pajares Z. Phys. C67, 489 (1995). 3.M. A. Braun, C. Pajares and J. Ranft Int. J. Mod. Phys. A14, 2689(1999). Beyond DPM Can interpret string fusion as an intermediate stage towards QGP formation.

8. Terence TarnowskyWWND, 3/12/06, La Jolla, CA8 Parton String Model (PSM) At high string densities, color fields overlap and fusion can occur. Monte Carlo model, based on DPM, but includes string interaction: –Fusion of soft string pairs. Fusion leads to: –Reduction in particle multiplicity (≈ 30%) compared to N bin scaling from pp. – enhancement. Conservation of energy-momentum. Pion 0.35 GeV/c in pp, 0.44 GeV/c in Au+Au. –Both effects seen in RHIC data. Similar to QGSM, A.B.Kaidalov, Phys. Lett. B116 (1982) 459

9. Terence TarnowskyWWND, 3/12/06, La Jolla, CA9 F-B Multiplicity Correlations Predicted in context of DPM. Test of multiple [partonic] scattering. Linear expression relating N b, N f found in hadron- hadron experiments (ex. UA5), “b” is correlation strength. –Function of √s and A. –Coefficient can be expressed as, LRC exists only if:

10. Terence TarnowskyWWND, 3/12/06, La Jolla, CA10 Measurement of Long-Range Multiplicity Correlations A gap about midrapidity will eliminate effect of short-range correlations (e.g.from clustering, jets, …) –DPM assumes short-range correlations confined to individual strings. –Long-range correlations due to superposition of fluctuating number of strings. Fluctuation in # of inelastic collisions

11. Terence TarnowskyWWND, 3/12/06, La Jolla, CA11 STAR Detector

12. Terence TarnowskyWWND, 3/12/06, La Jolla, CA12 η η1η1 η2η2 - η 1 - η 2 0 Forward n f Backward n b Rapidity Gap Rapidity interval High Energy Long Range Short + Long Range Low Energy Strings

13. Terence TarnowskyWWND, 3/12/06, La Jolla, CA13 Analysis 1.Au+Au at 200 GeV. 2.For Au+Au, eight centrality bins as defined by STAR charged particle reference multiplicity: 0-10%, 10-20%, …, 70-80%. - Primary tracks - |  | < 0.5 - TPC fit points >= 10 - dca < 3 cm 3. Eliminate short-range correlation by considering backward and forward intervals (0.2 units) separated by at least 1.5 pseudorapidity units. 4.The forward region is 0.8 <  < 1.0, while the backward region is -1.0 <  < - 0.8. Intervals are symmetric with a gap of  =1.6. 6. 0.1 < p T < 1.2 GeV, |v z | < 30 cm.

14. Terence TarnowskyWWND, 3/12/06, La Jolla, CA14 Calculating Dispersion Calculate,, 2, and as functions of STAR reference multiplicity. N ch N ch STAR Preliminary N ch STAR Preliminary

15. Terence TarnowskyWWND, 3/12/06, La Jolla, CA15 Calculating Dispersion Previous quantities now expressed as function of N ch, eg. Use to calculate respective dispersions as function of N ch,

16. Terence TarnowskyWWND, 3/12/06, La Jolla, CA16 Uncorrected Dispersion Results Results *before* corrections for TPC tracking efficiency/acceptance. STAR Preliminary Non-zero long-range correlation!

17. Terence TarnowskyWWND, 3/12/06, La Jolla, CA17 Binned Results STAR Preliminary Can now be binned according to STAR minbias centrality cuts. Results corrected for tracking efficiency & detector acceptance.

18. Terence TarnowskyWWND, 3/12/06, La Jolla, CA18 Comparison to Independent PSM Independent string picture shows: - Good agreement in peripheral collisions. - Large discrepancy in central collisions STAR Preliminary

19. Terence TarnowskyWWND, 3/12/06, La Jolla, CA19 STAR Preliminary Comparison to Collective PSM PSM w/ string fusion describes RHIC, 200 GeV Au+Au data: Multiplicity enhancement. Particle ratios. Strangeness production. PSM w/ 2 String Fusion: Introduction of collective effect via fusion of strings. PSM minbias multiplicity distribution matched corrected data. Armesto, et. al. Phys.Lett. B527 (2002) 92-98

20. Terence TarnowskyWWND, 3/12/06, La Jolla, CA20 Further Study Determine energy and system size dependence of correlations. –Studies of d+Au and pp done. –62.4 GeV Au+Au. –200, 62.4, 22.4 GeV Cu+Cu. Rapidity dependence over entire STAR acceptance. –Midrapidity (TPC, -1.0<  <1.0) –Forward rapidity (FTPC, 2.8<|  |<3.8) Possible threshold effect?

21. Terence TarnowskyWWND, 3/12/06, La Jolla, CA21 Summary Measurement of long-range correlations in high energy, heavy ion collisions. Suppression of correlation strength in Au+Au, compared to the independent string picture, indicates a dynamical reduction in the number of particle sources. Overlap and interaction of color strings has been considered to explain this additional collectivity. Can interpret long-range correlation results and string fusion as a precursor of high energy density, quark-gluon matter produced in central Au+Au collisions.