Leading Hadron Correlation Analysis at RHIC

1. Leading Hadron Correlation Analysis at RHIC Fuqiang Wang Purdue University The Art Poskanzer School

2. Physics motivation To create and study QGP – a state of deconfined, thermalized quarks and gluons predicted by QCD at high energy density. Lattice QCD prediction: Penetrating probe: High pT and jets F. Karsch, hep-lat/0401031. • Can be calculated from pQCD thus are well calibrated in vacuum. • Are expected to be modified in nuclear medium hence provide information on medium properties. TC ~ 1708 MeV eC ~ 0.5 GeV/fm3 The Art Poskanzer School

3. Jet quenching – final state effect STAR, PRL 91, 072304 (2003). d+Au ~ pp. near side Au+Au ~ pp. away side Au+Au ~ 0. “surface”emission strongabsorption Vitev, Gyulassy, PRL 89, 252301 (2002); X.-N. Wang, PLB 595 (2004) 165. pQCD model calculations of partonic energy loss: x30 gluon density, x100 energy density in central Au+Au, e=10-20 GeV/fm3, well above the predicted critical eC. The Art Poskanzer School

4. But… Baryon/meson puzzle! PHENIX, PRL 91, 172301 (2003) Fries et al, PRC 68 044902 (2003); Greco et al, PRC 68, 034904 (2003); Hwa et al, PRC 70, 024905 (2004). QM’04 QM 04 Identified jet correlations! PHENIX – nucl-ex/0408007. STAR – preliminary results The Art Poskanzer School

5. State of Affair Experimental evidence of jet quenching well established. But baryon/meson puzzle! Key questions to ask: • Where does the energy go? • Amount of energy loss? medium contribution? • How is energy distributed? thermalization? The Art Poskanzer School

6. High pT particle High pT particle e+ + e- jet + jet p + p  jet + jet Au + Au  stuff + jet + jet measure those… in this?! Where did the energy go? need to measure the entire jet including low pT. We can do it but with some care… angular correlation with a leading hadron – combinatorial background from mixed-events. The Art Poskanzer School

7. High pT particle High pT particle p+p Jet-like structures Au+Au p+p (1/Ntrig) dN/d(Df) Signal Au+Au top 5% background Df Reconstructing low pT associated particles • Take trigger particle. • FormDfandDhcorrelations of other hadrons with trigger. • Background from mix-events. Add v2 modulation. Normalize in0.8<|Df|<1.2. • Efficiency correction on associated particles. • Take difference and normalize per trigger. Systematic uncertainties: background normalization and v2 correction. The Art Poskanzer School

8. Correlation functions STAR, nucl-ex/0501016. Enhanced and broadened distribution at low pT. Away side suppression at high pT. The Art Poskanzer School

9. M.G. Albrow et al. NPB145, 305 (1978). Re-appearing at low pT High pT Separation at 1 radian. Definition: near side: |Df|<1, |Dh|<1.4away side: |Df|>1, |h|<1 Low pT The Art Poskanzer School

10. Associated multiplicity and “energy” Same pT final trigger particle appears to select larger energy jet in central AA than in pp. Is this the amount of energy loss? p+p The Art Poskanzer School

11. } DE = 1.4 – 2.2 GeV Jet quenching model X.-N. Wang, PLB 579 (2004) 299, nucl-th/0307036 with energy loss without energy loss The Art Poskanzer School

12. Leading hadrons Medium Vector momentum balance? Total scalar pT:Initial parton energy + medium contribution TPC acceptance of away side partner. Medium contribution to the away side associated energy? The Art Poskanzer School

13. Medium contribution to associated energy? • Excess of energy on the away side most prominent at p  1. How does medium energy become correlated with the trigger? • Shower-thermal recombination: • Hwa, Yang, PRC 70, 024905 (2004): TS largest contribution to high pT particles. • Mach shock waves: • Stoecker, nucl-th/0406018.Casalderra, Shuryak, Teaney, hep-ph/0411315. The Art Poskanzer School

14. Preliminary Preliminary Correlations vs centrality The Art Poskanzer School

15. Preliminary RMS size Preliminary Correlations vs pT The Art Poskanzer School

16. 4 < pTtrig < 6 GeV/c 2.5 < pTtrig < 3 GeV/c 0.3<pTassoc<0.8 GeV/c 0.8<pTassoc<1.3 GeV/c 1.3<pTassoc<1.8 GeV/c Shapes varies with pT Preliminary Shape varies with pT, becomes broader and appears doublepeaked at large pTassoc. Effect is more pronounced for lower pTtrig ! Vitev, hep-ph/0501255: should not have peak structure. The Art Poskanzer School

17. Associated particles pT distributions 4 < pTtrig < 6 GeV/c syst. error Away side: softening of spectra from pp to central Au+Au energy from initial parton converted to low pT particles. energy loss in medium! Near side: overall enhancement from pp to AA larger initial parton energy (and modest energy loss)? The Art Poskanzer School

18. Leading hadrons Medium Away side <pT> <pT> from away jets Two sources of particles:hard: jet fragmentation products.soft: bulk medium decay products. Peripheral: <pT> very differentCentral: <pT> not much different Gradual decrease with centrality. Similar for two trigger pT windows. Whatever interaction mechanisms, away-side jet products approach equilibrium with the bulk medium traversed  thermalization of the bulk itself quite plausible. <pT> from medium decay The Art Poskanzer School

19. Preliminary Leading hadrons Medium Novel behavior of away <pT> <pT> more robust than correlation functions. Novel dip structure observed in central AA. Energy loss effect? Mach shock wave? The Art Poskanzer School

20. Away <pT> vs centrality Preliminary Away core <pT> drops with centralityfaster than corona <pT>. Core hadrons almost identical to medium in central collisions. Energy loss pattern: path-length effect? Mach shock wave manifestation? The Art Poskanzer School

21. Mach cone and/or deflected jets Deflected jets Mach cone The Art Poskanzer School

22. Statistical reconstruction of jets in pp, dA and AA. Connection between high pT and low pT physics. Same trigger pT appears to select larger energy jets in AA than in pp. Near side associated multiplicity is enhanced. Away side correlation disappears at high pT, and reappears at low pT. Correlations functions broadened. Interplay between energy loss and Mach shock wave? Significant softening of spectra from pp to central AA. Partial thermalization between jets and bulk medium. Imply high degree of thermalization in medium itself. Summary and open questions To create and study QGP – a state of deconfined thermalized quarks and gluons predicted by QCD at high enerdy density ?   The Art Poskanzer School

23. ---Backup slides--- Backup Slides The Art Poskanzer School

24. Measuring the lost energy? possible… by going to low pT. S. Pal, S. Pratt, PLB574 (2003) 21. X.-N. Wang, PLB 579 (2004) 299, nucl-th/0307036. C.A. Salgado, U.A. Wiedemann, hep-ph/0310079. M. Gyulassy, I. Vitev, X.-N. Wang, B.-W. Zhang, nucl-th/0302077. …… Pal, Pratt, PLB 574 (2003) 21 • How is energy distributed? • amount of energy loss? • contribution from medium? The Art Poskanzer School

25. } DE = 1.4 – 2.2 GeV Jet quenching model X.-N. Wang, PLB 579 (2004) 299, nucl-th/0307036 with energy loss without energy loss Caution: cannot be readily compared to data yet. The Art Poskanzer School

26. Thermalization at work? • yes… by putting two sources of particles together: • one from jet fragmentation that are initially hard. • the other from bulk medium that are soft. going to low pT. jet medium The Art Poskanzer School

27. Existing pp, pA results M.G. Albrow et al. NPB145, 305 (1978) G. Boca et al. ZPC49, 543 (1991) p+p @ ISR B. Alper, NPB 87 (1975) 41 The Art Poskanzer School

28. IAA – new vs old Line = new with old v2. Old New IAA Centrality dN/dh The Art Poskanzer School