1. Jets at RHIC Jiangyong Jia jjia@skipper.physics.sunysb.edu

2. Outline n Jet and it’s importance in RHIC u Jets and hard scattering u soft vs hard u pQCD approach F pp F pA F AA n Angular correlation u some examples u Phenix experiment u my angular correlation study u outlook n Summary

3. Relativistic Heavy-Ion Collider (RHIC) n Goal u Searching for the quark gluon plasma(QGP) u exploring the physics of this new state of matter. n Jet quenching as probe Au Au at

4. Jet quenching: a QGP signature n What is a Jet ? n QCD energy loss in deconfined dense matter n Theory prediction dE/dx = 2-4GeV/fm n QGP suppresses high pt particles and angular correlations b a c d

5. Ref, K.Geiger

6. Jet and hard scattering at n Jet production rate (K.J.Eskola,hep-ph/9610365 ) n Hard scattering contribution to particle production is important( )

7. d  /p T dp T string model hydrodynamic model pQCD (Hijing,PCM) pTpT soft Semi-hard hard 1GeV5GeV soft process vs hard process Jet

8. Soft/hard boundary? n At SPS ( ) u Hydrodynamic models. u pQCD(X.N.Wang, hep-ph/9804357 ) u at SPS : both works. u Small jet cross-section, measure only to n At RHIC ( ) u increase, larger jet cross-section,measure to high pt ( ). u Angular correlation

9. Hydrodynamic Model for SPS Plot created by Jane Burward Hoy

10. pQCD calculation X.N.Wang,nucl-th/9812021

11. Jet production (X.N.Wang,nucl-th/9812021) n pQCD approach Schematic representation of a high-pt reaction factorized into parton distribution function (f), parton fragmetation function D and a hard-scattering subprocess parton-parton collision convolution Cross-section n Cross-section

12. pp--Initial Kt n Need to take into account intrinsic pt of partons u Uncertainty principle u high order pQCD process(initial state radiation,etc) n modify parton distribution function u where

13. pA-- Modification of hard scattering n Assume only one hard parton- parton collision. n Enhancement of high Pt spectra (Cronin effect ) u decrease with 1/p t 2 and  A (b) is number of scattering assume hard sphere distribution  2 is the soft Kt kick, it has following form n Modification of nuclear structure function (Shadowing) u assume parton distribution:

14. Cronin and Shadowing in pA R pAu p + Au

15. AA--Jet quenching n If we have QGP, multiple interactions of parton with the medium lead to loss of energy. n Time scale (  h  1/p 0  0.1fm/c, p 0  2GeV/c,  s  1/  QCD  1 fm/c) High pt parton collisions happen in the earliest stage of collision. Then they suffer energy loss in the medium. n Hijing Assume (model dependent): u constant energy loss u incoherent multiple scattering.

16. R AA (PT)

17. Angular correlation At RHIC n Back-to-Back correlation: u QGP F (Di-)Jets suppression F enhanced acoplanarity. n Study the centrality (impact parameter) dependence u From peripheral to central n Some examples

18. CCOR At ISR pp forwardbackward Ref, M.J.Tannenbaum

19. X.N.Wang,Phys.Rep.280,287(1997).

20. Phenix Detector n Good Charged particle tracking u high pt resolution, u high interaction rate, L=10 26~27 cm 2 /s (read out 50Hz ) n Phenix detector acceptance u default acceptance: F Pt  0.2 GeV/c; F 70  <  <110  or |  |<0.35 F -33.75  <  <56.25 , 123.75  <  <213.75  u 1/2*sin(  /2) = 17  of 4  u acceptance in azimuthal  leads to an intrinsic jet shape Phenix acceptance : http://skipper.physics.sunysb.edu:80/talks/jjia

21. DC  (degree)  (degree) -90 270 0180  0.35 110 -0.35 70 90 Detector LayoutDetector Acceptance EMCal TEC RICH

23. Studies of pp collisions at n Pythia Generator u 100000 pp events at u min jet pt = 20GeV/c. n Analysis scheme (as CCOR): u study  distributions: F back to back correlation of jets ( w/o  acceptance) F modification with a HIC background (RQMD) one Pythia event(two jets) mixed with one RQMD event F effect of Phenix  acceptance.

24. Leading Pt>2.0

25. 1<Pt<2 4<Pt<53<Pt<4 2<Pt<3

30. Outlook n RQMD (Hadrons + Strings) use other models as background (Hijing, Strings + Minijets) n Determine methods to correct for  and  acceptance of Phenix(limited acceptance) u event by event acceptance correction u investigate the fiducial region( , ,pt) n Study angular correlation function: n Rate estimate(1/2000) n when we have the data…. u Study angular correlation as a function of centrality. Fiducial region Detector acceptance  

31. Summary n Large pt partons or Jets are good probes of the dense matter in ultra- relativistic heavy-ion collisions. n In RHIC, can use pQCD based models to calculate high pt spectra. u Need to combine soft and hard processes together. n Study back to back jets angular correlation u if QGP is generated, angular correlation will be affected by jet quenching u Phenix detector have limited acceptance, we can: F increase pt and use the fiducial region F learn how to correct for  and  acceptance. n We will further our study on jet angular correlation and look for jet quenching as a probe of QGP formation at RHIC.

32. References n K.J.Eskola,hep-ph/9601365. u Give the parton production rate. n Also K.J.Eskola,K.Kajantie,and J.Lindfors Nucl.Phys.B323,37(1989) u it calculate the parton production rate, saying: F for RHIC, U + U, have 290 partons Pt>2GeV, and 75 partons Pt>3GeV. F For hard Et,SPS 5%, RHIC 50%, Tevatron 80%. n X.N.Wang,nucl-th/9812021. u Base of this talk. n X.N.Wang,Phys.Rep.280,287(1997). u Base of this talk. n J.F.Owens,Rev.Mod.Phys. 59, 465 (1987). u Gives the jet cross section formula. n X.N.Wang,hep-ph/9804357. u Calculate the jet quenching under simple assumption. n M.Arneodo,Phys.Rep.240,301(1994) u shadowing effect. n K.Geiger. Ultra-Relativistic nuclear collisions in a QCD based space-time description: the parton cascade model u a very good article delving into the history of AA collision, comparing with Hijing, and have a lot of interesting graph. n Nucl.Phys.B480 406. u Having UA1 Jet cross section measurement

35. PP pA AA Single Inclusive cross section

36. 1<Pt<2 4<Pt<5 3<Pt<4 2<Pt<3