What do we learn from PHENIX high pt results Jiangyong Jia For the PHENIX Collaboration State University of NewYork at

@ INT/RHIC workshop12/15/20022Jiangyong Jia Outline l Quick overview of high pT results from 200GeV l Jet-like angular correlation identified l High pT suppression continues to highest pT measured l Large v2 at high pT l High pT proton and antiproton from PHENIX l Analysis l Yield and scaling behavior l What have we learned l Comparison with simple geometrical model calculation. l Consistent with high pT yield and di-jet suppression l Insufficient to describe v2 l Conclusion

@ INT/RHIC workshop12/15/20023Jiangyong Jia Direct observation of jets l Leading particle + angular correlation Trigger photon E  >2.5 GeV l Correlate with partner charged particle l Jet like near angle correlation for p+p and Au+Au l Similar width l Jet fragmentation not modified much? PHENIX Preliminary raw differential yields 2-4 GeV  Pair distribution Subtracted distribution Mixed distribution 20-40% STAR measure the same and away side jet yields – D. Hardtke

@ INT/RHIC workshop12/15/20024Jiangyong Jia Spectra shape at high pT l Inverse slope increase with pT l Spectra is more power law l =  p T  - p T min as function of centrality l Nearly flat at high pT l pT>4 GeV/c are jet like hh Slope~constant at high pT Low p T ‘flow’ pattern

@ INT/RHIC workshop12/15/20025Jiangyong Jia Centrality dependence of high pT suppression l Continues decrease as function of centrality l Charged : factor ~3.5 from peripheral to central  0 : factor ~5 from peripheral to central Nuclear Modification Factor as a function of N part Binary-scaled yield as a function of N part PHENIX Preliminary 4 < p T < 6 GeV/c h+ + h- 00

@ INT/RHIC workshop12/15/20026Jiangyong Jia Anisotropy in momentum space = v2 l V2 saturates at high pT l Can be described by pure energy loss? l hydro pic: v2 created by pressure. l Jet pic: l Different energy loss along different path l Sensitive to geometrical profile l Decrease with pT? M. Gyulassy, I. Vitev and X.N. Wang PRL 86 (2001) 2537 PHENIX PRELIMINARY Cylindrical Wood-Saxon

@ INT/RHIC workshop12/15/20027Jiangyong Jia l Using High Resolution TOF PID device and Drift Chamber. l Making p T dependent 2  cut in squared mass l Range and Systematic Error l proton, pbar: up to 4GeV/c l p T dependent: 11% l Overall normalization: Central 18%, Peripheral 16.4% Analysis of high pT proton and antiproton

@ INT/RHIC workshop12/15/20028Jiangyong Jia Identified hadron spectra at sqrt(s) = 200 GeV l Excellent agreement between charged and neutral pions l anti(proton) yields increase with centrality relative to the pion yield at high pT

@ INT/RHIC workshop12/15/20029Jiangyong Jia Centrality and pT dependence of p/  p/  ratio for AuAu at pT>2GeV/c l ~ 1 in central collisions l ~ 0.4 in peripheral collisions l ~ 20% lower for anti-proton l Above gluon jet value Thanks Barbara V. Jacak If the observed anti(proton) are from fragmentation, then it is not standard fragmentation

@ INT/RHIC workshop12/15/200210Jiangyong Jia _ Scaling of the p p spectra Collective flow Binary scaling???? 2-4 GeV/c

@ INT/RHIC workshop12/15/200211Jiangyong Jia Are proton and antiproton suppressed? protons  , h Proton yield goes down?

@ INT/RHIC workshop12/15/200212Jiangyong Jia What have we leaned? l Strong centrality dependence of suppression, v2, away side jets at high pT l Suggestive of surface emission of jets or mono-jet production? l Saturation(initial state), Jet quenching(final state) l Binary scaling of protons yield between 2-4 GeV/c l Soft or hard or in between? l Baryon transport Inspired by E. Shuryak Phys.Rev. C66 (2002) l Which effect can be explained by jet absorption and collision geometry? l Consistent with high pT yield and di-jet suppression. l Insufficient to describe v2 l Can’t describe proton yield since there is no absorption. ?

@ INT/RHIC workshop12/15/200213Jiangyong Jia Simple Toy Geometrical Model for Jet absorption l Jets are absorbed in overlap region according to l Density of matter in transverse plane determined by participant density l Azimuth isotropic di-jets production according to binary collision profile l Hadron spectra are related to jet distribution via parton-hadron duality  ~  Npart  Ncoll

@ INT/RHIC workshop12/15/200214Jiangyong Jia Density distribution calculated from glauber model 0-5%75-80% Wood-saxon nuclear density profile  Npart  Ncoll

@ INT/RHIC workshop12/15/200215Jiangyong Jia Model Assumptions to Compare with Data l Model is simplistic and can only describes main features of geometry l Assume all particles above 4 GeV/c from jets l Assume jets are back-to-back l Ignore the fragmentation l Contains no pT and  s and flavor dependence l Try different kind of absorption : l  is the only free parameter Adjust absorption strength k to reproduce suppression factor of 3.5(charged) and 5(   ) in most central collisions. l Predict centrality dependence of yield suppression l Predict centrality dependence of di-jet suppression l Predict centrality dependence of v2 Normal nuclear absorption Energy loss style absorption Absorption + expansion, l 0 ~ 0.2 fm

@ INT/RHIC workshop12/15/200216Jiangyong Jia Scaling behavior of the yields l Qualitatively describe the centrality dependence of the yield l Not sensitive to the absorption pattern Ncoll Npart/2 Solid line factor 3.5, dash line factor 5 h , 4-8 GeV/c   0, GeV/c

@ INT/RHIC workshop12/15/200217Jiangyong Jia Centrality dependence of back-back jets l Compare STAR back-back jet measurement for 4 <pT<6 GeV/c l By construction, same side jet will always be 1 l Qualitatively describe the centrality dependence of the away side

@ INT/RHIC workshop12/15/200218Jiangyong Jia Centrality dependence of v2 l NB: in these models,v2 are purely geometrical origin, does not consider detailed modification of momentum distribution l Geometrical anisotropy is insufficient to produce observed v2 by jet absorption l V2 is sensitive to absorption model, smallest for longitudinal expanding source l V2 will increase using hard sphere or cylindrical nuclear profile, but unphysical

@ INT/RHIC workshop12/15/200219Jiangyong Jia Varying  l Maximum v2 produce by surface. l Different geometrical profile have different geometrical limit. l v2 is below geometrical limit at experimental observed suppression value Suppression factor for 0-5% centrality  V2 for 50-55% centrality Away side jet for 0-5% centrality hard sphere profile For sphere, surface volume is cylindrical profile S. Voloshin ws profile

@ INT/RHIC workshop12/15/200220Jiangyong Jia Conclusion l Exciting high pT results from 200GeV AuAu l Direct observation of jets l Strong high pT suppression l Puzzle1 : Large v2 at high pT l Puzzle2: High pT proton and antiproton Binary scaling between 2-4GeV/c Mysterious particle composition at high pT. l Jet absorption gives characteristic centrality dependence of observables l Consistent with high pT yield and di-jets suppression l Insufficient to describe v2 and proton yield

@ INT/RHIC workshop12/15/200221Jiangyong Jia Discussion on Scaling Absorption model naturally lead to stronger suppression in large  Ncoll region l Reduce binary scaling binary scaling suppression Red is “black hole” model, which scale even slower than participant  (fm -2 ) r (fm)  coll  part /2 Density distribution for surviving jets (b<3fm) Suppression can lead to Npart scaling

@ INT/RHIC workshop12/15/200222Jiangyong Jia Hard sphere vs Saxon-Woods eccentricity sheer almond  = b/2R HS   b/2R Npart    cent/2 HS overpredict eccentricity by factor of 2. Any meaningful geometrical estimate has to be infered from SW Made by Jan. Rak

@ INT/RHIC workshop12/15/200223Jiangyong Jia

@ INT/RHIC workshop12/15/200224Jiangyong Jia

@ INT/RHIC workshop12/15/200225Jiangyong Jia Some Simple Mathematics l We look at particle yield above 4 GeV/c l Spectra have similar shape as pp psps pT dN/d 2 p T d  EE p s +  E Assume spectra is: Integrated yield above p s is: Assume energy loss  E (p T ) is independent of pT: For power law shape, assumption is good for small  E,  E  1/T ~ 1 GeV for pT=10 GeV/c Hadron spectra and jet spectra are related via parton-hadron duality f Left shift(eloss) is effectively a down shift(absorption), one can obtain the similar result  1/T

@ INT/RHIC workshop12/15/200226Jiangyong Jia  /h at higher p T

@ INT/RHIC workshop12/15/200227Jiangyong Jia STAR yield per trigger