J/psi production in Au+Au and Cu+Cu collisions at RHIC-PHENIX Susumu Oda (Doctor course student) Hamagaki group, CNS, University of Tokyo 2007/08/28 CISS07, Student/post-doc session Susumu Oda (Doctor course student) Hamagaki group, CNS, University of Tokyo 2007/08/28 CISS07, Student/post-doc session 1/11

My interest is … Create QGP (Quark Gluon Plasma) and study its property experimentally. A theoretical view of QGP will be given in Dr. Hirano’s lecture (Thu. afternoon). QGP is a state in which quarks and gluons are deconfined. In ordinal matter, quarks and gluons are confined. We cannot extract single quark nor single gluon from the matter. This state might exist in early universe. QGP may be created in high temperature and high density circumstances. 2/11

How do we create such high temperature and density environment? Collides heavy ion with extremely high energy (about 100A GeV + 100A GeV=200 GeV per nucleon-pair in C.M.S.). 197 Au, 63 Cu, 208 Pb, … We’re only interested in only mass number A. We don’t care about those nuclear structure. BNL-AGS, CERN-SPS (1980s-) : ~ 4-17 GeV/nucleon- pair BNL-RHIC (USA) (2000-) : 200 GeV/nucleon-pair CERN-LHC (Switzerland) (2008-) : 5.5 TeV/nucleon-pair 3/11

Our group … Participates in the PHENIX experiment at BNL-RHIC (circumference=3.8km). Starts to participate in ALICE experiment at CERN-LHC (27km). These facilities are very very large to collide particles with very high energy. 4/11 高原 Takahara LHC This is me  He is our boss 

What are the signals of QGP? How can we know whether QGP is created or not? Really big problem. No definitive conclusion. But, one good candidate is J/psi. J/psi is a bound state of a charm quark and an anti-charm quark. J/psi will be created by only initial collisions. J/psi would melt and disappear in hot QGP. Yield would be suppressed. If J/psi melt in QGP, we detect the less number of J/psi’s than expected. I study J/psi production in Cu+Cu collisions. 5/11

How do we measure J/psi? J/psi has lepton-pair decay channels. Branching ratio (J/psi  e + e - )=5.94%, (J/psi   +  - )=5.93% Electron (Cherenkov light, electromagnetic interaction) and muon (less absorption cross section by material) are easily identified. 6/11 Cherenkov light ring

PHENIX detector is … 7/11 Vertex, centrality Timing, charged particle multiplicity BBC Spectator neutron ZDC Forward rapidity (1.2<|y|<2.2,  +  - pair) Tracking MWPC PID Drift tube, absorber Mid rapidity (|y|<0.35, e + e - pair) Tracking DC, MWPC PID RICH, EMCal

J/psi peaks at 3.097GeV/c 2 in Cu+Cu 8/11 Invariant mass of e + e - Background subtraction Unlike sign pair (e + e - ) – Like sign pair (e + e +, e - e - ) Mass(ee) (GeV/c 2 ) Counts (0.01GeV/c 2 ) -1

Ratio of measured yield to expected yield : R AA If there is no hot nuclear effect nor cold nuclear effect, a heavy ion collision can be understood as superposition of nucleon-nucleon collisions (p+p, p+n, n+n). p+p : No nuclear effect p(d)+A : cold nuclear effect Hot region is limited and is soon cooled down. A+A : hot nuclear effect (QGP) + cold nuclear effect Large hot region isn’t soon cooled down. We can know hot nuclear effect by (A+A)/(p+p)-(d+A)/(p+p) (hot+cold)-cold = hot nuclear effect 9/11 p+p d+A A+A

R AA vs N part (the number of participating nucleon) J/psi seems to be melted and QGP seems to be created at RHIC.10/11 absorption 0 mb 3 mb Red : Au+Au |y|<0.35 Magenta : Cu+Cu |y|<0.35 Blue : Au+Au 1.2<|y|<2.2 Aqua : Cu+Cu 1.2<|y|<2.2 peripheral central no nuclear effect cold nuclear effect from d+Au data Hot and cold nuclear effects

J/psi seems to be melted and QGP seems to be created. However, … Our knowledge on cold nuclear matter is limited. More d+A (or p+A) data is needed. There is feed down from excited states. We need to measure those excited states, but it is difficult measure them. Regeneration from uncorrelated charm. Statistics of J/psi data at RHIC is limited by its small production cross section. At LHC energy (RHIC energy x28) J/psi cross section is much larger and we can collect larger data samples. With the large data samples, we can study the property of QGP. 11/11 J/  c c-bar c 0 mb 3 mb deuterongold