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J/psi production in Au+Au and Cu+Cu collisions at RHIC-PHENIX

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. 1/11. My interest is …. Create QGP (Quark Gluon Plasma) and study its property experimentally.

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J/psi production in Au+Au and Cu+Cu collisions at RHIC-PHENIX

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  1. 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 1/11

  2. 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

  3. 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.). • 197Au, 63Cu, 208Pb, … • 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

  4. He is our boss  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. This is me  高原 Takahara LHC 4/11

  5. 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

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

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

  8. J/psi peaks at 3.097GeV/c2 in Cu+Cu • Invariant mass of e+e- • Background subtraction • Unlike sign pair (e+e-) –Like sign pair (e+e+, e-e-) Counts (0.01GeV/c2)-1 Mass(ee) (GeV/c2) 8/11

  9. Ratio of measured yield to expected yield : RAA • 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 p+p 9/11 d+A A+A

  10. 10/11 RAA vs Npart (the number of participating nucleon) no nuclear effect absorption 0 mb cold nuclear effect from d+Au data 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 Hot and cold nuclear effects peripheral central J/psi seems to be melted and QGP seems to be created at RHIC.

  11. J/y c c-bar c 0 mb J/psi seems to be melted and QGP seems to be created. However, … 3 mb • 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. deuteron gold 11/11

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