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

J/psi production in J/psi production in Au+Au and Cu+Cu Au+Au and Cu+Cu collisions at RHIC-collisions at RHIC-PHENIXPHENIXSusumu Oda (Doctor course Susumu Oda (Doctor course student)student)Hamagaki group, CNS, University Hamagaki group, CNS, University of Tokyoof Tokyo

2007/08/282007/08/28CISS07, Student/post-doc sessionCISS07, Student/post-doc session

Susumu Oda (Doctor course Susumu Oda (Doctor course student)student)Hamagaki group, CNS, University Hamagaki group, CNS, University of Tokyoof Tokyo

2007/08/282007/08/28CISS07, Student/post-doc sessionCISS07, Student/post-doc session

1/111/11

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. 2/112/11

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.).

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-

pairCERN-LHC (Switzerland) (2008-) : 5.5

TeV/nucleon-pair

3/113/11

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.

4/114/11

高原TakaharaLHC

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.

5/115/11

How do we measure J/psi?

J/psi has lepton-pair decay channels.

Branching ratio (J/psie+e-)=5.94%, (J/psi+-)=5.93%

Electron (Cherenkov light, electromagnetic interaction) and muon (less absorption cross section by material) are easily identified.

6/116/11

Cherenkov light ring

PHENIX detector is …

7/117/11

Vertex, centralityTiming, charged particle multiplicity

BBC

Spectator neutronZDC

Forward rapidity (1.2<|y|<2.2, +- pair)

TrackingMWPC

PIDDrift tube, absorber

Mid rapidity (|y|<0.35, e+e- pair)

TrackingDC, MWPC

PIDRICH, EMCal

J/psi peaks at 3.097GeV/c2 in Cu+Cu

8/118/11

Invariant mass of e+e-

Background subtraction Unlike sign pair (e+e-) – Like sign pair (e+e+, e-e-)

Mass(ee) (GeV/c2)

Counts (0.01GeV/c2)-1

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 effectp(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

9/119/11

ppcoll

AAAA YieldN

YieldR

p+p d+A A+A

RAA vs Npart (the number of participating nucleon)

J/psi seems to be melted and QGP seems to be created at RHIC.

10/1110/11

absorption0 mb

3 mb

Red : Au+Au |y|<0.35Magenta : Cu+Cu |y|<0.35Blue : Au+Au 1.2<|y|<2.2Aqua : Cu+Cu 1.2<|y|<2.2

peripheral central

no nuclear effectno nuclear effect

cold nuclear effectcold nuclear effectfrom d+Au datafrom d+Au data

HotHot and cold and cold nuclear nuclear effectseffects

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. 11/1111/11

J/c

c-bar c

0 mb

3 mb

deuteron gold