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1. Measurement of charmonia at mid-rapidity at RHIC-PHENIX c c J/ yg e + e - g in p+p collisions at √ s=200GeV. Susumu Oda CNS, University of Tokyo For the PHENIX collaboration 2007/09/24 62nd annual JPS meeting Hokkaido University. 2. 0 mb. 3 mb. Red : Au+Au |y|
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Measurement of charmonia at mid-rapidity at RHIC-PHENIX
cJ/e+e- in p+p collisions at √s=200GeV
Susumu OdaCNS, University of Tokyo
For the PHENIX collaboration
2007/09/2462nd annual JPS meeting
Hokkaido University
1
Motivation
0 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
2
A paper about J/ production in Cu+Cu collisions will be submitted in few weeks. • Quarkonia are good p
robes of QGP. • J/ is the most studie
d quarkonium in heavy ion collisions.
• Feed down from c into J/ is important.
Direct J/cJ/X’J/XBJ/X
Charmonium system3
c(1S)
c(2S)
J/(1S)
(2S)
c0(1P)c1(1P) c2(1P)hc(1P)
JPC 0-+ 1-- 0++ 1++ 1+- 2++
e+e- BR=5.94%
DDbar threshold
Fraction of J/ from c decay
2
0
1
JcJcJ JBR
JR
c
Measurement of c at RHIC is required.
RHIC energy
4
Precise measurements onlyError of Rc<=0.1
CDFHERA-BE705
E672/E706E369
WA11
E610
Theoretical model predictions
Color Evaporation ModelCSM+Comover
NRQCD Color Singlet Model
Measurement of c at RHIC is requiredto understand quarkonia production.
5
How to measure Rc
• Find J/e+e- (2.9<Mee<3.3GeV).
• Find cJ/ (M=Mee-Mee~0.44GeV).
• Correct acceptance event by event.
• Subtract background by event mixing of J/ and . – Normalization regions : 0.1-0.3GeV and 0.6-0.8GeV
• Run-5 (2005, 3.8 pb-1) and Run-6 (2006, 10.7 pb-1)
p+p 200GeV data is used.
N
i JTLVLJTeeaccJcTJ
JaccLVLeeaccJJ c cc
c pppyyNR
1 /,1/,/,detected /
/
1
1//
11111
c acceptance
Average over J/
6
c conditional efficiency if J/ is detected
J/ acceptance
e-
e+
p
p
PHENIX detector• Beam beam counter
– Collision vertex
• Drift chamber, pad chamber– Charged particle tracking
• Ring imaging Cherenkov counter – Electron identification
• Electromagnetic calorimeter– Photon identification and
energy measurement– Electron identification
7
p+p c+X J/+X e+e-+X
Cut parameters and peaksPhoton cut• Energy cut (E >0.3 GeV) • Electromagnetic shower profile• Fiducial cut (noisy EMC towers
are removed)• Charged particle veto (35cm x 35cm)
Event cut• |Zvertex|<30 cm
Electron cut • RICH nPMT>=2• pT>0.2 GeV• 0.5<Energy/momentum<2
Pair cut• 2.9<mass(e+e-)<3.3GeV
8
EMCal energy resolution (E)=58MeV (PbSc)(E)=42MeV (PbGl) @ E=500MeV
NJ/=3679Red : N+-=4040Blue : N+++N--=218
J/e+e-
Run-5+6p+p 02Run-6 p+p
0.6<pT<0.65GeV/cE>0.2GeV
mainly 02
PYTHIA simulation (c1, |y|<0.5)
J/ acceptance and c conditional efficiency if J/ is detected from
GEANT (PISA) simulation
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pT,J/ (GeV/c) pT,c (GeV/c)
J/e+e-
~2% for |yJ/|<0.5
cJ/e+e-~10%
c acceptance~2%*10%=0.2%1/30,000 of produced c is detected by PHENIX central arm
Feasibility study using PYTHIA and GEANT simulation
Black : ForegroundBlue : BackgroundRed: Foreground-backgroundGreen : Normalization regions (0.1<M<0.3GeV and 0.6<M<0.8GeV)
Input Rc=0.32N(direct J/):N(c1J/):N(c2J/)=68%:16%:16% NJ/=3744
10
Feasibility study using simulation (continued)
11
Input Rc=0
Input Rc=0.32
Input Rc=0.68
Input Rc=1
Black : ForegroundBlue : BackgroundRed: Foreground-backgroundGreen : Normalization regions
Real data (Run-5 and Run-6 p+p 200GeV)
Black : ForegroundBlue : BackgroundRed: Foreground-backgroundGreen : Normalization regions
12
The fraction of J/ from c feed down (Rc) seems to be small.
Summary and outlook13
RHIC energy
• The contribution of c is important to understand the J/ data in heavy ion collisions.
• Search for the c meson via J/ decay in p+p collisions is ongoing.
• The fraction of J/ from c feed down (Rc) seems to be small.
• The Rc value will be obtained soon.
• More and more statistics are needed
(Run-8, 9, …) for detail study.
Backups
Acceptance of 0
Ratio of cross sections
1)(
)(
2
1
2
1
c
c
JBR
JBR
c
c
2
1
c
c
For simplicity, I assumed
Limited knowledge
Green : ABlue : pAAqua : ppbar
And I used mean of masses in simulation.(3510.66MeV+3556.20MeV)/2
Expected width of the convoluted peak (Gaussian sigma) is ~50MeV.
I neglect c0 contribution.
(c - J/) Mass (GeV/c2)
PHENIXRun 5 200GeV p+p
(c - J/) Mass (GeV/c2)
Previous result, Run-5 p+p 200GeVNJ/=960
Questions from audience
Question 1• Is it better to use muon pairs? The statistics of muon pairs are 5 tim
es larger than electron pairs.
• No. • The fraction of decays with J/ going to muon arm and gamma goin
g to central arm is small. • So, the statistics of J/+ in muon+central arms and the statistics in
central arm are almost equivalent. • But, the energy of gamma in muon+central arm configuration is low,
E~0.1(0.2)GeV. • This is worse situation than the central arm case with E~0.4GeV.
• Does the fact mean that the c measurement is not possible at RHIC-PHENIX?
• No. • It can be possible in p+p collisions as I showed, while the larger stati
stics is needed. • But, it is very hard in heavy ion collisions. • (The measurement with NCC+FVTX+muon trigger is interesting eve
n in heavy ion collisions, but the statistics are still necessary.)
Question 2
• Is it better to use the isolation cut (0 veto)?
• No.
• The acceptance of low-pT 0 is small, ~3% at 0 pT=0.6GeV/c (slide 15).
• So, the 0 veto will not be effective for the c measurement and it will introduce larger systematic error only.
Question 3
• You did not take into account the c0 contribution in your PYTHIA+GEANT simulation. Why?
• Because the branching ratio of c0J/ decay is small, only 1.3% (slide 3).
• If the production cross section of c0 is much larger than ones of c1 and c2, we cannot neglect it.
• But, we know the c0 fraction is not large in the fixed target experiment and Tevatron.
• So, the c0 contribution can be negligible.
Question 4• In the PYTHIA+GEANT simulation, the net (foreground-b
ackground) distribution is lower than zero at the lower side of the c peak. Why?
• There is correlation between J/ and in the foreground and most of come from 02 decays. The correlation leads high mass of J/ pairs. In the background, however, there is no correlation between J/ and , and the J/ pair mass is smaller. Therefore, the net distribution is lower than zero in simulation in the lower side. But, actually, this fact is not observed in the real data. Though, the J/ statistics is the same in the simulation and real data.
• Why don’t you include such effect in your background subtraction?
• I don’t believe the prediction capability of PYTHIA at such level.