1. Systematic measurements of light vector mesons in RHIC-PHENIX
Yoshihide Nakamiya
Hiroshima University, Japan
for the PHENIX collaboration
Quark Matter 2008, Jaipur, India
~ Contents ~
Topics in this talk
PHENIX experiment
Results
Summary

2. Topics in this talk
<Topic 1> Mass modification of light vector mesons
- as a probe of the chiral phase transition
- in the low pT region
Question 1 : Have we observed changes in line shape and/or yield?
Mass Line Shape
Possible modification of line shape of the invariant mass distribution for f/w/r is expected to be observed.
　　 ->Effects are small and can’t be detected with current statistics and
signal to background ratio.
Yield difference between fe+e- and f K+K-
Branching ratio between e+e- and K+K- may be sensitive to mass modification, since Mphi is approximately 2  MK.
-> Compare yields of fe+e- and f K+K-
e+e- in Au+Au √sNN=200 GeV ω f

3. Topics in this talk (Cont’d)
<Topic 2 > Particle yield suppression of light vector mesons in medium
- as a probe of medium effects
- at relatively high pT
Systematic measurements give information about properties of the medium:
pT/mT spectra of f and w in several decay channels
Nuclear modification factors (RAA and RdA) as functions of pT
We are trying to answer the following questions:
Question 1 : Does the particle yield suppression depend on mass or
on quark number ?
-> Nuclear modification factor RAA of the f meson
is compared to proton results.
Question 2 : Does RAA of mesons have a mass or flavor dependence?
->RAA of several mesons are compared to each other.
(p, h, w, f, …)
<Baseline> Results of p+p and d+Au are also shown.
All data shown in this talk are taken at sNN = 200 GeV.

4. Electron, hadron and photon in PHENIX
f/w  e+e-
Momentum
Electron ID
f,w e+ e-
PHENIX acceptance
-0.35 < η < 0.35
2 x 90°in azimuthal angle for two arms
Event selection
BBC
Electron ID
RICH
EMCal
photon ID
EMCal
Hadron ID
TOF
EMCal-TOF
w  p+p-p0, p0g
f  K+K- p+ w g
g Energy
Momentum
Hadron ID p- p0 f
Momentum
Hadron ID K+ K-

5. Results for p+p and d+Au as baseline measurement

6. d+Au d+Au p+p p+p Extended f  K+K- analysis
Consistency between f  K+K- and f e+e-
d+Au
0-20% f
p+p
　　No ID
　　Single ID
　　Double ID
　　e+e-
M.B. f
f candidates
Double ID analysis
no ID analysis
Single ID analysis K+
K+ or K- K- h+ h-
h+ or h-
d+Au
0-20%
　　No ID
　　Single ID
　　Double ID
M.B.
p+p
In p+p, spectra of e+e- and K+K- show reasonable agreement!
fK+K- measurements have been extended to both higher and lower pT using new methods, i.e. no kaon ID and single kaon ID methods.
The three independent kaon analyses are consistent with each other.

7. d+Au p+p Measurements of w in wide pT range w
pT spectra of w are measured for several decay modes in d+Au and p+p.
wp0g dAu MB (PRC )
wp0p+p- dAu MB(PRC )
w e+e- pp MB (PHENIX preliminary)
wp0g pp MB (PRC )
wp0p+p- pp MB(PRC )
wp0g pp ERT (PHENIX preliminary)
wp0p+p- pp ERT (PHENIX preliminary) w
d+Au
p+p
Spectra show good agreement among several decay channels.

8. RdA of f and w mesons in 200 GeV
As a baseline check, RdA is calculated for f and w and compared to other mesons.
RdA f
RdA w
0-20%
0-20%
wp0p+p-
wp0g
hgg
p0gg
fK+K-hgg
p0gg
M.B.
M.B.
RdA does not show suppression in central arm.
f and w results are consistent with p0 and h.

9. f/p, w/p ratios in p+p and d+Au 200 GeV f/p, f/K w/p
f/p dAu
f/K pp pp
f/p pp
f/p and w/p ratio have little or no pT dependence at pT >2.0 GeV/c.
/0 in p+p √s = GeV = 0.81 ± 0.02(stat) ± 0.07(syst)
/0 in d+Au √sNN = 200 GeV = 0.94 ± 0.08(stat) ± 0.12(syst)

10. Chiral symmetry restoration
Topic 1
Chiral symmetry restoration

11. Yield comparison between fe+e- and f K+K-
Question 1’: Have we observed changes of yield between e+e- and K+K- ?
Comparison of integrated yield is not enough, because
mass modification effects depend on the pT region.
Low pT mesons tend to decay inside the hot/dense matter f f
Low pT
High pT
In addition,
To determine the integrated yield, an extrapolation to lower pT is needed.
There is a large uncertainty in the calculation.
Thus, pT-dependent information is essential for comparison.
Now, we should ask
Have we observed changes of spectra between e+e- and K+K- ?

12. Au+Au Spectra comparison between fe+e- and f K+K-
f e+e- AuAu MB
f e+e % x 10-3
f e+e % x 10-1
f K+K- AuAu MB (no PID)
f K+K- AuAu MB (double PID)
f K+K- AuAu MB (PRC )
f K+K % x 10-3 (double PID)
f K+K % x 10-1 (double PID)
f K+K % x 10-1
(PRC )
M.B.
40-92%
20-40%
Errors are too large to make any clear statement about the comparison of spectra for f  e+e- and f  K+K-.

13. Nuclear modification factors
Topic 2
Nuclear modification factors

14. Au+Au fK+K- in Au+Au is also extended to higher mT
　　No ID
　　Single ID
　　Double ID
0-10%
60-90%
p+p
M.B.
f candidates
Double ID analysis
no ID analysis K+ K- h+ h-
fK+K- measurement has been extended to higher mT using no kaon ID method.
mT region is extended to ~ 5 GeV.
The two independent hadron decay analyses are consistent with each other in Au+Au.

15. Is RAA suppression carried by mass or quark number?
Question 1 : Is particle yield suppression carried by mass or quark number ?
RAA of proton (mp=938 MeV/c2)
Comparison between f and p:
RAA of f meson (mf=1019 MeV/c2)
60-93%
MinBias
0-10%
RAA of f in central collisions is lower than in peripheral at high pT.
RAA of protons is nearly independent of centrality.
f RAA shows a different trend as compared to the proton.
Difference of RAA between f and proton suggests that energy loss occurs at the partonic level.

16. w mesons in Au+Au Background estimate is improved in ωπ０γ analysis
pT spectra of w are measured for several centralities and at high pT.
[GeV/c2]
Magenda =
Red + Green + Blue
3 BG sources
Invariant mass reconstructed by 3g
PHENIX preliminary
w  e+e-, AuAu MB x 102
w  p0g, AuAu MB x 102
w  p0g, AuAu % x 104
 p0g, AuAu % x 10
w  p0g, AuAu 60-92%
0-20%
M.B.
Details are in M.Ouchida’s
poster
20-60%
Background and shape are carefully estimated.
60-92%
Measurement of w mesons up to 10 GeV/c is made.

17. Mass dependence of RAA between mesons
Question 2 : Does RAA of mesons have a mass or a flavor dependence? f w
f meson has a different RAA for pT < 5 GeV/c.

18. Summary <Topic 1> Mass modification of light vector mesons
- as a probe of chiral phase transition
- in low pT region
Question 1 : Have we observed changes of line shape, yield, and/or spectra?
Answer 1 : We are still trying to quantify the difference.
Improvement of statistics and signal to background ratio
in the next run will improve existing measurements.
<Topic 2 > Particle yield suppression of light vector mesons in medium
- as a probe of medium effect
- at relatively high pT
Question 1 : Is particle yield suppression carried by mass or quark number ?
Answer 1 : Difference between RAA of f meson vs proton suggests that
energy loss occurs at the partonic level .
Question 2 : Does RAA of mesons have a mass or flavor dependence ?
Answer 2 : f meson has a different RAA compared to other mesons (p, h).

19. Thank you for inviting me to Quark Matter 2008 !
I’d like to say thanks to all participants and collaborators

20. Back up

21. Yield and temperature for φ mesons
After several experimental checking, we found integrated
information is not enough to determine the difference between
e+e- and K+K-.
Need a careful check of mT spectra.

22. The invariant mass spectra for φ mesons
f-> e+e- p+p
f-> e+e- d+Au
f->e+e- Au+Au φ φ
f->K+K- (double PID) d+Au
f-> K+K- (double PID) Au+Au

23. The invariant mass spectra for φ mesons
f->K+K- (no PID) pp
f->K+K- (single PID) pp
f->K+K- (no PID) AuAU
f->K+K- (no PID) dAu

24. The invariant mass spectra for ω mesons
w-> e+e- p+p
w->e+e- d+Au
w->e+e- Au+Au ω ω
w->p0p+p- p+p
w->p0g p+p
w->p0g Au+Au