1

2008 Oct. ATHIC @ Tsukuba

Misaki Ouchida　Hiroshima University For the PHENIX Collaboration

ωωω

e ＋

e ー

γ

γ

π+π0

γ

π ーπ0

γ γ

Low mass vector meson measurements at RHIC

Systematic Measurement ofomega mesons in PHENIX

ー　　　　　　　　　　　　　　　　　　　　　ーー　　　　　　　　　　　　　　　　　　　　　ー

2

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

OUTLINE

• Introduction Why Low Mass Vector mesons ?

• Experiment Which decay mode do we measure in PHENIX?

• Analysis Highlight How do we approach?

• Results & Discussion What do we see?

• Summary

3

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Introduction Why Low Mass Vector mesons?

Physics…

　　 Low pT High pT

Signal for Chiral Symmtery Restoration

p+p

d+ Au

A+ A

Systematic Study of Low Mass Vector Mesons

-different decay mode(lepton, hadron)-different collision mode(p+p, d+Au, A+A) Matter ( life time~10fm/c )

omega meson ( life time 23fm/c )

phi meson ( life time 46fm/c )

Promising probe to study the properties of the deconfined state

Rec

on

stru

cted

Rec

on

stru

cted

Eff

icie

ncy

Eff

icie

ncy

e+e- (BR:7x10-3%)

(BR:9%)

ωpTωpT

Signal for Jet Quenching

4

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Suppression as a Probe of QGP

PRL 91. 072301 (2003)

)/(

/

Tpp

AB

TAA

AA dydpdT

dydpdR

Nuclear Modification Function

QGP

In the absence of nuclear effects: RAA=1

The inclusive pi0 production in Au+Au

Hadron Production will be suppressed due to the jet quenching occurred in the heavy-ion collisions as an effect of the matter

Introduction Why Low Mass Vector mesons?

5

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

e+

e-

Momentum Electron ID

π-

φ→e+e-

ω→e+e-

π+

ω

γ

γπ0

γγ

γ

γ

π0

ω→π0π+π-

ω→π0γ

EnergyMomentum Hadron ID

PHENIX spectrometer<Global detector>• BBC & ZDC : Event trigger, Collision vertex, Centrality <Central arm>• Acceptance ⇒ pseud-rapidity range : |η| < 0.35 azimuthal angle : 2x90 degree• DC & PC : tracking, momentum• RICH & EMC : electron ID• TOF, EMC : hadron ID<Muon arm>• MuID : muon ID

⇒PHENIX consists of multi-purpose detector to measure rare probe from collisons.

Experiment Which decay mode do we measure ?

6

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

p+p, d+Aucollisions

Analysis Highlight How do we approach?p+p d+ Au

d+ Au

φ e+e- φ e+e-

+-

p+p

Both leptonic andhadronic decay channel are measured

7

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Quest for Low Mass Vector Mesons　　 in huge huge Background

Analysis Highlight How do we approach?

Challenge to A+A Collisions

8

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Analysis Highlight How do we approach?

Improving S/N

pT(ω) [GeV/c]

S/√

B (

sig

nif

ican

ce)

No Cuts

Best Cuts

• Cut Optimization e.g. @ Au+Au

Kinematical Cuts for Reconstruction

･ Transverse Momentum of 　　･ Photon Energy･Width of Invariant Mass

0 Rising Minimum Cuts

Use Best Cuts that improve S/√B (significance) the most

0

p[GeV/cp[GeV/c22] E[GeV] MassWidth] E[GeV] MassWidth

9

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Analysis Highlight How do we approach?

Subtracting Backgrounds ( 2 body: φ e+e-φ K+K- )

φBG

BG

conbinatorial backgrounds

Extract by Event Mixing

→ee

BGSignalSignal

10

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Black: FG

[GeV/c^2]

Peripheral (cent 60~92 %)3.5<pT<4.5[GeV/c]

Magenta:BG1+BG2+BG3 BG3

BG2

BG1

Gaussian (Mean and With are Fixed by Embedding simulation)

after subtraction of

BG1+BG2+BG3

coun

t

Reconstructed invariant mass

Mixed event

0sK

Analysis Highlight How do we approach?

Subtracting Backgrounds ( 3 body: ( 2)

BG1 BG2

11

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

• Spectra (p+p & d+Au)

Results & Discussion What do we see?

12

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

• Spectra (Au+Au) , e+e- @ Au+Au

Results & Discussion What do we see?

Suggesting Hadron suppression

Get

tin

g d

ow

n

Get

tin

g d

ow

n

in h

igh

er c

entr

alit

y

in h

igh

er c

entr

alit

y

13

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Results & Discussion What do we see?

Interesting systematic measurement of hadron suppression

14

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Results & Discussion What do we see?

Interesting systematic measurement of hadron suppression

15

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Summary

• PHENIX measured Low Mass Vector Meson, φandω production in both leptonic and hadronic channels in different collision system.– Spectra show good agreement among several deca

y channels in p+p and d+Au– A+A results have an ability to discuss hadron suppr

ession providing intriguing systematic results.

Physics…

　　 Low pT High pT

Signal for Chiral Symmtery Restoration

Signal for Hadron Suppression

yet to be discussed…provide intriguing result

Systematic measurement of omega in PHENIX will be published in near furtureSystematic measurement of omega in PHENIX will be published in near furture

16

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Back upBack up

17

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Chiral Symmetry Restoration

Chiral symmetry is restored<qq> → 0

Chiral symmetry is spontaneously broken <qq>~250 MeV

ｰ

3ｰ

(Heavy Ion Collider used for this study)

Phys.Rev.Lett.55(1985)158.Nucl.Phys.A443(1993)59c.

18

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Prediction of theory

T.Hatsuda and S.H.LeeP.R.C.46(1992)R34 →

R.Rapp,H.Hees and T.Stronghep-ph/0611339 ↓

There’s no clear consistent results for the theoritical approach to search for the effect of Chiral Symmetry Restoration.

This is the example where experiments has the potential to guide the theory!

19

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Phi results

φ K+K- @ Au+Au

φ e+e-φ K+K- @ Au+Au

20

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

d+Au results (omega)

@ d+Au

21

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

STAR results

22

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

RAA with direct photon

23

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Cut Optimization

･ Pi0 Momentum Cuts･ Photon Energy Cuts･ Pi0 Mass Width

Great influence on the peak significancePi0 Momentum

CutsPhoton Energy Cut

Pi0 Mass Width

Default

Cut#1

Cut#2

Cut#3

Cut#4

S/√B

ex. 4.5<ωpT<5.5 (GeV/c)

If there’s no cut, S/B< 1/1000….→Have to improve it by the selection

24

Misaki Ouchida2008 Oct. ATHIC @ Tsukuba

Estimation of omega cross-section