Measurement of ω mesons via radiative decay mode in A+A collisions

at √SNN=200GeV RHIC-PHENIX

Misaki Ouchida(Hiroshima University)For the PHENIX collaboration

2007 Autumn JPS Meeting

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OUTLINE

• Low Mass Vector Mesons• Hadron Suppression• RHIC-PHENIX• Apply Cuts• Estimate Background• Efficiency • Results• Discussion & Conclusion

Introduction

Experimental Setup

Analysis

Results

Conclusion

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Low Mass Vector Mesons

Introduction

QGP ~10fm/c

23fm/clife time: 46fm/c 0

Measure this!

• Short lifetime (23 fm/c)-> Include the information of QGP• Large branching ratio (9%)• No ρ-contribution (major problem for e+e-measurement)

Lots of advantages…Why ?

Why ?

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Physics…

　　 Low pT High pT

Siganl for Chiral Symmtery Restoration

Siganl for Hadron Suppression

Heavy Ion Collisions

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Suppression as a Probe of QGP

PRL 91. 072301 (2003)

)/(

)/)(/1(

Tpp

AB

TAA

evtAA dydpdT

dydpdNNR

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

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Data Set : Au+Au collisions√SNN=200 GeV(taken in 2003~2004),The number of event : 1.06 G

99.7% of the speed of light

circumference:3.8 km

Trigger detectors2 muon arms2central arms (include Electro Magnetic Calorimeter)

RHIC-PHENIX

PHENIX Detector

Experimental Setup

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Apply Cuts

Cuts for photon IDShower Shape, TOF Cut

Kinematical Cuts for Reconstruction

Cuts for pi0 legsChose the symmetric energy - both photons in the same sector

222 )(3

0 PEEM Analysis

Quest for omega in huge huge Backgroundat Au+Au Collisions!

~ Resolution 1 ~

pT(ω) [GeV/c]

S/√

B (

sig

nif

ican

ce)

No Cuts

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

0 Rising Minimum Cuts

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

0

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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

~ Resolution 2 ~

Estimate Background

There it is!!!!

Mixed event0sK

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Analysis

Efficiency＝

CentralPeripheral

Embedding to the background

Background

The number of measured ω

The number of input ω

Efficiency

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ResultsLines reporesent estimated yield from p+p collisions scaled by Ncoll Without

nuclear matter effect, measurements follow lines

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Results

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Discussion & Conclusion

We could extract omega via radiative decay mode in Au+Au by overcoming huge combinatorial backgrounds by Applying Best Cut, and Subtracting Background.From the results, we could suggest the sign of Hadron Suppression as the probe of the matter created in the heavy ion collisions.

It is suggested that omega meson yield suppressed in central Au+Au collisions

Out LookAu+Au Results should be finalized…(detail systematic study is needed)How about Cu+Cu collisions?

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Back Up

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Chiral Symmetry RestorationIntroduction

Hadron masses link to the quark condensate, <qq>.

Chiral Symmetry Restored<qq> → 0

Chiral Symmetry is spontaneously broken, <qq>~250 MeV3

There is a transition of the system that constitute mass

Hardron masses change !?

ｰ

ｰ

ｰ

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Correct Mass Distributionusing correlation between pi0 and omega

Omega mass [GeV/c^2]

Pi0

mas

s [G

eV/c

^2]

. ・・・・

Apply this correction function to all pT

PROFILEExpected Improvement of S/N

Resolution 3

782 [GeV/c]

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Other R_AA

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K0short Estimation Check~Question~

“Isn’t it too much?”

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

K0->2pi0 Production

AN535(Run5 p+p) ResultsFitted by Hagedorn function

Estimated Au+Au peripheral spectrum

Ncoll scaling

Calculate estimated number(much more than omega num.)

Ks/pi0 ratio --- 0.438 (AN535)Ks BR --- 31.05%

Omega/pi0 ratio --- 0.85(PPG64)Omega BR --- 8.92 %

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K0short Estimation Check

Efficiency of reconstructing 3 gamma from K0s must be much higher than reconstructing 4 gammas

catch 4 gammas and reconstruct

catch 3 gammas and reconstruct

Using K0s single simulation

about 10 times

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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

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Best Cuts