2008 Oct. Tsukuba 1 Misaki Ouchida Hiroshima University For the PHENIX Collaboration ω ω ω e＋e＋ eーeー γ γ π+π+ π0π0 γ πーπー π0π0 γ γ Low mass vector meson measurements at RHIC Systematic Measurement of omega mesons in PHENIX ー ー

Misaki Ouchida2008 Oct. Tsukuba 2 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

Misaki Ouchida2008 Oct. Tsukuba 3 Introduction Why Low Mass Vector mesons? Physics… Low pT High pT Signal for Chiral Symmtery Restoration p+p d+Au A+AA+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 Reconstructed Reconstructed Efficiency Efficiency   e + e - (BR:7x10 -3 %)     (BR:9%) ωpT Signal for Jet Quenching

Misaki Ouchida2008 Oct. Tsukuba 4 Suppression as a Probe of QGP PRL (2003) Nuclear Modification Function QGP In the absence of nuclear effects: R AA =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?

Misaki Ouchida2008 Oct. Tsukuba 5 e+e+ e-e- MomentumElectron ID π-π- φ→e + e - ω→e + e - π+π+ ω γ γ π0π0 γγ γ γ π0π0 ω→π 0 π + π - ω→π 0 γ Energy Momentum Hadron ID PHENIX spectrometer BBC & ZDC : Event trigger, Collision vertex, Centrality Acceptance ⇒ pseud-rapidity range : |η| < 0.35 azimuthal angle : 2x90 degree DC & PC : tracking, momentum RICH & EMC : electron ID TOF, EMC : hadron ID MuID : muon ID ⇒ PHENIX consists of multi-purpose detector to measure rare probe from collisons. Experiment Which decay mode do we measure ?

Misaki Ouchida2008 Oct. Tsukuba 6 p+p, d+Au collisions Analysis Highlight How do we approach? p+p d+Au      e+e-   +  -   p+p Both leptonic and hadronic decay channel are measured

Misaki Ouchida2008 Oct. Tsukuba 7 Quest for Low Mass Vector Mesons in huge huge Background Analysis Highlight How do we approach? Challenge to A+A Collisions

Misaki Ouchida2008 Oct. Tsukuba 8 Analysis Highlight How do we approach? Improving S/N pT(ω) [GeV/c] S/√B (significance) No Cuts Best Cuts Cut Optimization e.g.    Au+Au Kinematical Cuts for Reconstruction ･ Transverse Momentum of ･ Photon Energy ･ Width of Invariant Mass Rising Minimum Cuts Use Best Cuts that improve S/√B (significance) the most p[GeV/c 2 ] E[GeV] MassWidth

Misaki Ouchida2008 Oct. Tsukuba 9 Analysis Highlight How do we approach? Subtracting Backgrounds ( 2 body:  e+e-  K + K - )  BG conbinatorial backgrounds Extract by Event Mixing  →ee BGSignal

Misaki Ouchida2008 Oct. Tsukuba 10 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 count Reconstructed invariant mass Mixed event Analysis Highlight How do we approach? Subtracting Backgrounds ( 3 body:     (    2  )  BG1BG2 

Misaki Ouchida2008 Oct. Tsukuba 11 Spectra (p+p & d+Au) Results & Discussion What do we see?

Misaki Ouchida2008 Oct. Tsukuba 12 Spectra (Au+Au)    ,  Au+Au Results & Discussion What do we see? Suggesting Hadron suppression Getting down in higher centrality in higher centrality

Misaki Ouchida2008 Oct. Tsukuba 13 Results & Discussion What do we see? Interesting systematic measurement of hadron suppression

Misaki Ouchida2008 Oct. Tsukuba 14 Results & Discussion What do we see? Interesting systematic measurement of hadron suppression

Misaki Ouchida2008 Oct. Tsukuba 15 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 decay channels in p+p and d+Au –A+A results have an ability to discuss hadron suppression 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 furture

Misaki Ouchida2008 Oct. Tsukuba 16 Back up

Misaki Ouchida2008 Oct. Tsukuba 17 Chiral Symmetry Restoration Chiral symmetry is restored → 0 Chiral symmetry is spontaneously broken ~250 MeV ｰ 3 ｰ (Heavy Ion Collider used for this study) Phys.Rev.Lett.55(1985)158. Nucl.Phys.A443(1993)59c.

Misaki Ouchida2008 Oct. Tsukuba 18 Prediction of theory T.Hatsuda and S.H.Lee P.R.C.46(1992)R34 → R.Rapp,H.Hees and T.Strong hep-ph/ ↓ 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!

Misaki Ouchida2008 Oct. Tsukuba 19 Phi results  K + K Au+Au  e+e-  K + K Au+Au

Misaki Ouchida2008 Oct. Tsukuba 20 d+Au results (omega)          d+Au

Misaki Ouchida2008 Oct. Tsukuba 21 STAR results

Misaki Ouchida2008 Oct. Tsukuba 22 R AA with direct photon

Misaki Ouchida2008 Oct. Tsukuba 23 Cut Optimization ･ Pi0 Momentum Cuts ･ Photon Energy Cuts ･ Pi0 Mass Width Great influence on the peak significance Pi0 Momentum CutsPhoton Energy CutPi0 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

Misaki Ouchida2008 Oct. Tsukuba 24 Estimation of omega cross-section