Systematic measurement of light vector mesons at RHIC-PHNEIX Yoshihide Nakamiya Hiroshima University, Japan (for the PHENIX Collaboration) Quark Matter 2008, Variable Energy Cyclotron Centre,Jaipur,India

2Outline Physics motivation PHENIX experiments at RHIC PHENIX experiments at RHIC Improved Analysis Improved Analysis １） new analysis for φ → K + K - ) １） new analysis for φ → K + K - ) - PID, noPID, one leg PID - PID, noPID, one leg PID ２） background estimation for ω->π 0 γ ２） background estimation for ω->π 0 γ Result (φ mesons and ω mesons) Result (φ mesons and ω mesons) - pT spectra - pT spectra - comparison between electron channels and hadron - comparison between electron channels and hadron channels. channels. - R AA - R AA - Npart scaling - Npart scaling Summary Summary

3 Lattice QCD predicts a phase transition to a deconfined partonic matter at a temperature of about 170 MeV.  Heavy-ion collision is the unique method to produce a phase transition at the regime of high energy density and low baryon density (cross over regions).  Several kinds of phase transition has happened in cross over regions. -chiral condensate ->chiral phase transition -quark number susceptibility -> deconfinment -polyakov loop ->deconfinment Physics Background Acta Phys. Pol. B 31 (2000) 3021 At RHIC Heavy-ion collisions at RHIC has capability of studying a phase transition In a cross over region. Measurements from various viewpoints Is needed to reveal the property of a partoic matter.

4 Why light vector mesons ? - deconfinement(shape of thermal radiation) -> Spectral function has been changed in a deconfined partonic matter. - chiral phase transition (chiral symmetry restoration) -> Mass modification will be expected to happen in the deconfined partonic matter. - Hydrodynamic calculation expects that duration time of a deconfined matter is about 10 fm/c. -> Short lived vector mesons are desirable as the target of measurement （ τ QGP = 10 fm/c, τ φ = 46 fm/c, τ ω = 23 fm/c, τ ρ = 1.3 fm/c) Measurement of mass state for light & short lived mesons are suitable for the study of the partonic matter. ⇒ φ and ω mesons can be measured in PHNIX. R. Rapp J. Phys G31 (2005) S217

5 Experimental setup RHIC perspective PHENIX overview PHENIX spectrometer BBC & ZDC : Event trigger, Collision vertex, Centrality Acceptance ⇒ pseud-rapidity range : |η| < 0.35 azimuthal angle : 2x90 degree(2 arms) DC & PC : tracking, momentum RICH & EMC : electron ID TOF, EMC : hadron ID MuID : muon ID ⇒ The PHENIX spectrometers are versatile devices to measure electrons, photons as well as hadrons at the same time. RHIC accelerator  Species : Au+Au, d+Au, proton+proton, Cu+Cu  Energy : √ ｓ _NN = 22.5, 62.5, 200, 500 GeV ⇒ The RHIC accelerator provides various collision systems at a broad range of c.m.s energy. (200Gev is the maximum energy for ion.)

6 What has been measured in PHENIX? φ mesons φ→e + e - Branching Ratio ~ φ→K + K - Branching Ratio ~ 50 % ω mesons ω→e + e - Branching Ratio ~ ω→π 0 γ Branching Ratio ~ 9 % ω→π 0 π + π - Branching Ratio ~ 90 % Line shape analysis (Mass peak and width) ⇒ Line shape modification (Mass peaks and width) may be small due to small fraction of φ&ω decay inside a deconfined matter. (τ QGP = 10 fm/c, τ φ = 46 fm/c, τ ω = 23 fm/c ) Yield analysis (Branching ratio) ⇒ The yield of mesons in case of each decay mode can induce significant change (Yiels trough e + e - compared to K + K - channels could be changed because m φ ~m k ).

[GeV/c^2] Magenta:BG1+BG2+BG3 The invariant mass spectra of 3γ ω peak BG2 : mixing between accidental π 0 candidate and event mixed γ. Improved analysis : Background estimation for ω→π 0 γ Background estimation for ω→π 0 γ Difficulty : It is difficult to estimate background shape of the invariant mass spectra in case of three-bodied decay. Methodology : We assume the background shape consists of 3 components shown below and reproduced background shape by their linear combination. BG3 : K 0 contribution BG1 ： mixing between π 0 candidate and event mixed γ.

Improved analysis : φ → K + K - analysis Kaon PID anaysis Kaon noPID analysisKaon single leg analysis (1) K+ and K- is identified by time of flight (TOF and EMCal) (2) Invariant mass is reconstructed (1) Invariant mass is reconstructed (2) φ meson is identified by mass peak. φ candidates K+K+ K-K- h+h+ h-h- K + or K - h + or h - φ candidates (1) K+ or K- is identified by time of flight (TOF and EMCal) (2) Invariant mass is Reconstructed (3) φ meson is identified by mass peak. No PID analysis : φ measurement is extended high pT region Single leg analysis : φ measurement is extended low pT region

Result : Yield Analysis Yield Analysis

mT spectra (φ → K + K - ) : comparison between with PID, no PID and legPID -The slope of mT spectrum is consistent between three independent analysis ( PID, single leg PID and no PID analysis) in overlap region. -Measurable mT region is extended by no PID and one leg PID analysis. -mT spectrum is different between PHENIX and STAR, especially low pT region. Au+Au p+p and d+Au

mT(pT) spectra (φ&ω mesons) PHENIX has measured several decay channels from light vector mesons.

Comparison of yield between φ→e + e - and φ→K + K - AuAu 200GeV pp, dAu 200 GeV  The shape of mT spectra are consistent between φ→e+e- and φ→K+K- in pp and dAu collisions  The shape of pT sprctra are consistent between between φ→e+e- and φ→K+K- in AuAu collisions

Comparison of yield between ω→e + e -,π 0 γand π 0 π + π - AuAu 200GeV pp 200GeV  PHENIX provides pT spectrum of ω mesons at large range in AuAu collisions by combination between ω→e + e - and π 0 γ.  pT spectra for ω→e + e -, ω→π 0 γ, ω→π 0 π + π - are consistent at p+p and d+Au collisions.

R AA (binary scaling) for φ and ω mesons ω→π 0 γ AuAu 200GeV φ→K + K -, AuAu 200GeV  R AA is suppressed in high pT region for φ→K+K- data, There are no convincing result for ω→π 0 γ data.  R AA suppression has a dependence on centralities.

Npart scaling for φ and ω mesons - R c has no dependence on pT for all Centralities. - R c is ~2-4 for all Centralities within errors, It is not consistent with particle production ratio (~1.5) between pp and AuAu (Right figure) √s=200GeV PRC (2006)

Summary  Systematic Measurement of light vector mesons are powerful to study the property of the partonic matter.  The phenix spectrometers are versatile devices to measure electrons, photons as well as hadrons at the same time.  Consistency between φ→e+e- and φ→K+K- are confirmed in AuAu, pp and dAu collisions at √s_NN = 200 GeV.  Consistency between ω→e+e- and ω→π0π+π- are confirmed in AuAu and pp collisions at √s_NN = 200 GeV.  R AA is suppressed in high pT region for φ→K+K- data, There are no convincing result for ω→π0γ data.  R AA is more suppressed in Central than peripheral.  Rc has no dependence on pT for all Centralities.  Rc is ~2-4 for all Centralities within errors, It is not consistent with particle production ratio (~1.5) between pp and AuAu.

17 Thank you for inviting me to Quark Matter 2008 ! I return thanks to all pariticipants and Collaborators!!

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19 Photon & Hadron measurement K+K+ K-K- φ→K + K - MomentumHadron ID π-π- π+π+ ω γ γ π0π0 γγ γ γ π0π0 ω→π 0 π + π - ω→π 0 γγ Energy Momentum Hadron ID Photon ID  Photon and hadron is separated by shower shape in EMC.  Electron is rejected RICH veto. Hadron ID  Hadron identification is mainly done by Time of flight. Time of flight for hadrons

20 Electron measurement e+e+ e-e- MomentumElectron ID Why electrons ?  Electrons carry the original information inside a deconfined matter due to no strong interaction in medium. Electron ID  Electron identification is mainly done by RICH and Energy-Momentum Matching. Energy-Momentum matching in Au+Au φ→e + e - ω→e + e -