Systematic measurement of light vector mesons at RHIC-PHNEIX

1. 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

2. Outline • Physics motivation • PHENIX experiments at RHIC • Improved Analysis - no PID methods (φ -> K+K-) - new background subtraction methods (ω->π0γγ) • Result (φ mesons and ω mesons) • - mT & pT slope • - Results of yield analysis • (dN/dy & temperature) • - Results of Line shape analysis • Summary

3. Acta Phys. Pol. B 31 (2000) 3021 At RHIC Physics Background • 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 <qq>->chiral phase transition -quark number susceptibility -> deconfinment -polyakov loop ->deconfinment 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 ? R. Rapp J. Phys G31 (2005) S217 R. Rapp J. Phys G31 (2005) S217 R. Rapp J. Phys G31 (2005) S217 <Light vector meson as probe > - 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 （τQGP = 10 fm/c, τφ = 46 fm/c, τω = 23 fm/c, τρ = 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.

5. Experimental setup • 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.) RHIC perspective • PHENIX spectrometer • <Global detector> • BBC & ZDC : Event trigger, Collision • vertex, Centrality • <Central arm> • 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 • <Muon arm> • MuID : muon ID • ⇒The PHENIX spectrometers are • versatile devices to measure electrons, • photons as well as hadrons at the same • time. PHENIX overview

6. What has been measured in PHENIX? • <Measured decay channels of light vector mesons in PHENIX> • φ mesons • φ→e+e- Branching Ratio ~ 10-4 • φ→K+K- Branching Ratio ~ 50 % • ω mesons • ω→e+e- Branching Ratio ~ 10-5 • ω→π0γ Branching Ratio ~ 9 % • ω→π0π+π-Branching Ratio ~ 90 % • <How can we knowthe property of light vector mesons ?> • 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. • (τQGP = 10 fm/c, τφ = 46 fm/c, τω = 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 mφ~mk).

7. Improved analysis : Background estimation for ω→π0γ 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. BG1 ：mixing between π0 candidate and event mixed γ. The invariant mass spectra of 3γ Magenta:BG1+BG2+BG3 BG2 : mixing between accidental π0 candidate and event mixed γ. ω peak BG3 : K0 contribution [GeV/c^2]

8. K+ K- h+ h- φ candidates K+ or K- h+ or h- φ candidates φ candidates Improved analysis : φ → K+K- analysis Kaon PID anaysis Kaon noPID analysis Kaon 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. (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. <Feature of analysis> No PID analysis : φ measurement is extended high pT region Single leg analysis : φ measurement is extended low pT region

9. Result : Yield Analysis

10. mT spectra (phi -> e+e-) Npart scaling Binary scaling -The left-top figure is mT spectra -The right-top figure is mT spectra scaled by Ncol -The right-bottom figure is mT spectra scaled by Npart

11. mT spectra (phi -> K+K-) : comparison between with PID, no PID and legPID Au+Au p+p and d+Au -The slope of mT spectrum is consistent between PID, single leg PID and no PID • analysis in overlap region. • -Measurable mT region is extended by no PID and one leg PID analysis.

12. Npart scaling mT spectra (phi -> K+K-) Binary scaling The left-top figure is mT spectra The right-top figure is mT spectra scaled by Ncol The right-bottom figure is mT spectra scaled by Npart

13. The invariant dN/dy and temerature for phi mesons

14. Npart scaling mT spectra (omega -> e+e-) Binary scaling The left-top figure is pT spectra The right-top figure is pT spectra scaled by Ncol The right-bottom figure is pT spectra scaled by Npart

15. Npart scaling mT spectra (omega -> pi0 gamma, pi0pi+pi-) Binary scaling The left-top figure is pT spectra The right-top figure is pT spectra scaled by Ncol The right-bottom figure is pT spectra scaled by Npart

16. Result : Line Shape Analysis

17. Line shape for φ→K+K- at AuAu 200GeV PRC 72 014903 (2007) • Mass centroid • ⇒ Mass centroid at all centralities are consistent with the PDG value • within errors. • Mass width • ⇒There is no convincing evidence of φ width variation as a • function of the number of participant nucleons.

18. Line shape for ω mesons at dAu, pp 200 GeV PRC 75 051902 (2007) <Line shape> ω mass measured in the π0π+π- decay as a function of pT in d+Au and p+p 200 GeV are consistent with the PDG value within errors.

19. 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. <Line Shape Analysis > φ mesons : There is no convincing evidence of mass and width as a function of number of participants nucleons ω mesons : Mass centroid and width is consitstent to the PDG value. <Yield Analysis>

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

21. Back up Back up

22. γ γ π0 π0 γ γ K+ π+ ω φ→K+K- ω→π0π+π- ω→π0γγ γ γ K- Hadron ID Energy Momentum Momentum Hadron ID Photon & Hadron measurement π- • 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

23. Electron measurement e+ e- φ→e+e- ω→e+e- Energy-Momentum matching in Au+Au Momentum Electron 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.