Systematic measurement of light Systematic measurement of light vector mesons at RHIC-PHNEIXvector mesons at RHIC-PHNEIX

Yoshihide NakamiyaHiroshima University, Japan

(for the PHENIX Collaboration)

Quark Matter 2008, Variable Energy Cyclotron Centre,Jaipur,India

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OutlineOutline Physics motivation Physics motivation

PHENIX experiments at RHICPHENIX experiments at RHIC

Improved AnalysisImproved Analysis - no PID methods - no PID methods (φ -> K+K-)(φ -> K+K-) - new background subtraction methods- new background subtraction methods 　　　 　　　 (ω->π(ω->π00γγ)γγ)

Result (φ mesons and ω mesons)Result (φ mesons and ω mesons) - mT & pT slope- mT & pT slope - Results of yield analysis - Results of yield analysis (dN/dy & temperature)(dN/dy & temperature) - Results of Line shape analysis- Results of Line shape analysis

SummarySummary

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• Lattice QCD predicts a phase transition to a deconfined partonic matter at a temperature of about 170 MeV.

Heavy-ion collision isthe unique method to produce a phase transition at the regime of high energy density and low baryon density (cross overregions).

Several kinds of phase transition has happened in cross over regions.

-chiral condensate <qq>->chiral phase transition-quark number susceptibility -> deconfinment-polyakov loop ->deconfinment

Physics BackgroundPhysics BackgroundActa Phys. Pol. B 31 (2000) 3021

At RHIC

Heavy-ion collisions at RHIC hascapability of studying a phase transition In a cross over region.Measurements from various viewpointsIs needed to reveal the property ofa partoic matter.

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Why light vector mesons ?Why light vector mesons ?

<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　　　　　　（ 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) S217R. Rapp J. Phys G31 (2005) S217R. Rapp J. Phys G31 (2005) S217

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Experimental setupExperimental setup

RHIC perspective

PHENIX overview

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.

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.)

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What has been measured in PHENIX?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 know the 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. 　　　 (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 mφ~mk).

[GeV/c^2]

Magenta:BG1+BG2+BG3

The invariant mass spectra of 3γ

ω peak

BG2 : mixing between accidental π0 candidate andevent mixed γ.

Improved analysis :Improved analysis :　　 Background estimation for ωBackground estimation for ω→→ππ00γγDifficulty : 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 : K0 contribution

BG1 ： mixing between π0 candidate and event mixed γ.

Improved analysis : φ Improved analysis : φ → → KK++KK-- analysis analysisKaon 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 identifiedby mass peak.

φ candidates

K+ K-h+ h-

φ candidates

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 identifiedby mass peak.

<Feature of analysis>No PID analysis : φ measurement is extended high pT regionSingle leg analysis : φ measurement is extended low pT region

Result : Result :

　　　　　　 Yield Analysis Yield Analysis

mT spectra (phi -> e+e-)

Binary scaling

Npart 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

mT spectra (phi -> K+K-) : comparison between with PID, no PID and legPID

-The slope of mT spectrum is consistent between PID, single leg PID and no PIDanalysis in overlap region.-Measurable mT region is extended by no PID and one leg PID analysis.

Au+Au

p+p and d+Au

mT spectra (phi -> K+K-)

Binary scaling

Npart scaling

The left-top figure is mT spectraThe right-top figure is mT spectra scaled by NcolThe right-bottom figure is mT spectra scaled by Npart

The invariant dN/dy and temerature for phi mesons

mT spectra (omega -> e+e-)

Binary scaling

Npart scaling

The left-top figure is pT spectraThe right-top figure is pT spectra scaled by NcolThe right-bottom figure is pT spectra scaled by Npart

mT spectra (omega -> pi0 gamma, pi0pi+pi-)

Binary scaling

Npart scaling

The left-top figure is pT spectraThe right-top figure is pT spectra scaled by NcolThe right-bottom figure is pT spectra scaled by Npart

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Result : Result :

　　　　　　 Line Shape Analysis Line Shape Analysis

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Line shape for φLine shape for φ →K→K++KK- - at AuAu 200GeV at AuAu 200GeVPRC 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.

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Line shape for ω mesons at dAu, pp 200 GeVLine shape for ω mesons at dAu, pp 200 GeVPRC 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 GeVare consistent with the PDG value within errors.

SummarySummarySystematic　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>　

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

Back up Back up

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Photon & Hadron measurement Photon & Hadron measurement

K+

K-

φ→K+K-

Momentum Hadron ID

π-

π+

ω

γ

γπ0

γγ

γ

γ

π0

ω→π0π+π-

ω→π0γγ

EnergyMomentum Hadron ID

Photon ID Photon and hadron is separated byshower shape in EMC. Electron is rejected RICH veto.

Hadron ID Hadron identification is mainly done by Time of flight.

Time of flight for hadrons

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Electron measurement Electron measurement

e+

e-

Momentum Electron IDWhy 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-