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 １） １） new analysis for φ new analysis for φ → → KK++KK--)) 　　　　 - PID, noPID, one leg PID- PID, noPID, one leg PID　　２） 　　２） background estimation for ω->πbackground estimation for ω->π00γγ

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- RAAAA

- Npart scaling- Npart scaling

•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→→ππ00γγ

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 : 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 (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-,π0γand π0π+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 π0γ.

pT spectra for ω→e+e-, ω→π0γ, ω→π0π+π- are consistent at p+p and d+Au collisions.

RAA (binary scaling) for φ and ω mesonsω→π0γ AuAu 200GeVφ→K+K-, AuAu 200GeV

RAA is suppressed in high pT region for φ→K+K- data,

There are no convincing result for ω→π0γ data.

RAA suppression has a dependence on centralities.

Npart scaling for φ and ω mesons

- 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 (Right figure)

√s=200GeVppdydpdN

ppart

AuAudydpdN

p

c

TT

TT

NR

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5.0

PRC 74 021902 (2006)

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.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.RAA　is　suppressed　in　high　pT　region　for　φ→K+K-　data,　　There　are　no　convincing　result　for　ω→π0γ　data.RAA　　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.

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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-