Measurement of Invariant Mass Spectraof Vector Meson

Decaying in Nuclear Matter

Measurement of Invariant Mass Spectraof Vector Meson

Decaying in Nuclear Matter Kyoto Univ.a , KEKb, RIKENc, CNS Univ. of Tokyod,

ICEPP Univ. of Tokyoe,Tohoku Univ.f

Megumi NARUKIa,

J. Chibab, H. En’yoc, H. Funahashia, H. Hamagakid, M. Ieirib, M. Ishinoe,

H. Kandaf , M. Kitaguchia, S. Miharae, T. Miyashitaa, T. Murakamia, R. Mutoa,

M. Nomachib, K. Ozawad, F. Sakumaa, O. Sasakib, H.D. Satoa, M. Sekimotob,

T. Tabaruc, K.H. Tanakab, S. Yadamaa, S. Yokkaichic, Y. Yoshimuraa

(KEK-PS E325 Collaboration)•Introduction•E325 Setup•Prelimirary Result of 2002 data analysis•Summary

PhysicsPhysics

In QCD vacuum

MeVm

MeVmm

s

du

500

300

Tqq

,

Chiral Symmetry restoration

In HOT/DENSE Matter

MeVm

MeVmm

s

du

150

5

The Origin of Quark Mass...

How to detect the quark mass modificatoin?

Vector Mesons

Vector MesonVector MesonMass of Vector Mesons, ρ, ω and φMV ≃ 2 x Mq + small Interaction term

ρ/ωMass Modification will be relatively large ～ 150MeV

φ

Narrow Width ～ 4.4MeV→Sensitive to the Mass Shape Modification

Small Q value ( QKK=32MeV )→Branching ratio Γ φ→K +K- / Γ φ→e +e-

will be another good probe

Mass Modification 20 ～ 40MeV

KEK-PS E325 -Expected Signals-KEK-PS E325 -Expected Signals-

We measure Vector Meson Decay Inside a Nucleus, in 12GeV p+A → ρ,ω,φ + X.

Expected Signals of φ→e+e- Invariant Mass Spectrum (Simulation using Hatsuda’s prediction)

HistoryHistoryφ→K+K−

ω→e+e−

φ→e+e−

1997 June

First Physics Run 　 with K+K− 99

1998 MayAlready Published (P.R.L. 86 (2001) 5019 )

9512

1999 July Hawaii JPS/QM2002/PANIC02

178～ 700～ 125

2000 June

Dec.

Production Run with newly

installed Vertex Chamber & Lead Glass Calorimeter ～ 4800×2

～ 930×22001 Nov.

Production Run ～ 570

2002 Feb.

LAST Production Run

Invariant Mass Spectrum of (’98 data)

Invariant Mass Spectrum of (’98 data)

　 Light Target(CH2/C ）

Heavy Target　　　 (Cu)

fit result

ωρ

φ

background

eeP.R..L.. vol.86 (2001)

p5019

12GeV proto

n

beam

Forward LG Calorimeter

Rear LG Calorimeter

Side LG Calorimeter

Barrel Drift Chamber

Cylindrical DC

Front Gas Cherenkov

Rear Gas Cherenkov

Hodoscope

Aerogel Cherenkov

Forward TOF

Set upSet up

Vertex DC

425mm

New DetectorsNew Detectors

Vertex Drift Chamber− momentum resolution− vertex resolution

Forward EM Calorimeter-electron ID efficiency

950

mm

year material

beam intensity

Interaction length

radiation length

’97

CH2/C/Pb

1.3x10８ 0.6% 4.9%

’98

CH2/C/Cu 1.6x109 0.12% 0.4%

’99

CH2/C/Cu 0.9x109 0.24% 0.8%

’’00-’0100-’01C/C/Cu(2)Cu(2) ~1x10~1x1099 0.22%0.22% 1.4%1.4%

’’0202C/C/Cu(4)Cu(4) ~1x10~1x1099 0.42%0.42% 2.2%2.2%

TargetTarget

90mm23mm

CCu

Invariant Mass Spectrum of e+e- (’02 Data)

Light Target (Carbon)

Heavy Target (Copper)

ωFit Result

ρφ

Back Ground

GeV/c2 GeV/c2

Counts/20MeV/c2 Counts/20MeV/c2

BackGround SubtractedInvariant Mass Spectrum of e+e- (’02 Data)

Light Target (Carbon)

Heavy Target (Copper)

ωFit Result

ρφ

GeV/c2 GeV/c2

Counts/20MeV/c2 Counts/20MeV/c2

SummarySummary

KEK PS-E325 detects 12GeV p+A→ρ,ω,φ+X reactions in both K+K- and e+e- channel. We measure the shape of the invariant mass and the branching ratio.In the 2002 e+e- data, we have observed excesses over the known hadronic sources below the ω peak. Obtained ρ/ ω ratio support that this excess is mainly due to the modifications of ρ meson.Some hint on φ meson modifications is seen.In near future, statistics will be about 2 times larger. We plan to obtain the dependence of the momentum of vector mesons.

Electron IDElectron ID

Electron ID PerformanceElectron ID Performance

Mass Resolution

Mass Resolution

　

ΛΛ→pπ→pπ-- KK00→π→π++ππ--

　φ→KK 2 ． 4MeV 　 φ→ee 12MeV