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