PS-E325
Ｓｔｕｄｙ of Chiral Property of Dense Nuclear Matter ThroughMeasurements of Meson Mass Modification in Medium

p+A→e+e- + X
Hideto En’
En’yo
RIKEN / RIKENRIKEN-BNL Research Center
forThe KEKPS
E325
Collaboration
KEK

PrefacePhysics motivation
Our Experiment
Results
SummaryC

KEK-PS2004

ω(783)

φ(1020)Hideto En'yo, RIKEN/RBRC

1History
1995
1995 March.
March. KEK-PS
KEK-PS PAC
PAC approved
approved
1996
July.
Construction
started1996 July. Construction started
1997 June
1998 May

1999 July

2000 JuneDec.

ω→e+e−
φ→K+K−First Physics Run with K+K−
First Physics Run with e+e− Publishedin P.R.L. 86 (2001) 5019
First Physics Run with e+e− & K+K−
Production Run

φ→e+e−

99
95
12〜700〜125178

with newly installed

Vertex Chamber & Lead Glass Calorimeter〜5000×2
2001 Nov.

Production Run

2002 Feb.

LAST Production Run〜600〜1000×2

The Biggest Nuclear Experiment @ KEK-PS
KEK-PS2004

Hideto En'yo, RIKEN/RBRC

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Facing at the closing of KEK-PS
1971 April: KEK was established.
1974 December : BOOSTER was completed, @ 500 MeV.

J/ψ1976 March: KEK-PS was completed, @ 8 GeV.
December : KEK-PS @ 11.8 GeV
1977 May: Experiments were started (bubble chamber and IT)
1978 April: Experiments with slow extracted beams
Mikamo’s exp. e+e-Welcome toHigh Energy Society
KEK-PS2004

Hideto En'yo, RIKEN/RBRC

3J/ψ Produced at the Lowest Energy

e＋e−Preliminary
Present Data

12GeV p+C→ J/ψ+X

RHIC(100+100GeV)

AGS(30GeV)
CERN-PS(24GeV)

×100 ?
Threshold
KEK-PS2004

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Physics Motivation of PS-E325•<qq> quark condensate : order parameter• to indicate how much the symmetry broken• but not an observable→ Mass of Vector Meson, ρ ω φ
Mv = 2 x Mqeff + small interaction term

Muroya, Nakamura, Nonaka, 03

Effective Mass of Quarks
At High ρ / TIn Vacuum
mu ≅ md ≅ 300 MeV

ms ≅ 500 MeV

mu ≅ md ≅ 5MeV

Spontaneous Breakingof Chiral Symmetry

ms ≅ 150 MeV

Lattice QCD
KEK-PS2004

Hideto En'yo, RIKEN/RBRC

5Moving Mesons in Media

OutsideInside22 +P2 M
E=be small• In-media meson modification– Observed Mass is not Lorentz Invariant• shift of resonance position• resonance broadening/narrowing→ DISPERSION
KEK-PS2004

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Experiments
CLUES/Signatures
Experiment

CERES/HELIOS-3
KEK-TANASHI ESGSI

Measurements
ρ modification
ρ modification
π modification

Interests
Temp. dep. ρis modified in Hot Matter
Density dep. ρis modified in He
Density dep. πis modified in Nucleus

KEK-PS: p+A→ρ/ωφ/+X→K+K−/e+e−)(Completed / Analyzing)

Present & future experiments
RHIC(running)/LHC(2008?)
SPring-8: γ + →φ+A*(φ→ K+K−)(running )GSI: d +A→3He+A* (ηω bound states) ( to run soon )GSI-HADES: π +A→ ω+A* (ω→e+e−) (running)
KEK-PS2004

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Some Tips of E325
• Very thin target to suppress the conversion electron background(typ. 0.1% interaction/0.2% radiation length of C)• To compensate the thin target, high intensity proton beam to collecthigh statistics (typ. 109 ppp -> 106Hz interaction)• Focus on slowly moving φ,ω,ρ 's, p =~1GeV/c(lab). About 10% of φ's
will decay inside a nucleus if nothing happens.
• Expected mass shift is 20~40 MeV for φ 〜140MeV for ρ、ω
– ( Hatsuda-Lee).

• natural width of φ, ω is narrow (4.4, 8.4MeV), but some broadening
can happen.. Estimations are:− Γφ = σφN βφρ0
Γφ <20MeV− σ{φN} < $10mb, total cross section (from γ+A→φ ) βφ=0.7,ρ0 =0.16/fm3− φ →Κ+*K−*(K−N→ΣX)− Klingle and Weise

KEK-PS2004

Γφ ~44MeV (at rest)

Hideto En'yo, RIKEN/RBRC84

E325 collaboration
Graduation• Kyoto University
T.Miyashita
H.Funahashi,, M.Kitaguchi, M.Miyabe, T.Murakami,
M.Naruki, F.Sakuma, H.D. Sato, S.Yamada
Y.Yoshimura• CNS, University of Tokyo
K.Hamada– H.Hamagaki, K.Ozawa• ICEPP, U-Tokyo– S.Mihara, M.Ishino• RIKEN– S.Yokkaichi, T.Tabaru, R.Muto,
R.Muto, H. EnyoDoctor thesis• Tohoku University
4 completed,4 to come– H. Kanda• KEK– J.Chiba, M.Ieiri, O.Sasaki, M.Sekimoto, K.Tanaka
Master Thesis• Osaka University
10 completed– M.Nomachi

KEK-PS2004

Hideto En'yo, RIKEN/RBRC

9Set up
Hodoscope

Forward LG Calorimeter

Aerogel Cherenkov

Rear LG Calorimeter

Forward TOF
Side LG Calorimeter

B

Barrel Drift Chamber

Cylindrical DCVGe12KEK-PS2004

probtoneamRear Gas Cherenkov
Vertex DC

Front Gas Cherenkov
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KEK-PS2004

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Around the targets• 3 target plate inline– C/CH2/Cu– 109/s protons，– 106/s interactios

Vertex Distribution• Vertex chamber– 1.75mm drift length

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Spectrometer PerformanceΛ → pπ -MΛ= 1115.5MeV/c2 (PDG1115.7MeV/c2)σΛ = 1.8MeV/c2(Sim. 1.9MeV)

K0→π+π-MK= 497.6MeV/c2 (PDG497.7MeV/c2)

σK = 3.8MeV/c2(Sim. 4.1MeV )Mass and Width are well reproduced by MC.

KEK-PS2004

Hideto En'yo, RIKEN/RBRC‘98 data (Electron Channel)

13

PRL, 2001
28 May, page 5019

ω → e+e-• ω→e+e− Significant Difference between C and Cu• The first observation of in-medium decay of vector mesons.
KEK-PS2004

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Invariant Mass Spectrum of e+e- (2002 data)CCω

e+e-CuCuωe+e-excess
excessexcessexcess

φ e+e-

φ e+eρ / ω ratio is consistent with zero

the excess over the known hadronic sources on the lowobserved.
KEK-PS2004 mass side of ω peak has beenHideto
En'yo, RIKEN/RBRC

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Toy model analysis including modification• Assumptions to include the nuclear size effect in the fitting
shape
nuclear density distribution : Woods-Saxon form
– meson production point : incident surface of nuclei– fly through the nucleus, decay with modified mass if the decay point is
inside nuclei––modification as :m*/m0 = 1- 0.16 ρ∗/ρ0(Hatsuda & Lee, '92,'95)( width modification & momentum dependence of modification
not taken into account)areρ/ω ratio is fixed to unity as measured in former exp.
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Fitting results by the toy model

CCu

Tendency of the data are reproduced qualitatively by the model
KEK-PS2004

φ (KK mode)

KEK-PS2004

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to be published

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Invariant Mass Spectrum of φ → e+e-CCu~1000φ~1000φ

Mass(GeV/c2)

Mass(GeV/c2)

KEK-PS2004

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Byproducts
12GeV p+C→ J/ψ+X

12GeV p+C→ θ＋+X
p+K0e＋e−

KEK-PS2004

Hideto En'yo, RIKEN/RBRC

2010

Conclusions
••

•
•
•

KEK-PS E325 measured the e+e-(&K+K- ) decay of slowly
moving vector mesons in nuclei produced by 12GeV protonbeam, to explore the chiral symmetry restoration at thenormal nuclear density.
Observed e+e- invariant mass spectra have excesses below
the ω meson peak, which cannot be explained by known
hadronic sources in normal (unmodified) shape. Thesesuggest modification of (at least) ρ meson.
Simple model calculation including predicted modification
reproduces the observed spectra qualitatively.
Analysis on φ meson is on going...
Signals seen for J/ψ、θ＋KEK-PS2004

Hideto En'yo, RIKEN/RBRC

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