physics motivation status experiment f →k + k － results & w/r →e ＋ e － results

JPS meetig, March 2001 Hideto En'yo, RIKEN 1

Measurements of in-medium Measurements of in-medium decay of vector mesonsdecay of vector mesons

Hideto En’yo Hideto En’yo RIKEN / RIKEN / Kyoto UniversityKyoto University

forfor The KEK-PS E325 CollaborationThe KEK-PS E325 Collaboration

Physics motivationPhysics motivation

Status ExperimentStatus Experiment

→→KK++KK －－ results & results & →e→e ＋＋ ee －－

results results

Discussion & SummaryDiscussion & Summary


Tantalizing hints for new state of Tantalizing hints for new state of mattermatter

CERN Press Release

Feb. 2000


What Theorists Say ?What Theorists Say ?

•<qq> quark condensate : order parameter • to indicate how much the symmetry broken• but not an observable

→ 　 Mass of Vector Meson, Mv = 2 x Mq

eff + small interaction term


Bound Nucleons, MesonsBound Nucleons, Mesons

• Imagine that a neutron ( or proton ) in Oxygen nuclei made GUT decay in Kamiokande. (assume that you have a perfect detector )

n → π+ + e

Mn2 → Eπ

+ Ee)2 Pπ + Pe)2

Mn = 939.6 MeV , Mn

= 938.3MeV ?????

• More precisely16O → π+ + e + 15O*

(Mn +M15O ) 2

→ 15O + Eπ + Ee )2 P15o

+ Pπ + Pe )2

0

1

2

3

4

0 1 2 3

p2 (GeV2)

E2 (

GeV2

)You measure 16O levels

E2 =M

2 +P2


Moving Mesons in MediaMoving Mesons in Media

be smallbe smallE2 =M2 +P2

• In-media meson modification– Observed Mass is not Lorentz Invariant

• shift of resonance position• resonance broadening/narrowing

→ 　 DISPERSION

Outside

Inside


CLUES

Experiment Measurements Interests

CERES/HELIOS-3 modification Temp. dep. ρis modified in Hot Matter

KEK-TANASHI ES modification Density dep. ρis modified in He

GSI modification Density dep. πis modified in He

Present & future experiments .

RHIC(running)/LHC(2006)KEK-PS: p+A→+X(→K+K/e+e) (Running)SPring-8: + →+A*(→ K+K) 　　　　 (Ready to run )GSI: d +A→3He+A* (bound states) (Ready to run )GSI-HADES: +A→ +A* (→e+e) (Preparation, 2001?)

ExperimentsExperiments


KEK-PS E325 KEK-PS E325 to measureto measure ρωφ ρωφ decaysdecays 　　 in nuclear matter in nuclear matter

KK Thresholdin Free Space

K modification ?modification ?

((=4.4MeV) =4.4MeV) Q=38MeVQ=38MeV

φ →K+Kφ →　 e+e Shape modification can Shape modification can bebe 　　 measured inmeasured in

φ →　 e+e


Some Tips of E325Some Tips of E325

• 109/sec primary protons on thin (0.1%) nuclear target to suppress conversions.• Focus on slowly moving 's, p =~1GeV/c(lab). About 10% of 's will decay insi

de a nucleus if nothing happens. • Expected mass shift is 20~40 MeV for φ 　～ 140MeV for ρ 、 ω

– ( Hatsuda-Lee).• Secondary peak may enhance when low 's are selected.• The ratio (→K+K)/(→e+e) is sensitive to modification of phi and/or K • natural width of , is narrow (4.4, 8.4MeV), but some broadening can happen.. Esti

mations are: = N 0 <20MeV

{N} < $10mb, total cross section (from +A→) 　 =0.7,0 =0.16/fm3

→+*K*(KN→X) 　 Klingle and Weise ~44MeV (at rest)


Brief Mile Stones and StatusBrief Mile Stones and Status

• 1994 March. KEK-PS PAC conditionally 　 approved• 1995 March. KEK-PS PAC approved • 1996 July. Construction started• 1996 November. Engineering Run (40.5shift of beam test)• 1997 June, First Physics Run with K+K. 17days 50 shifts

– Data accumulation mainly with K+K channel trigger– Beam Intensity 1~2 x108$ protons/spill on 0.6% interaction targets (106 interaction/spill)

• 1998 March. Completion of Spectrometer, • 1998 April –May. Production Running of 29 days 74shifts.

– Parallel Trigger. K+K-/ e+e- – Beam Intensity 1~2 x 109 protons/spill on 0.1% interaction target (106$ interaction/spill)

• 1999 June 57 shifts Data Taking performed– Parallel Trigger. K+K-/ e+e- – Beam Intensity 1~2 x 109 protons/spill on 0.2% interaction target (106$ interaction/spill)

• 2000 Jun, 35shifts• 2000 Dec. Data Taking to start now.• 104 shifts to go in 21st Century !

KK eeAn

aly

sis


• Kyoto UniversityH.Funahashi,, M.Kitaguchi, M.Miyabe, T.Murakami, R.Muto, M.Naruki, F.Sakuma, H.D. Sato, S.Yamada

• CNS, University of Tokyo – H.Hamagaki, K.Ozawa

• Tohoku University– H. Kanda

• KEK– J.Chiba, M.Ieiri, O.Sasaki, M.Sekimoto, K.Tanaka

• Osaka University– M.Nomachi

• RIKEN– S.Yokkaichi, T.Tabaru, H. Enyo

E325 collaborationE325 collaboration

ICEPP, U-TokyoS.MiharaM.Ishino

CompaniesT.Miyashita

Y.YoshimuraK.Hamada


E325 SETUPE325 SETUP


Around the targetsAround the targets

• 3 target plate inline

– C/CH2/Cu

– 109/s protons ，– 106/s interactios

• Vertex chamber – 1.75mm drift length


Spectrometer PerformanceSpectrometer PerformanceInvariant Mass Invariant Mass Spectrum)Spectrum)

M= 494.8MeV/c2 (PDG 497.7MeV/c2)

M= 6.1MeV/c2 (Sim 6.3MeV )

　

→→pp

→→

M= 1115.4-5MeV/c2 (PDG 1115.7MeV/c2)

M= 1.8-2.4MeV/c2 (Sim 1.9MeV)

φ→KK 2 ． 4MeV 　 φ→ee 9MeV 　


‘‘98 data (Electron Channel)98 data (Electron Channel)

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

2

2

[events / 50MeV/c ]

[GeV/c ]e e invariant mass

from lighttargets

e e e e

combinatorial

fit result

100

80

60

40

20

00 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

a)

2

from heavytarget

[GeV/c ]e e invariant mass

e e e e

combinatorial

fit result

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

b)

Nucl-ex-0011013 to appear in PRL


‘‘99 data (KK mode) 99 data (KK mode) to be publishedto be published 　　


Experiment

JAMAll come from string decays

JAM (Y.Nara, RBRC)JAM (Y.Nara, RBRC)Intra Nuclear Cascade Intra Nuclear Cascade CodeCode

Pt

Ｙ－ PtY

βγ

Resonance Production ( Low Energy)

String Excitation (Mid Energy)Parton-parton (High Energy)

K+K- Sources1. φ2. a0/f0

3. Non resonant (not large)4. PID back ground

C,CH2 data (χ2 = 34.5/37)

a0/f0 to φ 　　 37 ． 7±1

0 %

Gd,Cu data (χ2 = 38.8/37)

a0/f0 to φ 　　 27.2±10

． 1 ％

Kinematical Distributions are well Described by JAM


Target Mass Dependence ofTarget Mass Dependence of →K→K++KK(’97+’99 Data)(’97+’99 Data)

=1.010.09 EXP

=1.080.01 JAM

is surprisingly large but

　 explained by JAM.

For CarbonΩσ= 0 ． 19 　 0.030.09 μ ｂ　 E

XPΩσ= 0 ． 31 　 0.03 μ ｂ　　　　 J

AM

σ= 15.5 Aαμ ｂ　　 JAM


Target Mass Dependence ofTarget Mass Dependence of φφ→e→e++ee(’99 Data)(’99 Data)

= 　 0.63 　 ± 0.07 for ωpeak

= 　 1.03 　 ± 0.15 for φpeak

　ω→e+e－ C/CH2

φ→e+e－


What we have learned ?What we have learned ?• Meson modification is observed in

nucleus firstly in electron pair channel.• Does it means QCD chiral symmetry

restoration ? – NOT　YET ( life is more complicated)

Toy Model Calc.

– mass shift as predicted by Hatsuda– in-media broadening of 3 × free space ( D. Cabera et al.)– production of ρ ・ ω at the surface of a nucleus （ A 2/3 ）


What is missing What is missing then ?then ?• Theoretically

– How large the in-media broadening ?• SHAPE

• DECAY 　 RATE

Many theoretical works, not conversing

– Other trivial reasons ?• Collisional broadening

• Phase space (not important in E325)

• Experimentally– Statistics, Statistics, Statistics, to give

• Accurate shape

• Dispersion

– φ→e+e －

By Akaishi, Yamazaki


Summary and Outlook Summary and Outlook The ’97+’99 →K+Kdata have been analyzed. The results shows

No significant mass shape deformation (a0/f0 are problematic) Strong A dependence ( =1.01 0.09 ) in the production Reasonable agreement with the cascade model JAM.

The ‘98 ω→e+e- spectrum shows a surprising indication of in-medium decay of ρ/ω mesons The first observation of mesons decayed in nuclear matter. The physics underneath is not apparent yet, but very promising to go further.

The ‘99 e+edata are still preliminary, with a clear peak of φ →e+e- A 　 dependence of ω and 　 φ 　 productions are ~2/3 and ~3/3 , respectively

Statistics will be ＞ 5times at the end of assigned beam time, φ→e+e- 　 and dispersion data will be available

Will hopefully be the first measurements to address the chiral property of dense nuclear matter.

physics motivation status experiment f →k + k － results & w/r →e ＋ e － results

Documents

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e e beam intensity

precisely16o e

e preparation

f modification

e15o e ee

kkeeanalysishideto enyo