physics motivation our experiment results (k + k － & e ＋ e － channels) discussion...

YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 1

Nuclear media effects on Nuclear media effects on production and decay of vector production and decay of vector meson studied in 12 GeV p+A meson studied in 12 GeV p+A

interactioninteraction

Hideto En’yoHideto En’yo RIKEN / RIKEN-BNL Research CenterRIKEN / RIKEN-BNL Research Center

forfor

The KEK-PS E325 CollaborationThe KEK-PS E325 Collaboration

Physics motivationPhysics motivation

Our Experiment Our Experiment

Results (KResults (K++KK －－ & e& e ＋＋ ee －－ Channels) Channels)

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 Nucleus

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)


φ→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

History History 1995 March. KEK-PS PAC approved 1996 July. Construction started

History History 1995 March. KEK-PS PAC approved 1996 July. Construction started


• 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

• ICEPP, U-Tokyo– S.Mihara, M.Ishino

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

• Tohoku University– H. Kanda

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

• Osaka University– M.Nomachi

E325 collaborationE325 collaboration

GraduationT.Miyashita

Y.YoshimuraK.Hamada


E325 SETUPE325 SETUP


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

B


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 　


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

e+e-

‘‘98 data (Electron Channel)98 data (Electron Channel) PRL, 2001 28 May, page 5019


Major background souces are

•　 π0→γγ 　（ γ→ee)

• π0→ eeγ

•π+ π － invariant mass is well described with the mixed events.

•π+ π － Correlation is only significant for K0s

Spectrum of pair

K0s

It is reasonable to use ee mixed event for the combinatorial background

Combinatorial backgroundCombinatorial background


•450GeV p+Be→e+e- Helios/Na34


Cross Cross SectionSection

ch a n nn e lα Errorω electron 0.849 ± 0.0800

J AM 0.805 ± 0.0003φ electron 1.268 ± 0.2127φ kaon 1.014 ± 0.0769

J AM 1.172 ± 0.0030

Abs

olut

e C

ross

Sec

tion

Nuclear Mass Number

JAM Comparison

Acceptance Corrected


ω Meson ω Meson KinematicsKinematics

xxFF Dependence Dependence

ppTT Dependence Dependence Absolute Cross Sections are ~6x larger in JAM

Kinematical Distributions are well reproduced by JAM


How How & & are are produced produced

JAMJAM

Feynman X

Our Acceptance

Our Acceptance


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

e+e-

‘‘98 data (Electron Channel)98 data (Electron Channel) PRL, 2001 28 May, page 5019


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

Light Target (Carbon)

Heavy Target (Copper)

ωFit Result

ρφ

Back Ground

GeV/c2 GeV/c2

Counts/20MeV/c2 Counts/20MeV/c2Preliminary


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

Light Target (Carbon)

Heavy Target (Copper)

ωFit Result

ρφ

GeV/c2 GeV/c2

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

is 0.4 times smaller than

pp data

Some hints for modification

Not large mass dependence

(wait for momentum dependence analysis)

Preliminary


‘‘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±10 %

Gd,Cu data (χ2 = 38.8/37)

a0/f0 to φ 　　 27.2±10 ． 1 ％

Kinematical Distributions are well Described by JAM


What we have learned ?What we have learned ?• Meson modification is observed at normal

nuclear density 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 shift ?

• SHAPE

• DECAY 　 RATE

Many theoretical works, not conversing

– Other trivial reasons ?• Collisional broadening

• Phase space (not important in E325)

• Experimentally– Statistics to give

• Accurate shape (Partially achieved)

• Dispersion (to come)

– φ→e+e － / K+K － comparison

By Akaishi, Yamazaki


Conclusions Conclusions The ‘98 ω→e+e- spectrum has shown an indication of in-medium deca

y of ρ/ω mesons, over the known hadronic sources below the ω peak. The first observation of mesons decayed in nuclear matter.In the 2002 e+e- data, we have confirmed the above excess. Obtained ρ/ω ratio supports that this excess is mainly due to the modifications of ρ meson. The physics underneath is not apparent yet, but very promising to go further. Some hint on φ meson modifications is seen.

The ’97+’99 →K+Kdata have shown Low mass side enhancements (a0/f0 or modification ?) seen.

PRODUCTION The measured production cross section of ω is consistent with the previouse measureme

nt. JAM calculation predict ~6 times larger. A dependence of φ and ω productions can be reproduced by JAM.

KEY is in detail analyses we have in our hand.


Origine of Large α observed in φ production Origine of Large α observed in φ production

• α seems to be larger than α

• Same tendency also in JAM.

• Most of φ production is from secondary interactions (JAM).

eeKK

JAM

JAM


’’99+’98 data (Electron Channel)99+’98 data (Electron Channel)

Statistics improved by factor 5. Consistently the excess was seen.

Preliminary


Electron efficiency and pion contaminationElectron efficiency and pion contamination

• We evaluated the electron efficiency and pion contamination　 in the momentum range greater than 400 MeV/c.

EM cal Energy.vs.Momentum

The remaining epair background was estimated to be about 13% in the final e+e- pair sample.

The contaminations like pair to be negligibly small.


• The kinematical coverage of the present data is shown.

• The combinatorial background is subtracted.

Light Target Heavy Target

Openingangle

Openinganglelab lab

TransverseMomentum

TransverseMomentum

Rapidity Rapidity

Kinematical distribution of electron pairKinematical distribution of electron pair


Meson production in JAM Meson production in JAM

physics motivation our experiment results (k + k － & e ＋ e － channels) discussion...

Documents

e e hideto enyo

e e runningspring

f modification

precisely16o e

e preparation

hamadahidet enyo

production runhideto

e15o e ee