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Measurements of in-medium decay of vector mesons Hideto En’yo RIKEN / Kyoto University for The KEK-PS E325 Collaboration. Physics motivation Status Experiment f →K + K - results & w/r →e + e - results Discussion & Summary. Tantalizing hints for new state of matter. - PowerPoint PPT Presentation
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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
JPS meetig, March 2001 Hideto En'yo, RIKEN 2
Tantalizing hints for new state of Tantalizing hints for new state of mattermatter
CERN Press Release
Feb. 2000
JPS meetig, March 2001 Hideto En'yo, RIKEN 3
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 4
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 5
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 6
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 7
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 8
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} < $10mb, total cross section (from +A→) =0.7,0 =0.16/fm3
→+*K*(KN→X) Klingle and Weise ~44MeV (at rest)
JPS meetig, March 2001 Hideto En'yo, RIKEN 9
Brief Mile Stones and StatusBrief Mile Stones and Status
• 1994 March. KEK-PS PAC conditionally approved• 1995 March. KEK-PS PAC approved • 1996 July. Construction started• 1996 November. Engineering Run (40.5shift of beam test)• 1997 June, First Physics Run with K+K. 17days 50 shifts
– Data accumulation mainly with K+K channel trigger– Beam Intensity 1~2 x108$ 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
JPS meetig, March 2001 Hideto En'yo, RIKEN 10
• 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
JPS meetig, March 2001 Hideto En'yo, RIKEN 11
E325 SETUPE325 SETUP
JPS meetig, March 2001 Hideto En'yo, RIKEN 12
JPS meetig, March 2001 Hideto En'yo, RIKEN 13
Around the targetsAround the targets
• 3 target plate inline
– C/CH2/Cu
– 109/s protons ,– 106/s interactios
• Vertex chamber – 1.75mm drift length
JPS meetig, March 2001 Hideto En'yo, RIKEN 14
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 15
‘‘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
JPS meetig, March 2001 Hideto En'yo, RIKEN 16
‘‘99 data (KK mode) 99 data (KK mode) to be publishedto be published
JPS meetig, March 2001 Hideto En'yo, RIKEN 17
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 18
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 19
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-
JPS meetig, March 2001 Hideto En'yo, RIKEN 20
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 )
JPS meetig, March 2001 Hideto En'yo, RIKEN 21
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
JPS meetig, March 2001 Hideto En'yo, RIKEN 22
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.