Physics motivation Our Experiment Results (K + K - & e + e - Channels) Discussion &...
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Transcript of 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
YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 2
Tantalizing hints for new state of Tantalizing hints for new state of mattermatter
CERN Press Release
Feb. 2000
YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 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
YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 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
YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 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
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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
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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
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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)
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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
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• 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
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E325 SETUPE325 SETUP
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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
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YITP Kyoto, Oct 2002 Hideto En'yo, RIKEN/RBRC 14
Around the targetsAround the targets
• 3 target plate inline
– C/CH2/Cu
– 109/s protons ,– 106/s interactios
• Vertex chamber – 1.75mm drift length
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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
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• 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
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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
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•450GeV p+Be→e+e- Helios/Na34
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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
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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
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How How & & are are produced produced
JAMJAM
Feynman X
Our Acceptance
Our Acceptance
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• 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
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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
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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
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‘‘99 data (KK mode) 99 data (KK mode) to be publishedto be published
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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
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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 )
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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
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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.
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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
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’’99+’98 data (Electron Channel)99+’98 data (Electron Channel)
Statistics improved by factor 5. Consistently the excess was seen.
Preliminary
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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.
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• 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
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Meson production in JAM Meson production in JAM