Transcript PHENIX for the First Collider,RHIC Hideto En’yo Kyoto

Measurements of in-medium decay of
vector mesons at KEK-PS
Hideto En’yo
RIKEN / RIKEN-BNL Research Center
for
The KEK-PS E325 Collaboration
Physics motivation
Status Experiment
f →K+K－ results & w/r →e＋e－ results
Discussion & Summary
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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Tantalizing hints for new state of matter
CERN Press Release
Feb. 2000
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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What Theorists Say ?
•<qq> quark condensate : order parameter
• to indicate how much the symmetry broken
• but not an observable
→ Mass of Vector Meson, r w f
Mv = 2 x Mqeff + small interaction term
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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Bound 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 + + eMn2 → ( Eπ + Ee)2 -(Pπ + Pe)2
Mn = 939.6 MeV , Mn = 938.3MeV ????? 4
• More precisely
e-
+
15O*
3
2
→
π+ +
E (GeV )
16O
You measure
16O levels
2
2
(Mn +M15O ) 2
→ (E15O + Eπ + Ee )2 - (P15o + Pπ + Pe )2
1
0
0
1
p
JPS/DNP Maui, Oct 2001
2
2
(GeV
2
3
)
Hideto En'yo, RIKEN/RBRC
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Moving Mesons in Media
Outside
be small
Inside
• In-media meson modification
– Observed Mass is not Lorentz Invariant
• shift of resonance position
• resonance broadening/narrowing
→ DISPERSION
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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Experiments
CLUES
Experiment
CERES/HELIOS-3
KEK-TANASHI ES
GSI
Measurements
r modification
r modification
p modification
Interests
Temp. dep. ρis modified in Hot Matter
Density dep. ρis modified in He
Density dep. πis modified in He
Present & future experiments
.
RHIC(running)/LHC(2006)
KEK-PS: p+A→f+X(fK+K-/e+e-) (Running)
SPring-8: g + →f+A*(f→ K+K-)
(Ready to run )
GSI: d +A→3He+A* (hw bound states) (Ready to run )
GSI-HADES: p +A→ w+A* (w→e+e-) (Preparation, 2001?)
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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KEK-PS E325
to measure ρωφ decays in nuclear matter
KK Threshold
in Free Space
f modification ?
K modification ?
Shape modification can be
measured in
 / / → e+eJPS/DNP Maui, Oct 2001
f(G=4.4MeV) DQ=38MeV
 →K+K- / →e+eHideto En'yo, RIKEN/RBRC
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Some Tips of E325
• 109/sec primary protons on thin (0.1%) nuclear target to suppress g
conversions.
• Focus on slowly moving f,w,r 's, p =~1GeV/c(lab). About 10% of f's
will decay inside 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 b f's are selected.
• The ratio (f→K+K-)/(f→e+e-) is sensitive to modification of phi
and/or K
• natural width of f, w is narrow (4.4, 8.4MeV), but some broadening can
happen.. Estimations are:
- Gf = sfN bfr0
Gf <20MeV
- s{fN} < $10mb, total cross section (from g+A→f ) bf=0.7,r0 =0.16/fm3
- f +*K-*(K-N→SX)
- Klingle and Weise
JPS/DNP Maui, Oct 2001
Gf ~44MeV (at rest)
Hideto En'yo, RIKEN/RBRC
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Analysis
Brief Mile Stones and Status
•
•
•
KK ee•
•
1994 March. KEK-PS PAC conditionally approved
1995 March. KEK-PS PAC approved
1996 July. Construction started
1996 November. Engineering Run (40.5shift of beam test)
1997 June, First Physics Run with K+K-. 17days 50 shifts
– Data accumulation mainly with K+K- channel trigger
– Beam Intensity 1~2 x108$ 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, 35shifts
• 2001 Nov-Dec 104 shifts!
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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E325 collaboration
• Kyoto University
H.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
JPS/DNP Maui, Oct 2001
Graduation
T.Miyashita
Y.Yoshimura
K.Hamada
Hideto En'yo, RIKEN/RBRC
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E325 SETUP
JPS/DNP Maui, Oct 2001
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JPS/DNP Maui, Oct 2001
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Around the targets
• 3 target plate inline
– C/CH2/Cu
– 109/s protons，
– 106/s interactios
• Vertex chamber
– 1.75mm drift length
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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Spectrometer Performance (Invariant Mass Spectrum)
L→pp0→p-p+
ML= 1115.4-5MeV/c2 (PDG 1115.7MeV/c2)
dML = 1.8-2.4MeV/c2 (Sim 1.9MeV)
M= 494.8MeV/c2 (PDG 497.7MeV/c2)
dMk = 6.1MeV/c2 (Sim 6.3MeV )
φ→KK 2．4MeV φ→ee 9MeV
JPS/DNP Maui, Oct 2001
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‘98 data (Electron Channel)
PRL, the issue of
28 May, page 5019
w  e+e-
• ω→e+e－ Significant Difference between C and Cu
• The first observation of in-medium decay of vector mesons.
JPS/DNP Maui, Oct 2001
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Combinatorial background
K0s
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 p pair
JPS/DNP Maui, Oct 2001
It is reasonable to use ee mixed event
for the combinatorial background
Hideto En'yo, RIKEN/RBRC
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•450GeV p+Be→e+e- Helios/Na34
JPS/DNP Maui, Oct 2001
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’99+’98 data (Electron Channel)
Statistics improved by
factor 5. Consistently
the excess was seen.
JPS/DNP Maui, Oct 2001
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JPS/DNP Maui, Oct 2001
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‘99 data (KK mode)
JPS/DNP Maui, Oct 2001
to be published
Hideto En'yo, RIKEN/RBRC
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JAM (Y.Nara, RBRC)
Intra Nuclear Cascade Code
Pt
βγ
Y
Ｙ－Pt
Resonance Production ( Low Energy)
String Excitation (Mid Energy)
Parton-parton (High Energy)
K+K- Sources
1. φ
JAM
2. a0/f0
All come from string decays
3. Non resonant (not large)
4. PID back ground
Experiment
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％
JPS/DNP Maui, Oct 2001
Kinematical Distributions are well
Described by JAM
Hideto En'yo, RIKEN/RBRC
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Target Mass Dependence
Good consistency between  
and  
af =1.010.09 EXP(KK)
af =1.090.24 EXP(ee)
af =1.1570.003 JAM
a is surprisingly large but explained
by JAM. Reasonable agreement in the
absolute scale.
aw =0.850.09 EXP(ee)
aw =0.7870.001 JAM
a is smaller than φ both in the data
and JAM,
The absolute scale is factor 5 different.
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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Origine of Large α observed in φ production
s(f)/s(w)
ee
KK
JAM
JAM
• αf seems to be larger than αw
• Same tendency also in JAM.
• Most of φ production is from
secondary interactions (JAM).
JPS/DNP Maui, Oct 2001
Hideto En'yo, RIKEN/RBRC
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What we have learned ?
• Meson modification is observed in
nucleus firstly in electron pair
channel.
• Does it means QCD chiral symmetry
restoration ?
Toy Model Calc.
– NOT YET ( life is more complicated)
– 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/DNP Maui, Oct 2001
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What is missing 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/DNP Maui, Oct 2001
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Conclusions

The ’97+’99 f→K+K- data have been analyzed. The results shows




The ‘98 ω→e+e- spectrum shows a surprising indication of inmedium decay of ρ/ω mesons



No significant mass shape deformation (a0/f0 are problematic)
Strong A dependence (a =1.01 +- 0.09 ) in the production
Reasonable agreement with the cascade model JAM.
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+e- data are still preliminary, but comfirming the exess seen
in ’98 data with also a clear peak of φ →e+e

A dependence of φ is smaller than ω productions, seemingly due to the secondary
collision according to the JAM calculation.
The measured production cross section of ω is consistent with the previouse
measurement. JAM calculation predict 5 times larger.
KEY is to obtain the φ →e+e- spectrum with improved
statistics, which will be available 2000/2001 data analysis.
JPS/DNP Maui, Oct 2001
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Electron 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 ep pair background was estimated to be
about 13% in the final e+e- pair sample.
The contaminations like pp pair to be negligibly small.
JPS/DNP Maui, Oct 2001
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Kinematical distribution of electron pair
• The kinematical coverage of the present data is shown.
• The combinatorial background is subtracted.
Opening
angle
Transverse
Momentum
bglab
Rapidity
Light Target
JPS/DNP Maui, Oct 2001
Opening
angle
bglab
Transverse
Momentum
Rapidity
Heavy Target
Hideto En'yo, RIKEN/RBRC
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Meson production in JAM
JPS/DNP Maui, Oct 2001
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