Measurements of inmedium decay of vector mesons at

Measurements of in-medium decay of vector mesons at KEK-PS Hideto En’yo RIKEN / RIKEN-BNL Research Center for The KEK-PS E 325 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 1

Tantalizing hints for new state of matter CERN Press Release Feb. 2000 JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 2

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 3

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+ + e Mn 2 → ( Eπ + Ee)2 -(Pπ + Pe)2 Mn = 939. 6 Me. V , Mn = 938. 3 Me. V ? ? ? • More precisely 16 O → π+ + e- + 2 15 O* (Mn +M 15 O ) 2 → (E 15 O + Eπ + Ee )2 - (P 15 o + Pπ + Pe )2 2 +P 2 =M E You measure 16 O levels JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 4

Moving Mesons in Media 2 Outside 2 +P 2 M E= 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 5

Experiments CLUES Experiment CERES/HELIOS-3 KEK-TANASHI ES GSI Measurements 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→ 3 He+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 6

KEK-PS E 325 to measure ρωφ decays in nuclear matter KK Threshold in Free Space f modification ? K modification ? Shape modification can be measured in ω/ρ/φ → e+e. JPS/DNP Maui, Oct 2001 f(G=4. 4 Me. V) DQ=38 Me. V φ →K+K- /φ →e+e. Hideto En'yo, RIKEN/RBRC 7

Some Tips of E 325 • 109/sec primary protons on thin (0. 1%) nuclear target to suppress g conversions. • Focus on slowly moving f, w, r 's, p =~1 Ge. V/c(lab). About 10% of f's will decay inside a nucleus if nothing happens. • Expected mass shift is 20~40 Me. V for φ ～ 140 Me. V 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. 4 Me. V), but some broadening can happen. . Estimations are: - Gf = sf. N bfr 0 Gf <20 Me. V - s{f. N} < $10 mb, total cross section (from g+A→f ) bf=0. 7, r 0 =0. 16/fm 3 - f →K+*K-*(K-N→SX) - Klingle and Weise JPS/DNP Maui, Oct 2001 Gf ~44 Me. V (at rest) Hideto En'yo, RIKEN/RBRC 8

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. 5 shift of beam test) 1997 June, First Physics Run with K+K-. 17 days 50 shifts – Data accumulation mainly with K+K- channel trigger – Beam Intensity 1~2 x 108$ protons/spill on 0. 6% interaction targets (106 interaction/spill) • 1998 March. Completion of Spectrometer, • 1998 April –May. Production Running of 29 days 74 shifts. – 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, 35 shifts • 2000 Dec, 35 shifts • 2001 Nov-Dec 104 shifts! JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 9

E 325 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 10

E 325 SETUP JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 11

JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 12

Around the targets • 3 target plate inline – C/CH 2/Cu – 109/s protons， – 106/s interactios • Vertex chamber – 1. 75 mm drift length JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 13

Spectrometer Performance (Invariant Mass Spectrum) L→pp. K 0→p-p+ ML= 1115. 4 -5 Me. V/c 2 (PDG 1115. 7 Me. V/c 2) d. ML = 1. 8 -2. 4 Me. V/c 2 (Sim 1. 9 Me. V) MK= 494. 8 Me. V/c 2 (PDG 497. 7 Me. V/c 2) d. Mk = 6. 1 Me. V/c 2 (Sim 6. 3 Me. V ) φ→KK 2．4 Me. V φ→ee 9 Me. V JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 14

PRL, the issue of 28 May, page 5019 ‘ 98 data (Electron Channel) 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 Hideto En'yo, RIKEN/RBRC 15

Combinatorial background K 0 s 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 K 0 s 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 16

• 450 Ge. V p+Be→e+e- Helios/Na 34 JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 17

’ 99+’ 98 data (Electron Channel) i lim e r P y r na Statistics improved by factor 5. Consistently the excess was seen. JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 18

JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 19

‘ 99 data (KK mode) JPS/DNP Maui, Oct 2001 to be published Hideto En'yo, RIKEN/RBRC 20

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. a 0/f 0 All come from string decays 3. Non resonant (not large) Experiment 4. PID back ground C, CH 2 data (χ2 = 34. 5/37) a 0/f 0 to φ 37．7± 10 % Gd, Cu data (χ2 = 38. 8/37) a 0/f 0 to φ 27. 2± 10．1％ JPS/DNP Maui, Oct 2001 Kinematical Distributions are well Described by JAM Hideto En'yo, RIKEN/RBRC 21

Target Mass Dependence Good consistency between φ→KK and φ→KK 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 22

Origine of Large α observed in φ production s(f)/s(w) ee KK 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 23

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 Hideto En'yo, RIKEN/RBRC 24

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 E 325) • Experimentally – Statistics, to give • Accurate shape • Dispersion – φ→e+e－ By Akaishi, Yamazaki JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 25

Conclusions l The ’ 97+’ 99 f→K+K- data have been analyzed. The results shows Ø No significant mass shape deformation (a 0/f 0 are problematic) Ø Strong A dependence (a =1. 01 +- 0. 09 ) in the production Ø Reasonable agreement with the cascade model JAM. l The ‘ 98 ω→e+e- spectrum shows a surprising indication of inmedium decay of ρ/ω mesons Ø The first observation of mesons decayed in nuclear matter. Ø The physics underneath is not apparent yet, but very promising to go further. l The ‘ 99 e+e- data are still preliminary, but comfirming the exess seen in ’ 98 data with also a clear peak of φ →e+eØ A dependence of φ is smaller than ω productions, seemingly due to the secondary collision according to the JAM calculation. Ø 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 Hideto En'yo, RIKEN/RBRC 26

Electron efficiency and pion contamination • We evaluated the electron efficiency and pion contamination in the momentum range greater than 400 Me. V/c. EM cal Energy. vs. Momentum n n 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 Hideto En'yo, RIKEN/RBRC 27

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 28

Meson production in JAM JPS/DNP Maui, Oct 2001 Hideto En'yo, RIKEN/RBRC 29