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Physics motivation Our Experiment Results (K + K － & e ＋ e － Channels) Discussion & Summary

Nuclear media effects on production and decay of vector meson studied in 12 GeV p+A interaction Hideto En’yo RIKEN / RIKEN-BNL Research Center for The KEK-PS E325 Collaboration. Physics motivation Our Experiment Results (K + K － & e ＋ e － Channels) Discussion & Summary.

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Physics motivation Our Experiment Results (K + K － & e ＋ e － Channels) Discussion & Summary

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  1. Nuclear media effects on production and decay of vector meson studied in 12 GeV p+A interactionHideto En’yoRIKEN / RIKEN-BNL Research CenterforThe KEK-PS E325 Collaboration Physics motivation Our Experiment Results (K+K－& e＋e－ Channels) Discussion & Summary Hideto En'yo, RIKEN/RBRC

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

  3. 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 Hideto En'yo, RIKEN/RBRC

  4. 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- Mn2 → ( Eπ+ Ee)2 -(Pπ+ Pe)2 Mn= 939.6 MeV , Mn= 938.3MeV ????? • More precisely 16O → π+ + e- + 15O* (Mn +M15O )2 → (E15O +Eπ+ Ee )2 - (P15o+ Pπ+ Pe )2 E2=M2+P2 You measure 16O levels Hideto En'yo, RIKEN/RBRC

  5. Moving Mesons in Media • In-media meson modification • Observed Mass is not Lorentz Invariant • shift of resonance position • resonance broadening/narrowing →DISPERSION E2=M2+P2 Outside be small Inside Hideto En'yo, RIKEN/RBRC

  6. Experiments CLUES Experiment Measurements Interests CERES/HELIOS-3r modification Temp. dep. ρis modified in Hot Matter KEK-TANASHI ESr modification Density dep. ρis modified in He GSI p modification Density dep. πis modified in Nucleus 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?) Hideto En'yo, RIKEN/RBRC

  7. KEK-PS E325 to measure ρωφ decaysin nuclear matter f(G=4.4MeV) DQ=38MeV φ →K+K- /φ →e+e- KK Threshold in Free Space f modification ? K modification ? Shape modification can bemeasured in ω/ρ/φ →e+e- Hideto En'yo, RIKEN/RBRC

  8. 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 = sfNbfr0Gf <20MeV • s{fN} < $10mb, total cross section (from g+A→f )bf=0.7,r0 =0.16/fm3 • f →K+*K-*(K-N→SX) • Klingle and Weise Gf ~44MeV (at rest) Hideto En'yo, RIKEN/RBRC

  9. History • 1995 March. KEK-PS PAC approved • 1996 July. Construction started Hideto En'yo, RIKEN/RBRC

  10. E325 collaboration Graduation T.Miyashita Y.Yoshimura K.Hamada • 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 Hideto En'yo, RIKEN/RBRC

  11. E325 SETUP Hideto En'yo, RIKEN/RBRC

  12. Set up Hodoscope Aerogel Cherenkov Forward TOF Forward LG Calorimeter Rear LG Calorimeter Side LG Calorimeter B Barrel Drift Chamber Cylindrical DC 12GeV proton beam Rear Gas Cherenkov Vertex DC Front Gas Cherenkov Hideto En'yo, RIKEN/RBRC

  13. Hideto En'yo, RIKEN/RBRC

  14. Around the targets • 3 target plate inline • C/CH2/Cu • 109/s protons， • 106/s interactios • Vertex chamber • 1.75mm drift length Hideto En'yo, RIKEN/RBRC

  15. Spectrometer Performance (Invariant Mass Spectrum) L→pp- K0→p-p+ MK= 494.8MeV/c2 (PDG497.7MeV/c2) dMk = 6.1MeV/c2 (Sim 6.3MeV ) ML= 1115.4-5MeV/c2 (PDG1115.7MeV/c2) dML = 1.8-2.4MeV/c2 (Sim 1.9MeV) φ→KK 2．4MeVφ→ee9MeV Hideto En'yo, RIKEN/RBRC

  16. PRL, 2001 28 May, page 5019 ‘98 data (Electron Channel) w  e+e- • ω→e+e－　　SignificantDifferencebetween C and Cu • The first observation of in-medium decay of vector mesons. Hideto En'yo, RIKEN/RBRC

  17. Combinatorial background • 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 K0s It is reasonable to use ee mixed event for the combinatorial background Spectrum of p pair Hideto En'yo, RIKEN/RBRC

  18. 450GeV p+Be→e+e- Helios/Na34 Hideto En'yo, RIKEN/RBRC

  19. Cross Section Acceptance Corrected Absolute Cross Section JAM Comparison Nuclear Mass Number Hideto En'yo, RIKEN/RBRC

  20. ω Meson Kinematics pT Dependence • Absolute Cross Sections are ~6x larger in JAM • Kinematical Distributions are well reproduced by JAM xF Dependence Hideto En'yo, RIKEN/RBRC

  21. How w & fare produced JAM w f Our Acceptance Feynman X Our Acceptance Hideto En'yo, RIKEN/RBRC

  22. PRL, 2001 28 May, page 5019 ‘98 data (Electron Channel) w  e+e- • ω→e+e－　　SignificantDifferencebetween C and Cu • The first observation of in-medium decay of vector mesons. Hideto En'yo, RIKEN/RBRC

  23. Invariant Mass Spectrum of e+e- (’02 Data) Preliminary Counts/20MeV/c2 Counts/20MeV/c2 Fit Result ω ρ φ Back Ground Light Target (Carbon) GeV/c2 Heavy Target (Copper) GeV/c2 Hideto En'yo, RIKEN/RBRC

  24. BackGround SubtractedInvariant Mass Spectrum of e+e- (’02 Data) Preliminary Counts/20MeV/c2 Counts/20MeV/c2 Not large mass dependence (wait for momentum dependence analysis) Fit Result r is 0.4 times smaller than pp data Some hints for f modification ω ρ φ Light Target (Carbon) GeV/c2 Heavy Target (Copper) GeV/c2 Hideto En'yo, RIKEN/RBRC

  25. ‘99 data (KK mode) to be published Hideto En'yo, RIKEN/RBRC

  26. βγ Pt JAM (Y.Nara, RBRC)Intra Nuclear Cascade Code • Resonance Production ( Low Energy) • String Excitation (Mid Energy) • Parton-parton (High Energy) • K+K- Sources • φ • a0/f0 • Non resonant (not large) • PID back ground • C,CH2 data (χ2 = 34.5/37) • a0/f0 to φ37．7±10 % • Gd,Cu data (χ2 = 38.8/37) • a0/f0 to φ27.2±10．1％ JAM All come from string decays Ｙ－Pt Y Experiment Kinematical Distributions are well Described by JAM Hideto En'yo, RIKEN/RBRC

  27. What we have learned ? Toy Model Calc. • Meson modification is observed at normal nuclear density firstly in electron pair channel. • Does it means QCD chiral symmetry restoration ? • NOTYET ( 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） Hideto En'yo, RIKEN/RBRC

  28. What is missing then ? • Theoretically • How large the in-media broadening shift ? • SHAPE • DECAYRATE 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 Hideto En'yo, RIKEN/RBRC

  29. Conclusions • The ‘98 ω→e+e- spectrum has shown an indication of in-medium decay 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 f→K+K- data have shown • Low mass side enhancements (a0/f0 or f modification ?) seen. • PRODUCTION • The measured production cross section of ω is consistent with the previouse measurement. 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. Hideto En'yo, RIKEN/RBRC

  30. 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). Hideto En'yo, RIKEN/RBRC

  31. ’99+’98 data (Electron Channel) Preliminary Statistics improved by factor 5. Consistently the excess was seen. Hideto En'yo, RIKEN/RBRC

  32. Hideto En'yo, RIKEN/RBRC

  33. We evaluated the electron efficiency and pion contaminationin the momentum range greater than400 MeV/c. Electron efficiency and pion contamination 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. Hideto En'yo, RIKEN/RBRC

  34. Kinematical distribution of electron pair • The kinematical coverage of the present data is shown. • The combinatorial background is subtracted. Opening angle Opening angle bglab bglab Transverse Momentum Transverse Momentum Rapidity Rapidity Heavy Target Light Target Hideto En'yo, RIKEN/RBRC

  35. Meson production in JAM Hideto En'yo, RIKEN/RBRC

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