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Medium modifications on vector meson in 12GeV p+A reactions

Medium modifications on vector meson in 12GeV p+A reactions. Kyoto Univ. a , KEK b , RIKEN c , CNS Univ. of Tokyo d , Megumi Naruki, KEK, Japan J. Chiba b , H. En’yo c , Y. Fukao a , H. Funahashi a , H. Hamagaki d , M. Ieiri b ,

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Medium modifications on vector meson in 12GeV p+A reactions

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  1. Medium modifications on vector meson in 12GeV p+A reactions Kyoto Univ.a , KEKb, RIKENc, CNS Univ. of Tokyod, Megumi Naruki, KEK, Japan J. Chibab, H. En’yoc, Y. Fukaoa, H. Funahashia, H. Hamagakid, M. Ieirib, M. Ishinoe, H. Kandaf, M. Kitaguchia, S. Miharae, K. Miwaa, T. Miyashitaa, T. Murakamia, R. Mutob, T. Nakuraa, K. Ozawad, F. Sakumaa, O. Sasakib, M. Sekimotob, T. Tabaruc, K.H. Tanakab, M. Togawaa, S. Yamadaa, S. Yokkaichic, Y. Yoshimuraa (KEK-PSE325 Collaboration) • Result of r/we+e- analysis • Result of fe+e- analysis • Result of fK+K-analysis • A dependence of GKK/Gee • Future Plan

  2. KEK-PS E325 experiment We measure Invariant Mass ofe+e-, K+K- in 12GeV p + Ar, w, f + X • slowly movingr,w,f (plab~2GeV/c） • larger probability to decay inside nucleus • Beam • primary proton beam • (~109/spill/1.8s) • Target • interaction length • 0.2%/0.05% (C/Cu) • radiation length: • 0.4/0.5%(C/Cu) • History • ’93 proposed • ’96 construction start • NIM, A457, 581 (2001) • NIM, A516, 390 (2004) • ’97 first K+K- data • ’98 first e+e- data • r/w: PRL, 86, 5019 (2001) • ’99~’02 • x100 statistics in e+e- • r/w: PRL, 96, 092301 (’06) • f ee: PRL, 98, 042501 (‘07) • a : PRC, 75, 025201 (‘06) x6 statistics in K+K- • fKK: PRL, 98, 152302 (’07)

  3. Detector Setup Forward LG Calorimeter Start Timing Counter Hodoscope Rear LG Calorimeter Aerogel Cherenkov Side LG Calorimeter Forward TOF B 0.81Tm Rear Gas Cherenkov Front Gas Cherenkov M.Sekimoto et al., NIM, A516, 390 (2004). Barrel DC Cylindrical DC 1m 12GeV proton beam Vertex DC

  4. Experimental Effects Resonance Shape : Breit-Wigner + internal radiative correction experimental effect estimated by Geant4 simulation – energy loss, mass resolution, mass acceptance etc. detector simulation for f • Blue histogram : Detector Simulation • Red line : Breit-Wigner (gaussian convoluted) fitting result Experimental effects are fully taken into account we fit the data by the simulated shape, which fully includes the experimental effect

  5. Experimentalists face to reality - E325 simulation- e+e- 1g/cm2 1g/cm2 C Cu

  6. Spectrometer Performance L p p- Ks p+ p- M =496.8±0.3(MC 496.9±0.1)MeV/c2 s = 3.9±0.4(MC 3.5±0.1)MeV/c2 M =1115.71±0.02(MC 1115.53±0.01)MeV/c2 (s = 1.73±0.02(MC 1.62±0.01)MeV/c2) Mass spectra are well reproduced by the simulation Expected mass resolution for f = 10.7MeV/c2

  7. Invariant Mass Spectrum of e+e- we+e- we+e- C Cu fe+e- fe+e- we examine how well the data are reproduced with known hadronic sources & combinatorial background

  8. Invariant Mass Spectrum of e+e- we+e- we+e- Cu C c2/dof=161/140 c2/dof=154/140 fe+e- fe+e- the excess over the known hadronic sources on the low mass side of w peak has been observed.

  9. Invariant Mass Spectrum of e+e- (background subtracted) C Cu r/w ratio is consistent with zero. 95%C.L. allowed regions: Nr/Nw<0.04(stat.)+0.09(sys.) Nr/Nw<0.10(stat.)+0.21(sys.) most of r decay in nucleus due to their short lifetime; t~ 1.3fm

  10. Invariant Mass Spectrum of e+e- we+e- we+e- C Cu fe+e- fe+e- we examine how well the data are reproduced with known hadronic sources & combinatorial background

  11. e+e- Invariant Mass Distributions C Cu f f [GeV/c2] [GeV/c2] • fit with MC shape & quadratic curve • a hint on the spectrum of Cu data. • longer lifetime; t~50fm  kinematical dependence

  12. To see bg dependence Slowly moving f mesons have a larger probability to decay inside the target nucleus. We divided the data into three by bg ( = p/m ); bg<1.25, 1.25<bg<1.75 and 1.75<bg. bg distribution

  13. Invariant mass spectra of f e+e- 1.75<bg (Fast) bg<1.25 (Slow) 1.25<bg<1.75 Small Nucleus Large Nucleus Rejected at 99% confidence level PRL 98(2007)042501

  14. Model Calculationw/medium modification e e r/w f • dropping mass: M(r)/M(0) = 1 – k1 (r/r0) (Hatsuda & Lee) • width broadening: G(r)/G(0) = 1 +k2(r/r0) (k2:5~10)

  15. Mass modification at finite density r w f Hatsuda & Lee PRC46(1992)R34 dropping mass • Brown-Rho scaling (’91) • m*/m = 0.8 atr = r0 • QCD Sum Rule by Hatsuda & Lee (’92) • m*/m = 1 - 0.16 r/r0forr/w • m*/m = 1 - 0.03 r/r0 for f • Lattice Calc. by Muroya, Nakamura & Nonaka(’03) width broadening (at r0) • Klingl, Kaiser, Weise (’97-8) G*/G~10 for r/w/f • Rapp & Wambach(’99): G*r/Gr~2 • Oset & Ramos (’01) : DGf = 22MeV • Cabrera & Vicente (’03) : DGf = 33MeV Oset & Ramos r Cabrera & Vicente

  16. nuclear mass number dependence • Mass number dependence α: T. Tabaru et al. Phys. Rev. C74 (2006) 025201

  17. Fit Results of Model Calculation m*/m = 1 - 0.092r/r0 C Cu [GeV/c2] [GeV/c2] the excesses for both C and Cu are well reproduced by the model including the 9% mass decrease at r0.

  18. Width Broadening k1 = 0.08 k2 = 1 events[/10MeV/c2] events[/10MeV/c2] C Cu 「GeV/c2] 「GeV/c2] the best fit values are; k1 = 9.2 ± 0.6% k2 <0.32(90%C.L.) （Preliminary)

  19. Invariant spectra of fe+e-fit with modified M.C. ( k1=0.034, k2=2.6 ) 1.75<bg (Fast) bg<1.25 (Slow) 1.25<bg<1.75 Small Nucleus Large Nucleus

  20. Fit Results of model calculationm*/m = 1 – k1r/r0, G*/G = 1 + k2r/r0 Contours for k1 and r/w Contours for k1 and k2 of fe+e- 1 0.9 0.8 0.7 fit result f m(r)/m(0) fit result r/w The data were well reproduced with the model; mr/w decreases by 9%, mf decreases by 3% and Gfincreases by 3.6 at r0 prediction 0 0.5 1 r/r0 syst. error is not included

  21. fK+K- Invariant Mass Spectra C • from 2001 run data • C & Cu targets • acceptance uncorrected • fit with • simulated mass shape of f (evaluated as same as r/w) • combinatorial background obtained by the event mixing method counts/4MeV/c2 f(1020)  examine the mass shape as a function of bg

  22. Fitting Results of fK+K- 2.2<bg (Fast) bg<1.7 (Slow) 1.7<bg<2.2 Small Nucleus Large Nucleus modification is not statistically significant • Our statistics in the K+K- decay mode are very limited in the bg region in which we find the excess in the e+e- mode

  23. Kinematical Distributions of observed f • the detector acceptance is different between e+e- and K+K- • very limited statistics for fK+K- in bg<1.25 where the modification is observed in fe+e- the histograms for fK+K- are scaled by a factor ~3

  24. Partial Decay Width of f; GKK/Gee • mass decreases 2~4%  20-40MeV/c2 • narrow decay width (G=4.3MeV/c2) ⇒ sensitive to the mass spectrum modification • small decay Q value (QK+K-=32MeV/c2) • ⇒ the branching ratio is • sensitive to f or K modification f mass K+K- threshold r0:normal nuclear density for example… • f mass decreases  GfK+K- becomes small • K mass decreases  GfK+K- becomes large f : T.Hatsuda, S.H.Lee, Phys. Rev. C46(1992)R34. K : H.Fujii, T.Tatsumi, PTPS 120(1995)289.

  25. GfK+K-/Gfe+e- and Nuclear Mass-Number Dependence a • GfK+K-/Gfe+e- increases in a nucleus  NfK+K- /Nfe+e- becomes large • The lager modification is expected in the larger nucleus (A1>A2) • afK+K- becomes larger than afe+e- • The difference of a is expected to be enhanced in slowly moving f mesons

  26. - Da= e+e- K+K- ae+e- with corrected for the K+K- acceptance possible modification of the decay widths is discussed = Results of Nuclear Mass-Number Dependence a bg rapidity pT bg averaged (0.14+/-0.12) afK+K- and afe+e- are consistent

  27. Discussion onGfK+K- and Gfe+e- we expect ktot ~ kK since the f meson mainly decays into KK as long as such decays are kinematically allowed. • The values of expected Da are obtained by the MC. • f mesons are uniformly produced in a nucleus and decayed according to the values of kK and ke. • The measured Da provides constraints on kK and ke.

  28. Discussion on GfK+K- and Gfe+e- kK=1.4+/-1.1+/-2.1 (C&Cu) • 3. The constraint on kK is obtained from the K+K- spectra. • In the K+K- spectra, we fit again excluding the region 0.987(=2mk) ~ 1.01GeV/c2. • We obtain a surplus over the f peak and BG. • From the MC, we estimate the ratio of the number of f mesons decayed inside to outside Nin/Nout (inside = the half-density radius of the Woods-Saxon dist.). • When the surpluses are assumed as the f-meson decayed inside a nucleus, we obtain the constraint on kK by comparing Nsurplus/Nf with Nin/Nout. Cu Cu excluded from the fitting ~ Nsurplus/Nf MC Nin/Nout surplus data kK Nsurplus/Nf = 0.044+/-0.037+/-0.058 (C) 0.076+/-0.025+/-0.043 (Cu)

  29. nuclear mass number dependence of GfK+K- / Gfe+e- colored contour : MC 1.4 1.4 • kK/e was obtained from the amount of excess. • kK = 1.4±1.1(stat.)±2.1(syst.) • The measured Da provides constraints on kK and ke. F. Sakuma, Phys. Rev. Lett., 98 (2007) 152302 the first experimental limits of the in-medium broadening of the partial decay widths

  30. J-PARC Facility Hadron Beam Facility Materials and Life Science Experimental Facility Nuclear Transmutation 500 m Neutrino to Kamiokande 3 GeV Synchrotron (25 Hz, 1MW) 50 GeV Synchrotron (0.75 MW) Linac (330m) J-PARC = Japan Proton Accelerator Research Complex

  31. J-PARC E16 Electron pair spectrometer to explore the chiral symmetry in QCD high momentum beam line Hadron Hall 50-GeV PS A-Line Switch Yard E16 Split Point T1 Target T0 Target Beam Dump

  32. J-PARC E16 Electron pair spectrometer to explore the chiral symmetry in QCD primary proton beam at high momentum beam line + large acceptanceelectron spectrometer 107 interaction (10 X E325) 1010 protons/spill with 0.1% interaction length target  GEM Tracker eID : Gas Cherenkov + Lead Glass Large Acceptance (5 X E325) velocitydependence nuclear number dependence (p  Pb) centrality dependence systematic study of mass modification

  33. Summary We have observed the excess over the known hadronic sources at the low-mass side of w. Obtained r / w ratio indicates that the excess is mainly due to the modification of r. We also observed the excess at the low-mass side of f, only at the low bg region of Cu data. The data were well reproduced by the model calculation based on the mass modification. The fit results show that; r/w : the massdecreases by 9% at r0 . f :the mass decreases by 3%, and the width increases by a factor of 3.6 at r0. The mass modification is not statistically significant for the K+K- invariant mass distributions. The observed nuclear mass-number dependences of fe+e- and fK+K- are consistent. We have obtained limits on the in-medium decay width broadenings for both the fe+e- and fK+K- decay channels.

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