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有限密度における ベクター中間子の質量変化の検証

有限密度における ベクター中間子の質量変化の検証. 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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有限密度における ベクター中間子の質量変化の検証

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  1. 有限密度における ベクター中間子の質量変化の検証 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) • Introduction • Experimental Setup • Results • Future Plan

  2. Hadron Mass d u u Hot/Dense Matter QCD Vaccum Spontaneous Breaking of Chiral Symmetry Restoration current quarks ~MeV/c2 hadrons ~GeV/c2 constituent quarks ~300MeV/c2 higgs qq u u d vacuum vacuum

  3. 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

  4. KEK-PS E325 experiment e e r/w f measures Invariant Mass ofe+e-, K+K- in 12GeV p + A → r , w , f + X reactions • low energy : the mass modification at the normal nuclear density • dileptonmeasurement : free from final state interactions Expected Invariant Mass distribution of r and w Decay in vacuum In Copper Nuclei w mass modified by the formula : m*/m=1-0.16 r/r0 Prog.Theor.Phys.95(1996)1009 r

  5. 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)

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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)

  16. 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.

  17. 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)

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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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