1. 1 Medium modifications on vector meson in 12GeV p+A reactions Introduction Result of   e + e - analysis Result of   e + e - analysis Result of   K + K - analysis Kyoto Univ. a, KEK b, RIKEN c, CNS Univ. of Tokyo d, Megumi Naruki, RIKEN, Japan J. Chiba b, H. En’yo c, Y. Fukao a, H. Funahashi a, H. Hamagaki d, M. Ieiri b, M. Ishino e, H. Kanda f, M. Kitaguchi a, S. Mihara e, K. Miwa a, T. Miyashita a, T. Murakami a, R. Muto c, T. Nakura a, K. Ozawa d, F. Sakuma a, O. Sasaki b, M. Sekimoto b, T. Tabaru c, K.H. Tanaka b, M. Togawa a, S. Yamada a, S. Yokkaichi c, Y. Yoshimura a (KEK-PS E325 Collaboration)

2. 2 dropping mass Brown-Rho scaling (’91) – m*/m = 0.8 at  =   QCD Sum Rule by Hatsuda & Lee (’92) –m*/m = 1 - 0.16   for  –m*/m = 1 - 0.03  0 for  Lattice Calc. by Muroya, Nakamura & Nonaka(’03) width broadening (at  0 ) Klingl, Kaiser, Weise (’97-8)    ~  for  Rapp & Wambach (’99)  :       ~2 Oset & Ramos (’01) :    22MeV Cabrera & Vicente (’03) :    33MeV Mass modification at finite density    Hatsuda & Lee PRC46(1992)R34

3. 3 E325 experiment slowly moving  ( p lab ~2GeV/c ） larger probability to decay inside nucleus primary proton beam ~10 9 ppp thin targets: 0.2%/0.05% (C/Cu) radiation length: 0.4/0.5%(C/Cu) Invariant Mass of e + e -, K + K - in 12GeV p + A   + X History ’93 proposed ’96 construction start NIM, A457, 581 (2001). NIM, A516, 390 (2004). ’97 first K + K - data ’98 first e + e - data PRL, 86, 5019 (2001). ’99~’02 x100 statistics in e + e -  PRL 96, 092301 (‘06).   ee  nucl-ex/0511019  : PRC, 75, 025201 (‘06) x6 statistics in K + K -   KK : nucl-ex/0606029 beam B

4. 4 Invariant Mass Spectrum of e + e - CCu we examine how well the data are reproduced with known hadronic sources & combinatorial background e+e-e+e- e+e-e+e- e+e-e+e- e+e-e+e-

5. 5 Invariant Mass Spectrum of e+e- C Cu the excess over the known hadronic sources on the low mass side of  peak has been observed. e+e-e+e- e+e-e+e- e+e-e+e- e+e-e+e-  /dof    /dof  

6. 6 Invariant Mass Spectrum of e+e- (background subtracted) N  N  =0.0±0.02(stat.)±0.2(sys.) 0.0±0.04(stat.)±0.3(sys.) CCu most of  decay in nucleus due to their short lifetime;  ~ 1.3fm  ratio is consistent with zero

7. 7 Invariant Mass Spectrum of e + e - CCu we examine how well the data are reproduced with known hadronic sources & combinatorial background e+e-e+e- e+e-e+e- e+e-e+e- e+e-e+e-

8. 8 e + e - Invariant Mass Distributions CCu   [GeV/c 2 ] fit with MC shape & quadratic curve a hint on the spectrum of Cu data. longer lifetime;  ~50fm  kinematical dependence

9. 9 To see  dependence Slowly moving  mesons have a larger probability to decay inside the target nucleus. We divided the data into three by  ( = p/m );  <1.25, 1.25<  <1.75 and 1.75< .  distribution

10. 10 Invariant spectra of   e + e -  <1.25 (Slow)1.25<  <1.75 1.75<  (Fast) Large Nucleus Small Nucleus Rejected at 99% confidence level nucl-ex/0511019

11. 11 Energy Loss Resonance Shape : Breit-Wigner + internal radiative correction experimental effect estimated by Geant4 simulation – energy loss, mass resolution, mass acceptance etc. Blue histogram : Detector Simulation Red line : Breit-Wigner (gaussian convoluted) fitting result Experimental effects are fully taken into account detector simulation for  we fit the data by the simulated shape, which fully includes the experimental effect

12. 12 Model Calculation w/ medium modification  eeee   m*/m 1 – k 1    1 – k 1     */  1 1 + k 2  /  0 generation point surface uniform      PRC74(06)025201] 0.710±0.0210.937±0.049 momentum dist. measured density distribution Woods-Saxon, radius: C:2.3fm/Cu:4.1fm dropping mass: M(  )/M(0) = 1 – k 1 (  /  0 ) (Hatsuda & Lee) width broadening:  (  )/  (0) = 1 + k 2 (  /  0 ) (k 2 ~10 (Klingl et.al ))

13. 13 Fit Results of Model Calculation the excesses for both C and Cu are well reproduced by the model including the 9% mass decrease at  0. m*/m = 1 - 0.092   CCu [GeV/c 2 ]

14. 14 Invariant spectra of   e + e - fit with modified M.C. ( k 1 =0.034, k 2 =2.6 )  <1.25 (Slow)1.25<  <1.75 1.75<  (Fast) Large Nucleus Small Nucleus

15. 15 Fit Results of model calculation m*/m = 1 – k 1    */  = 1 + k 2  /  0 The data were well reproduced with the model; m  decreases by 9%, m  decreases by 3% and    increases by 3.6 at  0 Best Fit Values  k1k1 9.2 ± 0.2%3.4 +0.6 -0.7 % k2k2 0 (fixed)2.6 +1.8 -1.2  0.7 ± 0.1 (C) 0.9 ± 0.2 (Cu) - Contours for k 1 and k 2 of   e+e- syst. error is not included prediction 0 0.5 1  0 1 0.9 0.8 0.7 fit result  fit result  m(  )/m(0) Contours for k 1 and 

16. 16 Fitting Results of   K + K -  <1.7 (Slow)1.7<  <2.2 2.2<  (Fast) Large Nucleus Small Nucleus modification is not statistically significant Our statistics in the K+K- decay mode are very limited in the  region in which we find the excess in the e+e- mode

17. 17 nuclear mass number dependence of    K+K- /    e+e- the first experimental limits of the in-medium broadening of the partial decay widths F. Sakuma, nucl-ex/0606029 k K/e was obtained from the amount of excess. k K = 2.0±1.1(stat.)±2.2(syst.) The measured  provides constraints on k K and k e. colored contour : MC

18. 18 Summary We have observed the excess over the known hadronic sources at the low-mass side of . Obtained  ratio indicates that the excess is mainly due to the modification of . We also observed the excess at the low-mass side of , only at the low  region of Cu data. The data were well reproduced by the model calculation based on the mass modification. The fit results show that;  : the mass  decreases by 9% at  .  :  the mass decreases by 3%, and the width increases by a factor of 3.6 at  . The mass modification is not statistically significant for the K+K- invariant mass distributions. The observed nuclear mass-number dependences of   e+e- and   K+K- are consistent. – We have obtained limits on the in-medium decay width broadenings for both the   e+e- and   K+K- decay channels.