Results of KEK-PS E325 experiment Introduction E325 Experiment Results of data analysis   e + e - spectra   e + e - spectra   K + K - spectra nuclear mass-number dependences of   e + e - &   K + K - Summary F.Sakuma, RIKEN

2 effective mass in QCD vacuum m u ≒ m d ≒ 300MeV/c 2 m s ≒ 500MeV/c 2 chiral symmetry breaking Quark Mass bare mass m u ≒ m d ≒ 5MeV/c 2 m s ≒ 150MeV/c 2 How we can detect such a quark mass change? Physics Motivation chiral symmetry restoration even at normal nuclear density, the chiral symmetry is expected to restore partially at very high temperature or density, the chiral symmetry is expected to restore W.Weise NPA553,59 (1993)

3 Vector Meson Modification dropping mass width broadening Brown & Rho (’91) m*/m=0.8 (  =  0 ) Hatsuda & Lee (’92) m*/m=  0 for  m*/m=  0 for  Muroya, Nakamura & Nonaka (’03) Lattice Calc. Klingl, Kaiser & Weise (’97&98) 1GeV> for , 45MeV for  (  =  0 ) Oset & Ramos (’01) 22MeV for  (  =  0 ) Cabrera & Vicente (’03) 33MeV for  (  =  0 )

4  meson Vector Meson,  T.Hatsuda, S.H.Lee, Phys. Rev. C46(1992)R34. mass decreases 16%  130MeV/c 2 large production cross-section cannot distinguish  &   meson mass decreases 2~4%  20-40MeV/c 2 small production cross-section narrow decay width (  =4.3MeV/c 2 ), no other resonance nearby ⇒ sensitive to the mass spectrum change

5 Expected Modified Mass Spectra in e + e - p e e p e e  outside decayinside decay  m*/m=  0 small FSI in e + e - decay channel double peak (or tail-like) structure  m*/m=  0  lab ~1 inside-nucleus decay  second peak is caused by inside-nucleus decay  depends on the nuclear size & meson velocity  enhanced for larger nuclei & slower meson  

Invariant mass Invariant massAttenuation KEK-PS E325 Jlab CLAS g7 CBELSA/TAPSJlab Spring8 LEPS Reaction pA 12 GeV  A GeV  A GeV  A GeV  A GeV Momentu m 0 > 0.5 GeV/c p > 0.8 GeV/c p < 0.5 GeV/c 0.4 < p < 1.7 GeV/c p > 0.8 GeV/c 1.1 < p < 2.2 GeV/c   m  0  m(  0 )/m = -9% broadening  no broadening  m  0?   (  0 ) = MeV/c 2 →   N  70mb   m(  0 )/m = -3.4%   N  20mb   N  35mb   (  0 )/   15MeV/c 2 →   (  0 )  45 MeV/c 2 →   (  0 )  80 MeV/c 2 6 Experimental Results on the In-medium Mass and Width of the ,  and  meson R.S.Hayano and T.Hatsuda, arXiv: [nucl-ex] our report is minority report!? J-PARC E16

7 KEK-PS E325 Experiment

88 Very thin targets (X/ I =0.2/0.05%, X/X 0 =0.4/0.5% for C/Cu) History of E325 ’93 proposed ’96 construction start NIM,A (’01). NIM,A (’04). ’97 first K + K - data ’98 first e + e - data  : PRL, (’01). ’99~’02 x100 statistics in e + e -  : PRL, ('06).   ee: PRL, (’07).  : PR,C (’06). x6 statistics in K + K -   KK: PRL, (’07). ’02 completed Primary proton beam (~10 9 /spill/1.8s) Measurements Beam Target Invariant Mass of e + e -, K + K - in 12GeV p+A  , ,  +X reactions slowly moving vector mesons (p lab ~2GeV/c) large probability to decay inside a nucleus

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

10 E325 Spectrometer front view top view beam

11 M = 496.8±0.2 (MC 496.9) MeV/c 2 σ = 3.9±0.4 (MC 3.5) MeV/c 2 K0s  +-K0s  +-   p  - － Data － MC M = ±0.02 (MC ) MeV/c 2 σ = 1.73±0.04 (MC 1.63) MeV/c 2 [counts / 2MeV/c 2 ] [counts / 0.5MeV/c 2 ] Spectrometer Performance － Data － MC mass resolution for  -meson decays   e + e - : 10.7 MeV/c 2   K + K - : 2.1 MeV/c 2

12 C Cu   counts/10MeV/c 2 Observed Invariant Mass Spectra CCu e+e-e+e-e+e-e+e- K+K-K+K-K+K-K+K- counts/4MeV/c 2 K + K - threshold   

13 Result of   e + e - M.Naruki et al., PRL, (2006).

14 C counts/10MeV/c 2 e + e - Invariant Mass Spectra from 2002 run data (~70% of total data) C & Cu targets acceptance uncorrected M<0.2GeV/c 2 is suppressed by the detector acceptance  fit the spectra with known sources  

resonance –   e + e -,    0 e + e -,    e + e - – relativistic Breit-Wigner shape (with internal radiative corrections) – nuclear cascade code JAM gives momentum distributions – experimental effects are estimated through the Geant4 simulation (multiple scattering, energy loss, external bremsstrahlung, chamber resolution, detector acceptance, etc.) background – combinatorial background obtained by the event mixing method fit parameter – relative abundance of these components is determined by the fitting Fitting with known sources estimated spectrum using GEANT4 experimental effects + internal radiative correction e+e-e+e- relativistic Breit-Wigner

16 the excess over the known hadronic sources on the low mass side of  peak has been observed. C Cu the region GeV/c 2 is excluded from the fit, because the fit including this region results in failure at 99.9% C.L..  2 /dof=159/140  2 /dof=150/140 Fitting Results

 ratios are consistent with zero !  = 0.0±0.03(stat.)±0.09(sys.) 0.0±0.04(stat.)±0.21(sys.)  =1.0±0.2 in former experiment (p+p, 1974)  the origin of the excess is modified  mesons Fitting Results (BG subtracted) events[/10MeV/c 2 ] C Cu

18 pole mass: m*/m = 1-k  0 (Hatsuda-Lee formula) generated at surface of incident hemisphere of target nucleus –   ~2/3 [PR, C (2006).] – decay inside a nucleus: nuclear density distribution : Woods-Saxon mass spectrum: relativistic Breit-Wigner Shape no width modification p  eeee CCu  52%66%  5%10% CuC r=4.1fm r=2.3fm Simple Model Calculation

19 the excesses for C and Cu are well reproduced by the model including the mass modification. m*/m =  0 C Cu Fitting Results by the Simple Model  = 0.7±0.1  = 0.9±0.2

20 mass of  meson decreases by 9% at normal nuclear density. Contours for  and k Best-Fit values are k = 0.092±0.002  = 0.7±0.1 (C) 0.9±0.2 (Cu) C and Cu data are simultaneously fitted. free parameters – production ratio  – shift parameter k

21 Result of   e + e - R.Muto et al., PRL, (2007).

22   e + e - Invariant Mass Spectra from 2001 & 2002 run data C & Cu targets acceptance uncorrected fit with – simulated mass shape of  (evaluated as same as  ) – polynomial curve background  examine the mass shape as a function of  (=p/m) (anomaly could be enhanced for slowly moving mesons) 

23  <1.25 (Slow)1.25<  < <  (Fast) Large Nucleus Small Nucleus Rejected at 99% confidence level Fitting Results

24 Amount of Excess excluded from the fitting A significant enhancement is seen in the Cu data, in  <1.25  the excess is attributed to the  mesons which decay inside a nucleus and are modified To evaluate the amount the excess N excess, fit again excluding the excess region (0.95~1.01GeV/c 2 ) and integrate the excess area.

25 pole mass: m*/m = 1-k 1  0 (Hatsuda-Lee formula) width broadening:  */  = 1+k 2  0 (no theoretical basis) – e+e- branching ratio is not changed  * e+e- /  * tot =  e+e- /  tot uniformly generated in target nucleus –   ~1 [PR, C (2006).] – decay inside a nucleus (for  <1.25): CCu  3%6% Simple Model Calculation  p Simple model like  case, except for to increase the decay probability in a nucleus

26  <1.25 (Slow)1.25<  < <  (Fast) Large Nucleus Small Nucleus Fitting Results by the Simple Model well reproduce the data, even slow/Cu m*/m =  0,  */  =  0

27 Pole Mass Shift M*/M = 1–k 1  /  0 Width Broadening  /  = 1+k 2  /  0 Best-Fit values are C and Cu data are simultaneously fitted. free parameters – parameter k 1 & k 2 Contours for k 1 and k 2 of   e + e - mass of  meson decreases by 3.4% width of  meson increases by a factor of 3.6 at normal nuclear density.

28 Result of   K + K - F.Sakuma et al., PRL, (2007).

29   K + K - Invariant Mass Spectra from 2001 run data C & Cu targets acceptance uncorrected fit with – simulated mass shape of  (evaluated as same as  ) – combinatorial background obtained by the event mixing method  examine the mass shape as a function of   counts/4MeV/c 2 C

Fitting Results  <1.7 (Slow)1.7<  < <  (Fast) Large Nucleus Small Nucleus Mass-spectrum changes are NOT statistically significant However, impossible to compare   e + e - with   K + K -, directly

31 Kinematical Distributions of observed  the detector acceptance is different between e+e- and K + K - very limited statistics for   K + K - in  <1.25 where the modification is observed in   e + e - the histograms for   K + K - are scaled by a factor ~3

32 Summary of shape analysis

Summary of Shape Analysis Best Fit Values  k1k1 9.2 ± 0.2% % k2k2 0 (fixed)  0.7 ± 0.1 (C) 0.9 ± 0.2 (Cu) - syst. error is not included prediction 1 fit result  fit result  m(  )/m(0) m*/m = 1 – k 1    */  = 1 + k 2  /    33

34 Result of nuclear mass-number dependences of   e + e - &   K + K - F.Sakuma et al., PRL, (2007).

35 Vector Meson,   : T.Hatsuda, S.H.Lee, Phys. Rev. C46 (1992)R34.  0 :normal nuclear density mass decreases 2~4%  20-40MeV/c 2 narrow decay width (  =4.3MeV/c 2 ) ⇒ sensitive to the mass spectrum change small decay Q value (Q K+K- =32MeV/c 2 ) ⇒ the branching ratio is sensitive to  or K modification K + K - threshold simple example  mass decreases     K+K- becomes small K mass decreases     K+K- becomes large K : H.Fujii, T.Tatsumi, PTPS 120 (1995)289.  mass

36    K+K- /    e+e- and Nuclear Mass-Number Dependence     K+K- /    e+e- changes in a nucleus  N   K+K- /N   e+e- changes also The lager modification is expected in the larger nucleus difference between    K+K- and    e+e- could be found difference of  is expected to be enhanced in slowly moving  mesons (A 1 !=A 2 )

37 Results of Nuclear Mass-Number Dependence   averaged (0.13+/-0.12)    K+K- and    e+e- are consistent  rapiditypTpT possible modification of the decay widths is discussed  = - K+K-K+K- e+e-e+e-  e+e- with corrected for the K + K - acceptance =

We attempt to obtain the upper limit of the    K+K- and    e+e- modification 38 Discussion on    K+K- and    e+e- Theoretical predictions width broadening is expected to be up to ~x10 (Klingl, Kaiser & Weise, etc.) ① The measured  provides constraints on the    K+K- and    e+e- modification by comparing with the values of expected  obtained from the MC. ② The constraint on the    K+K- modification is obtained from the K + K - spectra by comparing with the MC calculation.

39 Discussion on    K+K- and    e+e- the first experimental limits assigned to the in-medium broadening of the partial decay widths broadening of    K+K- broadening of    e+e-

40 Summary KEK PS-E325 measured e + e - and K + K - invariant mass distributions in 12GeV p+A reactions. The significant excesses at the low-mass side of   e + e - and   e + e - peak have been observed. → These excesses are well reproduced by the simple model calculations which take Hatsuda-Lee prediction into account. Mass spectrum changes are not statistically significant in the K + K - invariant mass distributions. → Our statistics in the K + K - decay mode are very limited in the  region in which we see the excess in the e + e - mode. 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.

41 KEK-PS E325 Collaboration (2007) RIKEN Nishina Center H.Enyo(*), F. Sakuma, T. Tabaru, S. Yokkaichi KEK J.Chiba, M.Ieiri, R.Muto, M.Naruki, O.Sasaki, M.Sekimoto, K.H.Tanaka Kyoto-Univ. H.Funahashi, H. Fukao, M.Ishino, H.Kanda, M.Kitaguchi, S.Mihara, T.Miyashita, K. Miwa, T.Murakami, T.Nakura, M.Togawa, S.Yamada, Y.Yoshimura CNS,Univ.of Tokyo H.Hamagaki Univ.of Tokyo K. Ozawa (*) spokesperson