Results of KEKPS E 325 experiment F Sakuma

Results of KEK-PS E 325 experiment F. Sakuma, RIKEN • Introduction • E 325 Experiment • Results of data analysis l / e+e- spectra l f K+K- spectra lnuclear mass-number dependences of f e+e- & f K+K • Summary

Physics Motivation Quark Mass bare mass mu≒md≒ 5 Me. V/c 2 ms≒ 150 Me. V/c 2 chiral symmetry restoration chiral symmetry breaking effective mass in QCD vacuum mu≒md≒ 300 Me. V/c 2 ms≒ 500 Me. V/c 2 How we can detect such a quark mass change? at very high temperature or density, the chiral symmetry is expected to restore W. Weise NPA 553, 59 (1993) even at normal nuclear density, the chiral symmetry is expected to restore partially 2

Vector Meson Modification dropping mass l. Brown & Rho (’ 91) m*/m=0. 8 (r=r 0) l. Hatsuda & Lee (’ 92) m*/m=1 -0. 16 r/r 0 for r/w m*/m=1 -0. 03 r/r 0 for f l. Muroya, Nakamura & Nonaka (’ 03) Lattice Calc. width broadening l. Klingl, Kaiser & Weise (’ 97&98) 1 Ge. V> for r, 45 Me. V for f (r=r 0) l. Oset & Ramos (’ 01) 22 Me. V for f (r=r 0) l. Cabrera & Vicente (’ 03) 33 Me. V for f (r=r 0) 3

Vector Meson, / /f r/w meson lmass decreases 16% 130 Me. V/c 2 llarge production cross-section lcannot distinguish r & w f meson lmass decreases 2~4% 20 -40 Me. V/c 2 lsmall production cross-section lnarrow decay width (G=4. 3 Me. V/c 2), no other resonance nearby ⇒sensitive to the mass spectrum change T. Hatsuda, S. H. Lee, Phys. Rev. C 46(1992)R 34. 4

Expected Modified Mass Spectra in e+elsmall FSI in e+e- decay channel + ldouble peak (or tail-like) structure m*/m=1 -0. 16 / 0 Øsecond peak is caused by inside-nucleus decay e p e e r/w/f outside decay f m*/m=1 -0. 02 / 0 bglab~1 p r/w/f e inside decay Ødepends on the nuclear size & meson velocity Øenhanced for larger nuclei & slower meson 5

Experimental Results on the In-medium Mass and Width of the , and f meson R. S. Hayano and T. Hatsuda, ar. Xiv: 0812. 1702 [nucl-ex] Invariant mass KEK-PS E 325 Jlab CLAS g 7 g. A 0. 6 - 3. 8 Ge. V p > 0. 8 Ge. V/c Attenuation CBELSA/TAPS Jlab CLAS g 7 Spring 8 LEPS g. A 0. 6 - 3. 8 g. A 1. 5 - 2. 5 Ge. V 0. 4 < p < 1. 7 p > 0. 8 1. 1 < p < 2. 2 Ge. V/c the majority of experiments does not 0 > 0. 5 p < 0. 5 Momentum find for a mass shift. Ge. V/c evidence. Ge. V/c Dm ~ 0 [CBELSA/TAPS, ar. Xiv: 1005. 5694] Reaction p. A 12 Ge. V g. A 0. 7 - 2. 5 Ge. V Dm(r 0)/m = broadening 9% no broadening confirmation our report is. Gw(r 0) = 130150 Me. V/c 2 ~ 0? minority. Dmreport!? @ J-PARC E 16 →s ~ w. N 70 mb f Dm(r 0)/m = 3. 4% Gf(r 0)/G ~ 15 Me. V/c 2 sf. N ~ 20 mb sf. N ~ 35 mb → Gf(r 0) ~ 45→ Gf(r 0) ~ 80 Me. V/c 2 6

KEK-PS E 325 Experiment 7

KEK-PS E 325 Experiment Measurements History of E 325 Invariant Mass of e+e-, K+K’ 93 proposed in 12 Ge. V p+A , , f+X reactions ’ 96 construction start üNIM, A 457 581(’ 01). slowly moving vector mesons üNIM, A 516 390(’ 04). (plab~2 Ge. V/c) ’ 97 first K+K- data large probability +e- data ’ 98 first e to decay inside a nucleus ür/ : Beam Primary proton beam (~109/spill/1. 8 s) Target Very thin targets (X/l. I=0. 2/0. 05%, X/X 0=0. 4/0. 5% for C/Cu) PRL, 86 5019(’ 01). ’ 99~’ 02 x 100 statistics in e+e- ür/w: PRL, 96 092301('06). üf ee: PRL, 98 042501(’ 07). üa : PR, C 75 025201(’ 06). x 6 statistics in K+K- üf KK: PRL, 98 152302(’ 07). ’ 02 completed 8

Detector Setup M. Sekimoto et al. , NIM, A 516, 390 (2004). Start Timing Counter Forward LG Calorimeter Hodoscope Aerogel Cherenkov Rear LG Calorimeter Forward TOF Side LG Calorimeter Barrel Drift Chamber B 0. 81 Tm Cylindrical DC m ea b n 12 V Ge 1 m o t o pr Rear Gas Cherenkov Vertex DC Front Gas Cherenkov 9

E 325 Spectrometer front view top view bea m beam 10

Spectrometer Performance －Data －MC L pp[counts / 0. 5 Me. V/c 2] [counts / 2 Me. V/c 2] K 0 s p + p - －Data －MC M = 496. 8± 0. 2 (MC 496. 9) Me. V/c 2 M = 1115. 71± 0. 02 (MC 1115. 52) Me. V/c 2 σ= σ= 3. 9± 0. 4 (MC 3. 5) Me. V/c 2 1. 73± 0. 04 (MC mass resolution for f-meson decays f e+e- : 10. 7 Me. V/c 2 f K+K- : 2. 1 Me. V/c 2 1. 63) Me. V/c 2 11

C (783) counts/10 Me. V/c 2 e+ e- counts/10 Me. V/c 2 Observed Invariant Mass Spectra Cu f(1020) K+ Kthreshold f(1020) counts/4 Me. V/c 2 K+ K- counts/4 Me. V/c 2 f(1020) C (783) Cu f(1020) 12

Result of + / e e M. Naruki et al. , PRL, 96 092301 (2006). 13

e+e- Invariant Mass Spectra lfrom 2002 run data (~70% of total data) counts/10 Me. V/c 2 C (783) l. C & Cu targets lacceptance uncorrected f(1020) l. M<0. 2 Ge. V/c 2 is suppressed by the detector acceptance fit the spectra with known sources 14

Fitting with known sources lresonance – r/w/f e+e-, w p 0 e+e-, h ge+e– relativistic Breit-Wigner shape (with internal radiative corrections) – nuclear cascade code JAM gives momentum distributions – experimental effects are estimated through the Geant 4 simulation (multiple scattering, energy loss, external bremsstrahlung, estimated spectrum chamber resolution, using GEANT 4 detector acceptance, etc. ) lbackground – combinatorial background obtained by the event mixing method lfit parameter – relative abundance of these components is determined by the fitting f e+e- experimental effects + internal radiative correction relativistic Breit-Wigner

Fitting Results Cu C c 2/dof=159/140 c 2/dof=150/140 the excess over the known hadronic sources on the low mass side of w peak has been observed. the region 0. 60 -0. 76 Ge. V/c 2 is excluded from the fit, because the fit including this region results in failure at 99. 9% C. L. . 16

Fitting Results (BG subtracted) events[/10 Me. V/c 2] Cu C / 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

Simple Model Calculation • pole mass: m*/m = 1 -k / 0 (Hatsuda-Lee formula) • generated at surface of incident p e r/w e hemisphere of target nucleus – aw~2/3 [PR, C 75 025201 (2006). ] – decay inside a nucleus: C Cu r 52% 66% w 10% 5% Cu r=4. 1 fm C r=2. 3 fm • nuclear density distribution : Woods-Saxon • mass spectrum: relativistic Breit-Wigner Shape • no width modification 18

Fitting Results by the Simple Model m*/m = 1 - 0. 092 / 0 / = 0. 7± 0. 1 C / = 0. 9± 0. 2 Cu the excesses for C and Cu are well reproduced by the model including the mass modification. 19

Contours for / and k n C and Cu data are simultaneously fitted. n free parameters – production ratio r/w – shift parameter k n Best-Fit values are k = 0. 092± 0. 002 r/w = 0. 7± 0. 1 (C) 0. 9± 0. 2 (Cu) mass of / meson decreases by 9% at normal nuclear density. 20

Result of + f e e R. Muto et al. , PRL, 98 042501 (2007). 21

f e+e- Invariant Mass Spectra lfrom 2001 & 2002 run data l. C & Cu targets f(1020) lacceptance uncorrected lfit with – simulated mass shape of f (evaluated as same as r/w) – polynomial curve background examine the mass shape as a function of bg (=p/m) (anomaly could be enhanced for slowly moving mesons) 22

Fitting Results 1. 25<bg<1. 75<bg (Fast) Large Nucleus Small Nucleus bg<1. 25 (Slow) Rejected at 99% confidence level 23

Amount of Excess A significant enhancement is seen in the Cu data, in bg<1. 25 the excess is attributed to the f mesons which decay inside a nucleus and are modified To evaluate the amount the excess Nexcess, fit again excluding the excess region (0. 95~1. 01 Ge. V/c 2) and integrate the excess area. excluded from the fitting 24

Simple Model Calculation Simple model like / case, except for • pole mass: m*/m = 1 -k 1 / 0 (Hatsuda-Lee formula) • width broadening: G*/G = 1+k 2 / 0 to increase the decay probability in a nucleus (no theoretical basis) – e+e- branching ratio is not changed G*e+e-/G*tot=Ge+e-/Gtot • uniformly generated in target nucleus – af~1 [PR, C 75 025201 (2006). ] p f – decay inside a nucleus (for bg<1. 25): f C Cu 3% 6% 25

Fitting Results by the Simple Model m*/m = 1 - 0. 034 / 0, G*/G = 1 + 2. 6 / 0 1. 25<bg<1. 75<bg (Fast) Large Nucleus Small Nucleus bg<1. 25 (Slow) well reproduce the data, even slow/Cu 26

Contours for k 1 and k 2 of f e+e. Pole Mass Shift M*/M = 1–k 1 r/r 0 Width Broadening G*/G = 1+k 2 r/r 0 n C and Cu data are simultaneously fitted. n free parameters – parameter k 1 & k 2 n Best-Fit values are lmass of f meson decreases by 3. 4% lwidth of f meson increases by a factor of 3. 6 27 at normal nuclear density.

Result of + f K K F. Sakuma et al. , PRL, 98 152302 (2007). 28

lfrom 2001 run data l. C & Cu targets counts/4 Me. V/c 2 f K+K- Invariant Mass Spectra C f(1020) lacceptance uncorrected lfit with – simulated mass shape of f (evaluated as same as r/w) – combinatorial background obtained by the event mixing method examine the mass shape as a function of bg 29

Fitting Results 1. 7<bg<2. 2<bg (Fast) Large Nucleus Small Nucleus bg<1. 7 (Slow) Mass-spectrum changes are NOT statistically significant However, impossible to compare f e+e- with f K+K-, directly

Kinematical Distributions of observed f lthe detector acceptance is different between e+e- and K+Klvery limited statistics for f K+Kin bg<1. 25 where the modification is observed in f e+e- the histograms for f K+Kare scaled by a factor ~3 31

Summary of shape analysis 32

Summary of Shape Analysis m*/m = 1 – k 1 / 0, G*/G = 1 + k 2 / 0 m(r)/m(0) 1 Best Fit Values , f k 1 9. 2 ± 0. 2% 3. 4+0. 6 -0. 7% k 2 0 (fixed) 2. 6+1. 8 -1. 2 / 0. 7 ± 0. 1 (C) 0. 9 ± 0. 2 (Cu) fit result f fit result r/w 0. 9 0. 8 prediction - 0. 7 0 0. 5 1 r/r 0 syst. error is not included 33

Result of nuclear mass-number dependences of + + f e e & f K K F. Sakuma et al. , PRL, 98 152302 (2007). 34

Vector Meson, f lmass decreases 2~4% 20 -40 Me. V/c 2 lnarrow decay width (G=4. 3 Me. V/c 2) ⇒ sensitive to the mass spectrum change lsmall decay Q value (QK+K-=32 Me. V/c 2) ⇒ the branching ratio is sensitive to f or K modification simple example nf mass decreases Gf K+K- becomes small n. K mass decreases Gf K+K- becomes large f mass K+ Kthreshold r 0: normal nuclear density f : T. Hatsuda, S. H. Lee, Phys. Rev. C 46(1992)R 34. K : H. Fujii, T. Tatsumi, PTPS 120(1995)289. 35

Gf K+K-/Gf e+e- and Nuclear Mass-Number Dependence a l. Gf K+K-/Gf e+e- changes in a nucleus Nf K+K- /Nf e+e- changes also l. The lager modification is expected in the larger nucleus (A 1!=A 2) ldifference between af K+K- and af e+ecould be found ldifference of a is expected to be enhanced in slowly moving f mesons 36

Results of Nuclear Mass-Number Dependence a bg rapidity = Da= - K+ K- e+ e- p. T ae+e- with corrected for the K+K- acceptance bg averaged (0. 13+/-0. 12) possible modification of the decay widths is discussed af K+K- and af e+e- are consistent 37

Discussion on Gf K+K- and Gf e+e. We attempt to obtain the upper limit of the Gf K+K- and Gf e+e- modification ① The measured Da provides constraints on the Gf K+K- and Gf e+e- modification by comparing with the values of expected Da obtained from the MC. ② The constraint on the Gf K+K- modification is obtained from the K+K- spectra by comparing with the MC calculation. Theoretical predictions width broadening is expected to be up to ~x 10 (Klingl, Kaiser & Weise, etc. ) 38

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

Summary l. KEK PS-E 325 measured e+e- and K+K- invariant mass distributions in 12 Ge. V p+A reactions. l. The significant excesses at the low-mass side of e+e- and f e+e- peak have been observed. → These excesses are well reproduced by the simple model calculations which take Hatsuda-Lee prediction into account. l. 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 bg region in which we see the excess in the e+e- mode. l. The observed nuclear mass-number dependences of f e+eand 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 40 channels.

KEK-PS E 325 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 41