21世紀COE外国旅費補助　出張報告会 IX International Conference on Hypernulear and Strange Particle Physics (HYPE2006) “Search for Q+ via K+p -> p+X reaction with high-resolution spectrometer system” 原子核ハドロン物理学研究室 大樂　誠司

E559 collaboration Gifu U. T. Kameyama, K. Nakazawa, T. Watanabe KEK S. Ishimoto, T. Nagae, H, Noumi, Y. Sato, S. Sawada, M. Sekimoto, S. Suzuki, H. Takahashi, T. Takahashi, N. Tanaka, A. Toyoda Kyoto U. S. Dairaku, H. Funahashi, K. Imai*, K. Miwa, K. Shoji, M. Hayata, M. Miyabe, M. Niiyama, N. Saito, Y. Seki Ohio U. K. Hicks, R. Zavislak Osaka U. S. Ajimura Osaka EC U. T. Fukuda RCNP T. Nakano, M. Yosoi RIKEN M. Naruki, K. Tanida Tohoku U. S. Kinoshita, T. Koike, Y. Ma, Y. Miura, K. Shirotori, H. Tamura U. Paris-Sud J. Arvieux U. Tokyo H. Fujioka, T. Maruta, D. Nakajima, T. N. Takahashi

The + baryon Diakonov et al. LEPS at Spring-8 Theoretical prediction Chiral soliton model Anti-decuplet M=1530 MeV, < 15MeV Experiment LEPS LEPS at Spring-8 n    n M=154010 MeV <25 MeV 世界各地での研究のトリガーとなったのはこの理論と実験！ 世界各地での研究のトリガーとなったのはこの理論と実験の非常に良い一致でした。 Diakonov et al.はchiral soliton modelを用いてΘ＋をanti-decupletのメンバーとして予言し、その質量が1530MeVで幅が15MeV以下の狭い共鳴状態を予想した。これに動機付けられて実験結果を示したのがLEPSコラボレーションでした。彼らはbackward comptonで得られる1.6～2.4GeVのγ線を用いてγnK-K+n反応によってγnK-Xのmissing mass にΘ＋と考えられるピークを示した。Massが1540+-10MeVで幅が実験の分解能と一致しており25MeVの上限値のみが報告された。この理論と実験のよい一致は多くの理論的、実験的研究のトリガーとなった。

Purpose Search for Q+ Pentaquark ( E559 at KEK-PS K6) High statistics if Q+ exists, G< 1 MeV/c2 (M=1530 - 1540 MeV/c2) High Resolution spectrometer SKS & K6beamline ⇒resolution ： 2.4 MeV/c2 (FWHM) High statistics Hadronic reaction K+p -> p+X 1.2 GeV/c K+ beam and liquid H2 target Determination of decay angle distribution Large solid angle Drift Chamber & Range Counter downstream of target Spin and Parity

Setup p+ K+ SKS π+(0.5 - 0.6 GeV/c) mass2(GeV/c2)2 p+ 1.6 T For π+veto π+(0.5 - 0.6 GeV/c) Solid angle 0 - 60 deg 1.6 T SKS K+ p+ mass2(GeV/c2)2 p+ K+ (1.2GeV/c)

Data set RUN1 ( 2005/5/24 - 2005/7/1 ) H(K+,p+) run @1.2GeV/c for + K+ yield : 2.79x109 Empty target run @1.2GeV/c for B.G. H(p+,K+) run @1.1GeV/c for S+ RUN2 ( 2005/12/13 - 2005/12/28 ) H(K+,p+) run @1.2GeV/c for + K+ yield : 2.09x109 Empty target run @1.2GeV/c for B.G. H(p+,K+) run @1.1GeV/c for S+

Resolution for + and  M=1189.31 ± 0.03 MeV/c2 G=2.03 ± 0.06 MeV/c2 1st run Resolution K6 : p/p = 0.047% (FWHM) SKS : p/p = 0.43% (FWHM) (simulation) for S+ 1.98 MeV/c2 (FWHM) This is consistent with real data Mass(GeV/c2) (simulation) for  2.4 MeV/c2 (FWHM) 2nd run M=1189.33±0.03 MeV/c2 G=1.94±0.07 MeV/c2 Missing mass value 1st run is consistent with 2nd run Mass(GeV/c2)

Vertex distribution (before B.G. cut) 1st run 2nd run (K+, p+) (K+, p+) (p+, p+) (p+, p+) vertex z(mm) vertex z(mm) (K+, p+) reaction : large background from K+ decay

Suppression of K+ decay events (SDC1 analysis cut) π+veto Aerogel π+ K+ Target vertex SKS Beam line chamber SDC2 SDC1 RC drift chamber SDC1 analysis cut Even charged & Large scattered angle 98.0% of K+ decay events are suppressed (simulation) 70.1% of Q+ production events remain (simulation --- assume isotropic angular distribution) K+ p+( to SKS ) K+p reaction event K+ decay event

vertex distribution (after B.G. cut) 1st run 2nd run vertex z(mm) vertex z(mm) 16900 event (-30<z<100) 11900 event (-40<z<85)

Missing Mass (pX) Sum of 1st and 2nd runs 1530MeV/c2 s=50mb isotropic distribution Assumption Expected peak under assumption Preliminary

Missing Mass (pX) Preliminary 170 ( 90% C.L. upper limit)

Upper limit Preliminary 90% C.L. upper limit NQ Counts(90% C.L.) Ntgt 5.04x1023 NK+ 4.88x109 Survival rate 0.858 Interaction factor 0.94 K6 efficiency 0.935(K6 tracking) SKS efficiency 0.953(SdcOut)x0.875(SdcIn) x0.93(SksTrack)=0.775 SDC1 analysis cut 0.701 ( assume angular distribution ) vertex cut 0.85 Trigger efficiency 0.95(LC)x0.99(TOF) Acceptance 0.11sr(Laboratory frame) 0.0293(assume angular distribution) Preliminary

Cross section of H(K+,π+) reaction G=1MeV gK*NQ= ＋gKNQ gK*NQ= －gKNQ gK*NQ= 0 Y. Oh et al. Phys. Rev. D 69, 074016 √s=1.89GeV ( E559 exp. ) W/O F.F. L=1.2GeV

Cross section of H(K+,π+) reaction G=1MeV gK*NQ= ＋gKNQ gK*NQ= －gKNQ gK*NQ= 0 Y. Oh et al. Phys. Rev. D 69, 074016 Preliminary E559 exp. 90% C.L. upper limit W/O F.F. L=1.2GeV

Summary Search for Q+ via H(K+, p+) reaction at KEK-PS K6 beamline K+ beam yield 4.88x109 reaction event 28800 (after SDC1 cut) No significant peak (1520 － 1560 MeV/c2) cross section 7.0mb, 1.9mb/sr 90% C. L. upper limit (assume angular distribution) Preliminary much smaller than theoretical value under K* exchange (calculated by Y.Oh )

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