Search for  + via K + p   + X reaction with high-resolution spectrometer system Kyoto University S. Dairaku for E559 collaboration

E559 collaboration Gifu U.T. Kameyama, K. Nakazawa, T. Watanabe KEKS. 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 RCNPT. Nakano, M. Yosoi RIKENM. Naruki, K. Tanida Tohoku U.S. Kinoshita, T. Koike, Y. Ma, Y. Miura, K. Shirotori, H. Tamura U. Paris-SudJ. Arvieux U. TokyoH. Fujioka, T. Maruta, D. Nakajima, T. N. Takahashi

Purpose Search for  + Pentaquark ( E559 at KEK-PS K6) if  + exists,  < 1 MeV/c 2 (M=1530  1540 MeV/c 2 ) High Resolution spectrometer SKS & K6beamline ⇒ resolution ： 2.4 MeV/c 2 (FWHM) High statistics Hadronic reaction K + p  + X 1.2 GeV/c K + beam and liquid H 2 target Determination of decay angle distribution Large solid angle Drift Chamber & Range Counter downstream of target Spin and Parity

K + (1.2GeV/c) SKS K+K+ ++ For π + veto π + ( 0.5  0.6 GeV/c ) Solid angle 0  60 deg 1.6 T mass 2 (GeV/c 2 ) 2 ++ Setup

Data set RUN2 ( 2005/12/13  2005/12/28 ) H(K +,  + ) for  + K + yield : 2.79x10 9 Empty target for B.G. H(  +,K + ) for  + RUN1 ( 2005/5/24  2005/7/1 ) H(K +,  + ) for  + K + yield : 2.09x10 9 Empty target for B.G. H(  +,K + ) for  +

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

Vertex distribution (before B.G. cut) 1st run2nd run (K +,  + ) (  +,  + ) vertex z(mm) (K +,  + ) reaction : large background from K + decay (K +,  + ) (  +,  + )

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

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

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

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

Upper limit NN Counts(90% C.L.) N tgt 5.04x10 23 N K+ 4.88x10 9 Survival rate0.858 Interaction factor0.94 K6 efficiency0.935(K6 tracking) SKS efficiency0.953(SdcOut)x0.875(SdcIn) x0.93(SksTrack)=0.775 SDC1 analysis cut0.701 ( assume angular distribution ) vertex cut0.85 Trigger efficiency0.95(LC)x0.99(TOF) Acceptance0.11sr(Laboratory frame) (assume angular distribution) Preliminary 90% C.L. upper limit

Cross section of H(K +,π + ) reaction gK*N  = ＋ gKN  gK*N  = － gKN  gK*N  = 0 W/O F.F.  =1.2GeV Y. Oh et al. Phys. Rev. D 69,  =1MeV √s=1.89GeV ( E559 exp. )

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

Summary Search for  + via H(K +,  + ) reaction at KEK-PS K6 beamline K + beam yield 4.88x10 9 reaction event (after SDC1 cut) No significant peak (1520 － 1560 MeV/c 2 ) cross section 7.0  b, 1.9  b/sr 90% C. L. upper limit (assume angular distribution) much smaller than theoretical value under K* exchange (calculated by Y.Oh ) Preliminary

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peak at SDC1 position SDC1 SDC2 Decay K + beam RC Target 20cm (K +,  + ) (  +,  + ) SKS Gap 20cm Vertex collect near SDC1

Background in H(K +,  + )reaction K + decay event  *   SKS K +        K +        K +    e + e K +       K + p reaction event  SKS K + p  K +  +   + K + n K + p   + K + n K + p  K 0  ++   + K 0 p K + p  K  + p   + K 0 p K + p   + K 0 p 0.008

Angle cut study SKS Target K+K+ π+π+ 11 22 K+K+ n Selection of  2 select kinematics? No correlation between  (   ) and  (K +, p) Simulation  2 (degree)  1 (degree)

SDC1 analysis If we assume that  + decay is isotropic in center of mass frame, accepted ratio of each decay mode –K + n : –K 0 S p : –K 0 L p : Weighted mean with decay ratio ( 0.5:0.25: ) → 0.701

Q 2 of reactions Q 2 =q 2 -  2 [GeV 2 ] Angle [degree] LEPS CLAS E559 (K +,   ) 1.2GeV/c E522 (  ,K  ) 1.9GeV/c