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Experimental searches for the pentaquark baryon for the HERMES and CLAS collaborations Keith Griffioen email griff nikhef nl tel 31 20 592 2122 Nationaal Instituut voor Kernfysica en Hoge Energie Fysica NIKHEF College of William Mary Williamsburg VA Lunteren 10 10 03 p 1 20 Hadrons come in and Introduction configurations QCD does not prohibit other quark combinations The first observations of a have been made this year Pentaquarks had been proposed as early as 1976 but never seen Lipkin hep ph 9804218 pentaquark state Lunteren 10 10 03 p 2 20 d s d u u s s d u 4 u 3 1 p 0 D Diakonov et al Z Phys A359 97 305 chiral soliton model spin anti decuplet as anchor MeV MeV 2 Pentaquark Predictions u u d Lunteren 10 10 03 p 3 20 LEPS at SPring 8 T Nakano et al hep ex 0301020 PRL 91 03 012002 15 10 5 0 1 5 1 6 1 7 c MM K GeV c2 15 10 5 0 1 8 1 5 1 6 1 7 c MM K GeV c2 1 8 b Solid CH target signal sample Dashed LH target same cuts signal sample a CH target Solid Dashed tag showing 3 Events 0 02 GeV c2 MeV MeV b 20 0 C Events 0 02 GeV c2 a Lunteren 10 10 03 p 4 20 ITEP Bubble Chamber 0 A Dolgolenko et al hep ex 0304040 Xe Xe MeV MeV a all measured events events with b and in the forward direction and on opposite sides of the beam Lunteren 10 10 03 p 5 20 CLAS d Jefferson Lab S Stepanyan et al hep ex 0307018 35 30 MeV 25 Events signal solid events dotted 0 MeV 20 15 10 5 0 1 5 1 6 1 7 2 M nK GeV c 1 8 1 9 Lunteren 10 10 03 p 6 20 SAPHIR ELSA Bonn counts J Barth et al hep ex 0307083 40 a 35 40 30 25 K0s 1540 20 30 b counts 50 MeV 10 5 MeV 10 0 5 0 0 4 0 6 0 8 1 4 cut on 1 8 mass nK GeV spectrum for a 1 6 mass GeV b with subtraction 0 15 20 sideband background Lunteren 10 10 03 p 7 20 CLAS Jefferson Lab 22 5 P1 P2 P3 P4 20 32 58 27 26 59 1 537 0 1442E 01 7 631 8 156 0 3394E 02 0 4994E 02 0 8350 15 2 17 5 MeV N 20 MeV c MeV 0 V Kubarovsky et al hep ex 0307088 12 5 10 7 5 5 2 5 0 1 4 1 6 1 8 2 2 M nK GeV c 2 2 2 4 Lunteren 10 10 03 p 8 20 MeV 24 22 comb 10 MeV MeV Bub Ch FNAL Neon



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