IntroductionPentaquark PredictionsLEPS at SPring-8ITEP Bubble ChamberCLAS d, Jefferson LabSAPHIR, ELSA, BonnCLAS, Jefferson LabBEBC, CERN & $15^prime $ Bub. Ch., FNALHERMES, DESYThe HERMES experimentHERMES Event SelectionHERMES $K_s$ IdentificationHERMES MC and resultThe CLAS spectrometerCLAS DeuteronCLAS ProtonCLAS ProtonComparison of ExperimentsConclusionsExperimental searches for the pentaquarkbaryon(for the HERMES and CLAS collaborations).Keith Griffioenemail: [email protected], tel: +31-20-592-2122Nationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF)College of William & Mary, Williamsburg, VALunteren 10/10/03 – p.1/20IntroductionHadrons come inandconfigurationsQCD does not prohibit other quark combinationsPentaquarks had been proposed (as early as1976) but never seen (Lipkin, hep-ph/9804218).The first observations of apentaquark statehave been made this year.Lunteren 10/10/03 – p.2/20Pentaquark Predictions       ! "++...Θ+=+...p=uuuuuudddds−s−sD. Diakonov et al.,Z. Phys. A359(97)305chiral soliton modelspin-# $anti-decuplet%##& '(')*as anchor+,-'./)MeV01'.MeV2-3',4-)Lunteren 10/10/03 – p.3/20LEPS at SPring-8a)MMcγK+ (GeV/c2)Events/(0.02 GeV/c2)b)MMcγK− (GeV/c2)Events/(0.02 GeV/c2)051015201.5 1.6 1.7 1.80510151.5 1.6 1.7 1.8T. Nakano et al.,hep-ex/0301020PRL91(03)012002  (#$C) & *+,-'.)')MeV0.MeV-  -,3(a) CH target. Solid:  signal sample.Dashed:tag showing  & '.)*  (b) Solid: CH target signal sample. Dashed: LH$target, same cuts.Lunteren 10/10/03 – p.4/20ITEP Bubble ChamberA. Dolgolenko et al.,hep-ex/0304040 Xe Xe+,-'./MeV0MeV -(a) all measured events(b) events with andin the forward di-rection and on oppositesides of the beamLunteren 10/10/03 – p.5/20CLAS d, Jefferson LabM(nK+) [ GeV/c2 ]Events051015202530351.5 1.6 1.7 1.8 1.9S. Stepanyan et al.,hep-ex/0307018 & *+,-'..MeV0'MeV-./signal (solid)& '.)*events (dotted)Lunteren 10/10/03 – p.6/20SAPHIR, ELSA, Bonn010203040500.4 0.6 0.8mass(π+π-)/GeVK0Kscountsa-505101520253035401.4 1.6 1.8mass(nK+)/GeVΘ+ (1540)countsbJ. Barth et al.,hep-ex/0307083  +,-'.)MeV0.MeV -(a)spectrum for cut on(b) withsideband backgroundsubtractionLunteren 10/10/03 – p.7/20CLAS, Jefferson Lab02.557.51012.51517.52022.51.4 1.6 1.8 2 2.2 2.4 32.58 / 27P1 26.59 8.156P2 1.537 0.3394E-02P3 0.1442E-01 0.4994E-02P4 7.631 0.8350 M(nK+), GeV/c2 N/20 MeV/c2V. Kubarovsky et al.,hep-ex/0307088 & *+,-'.)')MeV0/MeV -Lunteren 10/10/03 – p.8/20BEBC, CERN &Bub. Ch., FNAL1.4 1.6 1.8 2 2.2 2.4 2.6024681012141618202224p) , GeVS0m(KNeon plus Deuteriumcomb. / 10 MeV1.5 1.6 1.7 1.8 1.9024681012141618Chi2 / ndf = 22.33 / 21 0.004737 ±mass = 1.533 0.002043 ±sigma = 0.008379 6.417 ±excess = 25.56 0.5881 ±p3 = 1.214 4.732 ±p4 = 17.71 p) , GeVS0m(Kcomb. / 10 MeVChi2 / ndf = 22.33 / 21 0.004737 ±mass = 1.533 0.002043 ±sigma = 0.008379 6.417 ±excess = 25.56 0.5881 ±p3 = 1.214 4.732 ±p4 = 17.71 A. Asratyan et al.,hep-ex/0309042 & * +,-'.//.MeV0)MeV -(Upper: full spectrumLower: expanded scalearound the peakLunteren 10/10/03 – p.9/20HERMES, DESYM(π+π-p) [GeV]Events/ 8 MeVe+D → Ks + p + XNs/Nb = 71.7/163.6in 2σ intervalFit Gauss+P4Chi2=1.4HERMES preliminaryM=1526 ± 2(stat) ±2(sys) MeVσ = 7.5 ± 2.4(stat) MeV010203040506070801.45 1.5 1.55 1.6 1.65 1.7Just released +,-'./MeV0'MeV -.Lunteren 10/10/03 – p.10/20The HERMES experiment102-1-2 mLUMINOSITYCHAMBERSDRIFTFC 1/2TARGETCELLDVCMC 1-3HODOSCOPE H0MONITORBC 1/2BC 3/4TRDPROP.CHAMBERSFIELD CLAMPSPRESHOWER (H2)STEEL PLATECALORIMETERDRIFT CHAMBERSTRIGGER HODOSCOPE H10 1 2 3 4 5 6 7 8 9 10RICH270 mrad270 mradMUON HODOSCOPEWIDE ANGLEFRONTMUONHODOMAGNETmIRON WALLe+27.5 GeV140 mrad170 mrad170 mrad140 mradMUON HODOSCOPESSILICONLunteren 10/10/03 – p.11/20HERMES Event Selection0KsDistance betweenand proton trackKs0Distance between decayand interaction pointDistance betweenπ2 tracksz coordinateΘCABProtonππ+- RICH PID -(GeVd targets from 1998-2000,''.GeVtrack distance'cm track distance)cm  decay length(cm.,.)MeVtarget vertex cutfiducial volume cutEliminate& '''*Lunteren 10/10/03 – p.12/20HERMESIdentification fromerror < 1 MeVbackground is smallwidth-(MeVcuts on 1 MeV agreementwith PDG mass for:&(()* & '))*  & '''* &'.)* Lunteren 10/10/03 – p.13/20HERMES MC and resultLeft: MC simulation with0-MeV,-'.)MeV.MC result:-'.))/MeV and-()MeV.Right: final spectrum 14.90 / 11Constant 240.5 13.30Mean 1.540 0.2692E-03Sigma 0.6994E-02 0.2385E-03Invariant Mass (π+π-p) (GeV)0501001502002501.4 1.45 1.5 1.55 1.6 1.65 1.7M(π+π-p) [GeV]Events/ 8 MeVe+D → Ks + p + XHERMES