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Cascade Spectroscopy at CLAS

Cascade Spectroscopy at CLAS. Lei Guo, JLAB for CLAS Collaboration. Overview : Cascade physics provides a window to baryon spectroscopy Ground state X(1320): g p →K + K + (X - ) Few photon data existed. New CLAS g11 data: ~70/pb -1, E 0 =4.0186 GeV Cross section measurement

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Cascade Spectroscopy at CLAS

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  1. Cascade Spectroscopy at CLAS Lei Guo, JLAB for CLAS Collaboration • Overview: Cascade physics provides a window to baryon spectroscopy • Ground state X(1320): gp→K+ K+(X-) • Few photon data existed. New CLAS g11 data:~70/pb-1, E0=4.0186 GeV • Cross section measurement • Production mechanism probe (Y*X K?) • Search forexcitedX states in X-  X0p- • gp→K+ K+ p-(X0) analysis • Summary Lei Guo, D. P. Weygand, NSTAR05

  2. Bremsstrahlung tagged photon facility, photon energy resolution ~0.2% (New Tagger Energy Calibration) CEBAF Large Acceptance Spectrometer@JLAB 6 Superconducting toroidal coils Electromagnetic calorimeters Beam line and the target Drift chambers TOF counters Cherenkov counters Tagger CLAS Detector Lei Guo, D. P. Weygand, NSTAR05

  3. g K+ K+ K- p Y* X- * X(1620) andSearch for X-*X 0p- • Fewer excited cascade states observed • X(1620)’s exotic nature: • Does it exist? • Is the mass too low • N’ partner? (Azimov et al) (nucl-th/0307088) • Dynamicaally generated? member of JP=1/2 – octet? Ramos et.al (nuclth/0204044 ) • CLAS ideal for X-*in exclusive reaction:gp→K+ K+ p-(X0) p- Lei Guo, D. P. Weygand, NSTAR05 X0

  4. Is there a X(1620)state?New Very high statistics results X 103 Inclusive reaction: S- (C, Cu)  (X-p+) X M(X- p+ ) 345GeV/c No mention of X0(1620); X0 (1690) claimed Adamovich et al. W89 Collaboration Eur. Phys. J. C5(1998) 621 After backgroud subtraction Lei Guo, D. P. Weygand, NSTAR05

  5. g11 K+K+ missing mass spectrain reaction gp→K+ K+(X-) X- (1320) X- Events/2MeV/c2 Events/2MeV/c2 X- (1530) MM(K+K+) (GeV/c2) MM(K+K+) (GeV/c2) Loose PID cuts Eg >2.6 GeV Tighter PID cuts: |TOF_Vtime – RFVtime|< 1ns Lei Guo, D. P. Weygand, NSTAR05

  6. Data Simulation comparison Cos*q(X) Cos*(q)_K+1,2 M(X- K1,2+) M(K+ K+ ) Y* input: M: 1.96GeV/c2 width: 220 MeV/c2 Simulation: t channel process gp→K+ Y*, Y*K+X- Lei Guo, D. P. Weygand, NSTAR05

  7. g11 X- Cross section extraction g K+ K- K+ p Y* s(nb) X- Preliminary Eg(GeV) s extracted from ds/dcos(qK ) and ds /dcos(qX ) Lei Guo, D. P. Weygand, NSTAR05

  8. X- differential Cross section extraction: ds /dcos(qX ) Eg: 3.09 GeV Eg: 3.19 GeV Eg: 3.29 GeV Eg: 3.39 GeV Eg: 3.49 GeV Eg: 3.59 GeV Eg: 3.69 GeV Eg: 3.79 GeV Data consistent with t channel process Lei Guo, D. P. Weygand, NSTAR05

  9. X- differential Cross section extraction: ds /dcos(qK ) Eg: 3.09 GeV Eg: 3.19 GeV Eg: 3.29 GeV Eg: 3.39 GeV Eg: 3.49 GeV Eg: 3.59 GeV Eg: 3.69 GeV Eg: 3.79 GeV Yield extracted when either K+ falls in dcos(qK+ ) Lei Guo, D. P. Weygand, NSTAR05

  10. X- differential Cross section extraction ds/dt(gK+fast ) Eg: 3.09 GeV Eg: 3.19 GeV Eg: 3.29 GeV Eg: 3.39 GeV Eg: 3.49 GeV Eg: 3.59 GeV Eg: 3.69 GeV Eg: 3.79 GeV Acceptance at very low t an issue Two identical bosons! Lei Guo, D. P. Weygand, NSTAR05

  11. Is X coming from Y* decay?gp→K+ Y*, Y*nK0 /pK -/ K+X- Eg> 3.4GeV gp→K+ K+X- Eg> 3.4GeV gp→K+ Y* M(nK0 ) /10MeV/c2 Events/10MeV/c2 M(pK- ) /5MeV/c2 M(X-K+) Information from ds/dM(KK),ds /dM(KX), ds /dcos(qX ) and ds /dcos(qK ) could be used to determine properties of Y* Lei Guo, D. P. Weygand, NSTAR05

  12. Is X coming from Y* decay?gp→K+ Y*, Y*nK0 /pK -/ K+X- • Statitics insufficient to be conclusive • Not inconsistent with multiple Y*XK • ds strength independent of Eg at low M(XK): Diffractive process? ds/dM(XK) ds(nb/GeV) M(XK) (GeV/c2) Lei Guo, D. P. Weygand, NSTAR05

  13. gp→K+ K+X-*, X-*  p-X0 MM(K+K+p-) M(X0p-) Preliminary Shaded events: Background from out of target events M(X0p-) Background subtracted Lei Guo, D. P. Weygand, NSTAR05

  14. Simulated pion background Preliminary p+ p+ g X Events/4MeV/c2 p- p0 N* p n MM(K+K+p-) M=1.675GeV, G=0.153GeV (to be tuned) X(1620)? Events/10MeV/c2 Background with only one p+ ---> K+to be added M(X0p-) Lei Guo, D. P. Weygand, NSTAR05 X(1530)

  15. Angular distributions CosHELqp VS M(X0p-) CosHELqp Around X(1530) Preliminary Cos*q(Xp) VS M(X0p-) Around X(1620)? Produced in background angles in CM frame Interesting structures Lei Guo, D. P. Weygand, NSTAR05

  16. Summary and outlook • CLAS good instrument for Cascade photoproduction • X-(1320) cross section obtained for Eg=2.74~3.84 GeV ( s(Eg) Eg?) • Data consistent with t channel production of Y* X- K+ • New way to study Y* through possible XK decay • Observation of X-(1620)??in g p→ p- K+ K+(X0 ) ? Angular distributions to be interpreted • Future high energy experiment desirable! Lei Guo, D. P. Weygand, NSTAR05

  17. X0p- invariant mass spectrain different Eg ranges Eg< 3.75GeV Eg> 3.75GeV Events/4MeV/c2 M(X0p-) (GeV/c2) M(X0p-) (GeV/c2) If the peak is due to reflection it will migrate when Eg /(w)changes Lei Guo, D. P. Weygand, NSTAR05

  18. gp→K+ K*0(X0) or gp→K+ K+X-*, X-*  p-(X0) X0 X0 gp→K+ K*0(X0) unlikely Lei Guo, D. P. Weygand, NSTAR05

  19. Do we see it in MM(KK) without detecting p-? M(K+)_TOF MM(K+K+) |TOFvtime-vtime| <1ns X- (1530) ? |TOFvtime-vtime| <200ps More pion background in gp→K+ K+(X*-) Lei Guo, D. P. Weygand, NSTAR05

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