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Exploring Baryon Spectroscopy with Cascade Physics at CLAS

This overview focuses on baryon spectroscopy using Cascade physics, particularly the ground state X(1320), with new CLAS g11 data providing insight into cross-section measurements and production mechanisms. The search for excited X states, including X(1620), is discussed, along with the potential exotic nature and dynamics of these particles. Various analyses and simulations are highlighted, demonstrating the capabilities of the CLAS facility at JLAB for exclusive reactions and differential cross-section extractions. The discussion includes the possibility of X originating from Y* decay and the importance of future high-energy experiments for further exploration.

robertplewis
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Exploring Baryon Spectroscopy with Cascade Physics 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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