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Open Charm Photoproduction at GlueX

Open Charm Photoproduction at GlueX. Reinhard Schumacher. March 2008. Introduction. Motivation J/ y elastic and inelastic Exclusive open charm photoproduction Experimental considerations Reaction channels Cross section estimates Simple parametric Monte Carlo study: Acceptances

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Open Charm Photoproduction at GlueX

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  1. Open Charm Photoproduction at GlueX Reinhard Schumacher March 2008

  2. Introduction • Motivation • J/y elastic and inelastic • Exclusive open charm photoproduction • Experimental considerations • Reaction channels • Cross section estimates • Simple parametric Monte Carlo study: • Acceptances • Resolutions • Rate estimates R. A. Schumacher, Carnegie Mellon University

  3. Motivation • J/y elastic and inelastic production* • Multi-gluon exchange near threshold: higher-twist dominance • Off deuteron: search for hidden color in w.f. • Look for intrinsic charm  contribution to spin crisis solution • Access to gluon GPD’s • Open charm: D0 Lc+ , D+,-,0 Sc0,++,+, D+D-p • Nearly nothing is known, experimentally • Exclusive charmed baryon photoproduction • Larger cross sections than J/y … but smaller branching fractions * S. Brodsky, E. Chudakov, P. Hoyer, J. M . Laget, Phys Lett. B 498 23 (2001) R. A. Schumacher, Carnegie Mellon University

  4. (slide from M. Osipenko / R. De Vita) Elastic production Two Gluon Exchange + t0 t0 Factorization for heavy meson exclusive photoproduction: D. Ivanov et al, EPJ C34 (04) gluon GPD 4-momentum fraction carried by gluon: Hard scale: In t0 limit gives Gluon Distribution in the proton: R. A. Schumacher, Carnegie Mellon University

  5. The Charmed Baryon States Charmed Baryons Light Strange Baryons • 12 GeV: over threshold for ~9 charmed non- • strange baryons • Most have *** status • Photoproduction cross sections near • threshold are unmeasured. • Neither J’s nor P’s of excited states are • measured. R. A. Schumacher, Carnegie Mellon University

  6. c u d Dynamical Ansatzes Photon-gluon fusion “inside” the nucleon Feynman propagator approach R. A. Schumacher, Carnegie Mellon University

  7. Thresholds & Decay Modes R. A. Schumacher, Carnegie Mellon University

  8. Cross Section Comparisons J/y elastic Open Charm at Eg=150 GeV; W=17 GeV at Eg=20 GeV; W=6.1 GeV We assume a similar ratio all the way down to threshold… P. Garbincius, FNAL-Conf-95/041 M. Binkley et al.(FNAL), PRL 48, 73 (82) R. A. Schumacher, Carnegie Mellon University

  9. Estimate via strangeness production Open Strangeness F ‘Hidden’ Strangeness Valid near-ish the threshold, from Eg=2 to 12 GeV Included contributions from KL, K+0S0+ , K+L(1520), K*S Consistent with previous charm production ratio estimate. R.Bradford et al.(CLAS), PRC 73, 035202 (06) R.M.Egloff et al.(FNAL), PRL 43, 657 (79) R. A. Schumacher, Carnegie Mellon University

  10. See Egle Tomasi-Gustafsson, (JLAB at 12 GeV Workshop (2000)) Basic s- and u-channel Feynman propagator approach Coupling gNDL is unknown Predicts sTOT ~ 10 – 100 nb at 11 GeV Predicts backward-peaked production of D0. Theory estimate of open charm production R. A. Schumacher, Carnegie Mellon University

  11. Experimental Considerations • Consider • Take advantage of the “narrowness” of charm states • Suppose we require exclusive detection (nothing missing) to permit energy conservation enforcement R. A. Schumacher, Carnegie Mellon University

  12. Monte Carlo Simulations • Parametric MC • Resolution roughly mimics D. Lawrence’s GlueX-doc-761 • Acceptance: “geometric” & > 0.2 GeV/c cut on momentum of charged tracks • Use 8 to 9 GeV photons (6 GeV threshold) • Multi-pion background : Signal = 99:1 • 2p 3p+ 2p- • Assume proton identified, but no K/p separation, no kinematic fit, but enforce energy conservation R. A. Schumacher, Carnegie Mellon University

  13. Monte Carlo Cut generated generated accepted accepted After cut After cut R. A. Schumacher, Carnegie Mellon University

  14. Observations • Exclusive kinematics can be used to separate signal/background in face of x100 background w/o without p/K PID • Lc+ resolution is ~12 MeV (s) • D- resolution is ~15 MeV (s) R. A. Schumacher, Carnegie Mellon University

  15. Monte Carlo Simulations • Parametric MC • Resolution roughly mimics D. Lawrence’s GlueX-doc-761 • Acceptance: “geometric” & > 0.2 GeV/c cut on momentum of charged tracks • Use 9.5 to 10.5 GeV photons • No background in simulation • Phase space production model • Assume proton identified, but no K/p separation, & no kinematic fit R. A. Schumacher, Carnegie Mellon University

  16. Particle distributions generated accepted R. A. Schumacher, Carnegie Mellon University

  17. Particle distributions R. A. Schumacher, Carnegie Mellon University

  18. Channel: • e = 68%  geometric & momentum acceptance • B.F. = 0.19% product of branching fractions (for exclusive detection) s=12MeV s=20MeV generated accepted R. A. Schumacher, Carnegie Mellon University

  19. Channel: • e = 73%  geometric & momentum acceptance • B.F. = 0.19% product of branching fractions (for exclusive detection) s=20MeV s=12MeV s=21MeV s=15MeV R. A. Schumacher, Carnegie Mellon University

  20. Channel: s=15MeV s=12MeV • e = 78%  geometric & momentum acceptance • B.F. = 0.48% product of branching fractions (for exclusive detection) s=12MeV R. A. Schumacher, Carnegie Mellon University

  21. Rate Estimates • Use Ng=108/s ; target length = 30 cm • Use kaon decay factor of k≈0.5 • Get Ndetect/stot = (451 events/hr/nb)xB.F.xek • .29 events/hr/nb • .31 events/hr/nb • .86 events/hr/nb R. A. Schumacher, Carnegie Mellon University

  22. Rate Estimates – “Background” A. Dzierba, GlueX-doc-856-v1  Rate estimates from data and from Pythia R. A. Schumacher, Carnegie Mellon University

  23. EgdNg/dEg Eg (GeV) 8.7 9.0 9.5 10.0 10.5 Possible ways to increase rate • (Untagged) bremsstrahlung difference method • Restrictive trigger: Ntrack> 4 • (s5prong+ s7prong)/sTOT ~ 1/3 • Raise beam intensity to singles rate limit (where is it?) • Use thicker nuclear target R. A. Schumacher, Carnegie Mellon University

  24. Discussion / Summary • Exclusive open charm photoproduction is an unexplored field • Production cross sections for up to 9 charmed baryons • Clues to reaction mechanism – need a real theory • Measure gNDLc • Acceptances quite good if GlueX can detect 5 to 7 charged tracks simultaneously • Rates are very low: need some tricks to increase yields • Kaon ID will be needed R. A. Schumacher, Carnegie Mellon University

  25. BACKUP SLIDES… R. A. Schumacher, Carnegie Mellon University

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