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Search for Exotic Pentaquark and in Jefferson Lab

 +.  ++. Search for Exotic Pentaquark and in Jefferson Lab. Motivation The Jlab experiments Conclusion. WangXu Duke University/MIT. The Anti-decuplet predicted by Diakonov et al. Symmetries give an equal spacing between “tiers”. Width < 15 MeV !. Summary of Experiments.

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Search for Exotic Pentaquark and in Jefferson Lab

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  1. + ++ Search for Exotic Pentaquark and in Jefferson Lab • Motivation • The Jlab experiments • Conclusion WangXu Duke University/MIT

  2. The Anti-decuplet predicted by Diakonov et al. Symmetries give an equal spacing between “tiers” Width < 15 MeV !

  3. Summary of Experiments *Gaussian statistical significance: estimated background fluctuation Negative Results: Not seen byCDF, HyperCP, E690, HERA-B, Aleph, Delphi, Phenix, BaBar, and SPHINX(07/2004) Conflicting results within NA49 ?and CLAS (g11). + (1) Summary talk by A. Dzierba at the Quark and Nuclear Physics Conference, May 2004; (2) J. Pochodzalla, hep-ex/0406077

  4. Q+ Isospin • One of several alternative explanation of Q+ Isotensor multiplet (Capstick et al., 2003) • - CLAS reported a preliminary hint for a Q++ candidate peak in pK+ near 1579 MeV (Pentaquark2004 workshop) • STAR reported a preliminary hint for possible peaks in pK+ and antip K- near 1530 MeV (J. Ma, APS meeting 05/01/2004) • Width ~ 8.7 MeV , S/sqrt(B) ~ 3.8 15 M events

  5. CEBAF Electron Accelerator • Up to 5 pass, .6 to 1.15 GeV per pass. • Recirculating linac design • 5.75 GeV max beam energy • 100% duty cycle • 2ns microstructure • E/E < 1∙10-4 (Halls A & C) • 180 A max current • Beam polarization up to 85% C A B

  6. Current Jlab Program • Pentaquark photoproduction experiments in Hall B (High Statistic) • g10 deuteron target. Eg~1 – 3.5 GeV. Verify n(d) IQ+ • Data taking complete. Order of magnitude increase in deuteron data. • g11 proton target. Eg~1 – 3.5 GeV. • Verifyand characterizepIQ+. • Search forpIQ+*. • Search forpIQ++. • Data taking complete. Factor of 10 increase in data expected. • Pentaquark eletroproduction experiment in Hall A (High Resolution) • E04-012/E05-009: proton/deuteron target.Verify n(d)/pIQ+ using “quasi real photo” techinique. Search for Q++andQ0states/Search for Q+state.

  7. Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Torus magnet 6 superconducting coils Liquid D2 (H2)target + g start counter; e minitorus Drift chambers argon/CO2 gas, 35,000 cells Gas Cherenkov counters e/p separation 648 mirrors, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers CEBAF Large Acceptance Spectrometer - CLAS

  8. M = 1.542 GeV G < 21 MeV Stat.sig. = 5.2s Q+ Gaussian background • Fitted mass 1.555 GeV • G< 28 MeV consistent with detector resolution • Significance 7.8s Simulated background Distribution ofL(1520) events M(nK+) CLAS - gp / gd Results g + p g p+ + K- + Q+Q+g n + K+ g + n g K- + Q+Q+g n + K+ Q+ Cosq*(p+) > 0.8 V. Kubarovsky et al., PRL, Jan.‘04 g + p g K0 + Q+Q+g n + K+ Hep-ph/0505134, No evident of Q+

  9. Hall A at Jefferson Lab Two HRS Spectrometers • 0.3 < p < 4.0 GeV/c • -4.5% < Δp/p < 4.5% • 6 msr at 12.5° <θ<150° • 4.5 msr at θ=6° with septum • -5cm<Δy<5cm Optics: (FWHM) • dp/p  2∙10-4 (achieved) • d=0.5 mrad, d=1 mrad • δy=1mm • Can take 1-100 μA • Luminosity ~ 1038 cm-2s-1 • Other devices: • BigBite (~40msr) open geom. spec., • GeN Neutron Detector: 1.6x4.8 m2

  10. E04-012 (Pentaquark Partner Q++-Search) Layout Θ++ search: 90% CL limit for a Γ=5 MeV state between 1500-1600 MeV is: σγ*p→KΘ++< 3 nb.

  11. Untagged quasi-real photons E ≈ 4 GeV Septum permits good coverage of K distribution at low t. Forward “tagged” K leads to low momentum +. Mass resolution of 2.1 MeV E05-009 (measurement of the + and its width) Layout Clean, direct measurement of Θ+ state. No re-scattering process required.

  12. Photoproduction process: Proposed Experiment I SOS K- (LH2 Target)  Beam Dump e_ ++ HMS P or K+

  13. Experimental Layout I HMS • P acceptance :  10% • ΔP/P: < 0.001 • Solid angle: >7.0 msr • Flight path: 25 m SOS • P acceptance :  20% • ΔP/P: < 0.001 • Solid angle: 9.0 msr • Flight path: 10 m

  14. Simulation Results(I) Crosscheck: ++ Crosscheck has a very low background. ++ 150 hours Total expected events: 23360 Sensitivity to ++: <100 pb/sr at 3 level ++ mass range from acceptance is 1500 to 1600 MeV

  15. Photoproduction process: Proposed Experiment II (K+K-n) √ SOS K-  Beam Dump e_ + (LH2 Target) HKS K+ Neutron counter Mass calibration (out-of-plane) (K+-n) √

  16. Experimental Setup Experimental Layout HKS physical angle 32 degree 10 meters from the target

  17. Σ- Simulation Results(II) + Mass Calibration: • Mass calibration using • particle, better than 0.3 MeV, width better than 1.3 MeV () 25 hours Total expected events: 5837 (952 with E cut: Ee-125 MeV <E<Ee-25 MeV) Sensitivity to +: 70 pb/sr at 3 level + mass range from acceptance is 1500 to 1600 MeV Important for checking two peaks!

  18. Neutron detector (Hall C/Hall A Gen experiment) Modification of existing legs for HKS platform New HKS detector support with local shielding A downstream iron magnetic shield outside the HKS splitter magnet pole and coil Beam steering test for SOS done (4.2 GeV beam, -1.74 GeV/c momentum setting at 22 degree), additional shielding around beam pipe helpful. Requirements II

  19. Search for Q+ and Q++ is still a challenging and interesting topic. This research project may carry on at SSRF in future. Conclusion Thank You !

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