1. Forum at Shanghai 1 ++ ++ June 28-29, 2005 Search for Exotic Pentaquark and in Jefferson Lab WangXu Duke University/MIT Motivation The Jlab experiments Conclusion ++  ++

2. Forum at Shanghai 2 ++ ++ June 28-29, 2005 The Anti-decuplet predicted by Diakonov et al. Symmetries give an equal spacing between “tiers” Width < 15 MeV !

3. Forum at Shanghai 3 ++ ++ June 28-29, 2005 Summary of Experiments WhereReactionMassWidth  ’s* LEPS  C  K + K - X1540 +- 10< 254.6 DIANAK + Xe  K 0 p X1539 +- 2< 94.4 CLAS  d  K + K - p(n)1542 +- 5< 215.2 SAPHIR  p  K + K 0 (n)1540 +- 6< 254.8 ITEP A  K 0 p X1533 +- 5< 206.7 CLAS  p   + K - K + (n)1555 +- 10< 267.8 HERMESe + d  K 0 p X1526 +- 313 +- 9~5 ZEUSe + p  e’K 0 p X1522 +- 3 8 +- 4~5 SVD-2P+N  p  +  - X1526 +- 310 +- 35.6 COSYpp  K 0 p  + 1530 +- 5< 184-6 *Gaussian statistical significance: estimated background fluctuation Negative Results: Not seen by CDF, 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. Forum at Shanghai 4 ++ ++ June 28-29, 2005 - CLAS reported a preliminary hint for a  ++ 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 StatecontentIzIz Strong decay model -- dddds-2 00 udddsnK 0 ++ uudds 0nK +,pK 0  ++ uuuds 1K+pK+p  +++ uuuus 2 One of several alternative explanation of  + Isotensor multiplet (Capstick et al., 2003)  + Isospin

5. Forum at Shanghai 5 ++ ++ June 28-29, 2005 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% A B C

6. Forum at Shanghai 6 ++ ++ June 28-29, 2005 Pentaquark photoproduction experiments in Hall B (High Statistic) –g10 deuteron target. E  ~1 – 3.5 GeV. Verify n(d)   + Data taking complete. Order of magnitude increase in deuteron data. –g11 proton target. E  ~1 – 3.5 GeV. Verify and characterize p   +. Search for p   +*. Search for p   . 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)/p   + using “quasi real photo” techinique. Search for   and  0 states/Search for   state. Current Jlab Program

7. Forum at Shanghai 7 ++ ++ June 28-29, 2005 CEBAF Large Acceptance Spectrometer - CLAS Liquid D 2 (H 2 )target +  start counter; e minitorus Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Drift chambers argon/CO 2 gas, 35,000 cells Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/  separation 648 mirrors, 256 PMTs Torus magnet 6 superconducting coils

8. Forum at Shanghai 8 ++ ++ June 28-29, 2005 M(nK + ) Fitted mass 1.555 GeV  < 28 MeV consistent with detector resolution Significance 7.8   + p    + K - +  +  +  n + K + Distribution of  (1520) events M = 1.542 GeV  < 21 MeV Stat.sig. = 5.2  ++ Simulated background Gaussian background  + n  K - +  +  +  n + K + Cos  *(  +) > 0.8 V. Kubarovsky et al., PRL, Jan.‘04 ++ CLAS -  p /  d Results  + p  K 0 +  +  +  n + K + Hep-ph/0505134, No evident of  +

9. Forum at Shanghai 9 ++ ++ June 28-29, 2005 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) ●  p/p  2∙10 -4 (achieved) ●  0.5 mrad,  1 mrad ● δy=1mm ● Can take 1-100 μA ● Luminosity ~ 10 38 cm -2 s -1 Other devices: BigBite (~40msr) open geom. spec., GeN Neutron Detector: 1.6x4.8 m 2

10. Forum at Shanghai 10 ++ ++ June 28-29, 2005 E04-012 ( Pentaquark Partner  ++ -Search ) Layout Θ++ search: 90% CL limit for a Γ=5 MeV state between 1500-1600 MeV is: σγ*p→KΘ++< 3 nb.

11. Forum at Shanghai 11 ++ ++ June 28-29, 2005 E05-009 ( measurement of the  + and its width) Layout 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 Clean, direct measurement of Θ + state. No re-scattering process required.

12. Forum at Shanghai 12 ++ ++ June 28-29, 2005 Proposed Experiment I Photoproduction process: (LH 2 Target) SOS K - HMS P or K +   ++ e_e_ Beam Dump

13. Forum at Shanghai 13 ++ ++ June 28-29, 2005 Experimental Layout I P acceptance :  10% ΔP/P: < 0.001 Solid angle: >7.0 msr Flight path: 25 m P acceptance :  20% ΔP/P: < 0.001 Solid angle: 9.0 msr Flight path: 10 m SOS HMS

14. Forum at Shanghai 14 ++ ++ June 28-29, 2005 Simulation Results(I) 150 hours Total expected events: 23360 Sensitivity to  ++ : <100 pb/sr at 3  level  ++ mass range from acceptance is 1500 to 1600 MeV Crosscheck: Crosscheck has a very low background.  ++

15. Forum at Shanghai 15 ++ ++ June 28-29, 2005 Proposed Experiment II Photoproduction process: (LH 2 Target) SOS K - HKS K + Neutron counter  ++ e_e_ (out-of-plane) (K + K - n) √ Mass calibration (K +  - n) √ Beam Dump

16. Forum at Shanghai 16 ++ ++ June 28-29, 2005 Experimental Setup Experimental Layout 10 meters from the target HKS physical angle 32 degree

17. Forum at Shanghai 17 ++ ++ June 28-29, 2005 Simulation Results(II) 25 hours Total expected events: 5837 (952 with E  cut: E e -125 MeV <E  <E e -25 MeV) Sensitivity to  + : 70 pb/sr at 3  level  + mass range from acceptance is 1500 to 1600 MeV Important for checking two peaks! Mass Calibration: Mass calibration using  particle, better than 0.3 MeV, width better than 1.3 MeV (  ) ++ Σ-Σ-

18. Forum at Shanghai 18 ++ ++ June 28-29, 2005 Requirements II 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.

19. Forum at Shanghai 19 ++ ++ June 28-29, 2005 Conclusion Search for  + and  ++ is still a challenging and interesting topic. This research project may carry on at SSRF in future. Thank You !