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 ++ ++
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 !
Forum at Shanghai 3 ++ ++ June 28-29, 2005 Summary of Experiments WhereReactionMassWidth ’s* LEPS C K + K - X < DIANAK + Xe K 0 p X < 94.4 CLAS d K + K - p(n) < SAPHIR p K + K 0 (n) < ITEP A K 0 p X < CLAS p + K - K + (n) < HERMESe + d K 0 p X ~5 ZEUSe + p e’K 0 p X ~5 SVD-2P+N p + - X COSYpp K 0 p < *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/
Forum at Shanghai 4 ++ ++ June 28-29, 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) ~ M events StatecontentIzIz Strong decay model -- dddds-2 00 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
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
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
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
Forum at Shanghai 8 ++ ++ June 28-29, 2005 M(nK + ) Fitted mass GeV < 28 MeV consistent with detector resolution Significance 7.8 + p + K - + + + n + K + Distribution of (1520) events M = 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/ , No evident of +
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 μA ● Luminosity ~ cm -2 s -1 Other devices: BigBite (~40msr) open geom. spec., GeN Neutron Detector: 1.6x4.8 m 2
Forum at Shanghai 10 ++ ++ June 28-29, 2005 E ( Pentaquark Partner ++ -Search ) Layout Θ++ search: 90% CL limit for a Γ=5 MeV state between MeV is: σγ*p→KΘ++< 3 nb.
Forum at Shanghai 11 ++ ++ June 28-29, 2005 E ( 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.
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
Forum at Shanghai 13 ++ ++ June 28-29, 2005 Experimental Layout I P acceptance : 10% ΔP/P: < Solid angle: >7.0 msr Flight path: 25 m P acceptance : 20% ΔP/P: < Solid angle: 9.0 msr Flight path: 10 m SOS HMS
Forum at Shanghai 14 ++ ++ June 28-29, 2005 Simulation Results(I) 150 hours Total expected events: Sensitivity to ++ : <100 pb/sr at 3 level ++ mass range from acceptance is 1500 to 1600 MeV Crosscheck: Crosscheck has a very low background. ++
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
Forum at Shanghai 16 ++ ++ June 28-29, 2005 Experimental Setup Experimental Layout 10 meters from the target HKS physical angle 32 degree
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-
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, GeV/c momentum setting at 22 degree), additional shielding around beam pipe helpful.
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 !