Pentaquark Search Summary

Transcription

1 Pentaquark Search Summary David J. Tedeschi University of South Carolina Supported by NSF

2 Pentaquark Structure Pentaquarks: rotational excitations of the soliton [rigid core surrounded by chiral (meson) fields] JW hep-ph/ JM hep-ph/ SZ hep-ph/ (ud) L=1 s Diakonov et al., Z. Phys A 359, 305 (1997). (ud) (ud) L=1 (uds) I=1,S=0 I=0,S=1/2 Karliner, Lipkin, hep-ph/ /21/05 D. Tedeschi, JUG2005 2

3 The Width of the Θ + Elastic K + p, K + d scattering (gold plated), and K + Xe reaction: Nussinov, Γ < 6 MeV. Arndt, Strakovsky, and Workman, Γ< a few MeV Cahn and Trilling looked at the K + Xe data from Diana, Γ = 0.9 +/- 0.3 MeV. COSY data (p p Σ + K 0 p) σ = 0.4 +/- 0.1 (stat) +/- 0.1(syst) μb. Γ 8 MeV From this we conclude that 1 MeV Γ 8 MeV 6/21/05 D. Tedeschi, JUG2005 3

4 Pentaquark History 5/6 Quark Publications Year Publications Experimental Reviews Year Hicks, hep-ex/ Dzierbia, Meyer, Szczepaniak, hep-ex/ Lipkin, hep-ph/ , Nucl. Phys A 625 (1997) /21/05 D. Tedeschi, JUG2005 4

5 Pentaquark Publicity /21/05 D. Tedeschi, JUG2005 5

6 Pentaquark Publicity /21/05 D. Tedeschi, JUG2005 6

7 Pentaquark Scorecard (April 2005) Positive Results Experiment s b Λ Λ(1520) Spring Spring SAPHIR CLAS(d) CLAS(p) DIANA ν 19 8 HERMES COSY ZEUS * 193 SVD NOMAD s b Ξ D* NA H * Estimate from cross section Negative Results Experiment Λ Λ(1520) φ Λ c E ALEPH 2800 CDF BaBar HERA-B SPHINX HYPERCP COMPASS BELLE SELEX 2,800,000 Ξ Ξ(1530) D D * E ALEPH CDF BaBar HERA-B ZEUS WA FOCUS /21/05 D. Tedeschi, JUG2005 7

8 Positive Evidence Spring8 DIANA JLab-d JLab-p 15 Events/(0.02 GeV/c 2 ) MM c γk (GeV/c 2 ) SAPHIR ITEP SVD/IHEP HERMES CERN/NA49 H1 ZEUS COSY-TOF pp Σ + Θ +. 6/21/05 D. Tedeschi, JUG2005 8

9 The Data Undressed Spring8 4.6σ DIANA 4.4σ JLab-d JLab-p 5.2σ 7.8σ ~5σ SAPHIR 4.8σ ITEP 6.7σ SVD/IHEP 5.6σ HERMES CERN/NA49 H1 Ξ -- 5 Ξ 0 Θ 0 c 5 4.2σ ~5.5σ ZEUS 4.6σ COSY-TOF ~5σ 6/21/05 D. Tedeschi, JUG2005 9

10 New Claims Since April 2005 STAR Collaboration (Θ ++ ) Ma, APS Meeting, Tampa, FL April Huang, International Conference on QCD and Hadronic Physics, Beijing, June 20, SPring-8 γd Θ + Λ(1520) Nakano, International Conference on QCD and Hadronic Physics, Beijing, June 20, /21/05 D. Tedeschi, JUG

11 GROUND STATE PENTAQUARK Θ(1530) LEPS,CLAS,HERMES,ZEUS

12 Observation Θ+ from LEPS Apply same Fermi motion correction to MM γk- Solid: signal sample Dashed: background from protons in upstream H 2 target, normalized to signal above 1590 MeV 19 +/- 2.8 events above background of 17 Mass /- 10 MeV Width < 25 90% CL LEPS Collaboration (T. Nakano et al.), PRL 91: , 2003; hep-ex/ /21/05 D. Tedeschi, JUG

13 SPring-8 γn K + K - n A proton is a spectator (undetected). Fermi motion is corrected to get the missing mass spectra. Tight φ exclusion cut is essential. Background is estimated by mixed events L(1520) preliminary 40 preliminary 25 γ p K + K - p 20 γ n K + K - n MM γκ+ (GeV) MM γκ (GeV) 6/21/05 D. Tedeschi, JUG

14 New Spring-8 Claim Cut on Lambda and recoiling kaon mass T. Nakano, Presented at International Conference on QCD and Hadronic Physics, Beijing, June 20, /21/05 D. Tedeschi, JUG

15 Hall B Analyses Data taking on d 2 and h 2 Order of magnitude increase in statistics g10 Channels γ + d Θ + +K - + (p) n + K + + K - + (p) γ + d Θ + +K - + p n + K + + K - + p γ + d Θ + +K - + (p) p + K 0 + K - + (p) p + π + + π - + K - + (p) γ + d Θ + +Λ 0 n + K + + p + π - g11 Channels γ + p Θ + + K 0 n + K + + π + + π - γ + p Θ + + K - + π + n + K + + Κ - + π + 6/21/05 D. Tedeschi, JUG

16 CLAS Cross Section Checks 6 dσ/dω CM (μb/sr) g10 preliminary (3375A) World data γn pπ < E γ < 1.15 GeV σ(μb) γp p ω CLAS g11 preliminary SAPHIR γp K + Λ CLAS g11 preliminary SAPHIR cosθ CM (π - ) E γ (GeV) 6/21/05 D. Tedeschi, JUG

17 Published spectrum Events/10 MeV MM(K - p) (GeV/c 2 ) 6/21/05 D. Tedeschi, JUG

18 High Statistics CLAS result Preliminary Two distributions statistically consistent with each other: 26% c.l. for null hypothesis from the Kolmogorov test (two histograms are compatible). Reduced χ 2 =1.15 for the fit in the mass range from 1.47 to 1.8 GeV/c 2 G10 mass distribution can be used as a background for refitting the published spectrum. With Fermi momentum being the only source of an energetic spectator proton, the cross section upper limit is 20nb. If we assume a more sophisticated model for an energetic spectator and take the Λ(1520) production as a guide, the cross section upper limit is 4-5 nb (model dependent). 6/21/05 D. Tedeschi, JUG

19 CLAS Proton Result Proposed measurement and Primary Goals: search for Θ + (1540) and possible excited states in γ-p interaction above threshold (E γ = GeV) collect more than 10 times the statistics of previous measurements in the same kinematics establish the mass of any observed peak with 2 MeV accuracy determine total and differential cross section Status of the experiment New experiment approved by JLab PAC25 in January Run in May-July 2004, with a total of triggers recorded (Luminosity ~70 pb -1 ) Data calibration and processing completed in January 2005 Preliminary results for this reaction γ p p γ Θ + K n 0 K π - 0 θ + K + π + 6/21/05 D. Tedeschi, JUG

20 CLAS Θ + Upper Limit Counts/4 MeV Counts/4 MeV Counts/4 MeV preliminary -0.8 < cosθ CM < -0.6 M(nK + )(GeV) M(nK + )(GeV) 0.6 < cosθ CM < 0.8 M(nK + )(GeV) 6/21/05 D. Tedeschi, JUG

21 SAPHIR Comparison SAPHIR Observed Yields Kinematics SAPHIR N(Θ Selection + )/N(Λ*) ~ of 63/630 forward ~ 10% angles of the K 0 in the γ-p center of mass N(Θ + )/N(Λ*) <110/53000 <0.2% (95%CL) K 0 CLAS Counts cosθ CM (K 0 ) > 0.5 Counts cosθ CM (K 0 ) > 0.5 γ Cross Sections Θ + SAPHIR σ γ p Θ + K 0 ~ 300 nb reanalysis 50 nb Energy limited to 2.6 GeV θ CM CLAS no hyperon rejection σ γ p Θ + K 0 < 2 nb (95%CL) p Counts M(nK 0 ) (GeV) Λ(1520) cosθ CM (K 0 ) > 0.5 g11@clas Counts preliminary M(nK + ) (GeV) cosθ CM (K 0 ) > 0.5 Θ + (1540)? M(nK 0 ) (GeV) M(nK + ) (GeV) 6/21/05 D. Tedeschi, JUG

22 Exclusive Result off the Proton γ γp π + K + K - (n) 3 <E γ <5.47 GeV π + π -N* Θ+ K - Detect K + K - π +, reconstruct neutron Compute Invariant mass M(nK+) M=1555±10 MeV/c 2 Background shape well understood Cuts: via PWA -MC cos(θ π+ ) >0.8 and cos(θ Κ+ )<0.6 Inset: cos(θ π+ ) >0.8 only V. Kubarovsky, et al., (CLAS Collaboration) hep-ex/ , PRL 92 (2004) /21/05 D. Tedeschi, JUG p K + n

23 HERA: HERMES Θ + pk 0 Airapetian et al., Phys. Lett. B 585 (2003) 213. M = 1528 ± 2.6 ± 2.1 MeV Width = 17 ± 9 ±3 MeV Additional π required Airapetian et al., Int l Workshop on DIS, Madison, /21/05 D. Tedeschi, JUG

24 Zeus Result Observe: Θ + mass=1.521 GeV width=6.1 MeV 230 Events on 1080 Background Phys. Lett. B591 (2004) 7. No Signal for: Ξ 5, Θ 0 c Fragmentation, Q 2 >20GeV 2 Production Mechanism: BGF See discussion of Chekanov, hepph/ (March 05). Σ? σ(ep eθx):125 ± 27(stat) Ren, Int l Workshop on DIS, Madison, (syst) pb 6/21/05 D. Tedeschi, JUG

25 ISOSPIN / DECOPLET PARTNERS Θ ++ (1540), Σ 5 STAR, HALL A

26 STAR Au-Au Results pk + STAR Preliminary pk pk + + pk A nice peak is also seen in AuAu 62.4 GeV data from 20-80% centrality bin The ratio of the number of signal from the channel to that from the pk + channel is /- 0.2 pk ratio in AuAu at 62.4 GeV from STAR p / pis about 0.5 6/21/05 D. Tedeschi, JUG

27 STAR d-au Results STAR Preliminary pk + Invariant mass pk Invariant mass + pk and pk invariant mass distribution from 18.8 Million dau events. + The signal appears in both pk and pk channels. The ratio of the number of signal from the pk channel to that from + the pk channel is / p / p ratio in dau at 200 GeV from STAR is about /21/05 D. Tedeschi, JUG

28 STAR Θ + (1540) dau data, K s0 was identified by topological method There is some excess at invariant mass around 1540 MeV/c 2, but it is not too significant statistically. STAR Preliminary No pk exotic signals have been seen in pp data. No signal for Φ -- (Ξ -- ) have been found. 6/21/05 D. Tedeschi, JUG

29 STAR Rate Estimates After acceptance and efficiency correction Assuming 100% branching ratio Spectrum includes Θ ++ and Θ -- Mt-exponential fit yields: dn/dy = T = MeV Θ ++ /φ ~ 2% Yields for some particles in dau Ks: L+Lbar: Xi+Xibar: Phi: /21/05 D. Tedeschi, JUG

30 STAR Conclusions + A clear peak is seen in the pk and pk invariant mass distribution in dau collisions at 200 GeV and AuAu collisions at 62.4 GeV. No signal is seen in pp collisions at 200 GeV. The peak mass is about 1530 MeV/c 2, width (convoluted with the detector resolution) is about 15 MeV No statistically significant signals are seen for the Ξ Ξ π from the current available data Θ + 0 pk s and Rate Estimate Θ ++ /φ~2% 6/21/05 D. Tedeschi, JUG

31 High resolution Hall A Studies E04-012: a search for θ + partners Look for missing mass in reaction H(e, e K + ) X 6/21/05 D. Tedeschi, JUG

32 Preliminary Results from the Σ 5 Search/ σ(σ 5 ) / σ(1520) < 1.7 % 6/21/05 D. Tedeschi, JUG

33 CASCADE PRODUCTION Ξ(1860) NA49, CLAS

34 Ξ -- Present Status COMPASS Collaboration, hep-ex/ (March 2005). 6/21/05 D. Tedeschi, JUG

35 NA49 Observation of Exotic Ξ 5 pp collisions at 158 GeV/c Blue - mixed event background M=1.862± GeV Γ<0.018 GeV Particle ID via de/dx in TPC s Reconstruct Ξ s from Λπ Imposed cuts to enhance signal! 12 cm primary vertex separation secondary vertex separation cuts Ratio to Ξ(1530) not consistent with other publications Combined spectra M(Ξπ) GeV/c 2 CERN SPS hep-ex/ /21/05 D. Tedeschi, JUG

36 Ξ -- Decay CLAS γ n K + K + Ξ 5 -- Ξ π Ξ - Ξ - π - Λ Λ π - p Electron beam We expect ~450 Ξ 5 -- in 20 days of 100% running, assuming 10 nb for production cross section and luminosity /21/05 D. Tedeschi, JUG

37 Particle Reconstruction p π - DOCA cut tight Λ mass cut m Ξ ~1322 MeV σ Λ ~ 5 MeV p π - DOCA cut m Λ ~1115 MeV (reconstructed) σ Λ ~ 2 MeV (reconstructed) Ξ photon beam 7% of the data 6/21/05 D. Tedeschi, JUG

38 CHARMED PENTAQUARK Θ c (3100)

39 Charmed Pentaquark Θ c (3100) Positive H1 Collaboration A. Aktas et al., Phys. Lett B 588 (2004) 17; Int l Workshop on DIS, Madison, Negative ALEPH (e + e - ) S. Schael et al., Phys. Lett. B 599 (2004) 1. FOCUS (γn) J.M. Link et al., Phys. Lett. B 586 (2004) 11; hepex/ (June 2005). pp CDF ( ) hep-ex/ BELLE (e + e - ) hep-ex/ ZEUS (ep) Chekanov et al., Eur. Phys. Jour. C 38 (2004) 29,Int l Workshop on DIS, Madison, Signal is ~ % of total D* rate. Ghost Track Study - Zavertyaev, hep-ex/ ! 6/21/05 D. Tedeschi, JUG

40 Charmed Pentaquark Θ c (3100) Signal also seen in photoproduction. Signal is ~1.5% of total D* rate. H1 Collaboration, A. Aktas et al., Phys. Lett B 588 (2004) 17. 6/21/05 D. Tedeschi, JUG

41 Charmed Pentaquark Θ c (3100) Situation similar to Θ(1540) Negative sightings outnumber positive H1 data appears robust Claim kinematical uniqueness Alternative explanations surfacing Recent analysis from FOCUS, ZEUS Need more time to resolve disagreements 6/21/05 D. Tedeschi, JUG

42 Pentaquark Scorecard (June 2005) Active Positive Results Experiment s b Λ Λ(1520) Spring Spring Spring 8(/\*) CLAS(p) HERMES COSY ZEUS * 193 STAR - theta++ Experiment CLAS(d) pk + K - final state CLAS(p) nk + K 0 final state Hall A (Σ 5 ) New Negative Results Must be careful to compare quantitatively! 6/21/05 D. Tedeschi, JUG

43 Outlook Analysis continuing at: Spring-8 JLab - Hall A and B COSY STAR H1, ZEUS, Hermes many other places New Experiments Planned JLab - Hall A and B Matured from bump hunting to calculating cross sections/ upper limits Critical mass in pursuit - claims are being seriously addressed 6/21/05 D. Tedeschi, JUG