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Searches for Pentaquark Production at LEP Steve Armstrong (ALEPH Collaboration)

Searches for Pentaquark Production at LEP Steve Armstrong (ALEPH Collaboration) Brookhaven National Laboratory 29 June 2004 6 th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04) Illinois Institute of Technology Chicago, Illinois, USA June 27 – July 3 2004. OUTLINE.

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Searches for Pentaquark Production at LEP Steve Armstrong (ALEPH Collaboration)

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  1. Searches for Pentaquark Production at LEP Steve Armstrong (ALEPH Collaboration) Brookhaven National Laboratory 29 June 2004 6th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04) Illinois Institute of Technology Chicago, Illinois, USA June 27 – July 3 2004 Steve Armstrong - Searches for Pentaquark Production at LEP

  2. OUTLINE • MOTIVATION FOR LEP PENTAQUARK SEARCHES • THE LEP EXPERIMENTAL PROGRAM AT CERN • SEARCHES FOR PENTAQUARK PRODUCTION • SUMMARY Steve Armstrong - Searches for Pentaquark Production at LEP

  3. PENTAQUARK MOTIVATION: THEORY _ • QCD does not forbid more complicated color singlet hadron states other than qq mesons and qqq baryons • Various quark models as well as Skyrme and chiral soliton models predict SU(3) J = 1/2 anti-decuplet {10} of “exotic” baryons • Diakonov et al. predict an isosinglet lowest mass member with mass near 1.53 GeV/c2 with a narrow width of ~ 15 MeV/c2 and valence quark configuration of uudds (i.e.,S = +1) now denoted as Q+ which is in astonishing agreement with compelling experimental evidence _ _ • Miraculously, the anti-decuplet also contains exotic X states (X-- and X0) consistent with NA49 observations of X states near 1.86 GeV/c2 • A natural consequence would be the replacement of anti-strange quark(s) with anti-charm or anti-beauty  heavy flavour pentaquarks (i.e.,Q+ and Q+) b c Steve Armstrong - Searches for Pentaquark Production at LEP

  4. PENTAQUARK MOTIVATION: EXPERIMENT (g N REACTIONS) • • • • • • Steve Armstrong - Searches for Pentaquark Production at LEP

  5. PENTAQUARK MOTIVATION: EXPERIMENT • • • • • Steve Armstrong - Searches for Pentaquark Production at LEP

  6. OUTLINE • MOTIVATION FOR LEP PENTAQUARK SEARCHES • THE LEP EXPERIMENTAL PROGRAM AT CERN • SEARCHES FOR PENTAQUARK PRODUCTION • SUMMARY Steve Armstrong - Searches for Pentaquark Production at LEP

  7. LEP PROGRAM AT CERN Large Electron Positron (LEP) Collider at CERN LEP1: Starting in 1989 at Ecm = 91 GeV (MZ) LEP2: Starting in 1995, sucessive upgrades to higher Ecm LEP1 (1989 – 1995) 200 pb–1 per experiment Terminated in November 2000 Accelerator Lattice and Experiments dismantled (for LHC) Steve Armstrong - Searches for Pentaquark Production at LEP

  8. THE ALEPH DETECTOR Muon Chambers Hadron Calorimeter Electromagnetic Calorimeter Time Projection Chamber Superconducting Magnet Coil Inner Tracking Chamber Silicon Vertex Detector Steve Armstrong - Searches for Pentaquark Production at LEP

  9. THE DELPHI DETECTOR Steve Armstrong - Searches for Pentaquark Production at LEP

  10. THE L3 DETECTOR Steve Armstrong - Searches for Pentaquark Production at LEP

  11. HADRON SYNTHESIS IN ELECTRON-POSITRON INTERACTIONS Hadronic Z Decays Two Photon Interactions Steve Armstrong - Searches for Pentaquark Production at LEP

  12. OUTLINE • MOTIVATION FOR LEP PENTAQUARK SEARCHES • THE LEP EXPERIMENTAL PROGRAM AT CERN • SEARCHES FOR PENTAQUARK PRODUCTION • HADRONIC Z DECAYS (ALEPH & DELPHI) • TWO PHOTON (L3) • SUMMARY Steve Armstrong - Searches for Pentaquark Production at LEP

  13. DATA AND MONET CARLO SAMPLES • ALEPH: Hadronic Z decays between 1991 – 1995 (LEP1) • DELPHI: Hadronic Z decays recorded during 1994 and 1995 during which Time Projection Chamber and Ring Imaging Cherenkov detectors were functioning optimally • L3: 1998-2000 (LEP2) data with Two Photon preselection for Wgg > 5 GeV • Hadronic Z: Based on JETSET with parameters tuned to agree with well-established measurements • Two Photon: PYTHIA with jet hadronization simulated with JETSET • Simulated only octet and decuplet Baryons • Full detector simulation DATA MONTE CARLO Steve Armstrong - Searches for Pentaquark Production at LEP

  14. ALEPH PARTICLE IDENTIFICATION To identify particles of type i, cuts are placed on pull of dE/dx from Time Projection Chamber 1.3x106 proton candidates selected: 52% purity in high momentum range 96% purity in low momentum range Steve Armstrong - Searches for Pentaquark Production at LEP

  15. DELPHI PARTICLE IDENTIFICATION Pions Kaons Protons Steve Armstrong - Searches for Pentaquark Production at LEP

  16. ALEPH NON-EXOTIC pK± MASS SPECTRA Smooth deviation from simulated pK+ mass spectrum observed at few percent level. Understood to be caused by imperfect simulation of dE/dx for spatially close track pairs. Corrected from doubly charged combinations. Excess pK– fit to L(1520) and eight established S* resonances Steve Armstrong - Searches for Pentaquark Production at LEP

  17. ALEPH NON-EXOTIC pK– RESULTS • Simultaneous fit to the strengths of eight more or less established resonances over background results in an L(1520) excess of 2814 ± 293 combinations. • If L(1520) excess is counted in 30 MeV/c2 window around 1.520 GeV/c2, result is 400 combinations lower  conservatively taken as systematic error • Average acceptance of 0.10 obtained from simulation as well as BR(L(1520)pK–) = 22.5% Steve Armstrong - Searches for Pentaquark Production at LEP

  18. ALEPH EXOTIC pK0 SPECTRA s K0 are selected from kinematic fit to two opposite charged pions emerging from secondary vertex  1.2 x 106 K0 candidates with 93% purity s s • Seach for maximum number of excess combinations in sliding window of width 20 MeV/c2 over smooth 3rd degree polynomial fit to data • Mass resolution is ~5 MeV/c2 • Maximum excess in interval of 1.525 to 1.545 GeV/c2 is 57 combinations over background of 2840 • Corresponding 95% confidence level upper limit on excess is 195 combinations Steve Armstrong - Searches for Pentaquark Production at LEP

  19. ALEPH EXOTIC pK0 RESULTS s • Use average acceptance of 0.063 and BR(Q+ p K0) = ¼ • 95% Confidence Level upper limit on the multiplicity of Q+ (plus its antiparticle) in hadronic Z decays • Ratio of Q+ to L(1520) production is Z decays • This limit is roughly a factor of 20 lower than the ratio in gd reactions measured by HERMES NQ+ < 0.0030 NQ+/NL(1520) < 0.13 Steve Armstrong - Searches for Pentaquark Production at LEP

  20. DELPHI pK MASS SPECTRA AND RESULTS pK– pK0 pK+ s No excess: NQ++ < 0.006 (95% C.L.) No excess: NQ+ < 0.015 (95% C.L.) 306 ± 55 events NL(1520) = 0.0224 ± 0.0027 Steve Armstrong - Searches for Pentaquark Production at LEP

  21. L3 pp and pK0 MASS SPECTRA(TWO PHOTON INTERACTIONS) s pK0 pp s No excess observed 95% C.L. limit set: s(e+e- e+e-Q+X) < 20 pb NL = (1.57 ± 0.11) x 10-2 per e+e- e+e- hadrons s(e+e- e+e-LX) = 197.8 ± 13.8 pb Steve Armstrong - Searches for Pentaquark Production at LEP

  22. ALEPH SEARCH FOR XpRESONANCES: MASS SPECTRA Sample of 3350 X- candidates with a purity of 76% within a mass window of ± 7 MeV/c2 No excess observed 95% C.L. limit set Steve Armstrong - Searches for Pentaquark Production at LEP

  23. ALEPH SEARCH FOR XpRESONANCES: RESULTS • Mass spectrum of doubly-charged combinations (X--) is well fitted by linear background from 1.62 to 2.1 GeV/c2 • In NA49 signal region (1.835 to 1.885 GeV/c2) observed excess is –2 combinations over background of 436 • Using acceptance of 0.021 and systematic uncertainty of 8%, a 95% Confidence Level upper limit is obtained NX(1862)--• BR(X(1862)–– X–p–) < 4 x 10–4 • For neutral combinations, X(1530)0 multiplicity is found to be • in good agreement with previous ALEPH and OPAL results NX(1530)0 + NX(1530)0 = (70 ± 8 ± 6) x 10–4 • 95% Confidence Level upper limit on Exotic/Non-Exotic X NX(1862)--• BR(X(1862)–– X–p–)/NX(1530)0 < 0.06 Steve Armstrong - Searches for Pentaquark Production at LEP

  24. ALEPH SEARCH FOR CHARM RESONANCES: D0p and D+p MASS SPECTRA No compelling excess observed 95% C.L. limit set Steve Armstrong - Searches for Pentaquark Production at LEP

  25. ALEPH SEARCH FOR CHARM RESONANCES: D*+p MASS SPECTRA No excess observed 95% C.L. limit set Steve Armstrong - Searches for Pentaquark Production at LEP

  26. ALEPH SEARCH FOR CHARM RESONANCES: RESULTS • No excess in D*–p channel: 2 combinations between 3.09 and 3.11 GeV/c2 (3.5 combinations expects from Monte Carlo) • D–p channel (not covered by H1), an slight excess is observed of 5.2 ± 3.7 combinations or Steve Armstrong - Searches for Pentaquark Production at LEP

  27. OUTLINE • MOTIVATION FOR LEP PENTAQUARK SEARCHES • THE LEP EXPERIMENTAL PROGRAM AT CERN • SEARCHES FOR PENTAQUARK PRODUCTION • SUMMARY Steve Armstrong - Searches for Pentaquark Production at LEP

  28. SUMMARY • No evidence of light pentaquark production Q(1530)+ observed in Hadronic Z Decays and Two Photon Interactions in ALEPH, DELPHI, L3 data NQ+ < 0.0030 s(e+e- e+e-Q+X)< 20 pb NQ+/NL(1520) < 0.13 • No evidence of light pentaquark production X(1862) observed in Hadronic Z Decays in ALEPH data NX(1862)- -• BR(X(1862)–– X–p–) < 4 x 10–4 • No evidence of heavy flavour pentaquark production Qc(3100)0 observed in Hadronic Z Decays in ALEPH data Steve Armstrong - Searches for Pentaquark Production at LEP

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