29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP1 Searches for Pentaquark Production at LEP Steve Armstrong (ALEPH Collaboration) Brookhaven National Laboratory 29 June th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04) Illinois Institute of Technology Chicago, Illinois, USA June 27 – July

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP2 ¶MOTIVATION FOR LEP PENTAQUARK SEARCHES ¶THE LEP EXPERIMENTAL PROGRAM AT CERN ¶SEARCHES FOR PENTAQUARK PRODUCTION ¶SUMMARY OUTLINE

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP3 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/c 2 with a narrow width of ~ 15 MeV/c 2 and valence quark configuration of uudds (i.e., S = +1) now denoted as  + which is in astonishing agreement with compelling experimental evidence Miraculously, the anti-decuplet also contains exotic  states (  -- and  0 ) consistent with NA49 observations of  states near 1.86 GeV/c 2 A natural consequence would be the replacement of anti-strange quark(s) with anti-charm or anti-beauty  heavy flavour pentaquarks (i.e.,  + and  + ) b c _ _ _

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP4 PENTAQUARK MOTIVATION: EXPERIMENT (  N REACTIONS)

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP5 PENTAQUARK MOTIVATION: EXPERIMENT

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP6 ¶MOTIVATION FOR LEP PENTAQUARK SEARCHES ¶THE LEP EXPERIMENTAL PROGRAM AT CERN ¶SEARCHES FOR PENTAQUARK PRODUCTION ¶SUMMARY OUTLINE

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP7 LEP PROGRAM AT CERN Large Electron Positron (LEP) Collider at CERN LEP1: Starting in 1989 at E cm = 91 GeV (M Z ) LEP2: Starting in 1995, sucessive upgrades to higher E cm Large Electron Positron (LEP) Collider at CERN LEP1: Starting in 1989 at E cm = 91 GeV (M Z ) LEP2: Starting in 1995, sucessive upgrades to higher E cm Terminated in November 2000 Accelerator Lattice and Experiments dismantled (for LHC) Terminated in November 2000 Accelerator Lattice and Experiments dismantled (for LHC) LEP1 (1989 – 1995) 200 pb –1 per experiment

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP8 THE ALEPH DETECTOR Muon Chambers Hadron Calorimeter Superconducting Magnet Coil Electromagnetic Calorimeter Time Projection Chamber Inner Tracking Chamber Silicon Vertex Detector

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP9 THE DELPHI DETECTOR

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP10 THE L3 DETECTOR

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP11 HADRON SYNTHESIS IN ELECTRON-POSITRON INTERACTIONS Hadronic Z Decays Two Photon Interactions

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP12 ¶MOTIVATION FOR LEP PENTAQUARK SEARCHES ¶THE LEP EXPERIMENTAL PROGRAM AT CERN ¶SEARCHES FOR PENTAQUARK PRODUCTION HADRONIC Z DECAYS (ALEPH & DELPHI) TWO PHOTON (L3) ¶SUMMARY OUTLINE

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP13 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: (LEP2) data with Two Photon preselection for W  > 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

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP14 ALEPH PARTICLE IDENTIFICATION To identify particles of type i, cuts are placed on pull of dE/dx from Time Projection Chamber 1.3x10 6 proton candidates selected: 52% purity in high momentum range 96% purity in low momentum range

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP15 DELPHI PARTICLE IDENTIFICATION Pions Kaons Protons

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP16 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  (1520) and eight established  * resonances Excess pK – fit to  (1520) and eight established  * resonances

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP17 ALEPH NON-EXOTIC pK – RESULTS Simultaneous fit to the strengths of eight more or less established resonances over background results in an  (1520) excess of 2814 ± 293 combinations. If  (1520) excess is counted in 30 MeV/c 2 window around GeV/c 2, result is 400 combinations lower  conservatively taken as systematic error Average acceptance of 0.10 obtained from simulation as well as BR(  (1520)  pK – ) = 22.5%

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP18 ALEPH EXOTIC pK 0 SPECTRA s K 0 are selected from kinematic fit to two opposite charged pions emerging from secondary vertex  1.2 x 10 6 K 0 candidates with 93% purity s s Seach for maximum number of excess combinations in sliding window of width 20 MeV/c 2 over smooth 3 rd degree polynomial fit to data Mass resolution is ~5 MeV/c 2 Maximum excess in interval of to GeV/c 2 is 57 combinations over background of 2840 Corresponding 95% confidence level upper limit on excess is 195 combinations

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP19 ALEPH EXOTIC pK 0 RESULTS Use average acceptance of and BR(  +  p K 0 ) = ¼ 95% Confidence Level upper limit on the multiplicity of  + (plus its antiparticle) in hadronic Z decays Ratio of  + to  (1520) production is Z decays This limit is roughly a factor of 20 lower than the ratio in  d reactions measured by HERMES N  + < N  + /N  (1520) < 0.13 s

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP20 DELPHI pK MASS SPECTRA AND RESULTS 306 ± 55 events N  (1520) = ± No excess: N  ++ < (95% C.L.) pK – pK + pK 0 s No excess: N  + < (95% C.L.)

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP21 L3 p  and pK 0 MASS SPECTRA (TWO PHOTON INTERACTIONS) s N  = (1.57 ± 0.11) x per e + e -  e + e - hadrons  (e + e -  e + e -  X) = ± 13.8 pb pp pK 0 s No excess observed 95% C.L. limit set:  (e + e -  e + e -   X) < 20 pb

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP22 Sample of 3350  - candidates with a purity of 76% within a mass window of ± 7 MeV/c 2 ALEPH SEARCH FOR  RESONANCES: MASS SPECTRA No excess observed 95% C.L. limit set

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP23 ALEPH SEARCH FOR  RESONANCES: RESULTS Mass spectrum of doubly-charged combinations (  -- ) is well fitted by linear background from 1.62 to 2.1 GeV/c 2 In NA49 signal region (1.835 to GeV/c 2 ) observed excess is –2 combinations over background of 436 Using acceptance of and systematic uncertainty of 8%, a 95% Confidence Level upper limit is obtained N     BR(  (1862) – –   –  – ) < 4 x 10 –4 For neutral combinations,  (1530) 0 multiplicity is found to be in good agreement with previous ALEPH and OPAL results N   + N  (1530) 0 = (70 ± 8 ± 6) x 10 –4 95% Confidence Level upper limit on Exotic/Non-Exotic  N     BR(  (1862) – –   –  – )/N  (1530) 0 < 0.06

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP24 ALEPH SEARCH FOR CHARM RESONANCES: D 0 p and D + p MASS SPECTRA No compelling excess observed 95% C.L. limit set

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP25 ALEPH SEARCH FOR CHARM RESONANCES: D *+ p MASS SPECTRA No excess observed 95% C.L. limit set

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP26 ALEPH SEARCH FOR CHARM RESONANCES: RESULTS No excess in D* – p channel: 2 combinations between 3.09 and 3.11 GeV/c 2 (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

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP27 ¶MOTIVATION FOR LEP PENTAQUARK SEARCHES ¶THE LEP EXPERIMENTAL PROGRAM AT CERN ¶SEARCHES FOR PENTAQUARK PRODUCTION ¶SUMMARY OUTLINE

29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP28 SUMMARY No evidence of light pentaquark production  + observed in Hadronic Z Decays and Two Photon Interactions in ALEPH, DELPHI, L3 data No evidence of light pentaquark production  observed in Hadronic Z Decays in ALEPH data No evidence of heavy flavour pentaquark production  c  0 observed in Hadronic Z Decays in ALEPH data N   BR(  (1862) – –   –  – ) < 4 x 10 –4 N  + < N  +/N  (1520) < 0.13  (e + e -  e + e -   X) < 20 pb