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Hadron Spectroscopy in ep Collisions at HERA

Lake Louise Winter Institute 2005 Alberta , Canada, February 20-26, 2005. Hadron Spectroscopy in ep Collisions at HERA. Bob Olivier – Birmingham Univ. on behalf of H1 and ZEUS collaborations. Search for Strange Pentaquarks q + , q ++ Search for Double Strange Pentaquarks X --

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Hadron Spectroscopy in ep Collisions at HERA

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  1. Lake Louise Winter Institute 2005 Alberta, Canada, February 20-26, 2005 Hadron Spectroscopy in ep Collisions at HERA Bob Olivier – Birmingham Univ. on behalf of H1 and ZEUS collaborations Search for Strange Pentaquarks q+, q++ Search for Double Strange Pentaquarks X-- Search for Charm Pentaquark q0c Lake Louise 2005

  2. The HERA Collider p e± 27.5 GeV 820, 920 GeV p ZEUS HERA H1 e -Q2 √s=319 GeV √s=300 GeV Q2 : virtuality of exchanged Boson Q2~ 0 GeV2: photoproduction Q2> 1 GeV2: electro-production (DIS) • HERA I data sample: • L ≈ 120 pb-1/ experiment • Two colliding experiments: • ZEUS, H1 • HERA II data taking on-going Lake Louise 2005

  3. The strange Pentaquark anti-decuplet + C H A R G E -2 -1 0 1 X−− STRANGENESS S +1 0 -1 -2 • Proposed by Diakonov, Petrov, Polyakov in 1997: • 3 exotic baryons at • corners, exotic quantum • numbers which can not be • explained by 3 quarks • Prediction of a width less • than 15 MeV for the • q+(1530) state • Many positive results • (mostly at low energy), • many null results QCD says no objection Lake Louise 2005

  4. Search forq+ p K0s / q- p K0s (ZEUS) m(pK0s) , m(pK0s) (GeV) • DIS sample (Q2>1 GeV2): • identify K0s p+p- (secondary vertex) • identify p, p (dE/dx) Peak = 1521.5 ± 1.5 (stat) +2.8-1.7 (sys) MeV Stat. Signif.: ~ 3.9 -4.6 s G: 8 ± 4 MeV Differential cross-sections derived Signal seen in both charges (insert, K0S-antiproton fit, ~ 3 s) If interpreted as q+ + q-  antipentaquark ? Lake Louise 2005

  5. Search forq++ K+ p + c.c. • Is q+ member of a I=1 triplet: (q0, q+, q++) ? • Search for q++ K+ p + c.c • identify K±, p (dE/dx) L(1520) p K- + c.c mass and natural width consistent withPDG: M = 1519.5 ± 1.0 MeV G = 15.6 ± 1.0 MeV q++(1530)p K+ + c.c no evidence for hypothetical q++(1530) Lake Louise 2005

  6. Search for Double Strange X--X-p- 3/2 X-- X-p- L0p- 3/2 pp- NA49 search for X --X-p- M = 1862 ± 2 MeV, ~3 s 3/2 Similar analysis of NA49 repeated using ZEUS DIS data NA49 X−− ? Lake Louise 2005

  7. Search for Double Strange X--X-p- 3/2 ZEUS – DIS. NOTHING ZEUS – high Q2 • Clean Ξ(1530) P13 • No pentaquark signal, evenfor Q2>20 GeV2 • Different production mechanism ? Lake Louise 2005

  8. The charm Pentaquark anti-decuplet What about ? q0c D*p Lake Louise 2005

  9. Search forcharmed PQ, qc D*p, in H1 • DIS and photoproduction samples • D*+ D0ps+  (K-p+)ps+ • identify p (dE/dx) Photoproduction DIS (Q2>1 GeV2) Non-charm background Signal at 3.1 GeV both in DIS and photoproduction samples • Data well described (except in the 3.1 GeV region) by • Non-charm background • D* combined with random p Lake Louise 2005

  10. Search forcharmed PQ, qc D*p, in H1 Significance estimatation Background + signalhypothesis: Mass: 3099±3(stat)±5(sys) MeV Width: 12 ± 3 MeV (consistent with experimental resolution) Numbers of signal and bg within 25 MeV: Nb=45.0 ± 2.8 Ns=50.6 ± 11.2 (~1% of D* yield) 5.4 s Background only hypothesis: Nb=51.7±2.7 Background fluctuation probability: 4x10-8 (Poisson)=5.4 s (Gauss) Lake Louise 2005

  11. Search forqc D*p :H1 / ZEUS Comparison of H1 and ZEUS in similar phase space region ZEUS didn’t observe qcsignal in a DIS data sample 1.7 times of H1 data sample (neither in photoproduction) Observation of ZEUS and H1 are not compatible Nq/ND* : < 0.0035 (ZEUS) ~ 0.01 (H1) More quantitative comparisons require detector efficiency corrections Lake Louise 2005

  12. Conclusions • q+(1530): evidence for a narrow baryonic state • at mass 1521.5 decaying to K0sp (ZEUS) • q++ (1530): no evidence for a state decaying to K+p (ZEUS) • X-- (1860): no evidence for a state decaying to X-p-(ZEUS) • q0c (3100):seen by H1, but not confirmed by ZEUS (H1, ZEUS) Overall HERA (and world) situation unclear • Need more results: q+, q++, X--(H1) • Need more final states: L0K0 ? • Need more statistics:HERA 2 Lake Louise 2005

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