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Investigating Pentaquark States Through Hadron Spectroscopy at HERA

The Lake Louise Winter Institute 2005 presented pioneering research on hadron spectroscopy focusing on pentaquarks during ep collisions at HERA. The collaboration of H1 and ZEUS explored the existence of strange and charm pentaquarks, specifically targeting states q+, q++, and q0c. Despite some evidence for a narrow baryonic resonance at mass 1521.5 MeV, searches for additional exotic states yielded inconclusive results. The complexities of data from both collaborations highlighted the need for further explorations and confirmations in this intriguing area of particle physics.

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Investigating Pentaquark States Through Hadron Spectroscopy 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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