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Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions with HERA-B

Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions with HERA-B. M. Medinnis, DESY For the HERA-B Collaboration ICHEP, Beijing Session on Hadron Spectroscopy and Exotics. HERA Experiments.  c 0   + ?. N. W. E.  + .  +  - -.  c 0   + . S.

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Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions with HERA-B

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  1. Search for Pentaquarks in 920 GeV Proton-Nucleus Collisions with HERA-B M. Medinnis, DESY For the HERA-B Collaboration ICHEP, Beijing Session on Hadron Spectroscopy and Exotics M. Medinnis, DESY Hamburg

  2. HERA Experiments c0   +? N W E + + - - c0   +  S M. Medinnis, DESY

  3. Experimental situation • According to a recent count*: • 12 reports of a narrow resonance (NR) in nK+ or pK0s near 1530 MeV/c2 (+). • 8 reports this year of negative results on searches for +. • H1 reports a NR decaying into D*p (0c) but Zeus reports non-observation. • NA49 reports a NR decaying into -- (--). The existence of pentaquarks is not established. If they exist, the production mechanism is unclear. *J. Pochodzalla, hep-ex/0406077 M. Medinnis, DESY

  4. HERA-B contribution Search for: +(1540)  p K0s  p +- --(1862)  - -  0 - -  p - - - At mid-rapidity in pA collisions at 920 GeV, using a large, clean (pileup  10%) minimum bias sample: 200 million interactions (A = C, Ti, W) M. Medinnis, DESY

  5. HERA-B Detector 920 GeV incident protons Main tracker MAGNET Wire Targets Vertex Detector RICH ECAL x z M. Medinnis, DESY

  6. RICH/ECAL Particle ID • For K0s,  reconstruction: no particle ID requirements • Otherwise: (where L  likelihood) • Pions: (weak) LRICH(e,,) > .01,LECAL(e) < 0.9 • Kaons: (strong) LRICH(K) > 0.95 mis-id < 2%, p range: 12 – 55 GeV/c • Protons: (strong) LRICH(p) > 0.95 mis-id < 1%, p range: 22 – 55 GeV/c M. Medinnis, DESY

  7. V0 Selection  K0s ~ DCA < 0.7mm, Mild lifetime cut: ptc > .05 GeV/ccm, K/ ambiguities are rejected M. Medinnis, DESY

  8. - (1520) - and (1520) Signals - recon: |mp-m| < 3, Cascade topology, z > 2.5cm M. Medinnis, DESY

  9. pK0s mass, Upper Limit pK0s mass (GeV/c2) for -0.3< rapidity < 0.3 event mixing mass=3.9 MeV/c2 @+ UL(95%): Carbon sensitivity 1.4 1.475 1.55 1.625 1.7 With N  A0.7, UL(95%)Bd/dy|y=0 =3.7 b/N @ 1530GeV/c2 M. Medinnis, DESY

  10. Counts / 3 MeV/c2 1.4 1.6 1.8 2 2.2 Mass GeV/c2  Mass HERA-B (p + C) NA49 -- 20 10 -+ Counts / 7.5 MeV/c2 +- 10 6 ++ 1.4 1.8 2.2 2.6 Mass GeV/c2 C. Alt et al. PRL 92, 042003 M. Medinnis, DESY

  11. NA49  Combined Plot, UL(95%) HERA-B Counts / 3 MeV/c2 Rapidity: -0.7 < y < 0.7 mass = 6.6 GeV/c2@ 1862 MeV/c2 -- B d/dy b/C Assuming N  A0.7, UL(95%) Bd/dy|y=0 = 2.5 b/N @ m(--) =1862 GeV/c2 M. Medinnis, DESY

  12. Signal Statistics Particle / anti-particle, : mass resolution *H.G.Fischer, S.Wenig hep-ex0401014 M. Medinnis, DESY

  13. See hep-ex/0408048 for more details Summary I: +  p K0s UL(95%) Bd/dy|y=0 = 3.7 b/N @ mpKs=1530 MeV Production ratios and comparison to predictions (%) (%) B(+  p K0s)  0.25 M. Medinnis, DESY

  14. See hep-ex/0408048 for more details Summary II: --(1862)  - - UL(95%) Bd/dy|y=0 = 2.5 b/N Production ratios and comparison to predictions, NA49 (%) (%) *N(0) from hep-ex/0401014, --/0 eff ratio = HERA-B M. Medinnis, DESY

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