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Pentaquarks : dead or alive? 

Pentaquarks : dead or alive? . T ome Anticic, K. Kadija, Tanja Sus a. Rudjer Boskovic Institute. NA61, feb 201 1, Warsaw. What are pentaquarks?. d. −1/3. u. s. +1/3. +2/3. d. u. −1/3. +2/3. New form of quark matter : baryons whose

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Pentaquarks : dead or alive? 

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  1. Pentaquarks: dead or alive? Tome Anticic, K. Kadija, Tanja Susa Rudjer Boskovic Institute NA61, feb 2011, Warsaw

  2. What are pentaquarks? d −1/3 u s +1/3 +2/3 d u −1/3 +2/3 • New form of quark matter: baryons whose • minimum quark content is 5 (qqqqq) • “Non-exotic” pentaquarks • The antiquark has the same flavor as one of the other quarks • Difficult to distinguish from 3-quark baryons • “Exotic” pentaquarks (qqqqQ) • The antiquark has a different flavor from the other 4 quarks • Quantum numbersdifferent from any 3-quark baryon • Example:uudds (exotic): • Baryon number = 1/3 + 1/3 + 1/3 + 1/3 - 1/3 = 1 • Strangeness = 0 + 0 + 0 + 0 + 1 = +1 Baryons with S = +1 cannot be made by qqq !!!!!

  3. The pentaquark anti-decuplet uudds S = +1 decay modes nK+,pK0 narrow width (few MeV) S = 0 Jp=1/2+ : exotic states S = -1 S = -2 ddssu uussd I=-1/2 I=-1 I=-3/2 I=1 I=3/2 I=0 I=1/2 Experimental searches were motivated by predictions of chiral soliton modelDiakonov, Petrov, Polyakov, Z.Physics A359 (1997). Jaffe and Wilczek had a quark-diquark model. Q+(1539) can be detected experimentally!! N(1650-1690) S(1760-1810) X+(1862)

  4. First evidence for Q+ • n→K+K-(n) (the neutron is bound inside 12C) Spring-8 LEPS at Spring-8 • Narrow peak observed • in K- missing mass spectrum • M = 1.54 ± 0.01GeV/c2  ≤ 0.025 GeV/c2 • S=19 B=17 • Significance: S/√B = 4.6 Q+ H1

  5. Positive signals JLab-d Spring8 DIANA ELSA ITEP SVD/IHEP JLab-p HERMES ZEUS COSY-TOF CERN/NA49 H1 pp  S+Q+.

  6. Positive experimental results Experiment Energy Reaction Mass Width Significance (GeV) (MeV) (MeV) + c+ 3/2

  7. Negative eksperimental results

  8. Orig/New NA49 X-- analysis y old analysis ?? prelim X– signal with new analysis  eff Entries Mid rap ~180 Xi1530 old analysis 550 Xi1530 new analysis All rap M(--)[GeV/c2] M()

  9. Timeline of positive and negative results Nomad SVD-2 2008

  10. Critical Comments For many experiments, the background shape is not clearly known. Some experiments have harsh angle cuts that could affect the mass spectra. In all cases, the signal is weak compared with standard resonances. Cuts are necessary to lower background. Several experiments retracted data with more data/further analysis But, some (not many…) positive results remain…

  11. New DIANA & LEPS results DIANA LEPS 0 K+Xe KS p Xe’ gd K+K-pn Statistics nearly doubled M =1.537 ± 0.002 GeV/c2 M =1.524 ± 0.002 GeV/c2 G = 0.00036 ± 0.00011GeV/c2 G < 30 GeV/c2 s/√s+b = 5.3  Significance: 5.1

  12. New SVD-2 results 0 pN KS p X Two independent K0s samples (inside & outside vertex) Sample I Sample II M = 1.523 ± 0.002 GeV/c2 G≤ 0.014 GeV/c2 Combined significance: s/√s+b = 8.0

  13. Conclusion/NA61 steps Pentaquarks, although knocked down, not completely dead yet, as there are a few experiments with consistently positive results. Seems/perhaps pp and pA low energy a possible channel for them. NA61, with improved statistics and analysis methods, could easily explore, across different energies and in pp, pA, and AA, for both particles and antiparticles: • p K0s • X p , X1530 p And publish a paper, either with positive or negative results for the pentaquark searches

  14. Back up slides

  15. Reconstruction 5-- --  - (BR = 99.887 %) • p-(BR= 63.9 %) 5---K-, -n(BR = 99.848 %)

  16.  invariant mass distribution Narow peak: M  1.86 GeV/c2 Known resonant State 0(1530)

  17.  more stringent selection Peak in the--distributioncandidate for the5-- state Indications of a peak in +-,+- ,++ distributions candidates for the50,50,5++state 1.850 < M < 1.8725 GeV/c2 M  1.86 GeV/c2

  18. Width and position of the peak 1.8 < M() < 1.9 GeV/c2 M = 1.862  0.002 GeV/c2 = 0.017  0.003 GeV/c2 M = 1.864  0.005 GeV/c2 = 0.019  0.003 GeV/c2

  19. Systematic studies and checks -: all negative particles -: negative pions RecVENUS p+p events • Analiza MC analysis • Background  candidates • Resonance reflection • Changing cuts

  20. New analysis • Improve geometry and residual corrections (Millepede) • Several bugs in chain corrected • - R3D corrected(outlier removal not used, 2 not in a • common block) • - TPC error, …. • Different  finder,  fitter developed (13-par fit) • Improve main vertex determination

  21. X old and new data J.M. Gago et al., “ X* Production in K- p Interactions at 14.3 GeV/c” Ecole-Polytechnique-Saclay-RHEL Collaboration, (CERN/EP/PHYS 76-50) J.W.Price,J.Ducote,J.Goetz,B.M.K.Nefkens, “Photoproduction of the double-strange X hyperons” For the CLASS Collaboration, (arXiv:nucl-ex/0402006) X0* X-*

  22. Example: BaBar : M(X -p +) : M(LK0S)

  23. Hyperon results overview y     eff X Mid rap Mid rap 1530 •  •  •  •  •  •  •  •   Mid rap Mid rap All First clear signal at SPS energies in p-p collisions

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