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Title: The narrow pentaquark

Abstract

The experimental status of the pentaquark searches is briefly reviewed. Recent null results by the CLAS collaboration are commented, and new strong evidence of a very narrow {theta}+ resonance by the DIANA collaboration is presented. On the theory side, I revisit the argument against the existence of the pentaquark - that of Callan and Klebanov - and show that actually a strong resonance is predicted in that approach, however its width is grossly overestimated. A recent calculation gives 2 MeV for the pentaquark width, and this number is probably still an upper bound.

Authors:
 [1]
  1. Petersburg Nuclear Physics Institute, Gatchina, 188 300, St. Petersburg (Russian Federation)
Publication Date:
OSTI Identifier:
21056825
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 892; Journal Issue: 1; Conference: QCHS7: 7. conference on quark confinement and the hadron spectrum, Ponta Delgada, Acores (Portugal), 2-7 Sep 2006; Other Information: DOI: 10.1063/1.2714388; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BARYONS; MEV RANGE; MULTIPARTICLE SPECTROMETERS; PARTICLE IDENTIFICATION; PARTICLE WIDTHS; QUARK MODEL; RESONANCE PARTICLES

Citation Formats

Diakonov, Dmitri. The narrow pentaquark. United States: N. p., 2007. Web. doi:10.1063/1.2714388.
Diakonov, Dmitri. The narrow pentaquark. United States. doi:10.1063/1.2714388.
Diakonov, Dmitri. Tue . "The narrow pentaquark". United States. doi:10.1063/1.2714388.
@article{osti_21056825,
title = {The narrow pentaquark},
author = {Diakonov, Dmitri},
abstractNote = {The experimental status of the pentaquark searches is briefly reviewed. Recent null results by the CLAS collaboration are commented, and new strong evidence of a very narrow {theta}+ resonance by the DIANA collaboration is presented. On the theory side, I revisit the argument against the existence of the pentaquark - that of Callan and Klebanov - and show that actually a strong resonance is predicted in that approach, however its width is grossly overestimated. A recent calculation gives 2 MeV for the pentaquark width, and this number is probably still an upper bound.},
doi = {10.1063/1.2714388},
journal = {AIP Conference Proceedings},
number = 1,
volume = 892,
place = {United States},
year = {Tue Feb 27 00:00:00 EST 2007},
month = {Tue Feb 27 00:00:00 EST 2007}
}
  • We report results of the first search for the pentaquark P{sub {bar c}s} which is predicted to be a doublet of states: P{sup 0}{sub {bar c}s}={vert_bar} {bar c}suud{r_angle} and P{sup {minus}}{sub {bar c}s}={vert_bar} {bar c}sddu{r_angle} . A search was made for the decay P{sup 0}{sub {bar c}s}{r_arrow} {phi}{pi}p in data from Fermilab experiment E791, in which a 500 GeV/c {pi}{sup {minus}} beam interacted with nuclear targets. We present upper limits at 90{percent} confidence level for the ratio of cross section times branching fraction of this decay to that for the decay D{sup {plus_minus}}{sub s}{r_arrow}{phi}{pi}{sup {plus_minus} } . The upper limitsmore » vary between 0.022 and 0.046 for M(P{sup 0}{sub {bar c}s} ) between 2.750 and 2.907 GeV/c{sup 2}, assuming a P{sup 0}{sub {bar c}s} lifetime of 0.4 ps. {copyright} {ital 1998} {ital The American Physical Society}« less
  • Heavy flavor hadron scattering and bound states give experimental information otherwise unobtainable on effective (qq){sub 6} and ({bar q}q){sub 8} interactions. All constituent quark model successes in (uds) hadron spectroscopy depend only on (qq){sub 3}, and ({bar q}q){sub 1} interactions. Reliable vertex detectors open new pentaquark search directions. Any event in with a proton emitted from a secondary vertex indicates a particle decaying weakly by proton emission and the discovery of a new particle if its mass is higher than that of known charmed baryons. There is no combinatorial background and striking decay signatures like p{phi}{pi}{sup {minus}} are no longermore » needed. {copyright} {ital 1997 American Institute of Physics.}« less
  • We examine cross sections for the processes {gamma} N {yields} NK{bar K} in the framework of a phenomenological Lagrangian. We include contributions from {Lambda} and {Sigma} resonances up to spin 3/2, as well as those from an exotic {Theta}{sup +}. We allow the {Theta}{sup +} to have spin 1/2 or 3/2, with either positive or negative parity in each case. We also allow the state to be either isovector or isoscalar. We find that the scenario that most closely matches observations at Jefferson Laboratory requires a very large coupling of the {Theta}{sup +} to NK*.
  • If the exotic baryon {Theta}{sup +}(1540) is a correlated udud{bar s} with J{sup P} = 1/2{sup +}, then there should exist an exotic meson, J{sup P} = 1{sup -} {var_theta}{sup +} (S = +2) {yields} K{sup +}K{sup 0} {approx} 1.6 GeV with width {Omicron}(10-100)MeV. The {pi}{sub 1} (1400;1600) may be broad members of 10 {+-} {ovr 10} in such a picture. Vector mesons in the 1.4 - 1.7 GeV mass range are also compared with this picture.
  • The Regge exchange model used by Dzierba et al. is shown to be questionable, since the pion pole term is not allowed. Hence the Regge amplitudes in their calculation are exaggerated. The amount of kinematic reflection in the mass spectrum of the (nK+) system, which is one decay channel of a possible pentaquark, is not well justified in the fitting procedure used by Dzierba et al., as shown by comparison with the (K+K-) invariant mass spectrum, which is one decay channel of the a{sub 2} and f{sub 2} tensor mesons. While kinematic reflections are still a concern in some papersmore » that have presented evidence for the pentaquark, better quantitative calculations are needed to demonstrate the significance of this effect.« less