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Title: Searches for exotic baryons of isospin 5/2 that consist of light quarks

Abstract

The status of isospin-5/2 exotic baryons consisting of light-quarks is considered. A brief survey of theoretical studies devoted to them is given. Experimental searches for exotic baryons are traced from the first publication on the subject to the present day. Among possible candidates for an exotic baryon, the pentaquark baryon E{sub 5/25/2} of mass M {approx} 1.44 GeV/c{sup 2} and width {gamma} < 0.05 GeV/c{sup 2} is the most probable. This state was recorded in six studies at five different facilities. Among these, there are two studies where the excess of the signal above the background is more than five standard deviations. The possibility of further searches for exotic baryons in various reactions is discussed.

Authors:
 [1]
  1. Institute of Theoretical and Experimental Physics (Russian Federation)
Publication Date:
OSTI Identifier:
21076061
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Atomic Nuclei; Journal Volume: 69; Journal Issue: 5; Other Information: DOI: 10.1134/S1063778806050139; Copyright (c) 2006 Nauka/Interperiodica; Article Copyright (c) 2006 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BARYONS; D QUARKS; GEV RANGE; ISOSPIN; MASS; S QUARKS; U QUARKS

Citation Formats

Nilov, A. F.. Searches for exotic baryons of isospin 5/2 that consist of light quarks. United States: N. p., 2006. Web. doi:10.1134/S1063778806050139.
Nilov, A. F.. Searches for exotic baryons of isospin 5/2 that consist of light quarks. United States. doi:10.1134/S1063778806050139.
Nilov, A. F.. Mon . "Searches for exotic baryons of isospin 5/2 that consist of light quarks". United States. doi:10.1134/S1063778806050139.
@article{osti_21076061,
title = {Searches for exotic baryons of isospin 5/2 that consist of light quarks},
author = {Nilov, A. F.},
abstractNote = {The status of isospin-5/2 exotic baryons consisting of light-quarks is considered. A brief survey of theoretical studies devoted to them is given. Experimental searches for exotic baryons are traced from the first publication on the subject to the present day. Among possible candidates for an exotic baryon, the pentaquark baryon E{sub 5/25/2} of mass M {approx} 1.44 GeV/c{sup 2} and width {gamma} < 0.05 GeV/c{sup 2} is the most probable. This state was recorded in six studies at five different facilities. Among these, there are two studies where the excess of the signal above the background is more than five standard deviations. The possibility of further searches for exotic baryons in various reactions is discussed.},
doi = {10.1134/S1063778806050139},
journal = {Physics of Atomic Nuclei},
number = 5,
volume = 69,
place = {United States},
year = {Mon May 15 00:00:00 EDT 2006},
month = {Mon May 15 00:00:00 EDT 2006}
}
  • The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitudes for the low-lying exotic baryons including the u, d quarks are calculated. The poles of the five-quark amplitudes determine the masses and the widths of uuuud and ddddu states (isospin I=5/2). The mass spectrum of the E{sup +++} exotic baryons with J{sup P}=(1{sup +}/2), (3{sup +}/2), (5{sup +}/2) is calculated.
  • Electric form factors for exotic baryons are calculated within the relativistic quark model in the region of low and intermediate momentum transfers, Q{sup 2} {<=} 1 GeV{sup 2}. The charge radii of E{sup +++} baryons are determined.
  • We investigate the possibility that the dark matter consists of clusters of the heavy family quarks and leptons with zero Yukawa couplings to the lower families. Such a family is predicted by the approach unifying spin and charges as the fifth family. We make a rough estimation of properties of baryons of these new family members, of their behavior during the evolution of the Universe and when scattering on the ordinary matter, and study possible limitations on the family properties due to the cosmological and direct experimental evidences.
  • In 3088 events of the reaction np..-->..p..pi../sup +/..pi../sup +/..pi../sup -/..pi../sup -/n at momentum 5.10 +- 0.17 GeV/c we have studied the effective mass spectra of ..delta../sup + +/..pi../sup +/(..delta../sup -/..pi../sup -/) combinations for the purpose of seeking and investigating exotic baryon resonances with isospin I = 5/2. Peaks are observed which exceed the background by 3--4 standard deviations at masses 1438, 1522, and 1894 MeV/c/sup 2/. The widths of these resonances are estimated as 23, < or =20, and < or =40 MeV/c/sup 2/, respectively. The sets of spins and parities for the resonance with mass 1438 MeV/c/sup 2/ aremore » 3/2/sup + -/ and 5/2/sup + -/, and those for the resonance with mass 1522 MeV/c/sup 2/ are 1/2/sup + -/, 3/2/sup -/, and 5/2/sup +/. The cross sections for production of these resonances in the given reaction are equal to several microbarns. The results are compared with various theoretical models.« less
  • A study is made of the properties of exotic baryon resonances a(I,S) with isospin I> or =5/2, whose existence follows from dispersion sum rules for Reggeon-particle scattering amplitudes. It is shown that the spins of these states are equal to the isospins (S = I) and that the intrinsic parities are positive. Expressions are found for the helicity vertices for coupling to the Regge trajectories with I = 1 (rho, A/sub 2/, ..pi..). A formula is obtained for the widths of the decays a(I, S)..-->..a(I-1, S-1)+..pi... The feasibility of an experimental search for these states is discussed.