22 research outputs found
Experimentalni program uz SPring-8
A highly-polarized photon beam produced via the backward Compton scattering of polarized laser photons off the high-energy electrons is utilized for nuclear and particle physics experiments at SPring-8. The present status of the experiments at the Laser Electron Photon beamline at SPring-8 (LEPS) is reported. From the recent results, the evidence for a five-quark baryon resonance is presented. A sharp baryon resonance peak was observed at 1.54 ± 0.01 GeV/c2 with a width smaller than 25 MeV/c2 in the γn → K+K−n reaction on 12C. The resonance has the strangeness quantum number S = +1 and it can not be formed by three quarks.Za istraživanja u nuklearnoj i čestičnoj fizici sa SPring-8 rabimo visoko-polarizirane fotone koji se postižu raspršenjem unatrag polariziranih laserskih fotona na elektronima visoke energije. Opisujemo napredak eksperimenata sa laserskoelektronskim fotonskim snopom. U nedavnim mjerenjima utvrdili smo petokvarkovsku barionsku rezonanciju. Opaža se kao oštar barionski rezonantni vrh u reakciji γn → K+K−n u meti 12C, na 1.54 ± 0.01 GeV/c2 , širine manje od 25 MeV/c2 . Ima kvantni broj stranosti S = +1 i ne može biti sastavljena od samo tri kvarka
Exotic Baryons in Two-Dimensional QCD
Two-dimensional QCD has often been used as a laboratory for studying the full
four-dimensional theory, providing, for example, an explicit realization of
baryons as solitons. We review aspects of conventional baryons in
two-dimensional QCD, including the classical and quantum contributions to their
masses. We then discuss the spectrum of exotic baryons in two-dimensional QCD,
commenting on the solitonic radius inferred from the excitation spectrum as
well as the two-dimensional version of the Goldberger-Treiman relation relating
meson couplings to current matrix elements. Two-dimensional QCD provides strong
overall support to the chiral-soliton picture for the structure of normal and
exotic baryons in four dimensions.Comment: 15 pages latex, no figure
Light hadron and diquark spectroscopy in quenched QCD with overlap quarks on a large lattice
A simulation of quenched QCD with the overlap Dirac operator has been
completed using 100 Wilson gauge configurations at beta = 6 on an 18^3 x 64
lattice and at beta = 5.85 on a 14^3 x 48 lattice, both in Landau gauge. We
present results for light meson and baryon masses, meson final state "wave
functions," and other observables, as well as some details on the numerical
techniques that were used. Our results indicate that scaling violations, if
any, are small. We also present an analysis of diquark correlations using the
quark propagators generated in our simulation.Comment: 28 LaTeX pages, 41 figures, v2: minor updates, version published in
JHE
Polarization in Hyperon Photo- and Electro- Production
Multiple polarization observables must be measured to access the amplitude
structure of pseudoscalar meson photoproduction off the proton. The
hyperon-producing reactions are especially attractive to study, since the weak
decays allow straightforward measurement of the induced and recoil polarization
observables. In this paper we emphasize ,
discussing recent measurements of , , and for this reaction. An
empirical constraint on the helicity amplitudes is obtained. A simplified model
involving spin-flip and spin non-flip amplitudes is presented. Finally, a
semi-classical model of how the polarization may arise is presented.Comment: Invited paper at NStar2007, Accepted for EPJ A 1-21-08, 6 pages, 6
figure
Spin 3/2 Pentaquarks
We investigate the possible existence of the spin 3/2 pentaquark states using
interpolating currents with K-N color-octet structure in the framework of QCD
finite energy sum rule (FESR). We pay special attention to the convergence of
the operator product expansion
Pentaquarks: review of the experimental evidence
Pentaquarks, namely baryons made by 4 quarks and one antiquark have been
predicted and searched for since several decades without success. Theoretical
and experimental advances in the last 2 years led to the observation of a
number of pentaquark candidates. We review the experimental evidence for
pentaquarks as well as their non-observations by some experiments, and discuss
to which extend these sometimes contradicting informations may lead to a
consistent picture.Comment: Contribution to the International Conference on 'Strangeness in Quark
Matter', 15-21 Sept. 2004, Cape Tawn, South Afric
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0
reactions are measured for the first time for Egamma=1.5-2.4 GeV and
0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the
Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are
positive and gradually increase with rising photon energy. The data are not
consistent with theoretical predictions based on tree-level effective
Lagrangian approaches. Including the new results in the development of the
models is, therefore, crucial for understanding the reaction mechanism and to
test the presence of baryon resonances which are predicted in quark models but
are sofar undiscovered