64 research outputs found
On the Existence of Heavy Pentaquarks: The large Nc and Heavy Quark Limits and Beyond
We present a very general argument that the analogue of a heavy pentaquark (a
state with the quantum numbers of a baryon combined with an additional light
quark and a heavy antiquark) must exist as a particle stable under strong
interactions in the combined heavy quark and large Nc limits of QCD. Moreover,
in the combined limit these heavy pentaquark states fill multiplets of
SU(4)xO(8)xSU(2). We explore the question of whether corrections in the
combined 1/Nc and 1/mQ expansions are sufficiently small to maintain this
qualitative result. Since no model-independent way is known to answer this
question, we use a class of ``realistic'' hadronic models in which a pentaquark
can be formed via nucleon-heavy meson binding through a pion-exchange
potential. These models have the virtue that they necessarily yield the correct
behavior in the combined limit, and the long-distance parts of the interactions
are model independent. If the long-distance attraction in these models were to
predict bound states in a robust way (i.e., largely insensitive to the details
of the short-range interaction), then one could safely conclude that heavy
pentaquarks do exist. However, in practice the binding does depend very
strongly on the details of the short-distance physics, suggesting that the real
world is not sufficiently near the combined large Nc, mQ limit to use it as a
reliable guide. Whether stable heavy pentaquarks exist remains an open
question.Comment: 11 pages; references adde
Radiative Corrections for Pion Polarizability Experiments
We use the semi-analytical program RCFORGV to evaluate radiative corrections
to one-photon radiative emission in the high-energy scattering of pions in the
Coulomb field of a nucleus with atomic number Z. It is shown that radiative
corrections can simulate a pion polarizability effect. The average effect was
estimated for pion energies 40-600 GeV. We also study the range of
applicability of the equivalent photon approximation in describing one-photon
radiative emission.Comment: 11 pages (LaTex), 6 figures, 1 table. No changes in the paper. New
submission because old files are corrupted in arXi
and Polarizabilities from {} Data on the Base of S-Matrix Approach
We suggest the most model-independent and simple description of the
process near threshold in framework of S-matrix
approach. The amplitudes contain the pion polarizabilities and rather
restricted information about interaction. Application of these
formulae for description of MARK-II \cite{M2} and Crystal Ball \cite{CB} data
gives: ,
(in units system ) at the experimental values of scattering lengths. Both
values are compartible with current algebra predictions.Comment: LaTeX, 14 pages plus 6 figures (not included, available upon request)
, ISU-IAP.Th93-03, Irkuts
First Measurement of pi e -> pi e gamma Pion Virtual Compton Scattering
Pion Virtual Compton Scattering (VCS) via the reaction pi e --> pi e gamma
was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c pi-
beam incident on target atomic electrons, detecting the incident pi- and the
final state pi-, electron and gamma. Theoretical predictions based on chiral
perturbation theory are incorporated into a Monte Carlo simulation of the
experiment and are compared to the data. The number of reconstructed events (9)
and their distribution with respect to the kinematic variables (for the
kinematic region studied) are in reasonable accord with the predictions. The
corresponding pi- VCS experimental cross section is sigma=38.8+-13 nb, in
agreement with the theoretical expectation sigma=34.7 nb.Comment: 10 pages, 12 figures, 4 tables, 25 references, SELEX home page is
http://fn781a.fnal.gov/, revised July 21, 2002 in response to journal referee
Comment
A-dependence of phi-meson production in p+A collisions
A systematic analysis of the A-dependence of phi-meson production in
proton-nucleus collisions is presented. We apply different formalisms for the
evaluation of the phi-meson distortion in nuclei and discuss the theoretical
uncertainties of the data analysis. The corresponding results are compared to
theoretical predictions. We also discuss the interpretation of the extracted
results with respect to different observables and provide relations between
frequently used definitions. The perspectives of future experiments are
evaluated and estimates based on our systematical study are given.Comment: 14 pages, 8 figure
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