89 research outputs found
Effective field theories for baryons with two- and three-heavy quarks
Baryons made of two or three heavy quarks can be described in the modern
language of non-relativistic effective field theories. These, besides allowing
a rigorous treatment of the systems, provide new insight in the nature of the
three-body interaction in QCD.Comment: 7 pages, 1 figure; published versio
Pion Generalized Dipole Polarizabilities by Virtual Compton Scattering
We present a calculation of the cross section and the event generator of the
reaction . This reaction is sensitive to the pion
generalized dipole polarizabilities, namely, the longitudinal electric
, the transverse electric , and the magnetic
which, in the real-photon limit, reduce to the ordinary electric
and magnetic polarizabilities and , respectively.
The calculation of the cross section is done in the framework of chiral
perturbation theory at . A pion VCS event generator has been
written which is ready for implementation in GEANT simulation codes or for
independent use.Comment: 33 pages, Revtex, 15 figure
Analysis of the doubly heavy baryons in the nuclear matter with the QCD sum rules
In this article, we study the doubly heavy baryon states ,
, and in the nuclear matter using the QCD
sum rules, and derive three coupled QCD sum rules for the masses, vector
self-energies and pole residues. The predictions for the mass-shifts in the
nuclear matter , , and
can be confronted with the
experimental data in the future.Comment: 10 pages, 4 figure
Heavy hadron spectroscopy and the bag model
Some time ago a slightly improved variant of bag model (the modified bag
model) suitable for the unified description of light and heavy hadrons was
developed. The main goal of the present work was to calculate the masses of the
ground state baryons containing bottom quarks in the framework of this model.
For completeness the predictions for other heavy hadrons are also given. The
reasonable agreement of our results with other theoretical calculations and
available experimental data suggests that our predictions could serve as a
useful complementary tool for the interpretation of heavy hadron spectra.Comment: 18 pages, 9 tables, references to experiments updated, rms deviations
given in some table
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
Charmed Exotics in Heavy Ion Collisions
Based on the color-spin interaction in diquarks, we argue that charmed
multiquark hadrons are likely to exist. Because of the appreciable number of
charm quarks produced in central nucleus-nucleus collisions at
ultrarelativistic energies, production of charmed multiquark hadrons is
expected to be enhanced in these collisions. Using both the quark coalescence
model and the statistical hadronization model, we estimate the yield of charmed
tetraquark meson and pentaquark baryon in heavy ion
collisions at RHIC and LHC. We further discuss the decay modes of these charmed
exotic hadrons in order to facilitate their detections in experiments
A new determination of the anomalous amplitude via data
We discuss the reaction with the purpose of
obtaining information on the anomalous amplitude . We compare a full calculation at in chiral
perturbation theory and various phenomenological predictions with the existing
data of Amendolia {\em et al}. By integrating our theory results using Monte
Carlo techniques we obtain nb at and nb after including the dominant electromagnetic correction. Both results
are in good agreement with the experimental cross section of nb. On the basis of the ChPT results one would extract from the the
experimental cross section as amplitudes GeV and
GeV, respectively, which have to be compared with the low-energy theorem
. We emphasize the need for
new data to allow for a comparison of experimental and theoretical
distributions and to obtain with smaller uncertainty.Comment: 23 pages, 14 figures, discussion of the ChPT calculation extende
Observation of the Cabibbo-suppressed decay Xi_c+ -> p K- pi+
We report the first observation of the Cabibbo-suppressed charm baryon decay
Xi_c+ -> p K- pi+. We observe 150 +- 22 events for the signal. The data were
accumulated using the SELEX spectrometer during the 1996-1997 fixed target run
at Fermilab, chiefly from a 600 GeV/c Sigma- beam. The branching fractions of
the decay relative to the Cabibbo-favored Xi_c+ -> Sigma+ K- pi+ and Xi_c+ ->
X- pi+ pi+ are measured to be B(Xi_c+ -> p K- pi+)/B(Xi_c+ -> Sigma+ K- pi+) =
0.22 +- 0.06 +- 0.03 and B(Xi_c+ -> p K- pi+)/B(Xi_c+ -> X- pi+ pi+) = 0.20 +-
0.04 +- 0.02, respectively.Comment: 5 pages, RevTeX, 3 figures (postscript), Submitted to Phys. Rev. Let
First Observation of the Doubly Charmed Baryon Xi_cc^+
We observe a signal for the doubly charmed baryon Xi_cc^+ in the charged
decay mode Xi_cc^+ --> Lambda_c^+ K- pi+ in data from SELEX, the charm
hadro-production experiment at Fermilab. We observe an excess of 15.9 events
over an expected background of 6.1 +/- 0.5 events, a statistical significance
of 6.3sigma. The observed mass of this state is (3519 +/- 1) MeV/c^2. The
Gaussian mass width of this state is 3MeV/c^2, consistent with resolution; its
lifetime is less than 33fsec at 90% confidence.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
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