337 research outputs found
Coupled-channel model for charmonium levels and an option for X(3872)
The effects of charmed meson loops on the spectrum of charmonium are
considered, with special attention paid to the levels above open-charm
threshold. It is found that the coupling to charmed mesons generates a
structure at the D \bar{D}* threshold in the 1++ partial wave. The implications
for the nature of the X(3872) state are discussed.Comment: 27 pages, 7 EPS figure
Development of antimicrobial resistance in Staphylococcus lugdunensis during treatment—report of a case of bacterial arthritis, vertebral osteomyelitis and infective endocarditis
Pion propagation in the linear sigma model at finite temperature
We construct effective one-loop vertices and propagators in the linear sigma
model at finite temperature, satisfying the chiral Ward identities and thus
respecting chiral symmetry, treating the pion momentum, pion mass and
temperature as small compared to the sigma mass. We use these objects to
compute the two-loop pion self-energy. We find that the perturbative behavior
of physical quantities, such as the temperature dependence of the pion mass, is
well defined in this kinematical regime in terms of the parameter
m_pi^2/4pi^2f_pi^2 and show that an expansion in terms of this reproduces the
dispersion curve obtained by means of chiral perturbation theory at leading
order. The temperature dependence of the pion mass is such that the first and
second order corrections in the above parameter have the same sign. We also
study pion damping both in the elastic and inelastic channels to this order and
compute the mean free path and mean collision time for a pion traveling in the
medium before forming a sigma resonance and find a very good agreement with the
result from chiral perturbation theory when using a value for the sigma mass of
600 MeV.Comment: 18 pages, 11 figures, uses RevTeX and epsfig. Expanded conclusions,
added references. To appear in Phys. Rev.
Angular distributions in states near threshold
A resonance X(3872), first observed in the decays , has been seen
to decay to . The mass spectrum peaks near
its kinematic upper limit, prompting speculation that the dipion system may be
in a . The decay also has been observed.
The reaction has been studied.
Consequently, angular distributions in decays of
states near threshold are of interest, and results are presented.Comment: 10 pages, no figures. To be submitted to Phys. Rev.
Possible Molecular States of System and Y(4140)
The interpretation of Y(4140) as a molecule is studied
dynamically in the one boson exchange approach, where , and
exchange are included. Ten allowed states with
low spin parity are considered, we find that the , ,
, and configurations are most
tightly bound. We suggest the most favorable quantum numbers are
for Y(4140) as a molecule, however,
and can not be excluded. We propose to search for the
and partners in the and final
states, which is an important test of the molecular hypothesis of Y(4140) and
the reasonability of our model. The molecule is
deeply bound, experimental search in the channel at Tevatron
and LHC is suggested.Comment: 13 pages,2 figure
Beyond CP violation: hadronic physics at BaBar
I report on recent studies of hadronic physics performed by the BaBar
Collaboration. Emphasis is given to the measurement of the properties of newly
discovered charmed hadrons and to the searches for light and heavy pentaquarks.Comment: 14 pages, 20 postscript figues, contributed to the Proceedings of the
First APS Topical Group Meeting on Hadron Physics, Fermilab, Batavia, IL
(October 24-26, 2004
A Study in Depth of f0(1370)
Claims have been made that f0(1370) does not exist. The five primary sets of
data requiring its existence are refitted. Major dispersive effects due to the
opening of the 4pi threshold are included for the first time; the sigma -> 4pi
amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest
require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and
3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass
and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19
standard deviation contribution. This alone is sufficient to demonstrate the
existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible
f0(1370) signal > 8 standard devations. In all cases, a resonant phase
variation is required. The possibility of a second pole in the sigma amplitude
due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi
elastic scattering are fitted well with the inclusion of some mixing between
sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690),
rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction
rewritten. Conclusions unchange
Chiral Lagrangian for strange hadronic matter
A generalized Lagrangian for the description of hadronic matter based on the
linear -model is proposed. Besides the baryon
octet, the spin-0 and spin-1 nonets, a gluon condensate associated with broken
scale invariance is incorporated. The observed values for the vacuum masses of
the baryons and mesons are reproduced. In mean-field approximation, vector and
scalar interactions yield a saturating nuclear equation of state. We discuss
the difficulties and possibilities to construct a chiral invariant baryon-meson
interaction that leads to a realistic equation of state. It is found that a
coupling of the strange condensate to nucleons is needed to describe the
hyperon potentials correctly. The effective baryon masses and the appearance of
an abnormal phase of nearly massless nucleons at high densities are examined. A
nonlinear realization of chiral symmetry is considered, to retain a Yukawa-type
baryon-meson interaction and to establish a connection to the Walecka-model.Comment: Revtex, submitted to Phys. Rev.
Evidence for two-quark content of in exclusive decays
Inspired by a large decay branching ratio (BR) of
measured by Belle recently, we propose that a significant evidence of the
component of in could be
demonstrated in exclusive decays by the observation of in
the final states and . We predict the BRs of to be () while
the unknown wave functions of () are chosen to fit the
observed decays of .Comment: 4 pages, 2 figures, Revtex4, version to appear in PR
Angular momentum coefficients for meson strong decay and unquenched quark models
In most meson strong decay and unquenched (coupled-channel) quark models, the
pair-creation operator is a scalar product of vectors in the spin and spatial
degrees of freedom. While differing in the spatial part, most models have the
same spin part, which creates a qq* pair coupled to spin triplet, with the
spins of the initial quarks as spectators. This is a basic assumption of the
3P0 model, and is well-known to arise also in the flux tube model, starting
from the strong coupling expansion of lattice QCD. In this article the same
structure is shown to emerge in the Cornell model, in the dominant
contributions of a more general microscopic decay model, and in the
pseudoscalar-meson emission model. A solution is obtained for arbitrary matrix
elements in these ``non-flip, triplet'' models, expressed as a weighted sum
over spatial matrix elements. The coefficients in the expansion, which involve
the spin degrees of freedom and the associated angular momentum algebra, are
model-independent. Tables of the angular momentum coefficients are presented
which can be used in future calculations, avoiding tedious Clebsch-Gordan sums.
The symmetry and orthogonality properties of the coefficients are discussed, as
well as their application to transitions involving hybrid mesons and states of
mixed spin. New selection rules are derived, and existing ones generalised. The
coefficients lead to model-independent relations among decay amplitudes and
widths which can be tested in experiment and lattice QCD. They can also be used
to explain how mass shifts in the unquenched quark model do not spoil
successful predictions of the ordinary (quenched) quark model.Comment: 45 pages, 4 figures, 16 table
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