1,084 research outputs found
Production of the X(3872) at the Tevatron and the LHC
We predict the differential cross sections for production of the X(3872) at
the Tevatron and the Large Hadron Collider from both prompt QCD mechanisms and
from decays of b hadrons. The prompt cross section is calculated using the
NRQCD factorization formula. Simplifying assumptions are used to reduce the
nonperturbative parameters to a single NRQCD matrix element that is determined
from an estimate of the prompt cross section at the Tevatron. For X(3872) with
transverse momenta greater than about 4 GeV, the predicted cross section is
insensitive to the simplifying assumptions. We also discuss critically a recent
analysis that concluded that the prompt production rate at the Tevatron is too
large by orders of magnitude for the X(3872) to be a weakly-bound charm-meson
molecule. We point out that if charm-meson rescattering is properly taken into
account, the upper bound is increased by orders of magnitude and is compatible
with the observed production rate at the Tevatron.Comment: 29 pages, 5 figure
The Renormalization Group Limit Cycle for the 1/r^2 Potential
Previous work has shown that if an attractive 1/r^2 potential is regularized
at short distances by a spherical square-well potential, renormalization allows
multiple solutions for the depth of the square well. The depth can be chosen to
be a continuous function of the short-distance cutoff R, but it can also be a
log-periodic function of R with finite discontinuities, corresponding to a
renormalization group (RG) limit cycle. We consider the regularization with a
delta-shell potential. In this case, the coupling constant is uniquely
determined to be a log-periodic function of R with infinite discontinuities,
and an RG limit cycle is unavoidable. In general, a regularization with an RG
limit cycle is selected as the correct renormalization of the 1/r^2 potential
by the conditions that the cutoff radius R can be made arbitrarily small and
that physical observables are reproduced accurately at all energies much less
than hbar^2/mR^2.Comment: 11 pages, 4 figure
Damping rate of plasmons and photons in a degenerate nonrelativistic plasma
A calculation is presented of the plasmon and photon damping rates in a dense
nonrelativistic plasma at zero temperature, following the resummation program
of Braaten-Pisarski. At small soft momentum , the damping is dominated by scattering processes corresponding to double longitudinal Landau
damping. The dampings are proportional to , where
is the Fermi velocity.Comment: 9 pages, 2 figure
Production of the X(3872) in B Meson Decay by the Coalescence of Charm Mesons
If the recently-discovered charmonium state X(3872) is a loosely-bound S-wave
molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be
produced in B meson decay by the coalescence of charm mesons. If this
coalescence mechanism dominates, the ratio of the differential rate for B^+ \to
\bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to
X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses
only. The identification of the X(3872) as a \bar D^0 D^{*0}/\bar D^{*0} D^0
molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0}
invariant mass distribution near the threshold. An estimate of the branching
fraction for B^+ \to X K^+ is consistent with observations if X has quantum
numbers J^{PC} = 1^{++} and if J/\psi \pi^+ \pi^- is one of its major decay
modes.Comment: 4 pages, 3 figures, revtex
Longitudinal and transverse fermion-boson vertex in QED at finite temperature in the HTL approximation
We evaluate the fermion-photon vertex in QED at the one loop level in Hard
Thermal Loop approximation and write it in covariant form. The complete vertex
can be expanded in terms of 32 basis vectors. As is well known, the
fermion-photon vertex and the fermion propagator are related through a
Ward-Takahashi Identity (WTI). This relation splits the vertex into two parts:
longitudinal (Gamma_L) and transverse (Gamma_T). Gamma_L is fixed by the WTI.
The description of the longitudinal part consumes 8 of the basis vectors. The
remaining piece Gamma_T is then written in terms of 24 spin amplitudes.
Extending the work of Ball and Chiu and Kizilersu et. al., we propose a set of
basis vectors T^mu_i(P_1,P_2) at finite temperature such that each of these is
transverse to the photon four-momentum and also satisfies T^mu_i(P,P)=0, in
accordance with the Ward Identity, with their corresponding coefficients being
free of kinematic singularities. This basis reduces to the form proposed by
Kizilersu et. al. at zero temperature. We also evaluate explicitly the
coefficient of each of these vectors at the above-mentioned level of
approximation.Comment: 13 pages, uses RevTe
Gluon fragmentation to quarkonia
Gluon fragmentation to heavy quarkonia is studied herein. We
compute these D-wave states' polarized fragmentation functions and find that
they are enhanced by large numerical prefactors. The prospects for detecting
the lowest lying charmonium state at the Tevatron are discussed.Comment: 10 pages with 4 uuencoded figures, CALT-68-195
Power counting and effective field theory for charmonium
We hypothesize that the correct power counting for charmonia is in the
parameter Lambda_QCD/m_c, but is not based purely on dimensional analysis (as
is HQET). This power counting leads to predictions which differ from those
resulting from the usual velocity power counting rules of NRQCD. In particular,
we show that while Lambda_QCD/m_c power counting preserves the empirically
verified predictions of spin symmetry in decays, it also leads to new
predictions which include: A hierarchy between spin singlet and triplet octet
matrix elements in the J/psi system. A quenching of the net polarization in
production at large transverse momentum. No end point enhancement in radiative
decays. We discuss explicit tests which can differentiate between the
traditional and new theories of NRQCD.Comment: 18 pages, 1 figure Replaced plot of the psi polarization parameter
alpha as a function of transverse momentum. Alpha is now closer to zero for
large transverse moment
Solution to the 3-Loop -Derivable Approximation for Massless Scalar Thermodynamics
We develop a systematic method for solving the 3-loop -derivable
approximation to the thermodynamics of the massless field theory. The
method involves expanding sum-integrals in powers of and m/T, where g is
the coupling constant, m is a variational mass parameter, and T is the
temperature. The problem is reduced to one with the single variational
parameter m by solving the variational equations order-by-order in and
m/T. At the variational point, there are ultraviolet divergences of order
that cannot be removed by any renormalization of the coupling constant. We
define a finite thermodynamic potential by truncating at order in g
and m/T. The associated thermodynamic functions seem to be perturbatively
stable and insensitive to variations in the renormalization scale.Comment: 57 pages, 10 figure
Mass Corrections to the Tau Decay Rate
In this note radiative corrections to the total hadronic decay rate of the
-lepton are studied employing perturbative QCD and the operator product
expansion. We calculate quadratic quark mass corrections to the decay rate
ration to the order and find that they
contribute appreciably to the Cabbibo supressed decay modes of the
-lepton. We also discuss corrections of mass dimension D=4, where we
emphasize the need of a suitable choice of the renormalization scale of the
quark and gluon condensates.Comment: 13 pages, LaTeX, no figures. This version fixes a typo in eq. (25) of
the original paper (Z. Phys. C59 (1993) 525) and an errror in a numerical
integration procedure which has resulted to a significant increase of the
O(\alpha_s^2) coefficient in eq. (27). As a consequence also some tables in
Section 4 have been modifie
Polarization of Prompt J/psi at the Tevatron
The polarization of prompt J/psi at the Fermilab Tevatron is calculated
within the nonrelativistic QCD factorization framework. The contribution from
radiative decays of P-wave charmonium states decreases, but does not eliminate,
the transverse polarization at large transverse momentum. The angular
distribution parameter alpha for leptonic decays of the J/\psi is predicted to
increase from near 0 at p_T = 5 GeV to about 0.5 at p_T = 20 GeV. The
prediction is consistent with measurements by the CDF Collaboration at
intermediate values of p_T, but disagrees by about 3 standard deviations at the
largest values of p_T measured.Comment: 4 pages, 2 figures, one reference added, accepted for publication in
Phys. Rev.
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