707 research outputs found
Instantaneous Bethe-Salpeter Equation and Its Exact Solution
We present an approach to solve a Bethe-Salpeter (BS) equation exactly
without any approximation if the kernel of the BS equation exactly is
instantaneous, and take positronium as an example to illustrate the general
features of the solutions. As a middle stage, a set of coupled and
self-consistent integration equations for a few scalar functions can be
equivalently derived from the BS equation always, which are solvable
accurately. For positronium, precise corrections to those of the Schr\"odinger
equation in order (relative velocity) in eigenfunctions, in order in
eigenvalues, and the possible mixing, such as that between () and
() components in () states as well, are
determined quantitatively. Moreover, we also point out that there is a
problematic step in the classical derivation which was proposed first by E.E.
Salpeter. Finally, we emphasize that for the effective theories (such as NRQED
and NRQCD etc) we should pay great attention on the corrections indicated by
the exact solutions.Comment: 4 pages, replace for shortening the manuscrip
QCD Radiative Corrections to the Leptonic Decay Rate of the B_c Meson
The QCD radiative corrections to the leptonic decay rate of the meson
are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate
short-distance and long-distance effects. The decay constant is factored
into a sum of NRQCD matrix elements each multiplied by a short-distance
coefficient. The short-distance coefficient for the leading matrix element is
calculated to order by matching a perturbative calculation in full
QCD with the corresponding perturbative calculation in NRQCD. This
short-distance correction decreases the leptonic decay rate by approximately
.Comment: Changed Eq. 2 to read 1/(8 \pi), put in a missing i M_{B_c} in Eq.
18, and put in a normalisation factor of 2 M_{B_c} in Eq. 19
CP Violation from Dimensional Reduction: Examples in 4+1 Dimensions
We provide simple examples of the generation of complex mass terms and hence
CP violation through dimensional reduction.Comment: 6 pages, typos corrected, 1 reference adde
Poor screening and nonadiabatic superconductivity in correlated systems
In this paper we investigate the role of the electronic correlation on the
hole doping dependence of electron-phonon and superconducting properties of
cuprates. We introduce a simple analytical expression for the one-particle
Green's function in the presence of electronic correlation and we evaluate the
reduction of the screening properties as the electronic correlation increases
by approaching half-filling. The poor screening properties play an important
role within the context of the nonadiabatic theory of superconductivity. We
show that a consistent inclusion of the reduced screening properties in the
nonadiabatic theory can account in a natural way for the - phase
diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review
Hadron yields and spectra in Au+Au collisions at the AGS
Inclusive double differential multiplicities and rapidity density
distributions of hadrons are presented for 10.8 A GeV/c Au+Au collisions as
measured at the AGS by the E877 collaboration. The results indicate that large
amounts of stopping and collective transverse flow effects are present. The
data are also compared to the results from the lighter Si+Al system.Comment: 12 pages, latex, 10 figures, submitted to Nuclear Physics A (Quark
Matter 1996 Proceedings
Nonequilibrium Evolution of Correlation Functions: A Canonical Approach
We study nonequilibrium evolution in a self-interacting quantum field theory
invariant under space translation only by using a canonical approach based on
the recently developed Liouville-von Neumann formalism. The method is first
used to obtain the correlation functions both in and beyond the Hartree
approximation, for the quantum mechanical analog of the model. The
technique involves representing the Hamiltonian in a Fock basis of annihilation
and creation operators. By separating it into a solvable Gaussian part
involving quadratic terms and a perturbation of quartic terms, it is possible
to find the improved vacuum state to any desired order. The correlation
functions for the field theory are then investigated in the Hartree
approximation and those beyond the Hartree approximation are obtained by
finding the improved vacuum state corrected up to . These
correlation functions take into account next-to-leading and
next-to-next-to-leading order effects in the coupling constant. We also use the
Heisenberg formalism to obtain the time evolution equations for the equal-time,
connected correlation functions beyond the leading order. These equations are
derived by including the connected 4-point functions in the hierarchy. The
resulting coupled set of equations form a part of infinite hierarchy of coupled
equations relating the various connected n-point functions. The connection with
other approaches based on the path integral formalism is established and the
physical implications of the set of equations are discussed with particular
emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with
non-equilibrium evolution beyond Hartree approx. based on the LvN formalism,
has been adde
Measurement of the D+ and Ds+ decays into K+K-K+
We present the first clear observation of the doubly Cabibbo suppressed decay
D+ --> K-K+K+ and the first observation of the singly Cabibbo suppressed decay
Ds+ --> K-K+K+. These signals have been obtained by analyzing the high
statistics sample of photoproduced charm particles of the FOCUS(E831)
experiment at Fermilab. We measure the following relative branching ratios:
Gamma(D+ --> K-K+K+)/Gamma(D+ --> K-pi+pi+) = (9.49 +/- 2.17(statistical) +/-
0.22(systematic))x10^-4 and Gamma(Ds+ --> K-K+K+)/Gamma(Ds+ --> K-K+pi+) =
(8.95 +/- 2.12(statistical) +2.24(syst.) -2.31(syst.))x10^-3.Comment: 10 pages, 8 figure
New Measurements of the D+ to K* mu nu Form Factor Ratios
Using a large sample of D+ to K- pi+ mu+ nu decays collected by the FOCUS
photoproduction experiment at Fermilab, we present new measurements of two
semileptonic form factor ratios: rv and r2. We find rv = 1.504 \pm 0.057 \pm
0.039 and r2 = 0.875 \pm 0.049 \pm 0.064. Our form factor results include the
effects of the s-wave interference discussed in a previous paper.Comment: 12 pages, 5 figure
Study of Hadronic Five-Body Decays of Charmed Mesons
We study the decay of D+ and Ds+ mesons into charged five body final states,
and report the discovery of the decay mode D+ -> K+K-Pi+Pi+Pi-, as well as
measurements of the decay modes D+ -> K-Pi+Pi+Pi+Pi-, Ds+ -> K+K-Pi+Pi+Pi-, Ds+
-> PhiPi+Pi+Pi- and D+/Ds+ -> Pi+Pi+Pi+Pi-Pi-. An analysis of the resonant
substructure is also included, with evidence suggesting that both decays
proceed primarily through an a1 vector resonance.Comment: 11 pages, 3 figure
Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-
Using the FOCUS spectrometer with photon beam energies between 20 and 160
\gev, we confirm the existence of a diffractively photoproduced enhancement in
at 1750 \mevcc with nearly 100 times the statistics of previous
experiments. Assuming this enhancement to be a single resonance with a
Breit-Wigner mass shape, we determine its mass to be
\mevcc and its width to be \mevcc. We find no
corresponding enhancement at 1750 \mevcc in , and again neglecting any
possible interference effects we place limits on the ratio . Our results are consistent with previous
photoproduction experiments, but, because of the much greater statistics,
challenge the common interpretation of this enhancement as the
seen in annihilation experiments.Comment: 10 pages, 5 figure
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