4,760 research outputs found
Towards a precision computation of f_Bs in quenched QCD
We present a computation of the decay constant f_Bs in quenched QCD. Our
strategy is to combine new precise data from the static approximation with an
interpolation of the decay constant around the charm quark mass region. This
computation is the first step in demonstrating the feasability of a strategy
for f_B in full QCD. The continuum limits in the static theory and at finite
mass are taken separately and will be further improved.Comment: Lattice2003(heavy), 3 pages, 2 figure
A perturbative study of two four-quark operators in finite volume renormalization schemes
Starting from the QCD Schroedinger functional (SF), we define a family of
renormalization schemes for two four-quark operators, which are, in the chiral
limit, protected against mixing with other operators. With the appropriate
flavour assignments these operators can be interpreted as part of either the
or effective weak Hamiltonians. In view of lattice
QCD with Wilson-type quarks, we focus on the parity odd components of the
operators, since these are multiplicatively renormalized both on the lattice
and in continuum schemes. We consider 9 different SF schemes and relate them to
commonly used continuum schemes at one-loop order of perturbation theory. In
this way the two-loop anomalous dimensions in the SF schemes can be inferred.
As a by-product of our calculation we also obtain the one-loop cutoff effects
in the step-scaling functions of the respective renormalization constants, for
both O(a) improved and unimproved Wilson quarks. Our results will be needed in
a separate study of the non-perturbative scale evolution of these operators.Comment: 22 pages, 4 figure
Investigation of the fine structure of antihydrogen.
At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2-5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2-2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2-2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system
String breaking and lines of constant physics in the SU(2) Higgs model
We present results for the ground state and first excited state static
potentials in the confinement "phase" of the SU(2) Higgs model. String breaking
and the crossing of the energy levels are clearly visible. We address the
question of the cut-off effects in our results and observe a remarkable scaling
of the static potentials.Comment: LATTICE99(Higgs), 3 pages, 4 figure
Effective heavy-light meson energies in small-volume quenched QCD
We study effective energies of heavy-light meson correlation functions in
lattice QCD and a small volume of (0.2 fm)^4 to non-perturbatively calculate
their dependence on the heavy quark mass in the continuum limit. Our quenched
results obtained here constitute an essential intermediate step of a first
fully non-perturbative computation of the b-quark's mass in the static
approximation that has recently been presented as an application of a new
proposal to non-perturbatively renormalize the Heavy Quark Effective Theory.
The renormalization constant and the improvement coefficients relating the
renormalized current and subtracted quark mass are determined in the relevant
parameter region at weak couplings, which allows to perform the numerical
simulations at several, precisely fixed values of the renormalization group
invariant heavy quark mass in a range from 3 GeV to 15 GeV.Comment: 24 pages including figures and tables, latex2e; version published in
JHEP, small additions, results unchange
A strategy for implementing non-perturbative renormalisation of heavy-light four-quark operators in the static approximation
We discuss the renormalisation properties of the complete set of four-quark operators with the heavy quark treated in the static
approximation. We elucidate the role of heavy quark symmetry and other symmetry
transformations in constraining their mixing under renormalisation. By
employing the Schroedinger functional, a set of non-perturbative
renormalisation conditions can be defined in terms of suitable correlation
functions. As a first step in a fully non-perturbative determination of the
scale-dependent renormalisation factors, we evaluate these conditions in
lattice perturbation theory at one loop. Thereby we verify the expected mixing
patterns and determine the anomalous dimensions of the operators at NLO in the
Schroedinger functional scheme. Finally, by employing twisted-mass QCD it is
shown how finite subtractions arising from explicit chiral symmetry breaking
can be avoided completely.Comment: 41 pages, 6 figure
Non-perturbative renormalization of the static axial current in two-flavour QCD
We perform the non-perturbative renormalization of matrix elements of the
static-light axial current by a computation of its scale dependence in lattice
QCD with two flavours of massless O(a) improved Wilson quarks. The
regularization independent factor that relates any running renormalized matrix
element of the axial current in the static effective theory to the
renormalization group invariant one is evaluated in the Schroedinger functional
scheme, where in this case we find a significant deviation of the
non-perturbative running from the perturbative prediction. An important
technical ingredient to improve the precision of the results consists in the
use of modified discretizations of the static quark action introduced earlier
by our collaboration. As an illustration how to apply the renormalization of
the static axial current presented here, we connect the bare matrix element of
the current to the B_s-meson decay constant in the static approximation for one
value of the lattice spacing, a ~ 0.08 fm, employing large-volume N_f=2 data at
beta=5.3.Comment: 33 pages including figures and tables, latex2e, uses JHEP3.cls;
version published in JHEP, small additions, results unchange
Mississippi Health Project Annual Report No. 5
The Mississippi Health Project was Great Depression era public health initiative sponsored by Alpha Kappa Alpha Sorority, Inc. The project aimed to provide proper health care to the African American community in the Mississippi Delta. This group often lacked access to proper health care.https://dh.howard.edu/aka_misshealth/1003/thumbnail.jp
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