890 research outputs found
Precision lattice QCD calculations and predictions of fundamental physics in heavy quark systems
I describe the recent success in performing accurate calculations of the
effects of the strong force on particles containing bottom and charm quarks.
Since quarks are never seen in isolation, and so cannot be studied directly,
numerical simulations are key to understanding the properties of these
particles and extracting information about the quarks. The results have direct
impact on the worldwide experimental programme that is aiming to determine the
parameters of the Standard Model of particle physics precisely and thereby
uncover or constrain the possibilities for physics beyond the Standard Model.
The numerical simulation of the strong force is a huge computational task and
the recent success is the result of international collaboration in developing
techniques that are fast enough to do the calculations on powerful
supercomputers.Comment: Invited talk at SCIDAC 2006, Denver, June 2006. 15 page
Accurate Determinations of from Realistic Lattice QCD
We obtain a new value for the QCD coupling constant by combining lattice QCD
simulations with experimental data for hadron masses. Our lattice analysis is
the first to: 1) include vacuum polarization effects from all three light-quark
flavors (using MILC configurations); 2) include third-order terms in
perturbation theory; 3) systematically estimate fourth and higher-order terms;
4) use an unambiguous lattice spacing; and 5) use an \order(a^2)-accurate QCD
action. We use 28~different (but related) short-distance quantities to obtain
.Comment: 4 pages, 2 figures, 1 table. The revised version differs from the
original because we now use 4-loop beta functions (rather than 3-loop). This
shifts the answer a little (mostly from the evolution from the lattice scale
to M_z -- lattice results aren't very different) and reduces the error
slightl
Quarkonium mass splittings in three-flavor lattice QCD
We report on calculations of the charmonium and bottomonium spectrum in
lattice QCD. We use ensembles of gauge fields with three flavors of sea quarks,
simulated with the asqtad improved action for staggered fermions. For the heavy
quarks we employ the Fermilab interpretation of the clover action for Wilson
fermions. These calculations provide a test of lattice QCD, including the
theory of discretization errors for heavy quarks. We provide, therefore, a
careful discussion of the results in light of the heavy-quark effective
Lagrangian. By and large, we find that the computed results are in agreement
with experiment, once parametric and discretization errors are taken into
account.Comment: 21 pages, 17 figure
Prospects for the Bc Studies at LHCb
We discuss the motivations and perspectives for the studies of the mesons of
the (bc) family at LHCb. The description of production and decays at LHC
energies is given in details. The event yields, detection efficiencies, and
background conditions for several Bc decay modes at LHCb are estimated.Comment: 20 pages, 5 eps-figure
Tuning Fermilab Heavy Quarks in 2+1 Flavor Lattice QCD with Application to Hyperfine Splittings
We report the non-perturbative tuning of parameters--- kappa_c, kappa_b, and
kappa_crit ---that determine the heavy-quark mass in the Fermilab action. This
requires the computation of the masses of Ds^(*) and Bs^(*) mesons comprised of
a Fermilab heavy quark and a staggered light quark. Additionally, we report the
hyperfine splittings for Ds and Bs mesons as a cross-check of our simulation
and analysis methods. We find a splitting of 145 +/- 15 MeV for the Ds system
and 40 +/- 9 MeV for the Bs system. These are in good agreement with the
Particle Data Group average values of 143.9 +/- 0.4 MeV and 46.1 +/- 1.5 MeV,
respectively. The calculations are carried out with the MILC 2+1 flavor gauge
configurations at three lattice spacings approximately 0.15, 0.12, and 0.09
fm.Comment: 34 pages, 8 figures, 26 tables; some sections rearranged for clarity;
conclusions unchanged; version accepted by Phys. Rev.
Progress in the Development of the 1 m Model of the 70 mm Aperture Quadrupole for the LHC Low- Insertions
Within the LHC magnet development program Oxford Instruments has built a one metre model of the 70Â mm aperture low-beta quadrupole. The magnet features a four layer coil wound from two 8.2 mm wide graded NbTi cables, and is designed for 250Â T/m at 1.9Â K. The magnet has previously been tested between 4.5Â K and 2.3Â K. In this paper we review the magnet rebuild and the subsequent tests. Results on magnet training at 4.3Â K and 1.9Â K are presented along with the results related to quench protection studies.
Sorafenib for the treatment of advanced hepatocellular cancer – a UK audit
Aims:
Sorafenib is the current standard treatment for advanced hepatocellular carcinoma. We carried out a national audit of UK patients treated with sorafenib as standard-of-care and those treated with systemic therapy in first-line trials.
Materials and methods:
Sorafenib-treated and trial-treated patients were identified via the Cancer Drugs Fund and local databases. Data were collected retrospectively from medical records according to a standard case report form. The primary outcome measure was overall survival, estimated by the Kaplan–Meier method.
Results:
Data were obtained for 448 sorafenib-treated patients from 15 hospitals. The median age was 68 years (range 17–89) and 75% had performance status ≤ 1. At baseline, 77% were Child-Pugh A and 16.1% Child-Pugh B; 38% were albumin–bilirubin grade 1 (ALBI-1) and 48% ALBI-2; 23% were Barcelona Clinic Liver Classification B (BCLC-B) and 72% BCLC-C. The median time on sorafenib was 3.6 months, with a mean daily dose of 590 mg. The median overall survival for 448 evaluable sorafenib-treated patients was 8.5 months. There were significant differences in overall survival comparing Child-Pugh A versus Child-Pugh B (9.5 versus 4.6 months), ALBI-1 versus ALBI-2 (12.9 versus 5.9 months) and BCLC-B versus BCLC-C (13.0 versus 8.3 months). For trial-treated patients (n = 109), the median overall survival was 8.1 months and this was not significantly different from the sorafenib-treated patients.
Conclusion:
For Child-Pugh A patients with good performance status, survival outcomes were similar to those reported in global randomised controlled trials. Patients with ALBI grade > 1, Child-Pugh B or poor performance status seem to derive limited benefit from sorafenib treatment
NLO QCD Corrections to -to-Charmonium Form Factors
The meson to S-wave Charmonia transition form factors are
calculated in next-to-leading order(NLO) accuracy of Quantum
Chromodynamics(QCD). Our results indicate that the higher order corrections to
these form factors are remarkable, and hence are important to the
phenomenological study of the corresponding processes. For the convenience of
comparison and use, the relevant expressions in asymptotic form at the limit of
for the radiative corrections are presented
Application of heavy-quark effective theory to lattice QCD: II. Radiative corrections to heavy-light currents
We apply heavy-quark effective theory to separate long- and short-distance
effects of heavy quarks in lattice gauge theory. In this approach, the inverse
heavy-quark mass and the lattice spacing are treated as short distances, and
their effects are lumped into short-distance coefficients. We show how to use
this formalism to match lattice gauge theory to continuum QCD, order by order
in the heavy-quark expansion. In this paper, we focus on heavy-light currents.
In particular, we obtain one-loop results for the matching factors of lattice
currents, needed for heavy-quark phenomenology, such as the calculation of
heavy-light decay constants, and heavy-to-light transition form factors.
Results for the Brodsky-Lepage-Mackenzie scale are also given.Comment: 32 pages, 8 figures. v2 corrects Eqs. (4.9) and (4.10) and adds a
reference. Program LatHQ2QCD to compute matching one-loop coefficients
available at http://theory.fnal.gov/people/kronfeld/LatHQ2QCD
Weak decays of the B_c meson to charmonium and D mesons in the relativistic quark model
Semileptonic and nonleptonic decays of the B_c meson to charmonium and D
mesons are studied in the framework of the relativistic quark model. The decay
form factors are explicitly expressed through the overlap integrals of the
meson wave functions in the whole accessible kinematical range. The
relativistic meson wave functions are used for the calculation of the decay
rates. The obtained results are compared with the predictions of other
approaches.Comment: 27 pages, 17 figures, 1 figure and 1 reference added, version to
appear in Phys. Rev.
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