arXiv subjects

A. El-Khadra

Publications and source records attributed to A. El-Khadra.

8 recordsLinked to original sources

arXiv2026

Towards a formalism for $ππ$ scattering from staggered lattice QCD

Scattering processes featuring the strong interactions can be studied using lattice QCD by means of the Lüscher formalism. This approach relies on analyticity and unitarity of the $S$-matrix to relate infinite-volume scattering amplitudes to finite-volume energy levels. However, lattice QCD simulations employing rooted staggered fermions manifest unitarity violation as an $\mathcal{O}(a^2)$ lattice artifact. Moreover, the meson sector of this theory contains multiple non-mass-degenerate pions (due to the so-called taste splitting), which only reduce to the physical pion in the continuum limit. These features restrict the applicability of the Lüscher formalism to staggered lattice data at non-zero lattice spacing. Hence, in this work, we discuss two complementary approaches to deal with the challenges of extracting $ππ$ scattering amplitudes from lattice QCD with staggered quarks: (1) using the corresponding effective theory, Rooted Staggered Chiral Perturbation Theory, to calculate one-loop amplitudes for the first time. These amplitudes can be used to explicitly check the validity of the quantization condition. And (2) generalizing the formalism to incorporate taste-splitting as well as fourth-rooting effects. We focus on the simpler case of $ππ$ scattering in the isospin-2 channel, and discuss prospects for other channels.

hep-lat↗

arXiv2017

$\overline{B}\rightarrow D^\ast\ell\overlineν$ at non-zero recoil

We present preliminary results from our analysis of the form factors for the $\overline{B}\rightarrow D^\ast\ell\overlineν$ decay at non-zero recoil. Our analysis includes 15 MILC asqtad ensembles with $N_f=2+1$ flavors of sea quarks and lattice spacings ranging from $a\approx 0.15$ fm down to $0.045$ fm. The valence light quarks employ the asqtad action, whereas the heavy quarks are treated using the Fermilab action. We conclude with a discussion of future plans and phenomenological implications. When combined with experimental measurements of the decay rate, our calculation will enable a determination of the CKM matrix element $|V_{cb}|$.

hep-lat↗

arXiv2009

Update on onium masses with three flavors of dynamical quarks

We update results presented at Lattice 2005 on charmonium masses. New ensembles of gauge configurations with 2+1 flavors of improved staggered quarks have been analyzed. Statistics have been increased for other ensembles. New results are also available for P-wave mesons and for bottomonium on selected ensembles.

hep-lat↗

arXiv2005

Onium Masses with Three Flavors of Dynamical Quarks

We have greatly extended an earlier calculation of the charmonium spectrum on three flavor dynamical quark ensembles by using more recent ensembles generated by the MILC collaboration. The heavy quarks are treated using the Fermilab formulation. The charmonium state masses are in reasonable agreement with the observed spectrum; however, some of the spin splittings may still be too small.

hep-lat↗

arXiv2004

Semileptonic decays of $D$ mesons in three-flavor lattice QCD

We present the first three-flavor lattice QCD calculations for $D\to πlν$ and $D\to K lν$ semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1/8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at $q^2=0$ are $f_+^{D\toπ}(0)=0.64(3)(6)$ and $f_+^{D\to K}(0) = 0.73(3)(7)$, where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the CKM matrix elements $|V_{cd}|=0.239(10)(24)(20)$ and $|V_{cs}|=0.969(39)(94)(24)$, where the last errors are from experimental uncertainties.

hep-ph↗

arXiv2003

High-Precision Lattice QCD Confronts Experiment

We argue that high-precision lattice QCD is now possible, for the first time, because of a new improved staggered quark discretization. We compare a wide variety of nonperturbative calculations in QCD with experiment, and find agreement to within statistical and systematic errors of 3% or less. We also present a new determination of alpha_msbar(Mz); we obtain 0.121(3). We discuss the implications of this breakthrough for phenomenology and, in particular, for heavy-quark physics.

hep-lat↗

arXiv2002

B Physics at the Tevatron: Run II and Beyond

This report provides a comprehensive overview of the prospects for B physics at the Tevatron. The work was carried out during a series of workshops starting in September 1999. There were four working groups: 1) CP Violation, 2) Rare and Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and Spectroscopy. The report also includes introductory chapters on theoretical and experimental tools emphasizing aspects of B physics specific to hadron colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a Summary.

hep-ph↗

arXiv1997

Structure Function Subgroup Summary

We summarize the studies and discussions of the Structure Function subgroup of the QCD working group of the Snowmass 1996 Workshop: New Directions for High Energy Physics.

hep-ph↗