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Aida X. El-Khadra

Publications and source records attributed to Aida X. El-Khadra.

At least 37 records · Page 2Linked to original sources
arXiv2020

Framework for simulating gauge theories with dipolar spin systems

Gauge theories appear broadly in physics, ranging from the standard model of particle physics to long-wavelength descriptions of topological systems in condensed matter. However, systems with sign problems are largely inaccessible to classical computations and also beyond the current limitations of digital quantum hardware. In this work, we develop an analog approach to simulating gauge theories with an experimental setup that employs dipolar spins (molecules or Rydberg atoms). We consider molecules fixed in space and interacting through dipole-dipole interactions, avoiding the need for itinerant degrees of freedom. Each molecule represents either a site or gauge degree of freedom, and Gauss law is preserved by a direct and programmatic tuning of positions and internal state energies. This approach can be regarded as a form of analog systems programming and charts a path forward for near-term quantum simulation. As a first step, we numerically validate this scheme in a small-system study of U(1) quantum link models in (1+1) dimensions with link spin S = 1/2 and S = 1 and illustrate how dynamical phenomena such as string inversion and string breaking could be observed in near-term experiments. Our work brings together methods from atomic and molecular physics, condensed matter physics, high-energy physics, and quantum information science for the study of nonperturbative processes in gauge theories.

quant-ph↗
arXiv2020

(1+1)-d U(1) Quantum link models from effective Hamiltonians of dipolar molecules

We study the promising idea of using dipolar molecular systems as analog quantum simulators for quantum link models, which are discrete versions of lattice gauge theories. In a quantum link model the link variables have a finite number of degrees of freedom and discrete values. We construct the effective Hamiltonian of a system of dipolar molecules with electric dipole-dipole interactions, where we use the tunable parameters of the system to match it to the target Hamiltonian describing a U(1) quantum link model in 1+1 dimensions.

hep-lat↗
arXiv2019

The \boldmath$B\to D^\ast\ellν$ semileptonic decay at nonzero recoil and its implications for $\ |V_{cb}\ |$ and $R(D^\ast)$

We present nearly final results from our analysis of the form factors for $B\to D^\ast\ellν$ decay at nonzero recoil. Our analysis includes 15 MILC asqtad ensembles with $N_f=2+1$ flavors of sea quarks and lattice spacings ranging from $a\approx0.15$ fm down to $0.045$ fm. The valence light quarks employ the asqtad action, whereas the $b$ and $c$ quarks are treated using the Fermilab action. We discuss the impact that our results will have on $\ |V_{cb}\ |$ and $R(D^\ast)$.

hep-lat↗
arXiv2019

Opportunities for lattice QCD in quark and lepton flavor physics

This document is one of a series of whitepapers from the USQCD collaboration. Here, we discuss opportunities for lattice QCD in quark and lepton flavor physics. New data generated at Belle II, LHCb, BES III, NA62, KOTO, and Fermilab E989, combined with precise calculations of the relevant hadronic physics, may reveal what lies beyond the Standard Model. We outline a path toward improvements of the precision of existing lattice-QCD calculations and discuss groundbreaking new methods that allow lattice QCD to access new observables.

hep-lat↗
arXiv2019

Disconnected hadronic vacuum polarization contribution to the muon g-2 with HISQ

We describe a computation of the contribution to the anomalous magnetic moment of the muon from the disconnected part of the hadronic vacuum polarization. We use the highly-improved staggered quark (HISQ) formulation for the current density with gauge configurations generated with four flavors of HISQ sea quarks. The computation is performed by stochastic estimation of the current density using the truncated solver method combined with deflation of low-modes. The parameters are tuned to minimize the computational cost for a given target uncertainty in the current-current correlation function. The calculation presented here is carried out on a single gauge-field ensemble of size $32^3\times48$ with an approximate lattice spacing of $\sim0.15$ fm and with physical sea-quark masses. We describe the methodology and the analysis procedure

hep-lat↗
arXiv2019

$B\to D^\ast\ellν$ at non-zero recoil

We present preliminary blinded results from our analysis of the form factors for $B\rightarrow D^\ast\ellν$ 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 $b$ and $c$ quarks are treated using the Fermilab action. We discuss the impact that our results will have on $\left|V_{cb}\right|$ and $R(D^\ast)$.

hep-lat↗
arXiv2014

Review of lattice results concerning low energy particle physics

We review lattice results related to pion, kaon, D- and B-meson physics with the aim of making them easily accessible to the particle physics community. More specifically, we report on the determination of the light-quark masses, the form factor f+(0), arising in semileptonic K -> pi transition at zero momentum transfer, as well as the decay constant ratio fK/fpi of decay constants and its consequences for the CKM matrix elements Vus and Vud. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)LxSU(2)R and SU(3)LxSU(3)R Chiral Perturbation Theory and review the determination of the BK parameter of neutral kaon mixing. The inclusion of heavy-quark quantities significantly expands the FLAG scope with respect to the previous review. Therefore, for this review, we focus on D- and B-meson decay constants, form factors, and mixing parameters, since these are most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. In addition we review the status of lattice determinations of the strong coupling constant alpha_s.

hep-lat↗
arXiv2014

Quark Flavor Physics Review

I review the status of lattice-QCD calculations relevant to quark flavor physics. The recent availability of physical-mass ensembles with large physical volumes generated by a growing number of lattice collaborations is an exciting development and I discuss their impact on the landscape of lattice flavor physics calculations. The activities of the newly formed FLAG-2 collaboration which provides averages of quantities calculated in lattice QCD that are relevant for quark flavor physics are also discussed. My talk covers (a subset of) the same quantities reviewed by FLAG-2, including results for $K$, $D_{(s)}$, and $B_{(s)}$ meson decay constants and semileptonic decay form factors, as well as for hadronic matrix elements of neutral ($K$, $D$, and $B_{(s)}$) meson mixing. I also briefly discuss recent progress towards understanding nonleptonic $K$ decay and long-distance contributions to $Δm_K$.

hep-lat↗
arXiv2013

Semileptonic decays $B\rightarrow D^{(*)}lν$ at nonzero recoil

We have analyzed the semileptonic decays $B\rightarrow D\ellν$ and $B\rightarrow D^*\ellν$ on the full suite of MILC (2+1)-flavor asqtad ensembles with lattice spacings as small as 0.045 fm and light-to-strange-quark mass ratios as low as 1/20. We use the Fermilab interpretation of the clover action for heavy valence quarks and the asqtad action for light valence quarks. We compute the hadronic form factors for $B\rightarrow D$ at both zero and nonzero recoil and for $B\rightarrow D^*$ at zero recoil. We report our results for $|V_{cb}|$.

hep-lat↗
arXiv2012

Form factors for semi-leptonic B decays

We report on form factors for the B->K l^+ l^- semi-leptonic decay process. We use several lattice spacings from a=0.12 fm down to 0.06 fm and a variety of dynamical quark masses with 2+1 flavors of asqtad quarks provided by the MILC Collaboration. These ensembles allow good control of the chiral and continuum extrapolations. The b-quark is treated as a clover quark with the Fermilab interpretation. We update our results for f_\parallel and f_\perp, or, equivalently, f_+ and f_0. In addition, we present new results for the tensor form factor f_T. Model independent results are obtained based upon the z-expansion.

hep-lat↗
arXiv2011

Form factors for $B$ to $Kll$ semileptonic decay from three-flavor lattice QCD

We study the $B \to Kl^+l^-$ semileptonic decay process in three-flavor lattice QCD. We analyze several ensembles generated by the MILC collaboration at different lattice spacings and sea-quark masses. We use the asqtad improved staggered action for the light quarks and the clover action with the Fermilab interpretation for the heavy $b$ quark. We present preliminary results for the vector current induced form factors for a range of kaon energies. Our analysis includes chiral and continuum extrapolations based on SU(2) staggered χPT.

hep-lat↗
arXiv2007

A determination of the B_s^0 and B_d^0 mixing parameters in 2+1 lattice QCD

We report on the advances in our unquenched calculation of the matrix elements relevant for the analysis of B^0-\bar B^0 mixing using the Asqtad (light quark) and Fermilab (heavy quark) actions. We have calculated the hadronic parameters for the mass and width differences in the neutral B meson system. Preliminary results are presented for f_{B_q}^2 B_q as well as for the ratio ξ^2=f_{B_s}^2 B_{B_s}/f_{B_d}^2 B_{B_d}.

hep-lat↗
arXiv2007

Perturbative matching of heavy-light currents at one-loop

We present results of a perturbative matching calculation performed at one-loop for heavy-light currents. We use the Fermilab action for the heavy quarks, the Asqtad action for the light quarks, and an improved gluon action. We also present results for heavy-heavy currents with Fermilab heavy quarks and improved glue.

hep-lat↗
arXiv2003

www.fermiqcd.net

A quick review of the features of FermiQCD, a C++ library for fast development of parallel Lattice QCD applications. FermiQCD is fully Object Oriented and is based on MPI but, it required no previsius knowledge of parallel programming. It includes parallel algorithms for Wilson, Clover, Staggered, Asqtad and Domain Wall fermions. Optimizations are based on M. Luescher's SSE2 macros.

hep-lat↗
arXiv2003

D_s spectrum and leptonic decays with Fermilab heavy quarks and improved staggered light quarks

We present preliminary results for the D_s meson spectrum and decay constants in unquenched lattice QCD. Simulations are carried out with 2+1 dynamical quarks using gauge configurations generated by the MILC collaboration. We use the ``asqtad'' a^2 improved staggered action for the light quarks, and the clover heavy quark action with the Fermilab interpretation. We compare our spectrum results with the newly discovered 0+ and 1+ states in the D_s system.

hep-lat↗
arXiv2003

Semileptonic decays of $D$ mesons in unquenched lattice QCD

We present our preliminary results for semileptonic form factors of $D$ mesons in unquenched lattice QCD. Simulations are carried out with $n_f=2+1$ dynamical quarks using gauge configurations generated by the MILC collaboration. For the valence quarks, we adopt an improved staggered light quark action and the clover heavy quark action. Our results for $D \to K$ and $D \to π$ form factors at $q^2=0$ are in agreement with the experimental values.

hep-lat↗
arXiv2002

Charmonium with three flavors of dynamical quarks

We present a calculation of the charmonium spectrum with three flavors of dynamical staggered quarks from gauge configurations that were generated by the MILC collaboration. We use the Fermilab action for the valence charm quarks. Our calculation of the spin-averaged 1P--1S and 2S--1S splittings yields a determination of the strong coupling, with $\ams(M_Z) = 0.119 (4)$.

hep-lat↗