100 research outputs found
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.Comment: USQCD whitepape
Short-distance matrix elements for D0-meson mixing from Nf=2+1 lattice QCD
We calculate in three-flavor lattice QCD the short-distance hadronic matrix elements of all five ΔC=2 four-fermion operators that contribute to neutral
D-meson mixing both in and beyond the Standard Model. We use the MILC Collaboration’s Nf=2+1 lattice gauge-field configurations generated with asqtad-improved staggered sea quarks. We also employ the asqtad action for the valence light quarks and use the clover action with the Fermilab interpretation for the charm quark. We analyze a large set of ensembles with pions as light as lattice gauge-field configurations generated with asqtad-improved staggered sea quarks. We also employ the asqtad action for the valence light quarks and use the clover action with the Fermilab interpretation for the charm quark. We analyze a large set of ensembles with pions as light as Mπ ≈ 180 MeV and lattice spacings as fine as a ≈ 0.045 fm, thereby enabling good control over the extrapolation to the physical pion mass and continuum limit. We obtain for the matrix elements in the MS−NDR scheme using the choice of evanescent operators proposed by Beneke et al., evaluated at 3 GeV, ⟨D0|Oi|¯D0⟩ = {0.0805(55)16),−0.1561(70)(31), 0.0464(31)(9), 0.2747(129)(55), 0.1035(71)(21)} GeV4 (i=1–5). The errors shown are from statistics and lattice systematics, and the omission of charmed sea quarks, respectively. To illustrate the utility of our matrix-element results, we place bounds on the scale of CP-violating new physics in D0 mixing, finding lower limits of about 10–50×103 TeV for couplings of O(1). To enable our results to be employed in more sophisticated or model-specific phenomenological studies, we provide the correlations among our matrix-element results. For convenience, we also present numerical results in the other commonly used scheme of Buras, Misiak, and Urban
-mixing matrix elements from lattice QCD for the Standard Model and beyond
We calculate---for the first time in three-flavor lattice QCD---the hadronic
matrix elements of all five local operators that contribute to neutral -
and -meson mixing in and beyond the Standard Model. We present a complete
error budget for each matrix element and also provide the full set of
correlations among the matrix elements. We also present the corresponding bag
parameters and their correlations, as well as specific combinations of the
mixing matrix elements that enter the expression for the neutral -meson
width difference. We obtain the most precise determination to date of the
SU(3)-breaking ratio , where the second error stems from
the omission of charm sea quarks, while the first encompasses all other
uncertainties. The threefold reduction in total uncertainty, relative to the
2013 Flavor Lattice Averaging Group results, tightens the constraint from
mixing on the Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle. Our
calculation employs gauge-field ensembles generated by the MILC Collaboration
with four lattice spacings and pion masses close to the physical value. We use
the asqtad-improved staggered action for the light valence quarks, and the
Fermilab method for the bottom quark. We use heavy-light meson chiral
perturbation theory modified to include lattice-spacing effects to extrapolate
the five matrix elements to the physical point. We combine our results with
experimental measurements of the neutral -meson oscillation frequencies to
determine the CKM matrix elements ,
, and , which differ from CKM-unitarity expectations by about
2. These results and others from flavor-changing-neutral currents point
towards an emerging tension between weak processes that are mediated at the
loop and tree levels.Comment: 75 pp, 17 figs. Ver 2 fixes typos; corrects mistakes resulting in
slight changes to results, correlation matrices; updates decay constants to
agree with recent PDG update; corrects uncertainties for tree-level CKM
matrix elements used in comparison, slightly reducing tensions; includes
additional analyses that support mostly-nonperturbative matching; expands
discussion of isospin-breaking effect
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