arXiv : Opportunities for lattice QCD in quark and lepton flavor physics

Lehner, Christoph; Christ, Norman H.; Hansen, Maxwell T.; Neil, Ethan T.; Sharpe, Stephen R.; Laiho, Jack; Van de Water, Ruth S.; Blum, Tom; Meinel, Stefan; Kronfeld, Andreas S.; El-Khadra, Aida X.

doi:10.1140/epja/i2019-12891-2

Article
Report number	arXiv:1904.09479 ; FERMILAB-PUB-19-173-T ; RBRC-1309
Title	Opportunities for lattice QCD in quark and lepton flavor physics
Author(s)	Lehner, Christoph (Brookhaven) ; Meinel, Stefan (Arizona U. ; RIKEN BNL) ; Blum, Tom (Connecticut U.) ; Christ, Norman H. (Columbia U.) ; El-Khadra, Aida X. (Illinois U., Urbana) ; Hansen, Maxwell T. (CERN) ; Kronfeld, Andreas S. (Fermilab) ; Laiho, Jack (Syracuse U.) ; Neil, Ethan T. (Colorado U. ; RIKEN BNL) ; Sharpe, Stephen R. (Washington U., Seattle) ; Van de Water, Ruth S. (Fermilab)
Publication	2019-11-14
Imprint	2019-04-20
Number of pages	19
Note	USQCD whitepaper
In:	Eur. Phys. J. A 55 (2019) 195
DOI	10.1140/epja/i2019-12891-2
Subject category	hep-ph ; Particle Physics - Phenomenology ; hep-ex ; Particle Physics - Experiment ; hep-lat ; Particle Physics - Lattice
Accelerator/Facility, Experiment	LATTICE USQCD
Abstract	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.
Copyright/License	publication: © 2019-2025 Societa Italiana di Fisica / Springer-Verlag GmbH Germany preprint: (License: arXiv nonexclusive-distrib 1.0)

$Indirect searches for new physics in the flavor sector and searches at high transverse momentum are complementary. Here one sees the constraints on the mass and coupling of a vector leptoquark $U$ \cite{Buttazzo:2017ixm}. The regions labeled ``$1\sigma$'' and ``$2\sigma$'' can explain the currently observed anomalies in two classes of $B$-meson decays, observed primarily by LHCb, Babar, and Belle (see Fig.~\protect\ref{fig:Banomalies}). The shaded regions in the left and top-left parts of the plot are excluded by searches at high transverse momentum with the ATLAS and CMS experiments. From Ref.~\cite{Buttazzo:2017ixm}.$ $Constraints on two of the four independent parameters of the Cabibbo-Kobayashi-Maskawa quark mixing matrix, as of summer 2018~\cite{UTfit}. These constraints are obtained by combining experimental measurements of decay rates and other observables with calculations in the Standard Model, in many cases using lattice QCD. The constraints presently all overlap in the small region outlined in black that corresponds to the apex of the unitarity triangle. With more precise lattice QCD calculations and future experimental data, inconsistencies due to physics beyond the Standard Model might be revealed. In fact, two classes of $B$ meson decay processes that are not included here already show tensions with the Standard Model (see Fig.~\protect\ref{fig:Banomalies}). From Ref.~\cite{UTfit}.$ $The smallest and least well known element of the CKM quark mixing matrix is $V_{ub}$. As illustrated here with the history of the values reported by the Particle Data Group~\cite{Tanabashi:2018oca}, there is a long-standing tension between two different methods of extracting $|V_{ub}|$: ``exclusive'', which combines measurements of the $B\to \pi \ell \bar{\nu}$ decay rate with lattice QCD calculations, and ``inclusive'', where the sum of the decay rates to all possible up-flavored hadrons in the final state is used.$ Show more plots

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