### Conveners

#### Weak Decays and Matrix Elements: Session 5-1 B

- Takashi KANEKO

#### Weak Decays and Matrix Elements: Session 5-2 B

- Matthew Wingate (University of Cambridge )

#### Weak Decays and Matrix Elements: Session 6-2 C

- Akira Ohnishi (Yukawa Inst, Kyoto University)

We present the first realistic lattice QCD calculation of the γW-box diagrams relevant for beta decays. The nonperturbative low-momentum integral of the γW loop is calculated using a lattice QCD simulation, complemented by the perturbative QCD result at high momenta. Using the pion semileptonic decay as an example, we demonstrate the feasibility of the method. By using domain wall fermions at...

Neutrinoless double beta decay, if detected, would prove that neutrinos are Majorana fermions and provide the direct evidence for lepton number violation. If such decay would exist in nature, then π−π− → ee and π− → π+ee (or equivalently π−e+ → π+e−) are the two simplest processes accessible via first-principle lattice QCD calculations. In this work, we calculate the long-distance...

In this talk I will briefly review our recent lattice calculations for matrix elements contributing to the mass and width differences of neutral $B$ mesons [arXiv:1907.01025, arXiv:1910.00970]. The calculations were done using the MILC ensembles generated with 4-flavours of sea quarks utilizing the highly improved staggered quark action. An improved nonrelativistic quark action was used for...

We are presenting our ongoing Lattice QCD study on $B-\bar{B}$ mixing. Comparing a variety of different methods, we are extracting bag parameters $B_{B_{s}}$ and $B_{B_{d}}$ on several RBC/UKQCD and JLQCD ensembles with 2+1 dynamical-flavour domain wall fermions, including physical-pion-mass ensembles. We are simulating a range of heavy quark masses on each ensemble from below the charm quark...

The 't Hooft limit of QCD, also referred to as large Nc limit, constitutes a simplification of the theory that preserves most of its non-perturbative properties, including confinement and spontaneous chiral symmetry breaking. It also leads to some definite predictions such as a non-existing Delta I=1/2 rule in the K-> pi pi isospin decay amplitudes. Many phenomenological approaches to hadron...

We present our results for the semileptonic formfactors of exclusive $B_s \to K \ell \nu$ and $B_s \to D_s \ell \nu$ decays. The calculation is based on RBC/UKQCD's set of 2+1 dynamical flavour gauge field ensembles spanning three lattice spacings. We use domain wall fermions for the valence up/down, strange and charm quarks whilst the bottom quark is simulated using the relativistic heavy...

We present our (HPQCD) latest lattice QCD calculation of the scalar and the vector form factors for the D → Klν semi-leptonic decay over a full range of q^2 including q^2 = 0. This calculation has been performed on the N_f=2+1+1 MILC HISQ ensembles with the physical and heavier than physical light quark masses.This calculation allows us to precisely determine the central CKM matrix element,...

We report on our calculation of the B->D(*)\ell\nu form factors in 2+1 flavor relativistic lattice QCD. Our simulations are carried out by employing the M\""obius domain-wall quark action at lattice cut-offs a^{-1} \sim 2.4, 3.6 and 4.5 GeV with the bottom quark masses up to 0.7 a^{-1}. We discuss the extrapolation of the form factors to the continuum limit and physical quark masses.

We present the results of HPQCD's recent calculation of the $B_c \rightarrow J/\psi$ semileptonic form factors and $R(J/\psi)$ for the first time from lattice QCD using the heavy-HISQ method. We also extend these results to angular observables which we compute in the standard model and in several new physics scenarios.

"D → Klν and B → Kl + l − are important heavy to strange semileptonic decay processes, giving us direct comparison with experiment, and access to CKM

matrix elements and potential new physics. We can calculate form factors for

both of these processes in lattice QCD and connect them together by determining heavy to strange form factors for heavy quark masses ranging from c to b. We can also...

The desire for additional determinations of the CKM matrix element $V_{ub}$ and a long-standing 2-3$\sigma$ discrepancy between results from inclusive $B\to X_u$ and exclusive $B\to\pi$ processes motivate the study of $B\to\pi$ semileptonic form factors on the lattice. The status of our preliminary $B\to\pi\ell\nu$ results will be discussed by highlighting updates to our analysis. The analysis...

On a lattice with 2+1-flavor dynamical domain-wall fermions at the physical pion mass, we calculate the decay constants of the charmed and light vector mesons including D/D*, Ds/Ds*, phi and K*. The lattice size is 48^3*96, which corresponds to a spatial extension of ~5.5 fm with the lattice spacing a~0.114 fm. For the valence quarks we use overlap fermions at several mass points close to...

The rare decay J/ψ→3γ, analog to Ortho-positronium decaying to 3γ in quantum electrodynamics, can provide a high precision test for the non-perturbative quantum chromodynamics. Such a decay process was first observed by CLEO collaboration in 2008 and then by BESIII in 2013. However, the relevant theoretical researches are very limited due to the dominant non-perturbative effects. We propose to...