Conveners
Quark and Lepton Flavor Physics
- Christopher Bouchard (University of Glasgow)
Quark and Lepton Flavor Physics
- Masaaki Tomii (UConn)
Quark and Lepton Flavor Physics
- Jonna Koponen (JGU Mainz)
Quark and Lepton Flavor Physics
- Maarten Golterman (San Francisco State University)
Quark and Lepton Flavor Physics
- Andreas Juettner (University of Southampton)
Quark and Lepton Flavor Physics
- Jun-sik Yoo (Stony Brook University)
Quark and Lepton Flavor Physics
- Justus Tobias Tsang (CERN)
Quark and Lepton Flavor Physics
- Steven Gottlieb (Indiana Univ.)
We report on our on-going study of the $B_s \to K\ell\nu$ decay in $N_f=2+1$ lattice QCD. The M\"obius domain-wall action is employed for all quark flavors at a lattice cutoff of $a^{-1} \sim 2.5$ GeV. We present preliminary results for the relevant form factors extracted from correlator ratios by inspecting their ground state saturation.
Heavy-light semileptonic decays provide an important channel to perform high-energy precision tests of the standard model, determine $|V_{ub}|$, and test lepton flavour universality. In this talk, the current status of exclusive $B_s\to K\ell\nu$ semileptonic decays within the RBC-UKQCD Relativistic Heavy Quark (RHQ) project will be presented. We will present recently-published form factor...
We compute the complete set of form factors for the $B\to \pi$, $B\to K$, and $B_s\to K$ amplitudes, which are needed to describe semileptonic $B$-meson decay rates for both the charged and neutral current cases. We use the highly improved staggered quark (HISQ) action for the sea and light valence quarks. The b quark is described by the Wilson-clover action in the Fermilab interpretation....
I discuss a model-independent framework for fitting hadronic
form-factor data, which is often only available at discrete
kinematical points, using parameterisations based on unitarity and
analyticity. The accompanying dispersive bound on the form factors
(unitarity constraint) is used to regulate the ill-posed fitting
problem and allow model-independent predictions over the...
We present recent progress on the lattice calculation of semileptonic form factors for $B \to D^{\ast} \ell \nu$ decay using linear fit method. We use the Oktay-Kronfeld (OK) action for the charm and bottom valence quarks. We use results of 2pt correlator fit of $B$ and $D^{\ast}$ meson as input parameters to the data analysis on the 3pt correlation functions. Here, the masses of charm and...
In this talk we present a lattice determination of the hadronic susceptibilities that, as a consequence of unitarity and analyticity, constrain the form factors entering the semileptonic $b\rightarrow c$ transitions. We evaluate the longitudinal and transverse susceptibilities of the vector, axial and tensor polarization functions at zero momentum transfer from the moments of appropriate...
We present an update for results on B-meson semileptonic decays using the highly improved staggered quark (HISQ) action for both valence and 2+1+1 sea quarks. The use of the highly improved action, combined with the MILC collaboration’s gauge ensembles with lattice spacings down to ~0.03 fm, allows the b quark to be treated with the same discretization as the lighter quarks. The talk will...
I will present preliminary results of next-generation lattice-QCD calculations of the $\Lambda_b \to p$, $\Lambda_b \to \Lambda$, and $\Lambda_b \to \Lambda_c$ form factors based on RBC/UKQCD gauge-field ensembles with 2+1 flavors of domain-wall fermions. Compared to the work published in 2015 and 2016, the new calculations include three additional ensembles (one with 139 MeV pion mass, one...
Recent experimental progress measuring the branching fractions of the heavy-baryon semileptonic decays $\Xi_c \to \Xi \ell \nu$ have stimulated theoretical interest and motivate precise lattice calculations of the form factors. Here we present such a calculation using domain-wall fermions for the up, down, and strange quarks, and an anisotropic clover action for the charm quark. We use four...
We present a study on the nonperturbative calculation of observables for inclusive semileptonic decays of $B_{(s)}$-mesons using lattice QCD. We focus on the comparison of two different methods to analyse lattice data of Euclidean correlation functions and address inverse problems, specifically Chebyshev and Backus-Gilbert approaches. This type of computation may eventually provide new insight...
We report on the progress in the analysis of the inclusive semi-leptonic decay of the $D_s$ meson. This analysis is based on a pilot simulation conducted for the $D_s \rightarrow X_s \ell\nu$ process where we employed Möbius domain-wall charm and strange quarks whose masses were tuned to be approximately physical and where we covered the whole kinematical region.
The focus of this talk is to...
I will present ongoing efforts, by the Budapest-Marseille-Wuppertal collaboration, concerning the staggered-fermion computation of the HVP two-point function, on new 0.048 fm lattices. In particular, I will focus on aspects of our GPU determination of the Omega baryon mass, used for scale setting, and that of the connected, light-quark contribution to the muon g-2.
I review the status of the RBC/UKQCD g-2 program with focus on updates for the hadronic vacuum polarization.
We present an update, from the Fermilab Lattice, HPQCD, and MILC collaborations, of our results for the hadronic vacuum polarization contribution to the muon’s anomalous magnetic moment. Preliminary results for light-quark-connected contributions to the intermediate and long-distance window quantities employ new, low-mode-improved, data sets on our finest ensembles. We also present updated...
In this study we employ staggered fermions to calculate the two-pion taste singlet states at rest. Leveraging the Clebsch-Gordan coefficients of the symmetry group associated with staggered fermions, we effectively compute the $\pi\pi$ contributions to the resting $\rho$-meson. To discern the distinct energy states involved, we adopt a generalized eigenvalue problem-solving approach. This work...
As several lattice collaborations agree on the result for the
window quantity of the hadronic vacuum polarization (HVP) contribution to
(g-2)_\mu, whilst being in tension with the calculation using the dispersive
approach, further effort is needed in order to pin down the cause for this
difference.
Here we investigate the isospin breaking corrections to the leading order HVP.
In...
We provide estimates for the light-quark-connected component of the RBC/UKQCD intermediate-window-hadronic contribution to the muon anomalous magnetic moment. We find significant tensions between our data-driven result,
$a_\mu^{W1,{\rmlqc}}=198.8(1.1)\times 10^{-10}$, and recent lattice computations.
Significant tensions are observed between the dispersive and the lattice QCD results for hadronic vacuum polarization (HVP). We will present a general framework that allows to compare the two approaches and to combine them, if they can be reconciled. We have applied this framework to determine the distance or energy scales that could be responsible for the observed tensions and we will present...
We present the first ab-initio calculation of the $\pi^0$, $\eta$ and $\eta^{\prime}$ transition form factors at the physical point using lattice QCD with staggered fermions on $N_f = 2 + 1 + 1$ gauge ensembles, generated by the Budapest-Marseille-Wuppertal collaboration. We compare our results with existing measurements and with other theoretical estimates. Using these transition form...
We present our computation of the pion and eta-meson transition form factors from twisted mass lattice QCD at physical quark masses. In particular, we report on the improvements we recently made in the calculation of the pion transition form factor, which finalizes the calculation with data presently available to us. We use the form factors to determine the pseudoscalar-pole contributions to...
We present the status of the Mainz group's lattice QCD calculation of the transition form factor $\mathcal{F}_{\pi^0\gamma^\ast\gamma^\ast}$, which describes the interaction of an on-shell pion with two off-shell photons. This form factor is the main ingredient in the calculation of the pion-pole contribution to hadronic light-by-light scattering in the muon $g-2$,...
Hadronic contributions dominate the uncertainty of the standard model prediction for the anomalous magnetic moment of the muon. In this talk, we will describe an ongoing lattice calculation of the hadronic, light-by-light, four-point function, performed with staggered fermions. The presence of quarks with different tastes complicates the analysis of this position-space correlation function. We...
Position-space schemes are very natural gauge-invariant non-perturbative renormalization schemes to implement on the lattice. The tradeoff is that the perturbative calculations required to convert to more typically used schemes such as MS are more theoretically involved. We present dimensionally regulated perturbative calculations of a set of HQET operators in position-space, allowing for...
We present an update of the study of bag parameters of neutral $B_{(s)}$-meson mixing, which constrains the Standard Model as well as BSM scenarios. Our calculations use an all-domain-wall-fermion approach. We combine three lattice spacings ($1.7 \mathrm{GeV} \leq a^{-1} \leq 2.7 \mathrm{GeV}$) including 2 physical pion mass ensembles generated by RBC/UKQCD with ensembles with three finer...
Neutral meson mixing and meson lifetimes are theory-side parametrised in terms four-quark operators which can be determined by calculating weak decay matrix elements using lattice QCD.
While calculations of meson mixing matrix elements are standard, determinations of lifetimes typically suffer from complications in renormalisation procedures because dimension-6 four-quark operators can mix...
In a not well known paper [JHEP01(2008)076] it was shown how to perform interpolations between relativistic and static computations in order to obtain results for heavy-light observables for masses from (say) $m_{\rm charm}$ to $m_{\rm bottom}$. All quantities are first continuum extrapolated and then interpolated in $1/m=1/m_{\rm heavy}$. Large volume computations are combined with finite...
We present preliminary results for B-physics from a combination of non-perturbative results in the static limit with relativistic computations satisfying $am_{\rm heavy}<<1$. Relativistic computations are carried out at the physical b-quark mass using the Schrödinger Functional in a $(0.5~{\rm fm})^4$ box. They are connected to large volume observables through step scaling functions that trace...
We discuss the applicability of lattice QCD to the long-distance (LD) two-photon contribution to the decay of a long-lived neutral kaon into a charged-muon pair (KL2mu). In the absence of QED, the flavor-changing neutral-current KL2mu process requires exchanging at least two W-bosons or a W- and a Z-boson, the short-distance (SD) contribution. Such a process is suppressed by two factors of...
Dilepton decays of the pseudoscalar mesons have been drawing particular interest, thanks to their sensitivity to both the QCD dynamics at low energy and also signals beyond the Standard model. In the first part of the talk, we present our work on an improved Standard-Model prediction for the rare decay $\pi^0 \to e^+e^-$, and compare it with the first determination on the lattice that...
Rare decays of charged and neutral Kaons will be discussed. Phenomenological works being done in collaboration with Enrico Lunghi and another one with Stefan Schacht will be discussed. Mode(s) that should be target for precision lattice study...
We report our recent results for $K\to\pi\pi$ matrix elements and $\varepsilon'$, the measure of direct CP violation, released on arXiv:2306.06781. This is RBC/UKQCD's first result for $\varepsilon'$ with periodic boundary conditions (PBC), while our earlier calculations were performed with G-parity boundary conditions, where the isospin-0 two-pion ground state corresponds to the on-shell...
We present progress towards extracting multi-hadron $D$ decay amplitudes, such as $D \to \pi \pi$, in a pilot study using three ensembles of stabilised Wilson fermions at the SU(3) flavour symmetric point, with $M_\pi = 410$ MeV. As the three ensembles differ only in the lattice spacing, with well matched physical volumes, it is possible to perform a continuum limit for finite-volume energies...
The rare hyperon decay $\Sigma \to p \ell^+ \ell^-$ is a flavour changing neutral current process that is sensitive to new physics beyond the Standard Model.
We present the current status of the first exploratory calculation of this decay on the lattice with 340 MeV pions using domain wall fermions.
We update our previous results and also determine $F_K$ and $F_\pi$ separately using Möbius domain-wall fermions computed on gradient-flowed $N_f$ = 2 + 1 + 1 highly-improved staggered sea-quark ensembles. We use five values of the pion mass ranging from 130 $\le$ $m_\pi$ $\le$ 400 MeV, four lattice spacings of a $\sim$ 0.15, 0.12, 0.09, 0.06 fm and multiple lattice volumes. The physical...
We determine the value of $|V_{us}|$ using the kaon semileptonic form
factor calculated from the PACS10 configurations, whose physical
volumes are more than (10 fm)$^4$ at the physical point. The configurations
were generated using the Iwasaki gauge action and $N_f=2+1$ stout-smeared
nonperturbatively $O(a)$ improved Wilson quark action at the three lattice
spacings, 0.085, 0.063, and...
Inclusive hadronic $\tau$ decays are very interesting from the phenomenological viewpoint since they give access to the CKM matrix elements $V_{ud}$ and $V_{us}$. In this talk, exploiting flavour diagonal vector and axial two-point correlators produced with high statistics by ETMC within the muon $g-2$ HVP project, we apply the HLT method for hadronic smeared spectral densities to study the...
We report on first computations of hadron masses and matrix elements with
charm quarks in O$(a)$ improved (2+1)-flavour lattice QCD in the framework of
stabilised Wilson Fermions.
Employing SU(3)-flavour-symmetric gauge field ensembles from the OpenLAT initiative, we study two strategies how to fix the physical charm quark mass.
In a first approach, we follow the standard procedure by...
In the region of hard photon energies, radiative leptonic decays represent important probes of the internal structure of hadrons. Moreover, radiative decays can provide independent determinations of Cabibbo-Kobayashi-Maskawa matrix elements with respect to purely leptonic or semileptonic channels. Prospects for a precise determination of leptonic decay rates with emission of a hard photon are...
We compute non perturbatively the RG running of the complete basis of $\Delta F=2$ four fermion operators in the chirally rotated Schrödinger Functional in the region of energies between the $W$ mass and the switching scale (4GeV).
We describe a first-principles method to apply lattice QCD to compute the order $\alpha_{\mathrm{EM}}$ corrections to $K\to\pi\ell\nu_\ell$ decay. This method formulates the calculation in infinite volume with the conventional infinite-volume, continuum treatment of QED. Infinite volume reconstruction is used to replace the QCD components of the calculation with finite-volume amplitudes...
The absence of a mass gap in QED requires handling of the zero-momentum modes of photons in finite-volume spacetimes. Once the problematic zero-momentum modes are removed using some prescription, the associated finite-volume effects in an observable typically scale with inverse powers of the spatial extent, $1/L$. In this talk, I discuss the analytical evaluation of these effects through order...
In the context of radiative corrections to pseudoscalar meson leptonic decay, it is well-known that the $\mathcal{O}(\alpha_{\mathrm{em}})$ corrections to the decay amplitude logarithmically diverges when the lepton mass goes to zero, a behavior known as collinear divergences. Since leptons are not massless, this is not per se a divergence of the process, but it greatly enhances the value of...
Recent investigations of tests of unitarity of the first row of the CKM matrix report roughly $3 \sigma$ tension. Nonperturbative calculations of the radiative corrections (RC) are needed to reduce the theory uncertainty in CKM matrix elements. Here we present the electroweak box contribution to the pion, kaon and neutron decays. For pion and kaon case, we present published results from eight...