Conveners
Quark and lepton flavour physics: LT3
- Jonathan Flynn (University of Southampton)
Quark and lepton flavour physics: LT3
- Craig McNeile (Plymouth University)
Quark and lepton flavour physics: LT3
- Patrick Fritzsch (Trinity College Dublin)
Quark and lepton flavour physics: LT3
- Tetsuya Onogi (Osaka University)
Quark and lepton flavour physics: LT3
- Antoine Gerardin (Centre de Physique Thรฉorique de Marseille)
Quark and lepton flavour physics: LT3
- Jonna Koponen (JGU Mainz)
Quark and lepton flavour physics: LT3
- Simon Kuberski (CERN)
Quark and lepton flavour physics: LT3
- Oliver Witzel (University of Siegen)
Quark and lepton flavour physics: LT3
- Tanmoy Bhattacharya (Los Alamos National Laboratory)
Quark and lepton flavour physics: LT3
- Elvira Gamiz (University of Granada)
We present the status of the ETMC computation of the leading-order hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment $a_\mu^{HVP-LO}$ employing $Nf = 2 + 1 + 1$ flavors of Wilson-clover twisted-mass quarks with physical pion mass. Here, we focus on the isospin symmetric QCD (isoQCD) contribution to $a_\mu^{HVP-LO}$.
We present the status of the Mainz group's lattice QCD calculation of the pion 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 $g-2$.
We use the $N_f = 2...
I will present the current status and future prospects of the RBC/UKQCD HVP program. The talk will include new results for the long-distance window contribution.
The largest uncertainty in the Standard Model (SM) prediction of the anomalous magnetic moment of the Muon ($a_\mu$) is due to strong interactions, particularly the Hadronic Vacuum Polarisation (HVP). To make the SM predictions comparable in precision to the new experimental results we need to compute the HVP from first principles lattice QCD with proper handling of all possible uncertainties....
We present an update on our ongoing computation of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon, focusing on short and long distance contributions in the time-momentum representation. By combining lattice QCD and perturbation theory at short distances and utilizing a broad range of lattice spacings, we achieve a controlled continuum extrapolation....
Present tensions within data-driven estimates of the Hadronic-Vacuum-Polarization contribution to the muon anomalous magnetic moment, and additional tensions in the so-called intermediate window between dispersive and lattice calculations, are severely limiting our ability to test the Standard Model, with high precision. Investigating the role of hadronic $\tau$ decays as a different input to...
We report on our preliminary results on the lattice computation of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon. We use twisted-mass fermions on $N_f = 2+1+1$ gauge ensembles at the physical point generated by the Extended Twisted Mass Collaboration (ETMC).
Hadronic contributions dominate the uncertainty of the Standard Model prediction for the anomalous magnetic moment of the muon. In this work, we present results on the hadronic light-by-light contribution obtained from the evaluation of the hadronic four-point function of electromagnetic currents using the position-space formalism developed by the Mainz group. The simulations are performed...
In this study we develop a novel method for computing the pion pole's contribution to hadronic light-by-light in the absence of a parametrization of the pion transition form factor. By introducing a pion structure function and performing the gegenbauer expansion, we demonstrate that the majority of the pion pole's contribution can be extracted in a model-independent manner.
The calculation is...
We give an update of our calculation of the light-quark, connected hadronic vacuum polarization contribution to the muon anomalous magnetic moment. The update includes preliminary results on a $2+1+1$ highly-improved staggered quark (HISQ) ensemble from the MILC collaboration with physical pion mass, $0.042$ fm lattice spacing, and size $144^3 \times 288$ sites. We discuss code and algorithm...
The current precision goal of the hadronic vacuum polarisation requires the inclusion of electromagnetic corrections as well as strong isospin-breaking effects. In finite-volume QED prescriptions such as QED$_\textrm{L}$, finite-volume effects scale as inverse powers of the volume, $L$. For the hadronic vacuum polarisation in QED$_\textrm{L}$ the volume effects enter at $1/L^3$ and are known...
We discuss the finite-volume corrections to the LO-HVP contribution to the muon g-2, computed in the latest BMW update for the dominant I=1 channel by using a combination of Meyer-Lellouch-Lรผscher and Hansen-Patella methods as well as dedicated lattice simulations. Particular attention is given to estimating the various systematics of the calculation.
We present preliminary results for $K \to l \nu_l l'^+ l'^-$ decays, which are mediated by an off-shell $W$ boson and a virtual photon. These decays are suppressed in the Standard Model since their rates start at $\mathcal{O}(\alpha_{em}^2)$, making them very interesting in the search for new physics.
We compute the four form factors needed to describe the structure-dependent part of the...
We discuss a method to generate form factor curves across the entire
kinematic range for semileptonic (SL) pseudoscalar to pseudoscalar
decays, for example $B \rightarrow \pi \mu \nu$ and $B_s \rightarrow K
\mu \nu$.
The work builds upon the Dispersive Matrix (DM) method. Using known
form factor information at specific discrete $q^2$ points as input,
the DM method allows...
Fermionic gradient flow in combination with the short flow time expansion provides a renormalisation scheme where hadronic matrix elements on the lattice are evolved along the flow time gradually removing UV divergences.
In this renormalisation scheme certain challenges such as mixing with operators of lower mass dimension are suppressed or shifted to the perturbative part of the procedure,...
$B$ decays are important for flavor physics. One of the difficulties of these calculations is to control excited states. A standard approach to overcome this issue is to use smeared interpolators to optimize B-meson ground state overlap. However, the ability of such interpolators to effectively suppress multi-hadronic state contributions remains an open question.
In this context, using Heavy...
We perform the first lattice calculation on the semileptonic decay of $J/\psi$ using the (2+1)-flavor Wilson-clover gauge ensembles generated by CLQCD collaboration. After a continuum extrapolation using three lattice spacings, we obtain the final branching fraction of $J/\psi\rightarrow D/D_s e\nu_e$. The ratios of the branching fractions between lepton $\mu$ and $e$ are also calculated and...
Semileptonic $B_{(s)}$โ decays are of great phenomenological interest
because they allow to extract CKM matrix elements or test lepton flavor
universality. Taking advantage of existing data, we explore extracting
form factors for vector final statesโ using the narrow width
approximation. Based on RBC-UKQCD's set of 2+1 flavor gauge field
ensembles with Shamir domain-wall fermion and...
We present an update on the analysis of semileptonic $ B\rightarrow D^{(*)} $ decays at non-zero recoil. Our computation employs 2+1+1 FNAL-MILC ensembles with highly improved staggered quark (HISQ) action for sea and light valence quarks, while the bottom quark is treated using the clover action in the Fermilab interpretation. Simulations are performed across several lattice spacings, ranging...
I present progress on the calculation of scalar, vector, and tensor form factors for the following meson decays: $B \rightarrow \pi$, $B_s \rightarrow K$, $D \rightarrow \pi$, and $D_s \rightarrow K$. The calculation uses the MILC $N_f = 2 + 1 + 1$ HISQ gluon field ensembles and HISQ valence quarks. We generate ensembles of correlator data with varying lattice spacings, as small as 0.044 fm. ...
We present a fully non-perturbative computation of the inclusive semileptonic $D_s\mapsto X\ell\nu$ decay and its leptonic moments from lattice QCD. A first principles computation of such observable has a phenomenological relevance since its comparison with experimental data allows for stringent Standard Model tests in the sector of Flavour physics. Additionally, this work sets the stage to a...
We analyse the semileptonic decay of the $D_s$ meson, focusing on the
$D_s \to X \ell \nu$ channel based on an Extended Twisted mass
ensembles at the physical pion mass value.
On the basis of four-point correlation functions, we use the HLT reconstruction
method to calculate the differential decay rate, allowing us to analyse the inclusive decay.
The analysis is performed at four...
We present our recent estimate of the $B_s\to \mu^+\mu^-\gamma$ decay rate at large $q^2$, computed on four lattice spacing of $N_f=2+1+1$ twisted mass simulations. The relevant form factors are extrapolated to physical $B_s$ meson mass from simulations carried out up to $2M_{D_s}$, covering the region of $\sqrt{q^2}>4.16\, {\rm GeV}$, and adopting a novel strategy to circumvent the problem of...
I will present an update of the currently available $B_c\to J/\psi$ form factors from HPQCD, computed using the heavy-HISQ method. This calculation uses our recent $\bar{b}c$ susceptibilities to perform a fully model-independent physical-continuum extrapolation, including unitarity bounds at all values of $m_h$.
We present preliminary new lattice QCD results for high-precision vector-to-pseudoscalar and tensor-to-vector ratios of decay constants of the $B^{(*)}$, $D^{(*)}$, $B_s^{(*)}$ and $D_s^{(*)}$ mesons, in which many uncertainties cancel, using the heavy-HISQ method. We use the Highly Improved Staggered Quark (HISQ) action for all valence quarks and second generation MILC $n_f = 2 + 1 + 1$ HISQ...
The standing tension between experimental and theoretical results regarding the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon motivates the development of novel methods to enhance theoretical estimates. We present a Lattice QCD study aimed at estimating the short-distance window to the HVP using an improved continuum extrapolation without the need...
Lattice calculations of the hadronic contributions to the muon anomalous magnetic moment are numerically highly demanding due to the necessity of reaching total errors at the sub-percent level. Noise-reduction techniques such as low-mode averaging have been applied successfully to determine the vector-vector correlator with high statistical precision in the long-distance regime, but display an...
In this talk I will present new blinded lattice results for the short-distance window observable of the anomalous muon magnetic moment. Results are obtained on several staggered ensembles covering lattice spacings down to a ~ 0.048 fm. I will discuss the details of the continuum extrapolation and of other sources of systematic uncertainties.
We report on the Fermilab Lattice, HPQCD and MILC collaboration effort to compute the hadronic vacuum polarization correction to the muon g-2. In particular, we present new results for the connected light-quark, strange, and charm contributions to the short- and intermediate-window quantities. For the short-distance observables, we compare with results from perturbative QCD. We outline our...
We present recent results on the Fermilab Lattice, HPQCD, and MILC collaborations project to compute the hadronic vacuum polarization (HVP) contribution to the muonโs anomalous magnetic moment. In this talk, we show preliminary results for the light-quark--connected HVP contribution, including low-mode--improved data sets on our finest ensembles. All ensembles use the 2+1+1 Highly-Improved...
We report on the Fermilab-HPQCD-MILC collaboration's effort updating our calculation of the HVP for the muon anomalous magnetic moment. Using physical $N_f=2+1+1$ HISQ ensembles at multiple lattice spacings, we focus on the isospin-symmetric, quark-line-disconnected contribution to the HVP for various windows quantities.
An ongoing project of the Fermilab Lattice, HPQCD, and MILC collaborations is the precision calculation of the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon. In this talk, we present the strong isospin breaking corrections to the light-quark connected and disconnected contributions to HVP. This calculation employs seven HISQ ensembles with...
In the anomalous magnetic moment of the muon, the determination of the hadronic vacuum polarization (HVP) contribution must reach sub-percent precision in order for the Standard Model prediction to match the precision of the experimental measurement. To achieve this, one needs to include QED corrections that break the isospin symmetry, which is usually imposed in lattice calculations. One...
The experimental precision for the muon (g-2) currently exceeds that of the Standard-Model based prediction. In the latter, the biggest contribution to the uncertainty results from the calculation of the Hadronic Vacuum Polarisation (HVP). To achieve a higher precision, one needs in particular to determine the small, QED induced corrections to the HVP. These corrections can be calculated at...
In the framework of the ongoing computation by ETMC of the leading-order hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment $a_\mu^{HVP}$ in QCD+QED, we present preliminary results about the valence quark-connected isospin--breaking corrections to $a_{\mu}^{\mathrm{HVP-LO}}$, at leading order in $\alpha_\text{em} = e^2/4\pi$ and...
At the current levels of precision reached in the measurement of the muon g-2 by Fermilab, it is essential to control QED and strong-isospin breaking corrections to the HVP contribution to the muon g-2. Here we present a number of cross-checks performed on the results for those corrections presented in the BMWโs collaboration 2020 computation.
We present a pilot study on extracting the P-wave form factors of the $B_s$ to $D_s$ semi-leptonic decays from the Bs four-point correlators. With their inclusive nature, four-point correlators include all the exclusive states from Bs with valence content of c and s quarks. We access the P-wave form factors by excluding the contributions from the S-wave final states. In this pilot study,...
A dominant source of uncertainty in theoretical determinations of ratios of inclusive lifetimes of heavy hadrons are 'Spectator effects', wherein the light degrees of freedom participate in the decay process. The heavy-quark expansion describes these effects as matrix elements of four-quark HQET operators in the heavy-hadron states of interest. Using a recently developed position-space scheme...
We report on the nonperturbative calculation of the inclusive decay rate for semileptonic decays of the $D_s$ meson from lattice QCD. In this talk we address systematic effects associated with the analysis. Namely, we focus on the systematic errors introduced by the finite polynomial order in the Chebyshev approximation used in the analysis and the error due to finite-volume effects. The...
We calculate the form factors for the kaon semileptonic decay process
using the PACS10 configurations, whose physical volume is more than
(10 fm)$^4$ at very close to the physical point. The configurations
were generated with 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 0.042...
In recent years the rare kaon decay has been computed directly at the physical point. However, this calculation is currently limited by stochastic noise stemming from a light and charm quark loop GIM subtraction. The split-even approach is an alternative estimator for such loop differences, and has shown a large variance reduction in certain quantities. We present an investigation into the use...
The decay of a long-lived kaon to a pair of charged muons is a clean rare kaon decay channel which has been measured to the percent-level from experiment. Although the short-distance part of this decay mode is well known from the Standard Model, a direct comparison between theory and experiment is not straightforward due to the sizeable long-distance contribution from the exchange of two...
In the lattice calculation ofย theย two-photon contribution to the $K_{\rm L}\longrightarrow \mu^+\mu^-$ decay amplitude, the unphysical contribution fromย theย $\eta$ intermediate stateย appearsย as a slowly decaying tail which is hard to remove due to the tinyย mass difference betweenย theย $K_{\rm L}$ and $\eta$. We have developed methods to remove suchย anย unphysical $\eta$ contributionย from our...
Calculation of $\varepsilon'$, a measure of direct CP violation, using periodic boundary conditions (PBC) is desired to complement our previous lattice calculations performed with G-parity boundary conditions (GPBC). This approach will also be an important step towards incorporating electromagnetic and isospin-violating effects. Last year, we published our first PBC result for $\varepsilon'$,...
Two second-order quantities related to K meson mixing, $\epsilon_{K}$ and $\Delta M_K$, are Standard Model observables that are highly sensitive to possible new physics. The RBC and UKQCD collaborations have presented results for $\Delta M_{K}$ with physical quark masses and the first lattice calculation of the long-distance part of $\epsilon_{K}$. Utilizing new-generation computers and new...
We present the first lattice QCD calculation of the universal axial $\gamma W$-box contribution $\square_{\gamma W}^{VA}$ to both superallowed nuclear and neutron beta decays.
This contribution emerges as a significant component within the theoretical uncertainties surrounding the extraction of $|V_{ud}|$ from superallowed decays.
Our calculation is conducted using two domain wall fermion...
We calculate the mixing matrices of four-quark operators that change flavor numbers by two units. Our approach employs two schemes: the coordinate-space Gauge Invariant Renormalization Scheme (GIRS) and the Modified Minimal Subtraction scheme. From our perturbative computations, we extract the conversion factors between these two renormalization schemes at the next-to-leading order. A...
In this talk I will present ongoing work to calculate quark-disconnected isospin-breaking corrections to leptonic meson decays at leading order on RBC-UKQCD physical-point domain-wall ensembles. We follow on from previous work at non-physical masses by making use of efficient estimators to address the computational challenges in estimating the relevant quark-disconnected subdiagrams....
This study investigates finite-volume effects in physical processes involving the combination of long-range hadronic matrix elements with electroweak loop integrals. We adopt the idea of implementing the electroweak part in the infinite-volume version. A general approach is established for correcting finite-volume effects in cases where the hadronic intermediate states are dominated by either...
In this talk we present a derivation of power-like electromagnetic finite-volume effects to charged hadron masses and leptonic decay rates, which only relies on hadronic matrix elements evaluated on shell. We make comparisons with existing calculations in the literature and discuss, more in general, the status and prospects of lattice calculations of electromagnetic corrections to hadronic...
Heavy quark observables on the lattice commonly suffer from ($am_q$)-sized discretisation errors, which affects their extrapolation to the continuum. We present results from a first numerical implementation of a massive NPR scheme, RI/mSMOM, with the aim of absorbing cutoff effects. In particular, we compute renormalisation constants for fermion bilinears at non-vanishing heavy quark masses...
