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J. T. Tsang

Publications and source records attributed to J. T. Tsang.

9 recordsLinked to original sources
arXiv2024

The long-distance window of the hadronic vacuum polarization for the muon g-2

We provide the first ab-initio calculation of the Euclidean long-distance window of the isospin symmetric light-quark connected contribution to the hadronic vacuum polarization for the muon $g-2$ and find $a_μ^{\rm LD,iso,conn,ud} = 411.4(4.3)(2.4) \times 10^{-10}$. We also provide the currently most precise calculation of the total isospin symmetric light-quark connected contribution, $a_μ^{\rm iso,conn,ud} = 666.2(4.3)(2.5) \times 10^{-10}$, which is more than 4$σ$ larger compared to the data-driven estimates of Boito et al. 2022 and 1.7$σ$ larger compared to the lattice QCD result of BMW20.

hep-lat↗
arXiv2024

Workshop summary -- Kaons@CERN 2023

Kaon physics is at a turning point -- while the rare-kaon experiments NA62 and KOTO are in full swing, the end of their lifetime is approaching and the future experimental landscape needs to be defined. With HIKE, KOTO-II and LHCb-Phase-II on the table and under scrutiny, it is a very good moment in time to take stock and contemplate about the opportunities these experiments and theoretical developments provide for particle physics in the coming decade and beyond. This paper provides a compact summary of talks and discussions from the Kaons@CERN 2023 workshop.

hep-ph↗
arXiv2024

Bayesian inference for form-factor fits regulated by unitarity and analyticity

We propose a model-independent framework for fitting hadronic form-factor data, which is often only available at discrete kinematical points, using parameterisations based on to unitarity and analyticity. In this novel approach the latter two properties of quantum-field theory regulate the ill-posed fitting problem and allow model-independent predictions over the entire physical range. Kinematical constraints, for example for the vector and scalar form factors in semileptonic meson decays, can be imposed exactly. The core formulae are straight-forward to implement with standard math libraries. We take account of a generalisation of the original Boyd Grinstein Lebed (BGL) unitarity constraint for form factors and demonstrate our method for the exclusive semileptonic decay $B_s\to K \ell ν$, for which we make a number of phenomenologically relevant predictions, including the CKM matrix element $|V_{ub}|$.

hep-ph↗
arXiv2023

Extrapolating semileptonic form factors using Bayesian-inference fits regulated by unitarity and analyticity

We discuss our recently proposed model-independent framework for fitting hadronic form-factor data, which are 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 entire physical range. Kinematical constraints, for example for the vector and scalar form factors in semileptonic meson decays, can be imposed exactly. The core formulae are straight-forward to implement with standard math libraries. We demonstrate the method for the exclusive semileptonic decay $B_s\to K\ellν$, an example requiring one to use a generalisation of the original Boyd Grinstein Lebed (BGL) unitarity constraint. We further present a first application of the method to $B \to D^*\ell ν$ decays.

hep-lat↗
arXiv2023

An update of Euclidean windows of the hadronic vacuum polarization

We compute the standard Euclidean window of the hadronic vacuum polarization using multiple independent blinded analyses. We improve the continuum and infinite-volume extrapolations of the dominant quark-connected light-quark isospin-symmetric contribution and address additional sub-leading systematic effects from sea-charm quarks and residual chiral-symmetry breaking from first principles. We find $a_μ^{\rm W} = 235.56(65)(50) \times 10^{-10}$, which is in $3.8σ$ tension with the recently published dispersive result of Colangelo et al., $a_μ^{\rm W} = 229.4(1.4) \times 10^{-10}$, and in agreement with other recent lattice determinations. We also provide a result for the standard short-distance window. The results reported here are unchanged compared to our presentation at the Edinburgh workshop of the g-2 Theory Initiative in 2022.

hep-lat↗
arXiv2022

QED with massive photons for precision physics: zero modes and first result for the hadron spectrum

The current precision reached by lattice QCD calculations of low-energy hadronic observables, requires not only the introduction of electromagnetic corrections, but also control over all the potential systematic uncertainties introduced by the lattice version of QED. Introducing a massive photon as an infrared regulator in lattice QED, provides a well defined theory, dubbed QEDM, amenable to numerical evaluation [arXiv:1507.08916]. The photon mass is removed through extrapolation. In this contribution we scrutinise aspects of QEDM such as the presence and fate of the zero modes contributions and we describe the determination of the photon mass corrections in finite and infinite volume. We demonstrate that the required extrapolations are well controlled using numerical data obtained on two ensembles which only differ in volume.

hep-lat↗
arXiv2018

Calculation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment

We present a first-principles lattice QCD+QED calculation at physical pion mass of the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. The total contribution of up, down, strange, and charm quarks including QED and strong isospin breaking effects is found to be $a_μ^{\rm HVP~LO}=715.4(16.3)(9.2) \times 10^{-10}$, where the first error is statistical and the second is systematic. By supplementing lattice data for very short and long distances with experimental R-ratio data using the compilation of Ref. [1], we significantly improve the precision of our calculation and find $a_μ^{\rm HVP~LO} = 692.5(1.4)(0.5)(0.7)(2.1) \times 10^{-10}$ with lattice statistical, lattice systematic, R-ratio statistical, and R-ratio systematic errors given separately. This is the currently most precise determination of the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. In addition, we present the first lattice calculation of the light-quark QED correction at physical pion mass.

hep-lat↗
arXiv2017

Heavy Domain Wall Fermions: The RBC and UKQCD charm physics program

We review the domain wall charm physics program of the RBC and UKQCD collaborations based on simulations including ensembles with physical pion mass. We summarise our current set-up and present a status update on the decay constants $f_D$, $f_{D_s}$, the charm quark mass, heavy-light and heavy-strange bag parameters and the ratio $ξ$.

hep-lat↗