Conveners
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model I
- Hartmut Wittig
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model II
- Steven Gottlieb (Indiana University)
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model III
- Marcus Petschlies (Helmholtz-Institut für Strahlen- und Kernphysik)
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model IV
- Robert Harlander
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model V
- Carleton DeTar (University of Utah)
QCD in searches for physics beyond the Standard Model: QCD in searches for physics beyond the Standard Model VI
- Martin Hoferichter (University of Bern)
In our previous work, we showed that unresolved excited state contaminations provide a major source of systematic uncertainty in the calculation of the nucleon electric dipole moment due to the QCD topological term theta. Here we extend this result to the calculation of the nucleon electric dipole moment due to the quark chromo-electric dipole moment operator. We also show quantitatively the...
We report our calculation of the neutron electric dipole moment (EDM) induced by the theta term. We use overlap fermions on three 2+1-flavor RBC/UKQCD domain wall lattices with pion mass ranging from ~300 to ~500 MeV. The use of lattice chiral fermions guarantees a correct chiral limit even at finite lattice spacings and enables us to reliably extrapolate our result from heavy pion masses to...
At the TeV scale, low-energy precision observations of neutron characteristics provide unique probes of novel physics. Precision studies of neutron decay observables are susceptible to beyond the Standard Model (BSM) tensor and scalar interactions. The neutron electric dipole moment also has high sensitivity to new BSM CP-violating interactions. To fully utilise the potential of future...
By far the biggest contribution to hadronic vacuum polarization (HVP) arises from the two-pion channel. Its quark-mass dependence can be evaluated by combining dispersion relations with chiral perturbation theory, providing guidance on the functional form of chiral extrapolations, or even interpolations around the physical point. In addition, the approach allows one to estimate in a controlled...
In this contribution we report on progress in the determination of the isospin breaking corrections to the vector-vector correlator in QCD from the RBC/UKQCD collaborations. They are relevant to estimate the hadronic contributions to the muon anomalous magnetic moment directly from first-principles lattice QCD simulations, and indirectly from cross sections measured in tau decay experiments.
We present a calculation of the intermediate window quantity of the
hadronic vacuum polarization contribution to the muon g-2 using a
Lorentz-covariant coordinate-space method at a fixed pion mass of ~350
MeV. This method is more flexible in the choice of the integration
kernel than the time-momentum representation and gives a different
perspective on the systematic errors of the g-2...
We present a lattice determination of the disconnected contributions to the leading-order hadronic vacuum polarization (HVP) to the muon anomalous magnetic moment in the so-called short and intermediate time-distance windows. We employ gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with $N_f = 2+1+1$ flavors of Wilson twisted-mass clover-improved quarks with masses...
We present new lattice results of the ETM Collaboration for the SM prediction of the so-called intermediate window (W) and short-distance (SD) contributions to the leading-order hadronic vacuum polarization (HVP) term of the muon anomalous magnetic moment, $a_\mu^{HVP}$.
Our results are obtained from extensive simulations of twisted mass lattice QCD with dynamical up, down, strange and charm...
With the publication of the new measurement of the anomalous magnetic moment of the muon, the discrepancy between experiment and the data-driven theory prediction has increased to $4.2\sigma$. Recent lattice QCD calculations predict values for the hadronic vacuum polarization contribution that are larger than the data-driven estimates, bringing the Standard Model prediction closer to the...
We employ $N_\mathrm{f}=2+1$ flavours of $O(a)$ improved Wilson fermions to determine the hadronic vacuum polarisation functions $\bar{\Pi}^{\gamma\gamma}$ and $\bar{\Pi}^{\gamma Z}$ for Euclidean squared momenta $Q^2\leq 7$ $\mathrm{GeV}^2$. We extrapolate the results to the physical point using ensembles at four lattice spacings and several pion masses, including its physical value. We...
We discuss the conversion of our lattice result for the hadronic running of the electromagnetic coupling, $\Delta\alpha(-Q^2)$, computed for Euclidean momenta into an estimate for $\Delta\alpha^{(5)}_{\rm had}(M_Z^2)$ using the Euclidean split technique (Adler function approach). We focus specifically on the running in the spacelike regime from momentum scales below $7\,\rm GeV^2$ up to...
We present an update on including isospin breaking effects in the determination of HVP using C$^{\star}$ boundary conditions. We use QCD+QED configurations with 1+2+1 flavors of Wilson-Clover fermions produced by RC$^{\star}$ collaboration, where the action parameters are chosen to highlight isospin breaking effects. In this series of two talks, we show preliminary results for three $32^3...
We present an update on including isospin breaking effects in the determination of HVP using C$^\star$ boundary conditions. We use QCD$+$QED configurations with $1+2+1$ flavors of Wilson clover fermions produced by the RC$^\star$ collaboration, where the action parameters are chosen to highlight isospin breaking effects. In this series of two talks, we show preliminary results for three $32^3...
The muon $(g−2)$ is a compelling quantity due to the current standing tensions among the experimental average, data-driven theoretical results, and lattice results. Matching the final target accuracy of the experiments at Fermilab and J-PARC will constitute a major challenge for the lattice community in the coming years. For this reason, it is worthwhile to consider different options to keep...
The ratio of the cross sections for $e^+e^- \to hadrons$ and $e^+e^-\to \mu^+\mu^-$ at c.o.m energy $E$, i.e. $R(E)$, is an extremely interesting observable. Its measurements are used in dispersive analyses of the leading hadronic vacuum polarization (HVP) contributing to the muon $g-2$, and the results of these analyses for a certain window observable are in significant tension with those...
Quark chromomagnetic dipole operators encode low-energy effects of heavy particles on flavor observables related to neutral Kaon mixing or Kaon decays, for example. However, their renormalization on the lattice is complicated by the power-divergent mixing with lower-dimensional operators. The gradient flow provides a promising scheme to circumvent this problem. The matching to the MSbar scheme...
Pseudoscalar pole diagrams provide the bulk of the contribution -- as well as a large fraction of the error budget -- of dispersive estimates of the hadronic light-by-light (HLbL) piece of the muon g-2. We report on a calculation of the pion transition form factor $F_{P\rightarrow \gamma\gamma}$ over a range of kinematics, including broad regions which are inaccessible from experimental data,...
We report on our computation of the eta transition form factor $\mathcal{F}_{\eta \rightarrow \gamma^* \gamma^*}$ from
twisted mass lattice QCD at physical quark masses and at a single lattice spacing.
On the lattice, we have access to a broad range of (space-like) photon momenta and
can therefore produce data complementary to the experimentally accessible singly
virtual case. We use the...
$K^+\to\pi^+\ell^+\ell^-$ is a highly suppressed decay mode in the Standard Model, and is therefore expected to be sensitive to new physics. In this talk, we present the first lattice calculation of the long-distance electromagnetic form factor $V$ at physical light-quark masses for this decay. Our calculation features an explicit GIM subtraction, with dynamical zMöbius quarks and Möbius...
The rare Hyperon decay $\Sigma^+ \to p \ell^+ \ell^-$ is an $s \to d$ flavour changing neutral
current process, which is highly suppressed within the Standard Model, and is therefore sensitive to new physics. Due to recent improvements in experimental measurements of this decay, the Standard Model theory prediction must also be improved in order to identify any new physics in this...
The rare Hyperon decay $\Sigma^+ \to p \ell^+ \ell^-$, potentially sensitive to new physics beyond the Standard Model, is currently being pursued in an exploratory calculation by the RBC/UKQCD collaboration. At the physical pion mass, intermediate $N \pi$ states lead to poles in lattice quantities, which need to be removed to extract the physical amplitude. We present the formalism to achieve...
The electromagnetic coupling constant, $\alpha$, is one of the fundamental parameters of the Standard Model (SM). Its value at the Z boson mass, $\alpha(M_Z)$, is of particular interest as it enters electroweak precision tests. When running $\alpha$ from low energies up to the Z mass, five orders of magnitude in precision are lost. This makes it one of the least well determined parameters of...
It is well known that the electromagnetic coupling constant alpha is an energy scale dependent quantity. Some of these dependencies originate from hadrons and can therefore be computed using Lattice QCD. The value at the mass of the Z boson is of particular interest. The large energy range makes a direct simulation unfeasible, so it has to be split up into several ranges. Setting the scale of...
This talk presents a determination of the short-distance contributions to the unphysical $\pi^-\rightarrow\pi^+ e^- e^-$ decay through lattice QCD calculations. The hadronic contributions to the transition amplitude are described by the pion matrix elements of five Standard Model Effective Field Theory operators, which are computed on five ensembles of domain-wall fermions with $N_f = 2 + 1$...
Experimental searches for neutrinoless double-beta decay aim to determine whether the neutrinos are Dirac or Majorana fermions. Interpreting double-beta half-lives or experimental exclusions in terms of neutrino physics requires knowledge of the nuclear matrix elements, which are currently estimated from various nuclear models and carry a large model uncertainty. This talk will present...
The Budapest-Marseille-Wuppertal collaboration computed the leading hadronic vacuum polarization contribution to the anomalous muon magnetic moment with unprecedented accuracy on the lattice. The result was obtained using staggered fermions. Here we present an improved crosscheck of the staggered result for the intermediate window observable using a mixed action setup: overlap valence quarks...
We present preliminary results toward the extraction of the transition form factors $\mathcal{F}_{p\to \gamma^*\gamma^*}$ ($p=\pi^0,\eta,\eta^{\prime}$) using lattice QCD with staggered fermions on $N_f=2+1+1$ gauge ensembles generated by the Budapest-Marseille-Wuppertal collaboration. These form factors are essential ingredients for the computation of the light pseudoscalar pole contributions...
The Fermilab Lattice, HPQCD, and MILC collaborations are engaged in multi-year projects to compute the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon with high precision. In this talk, we present the status of our calculation of the light-quark connected contributions to HVP. The calculation relies on four ensembles of gauge configurations...
We discuss ongoing improvements to the hadronic vacuum polarization computation by the Budapest-Marseille-Wuppertal collaboration.
Isospin-breaking corrections to the HVP component of the anomalous magnetic moment of the muon are needed to ensure the theoretical precision of $g_\mu\!-\!2$ matches its experimental precision. To this end we describe the status of our work calculating, on the lattice, the QED IB correction to the light connected HVP. We report results using physical $N_f=2+1+1$ HISQ ensembles at 3 lattice...
We present a lattice calculation of the window contribution ($t_0=0.4~\mathrm{fm}$, $t_1=1.0~\mathrm{fm}$, $\Delta=0.15~\mathrm{fm}$) of the leading order hadronic vacuum polarization contribution to the muon g-2 using overlap valence fermions on 4 physical-point ensembles. Two 2+1 flavor ensembles use the domain wall fermion (DWF) and Iwasaki gauge actions at $a = 0.084$ and 0.114 fm, and two...
We present new results for the light-quark connected part of the leading order hadronic-vacuum-polarization (HVP) contribution to the muon anomalous magnetic moment, using staggered fermions. We have collected more statistics on previous ensembles, and we added two new ensembles. This allows us to reduce statistical errors on the HVP contribution and related window quantities significantly. We...
This talk gives an update of the HVP contribution to the muon g-2 from the RBC/UKQCD collaborations.
The QCD theta term is a source of CP-violation that could potentially induce a non-vanishing neutron electric dipole moment (nEDM). Previous lattice calculations have had difficulties in extracting the nEDM, especially when close to the physical value of the pion mass. In this contribution we present first results obtained with Stabilized Wilson Fermions. We focus on SU($3$) flavor-symmetric...
The hadronic vacuum polarization (hvp) function $\Pi$ is the basis quantity for high-precision lattice calculations of the hvp contribution to the muon anomalous magnetic moment, $a_\mu^{\mathrm{lo-hvp}}$.
Recently, tensions have emerged between lattice QCD based determinations of intermediate time-distance hvp ("window") contributions to $a_\mu^{\mathrm{lo-hvp}}$ and their counterparts based...
