118495086
The leading hadronic vacuum polarisation on the lattice
After discussing the relevance of a first principles theory‐prediction of the hadronic vacuum polarisation for Standard Model tests, the theoretical challenges for its computation in lattice QCD are reviewed. New ideas that will potentially improve the quality of lattice simulations will be introduced and the status of ongoing simulations will be presented briefly.
118724275
The shape of covariantly smeared sources in lattice QCD
A bstractCovariantly smeared sources are commonly used in lattice QCD to enhance the projection onto the ground state. Here we investigate the dependence of their shape on the gauge field background and find that the presence of localized concentrations of magnetic field can lead to strong distortions which reduce the smearing radii achievable by iterative smearing prescriptions. In particular, as a → 0, iterative procedures like Jacobi smearing require increasingly large iteration counts in order to reach physically-sized smearing radii rsm ~ 0.5 fm, and the resulting sources are strongly distorted. To bypass this issue, we propose a covariant smearing procedure (“free-form smearing”) that allows us to create arbitrarily shaped sources, including in particular Gaussians of arbitrary radius.
118356945
Excited state systematics in extracting nucleon electromagnetic form factors
We present updated preliminary results for the nucleon electromagnetic form factors for nonperturbatively O(a) improved Wilson fermions in N f = 2 QCD measured on the CLS ensembles. The use of the summed operator insertion method allows us to suppress the influence of excited states in our measurements. A study of the effect that excited state contaminations have on the Q2 dependence of the extracted nucleon form factors may then be made through comparisons of the summation method to standard plateau fits, as well as to excited state fits.
119285776
Study of the anomalous magnetic moment of the muon computed from the Adler function
We compute the Adler function on the lattice from vacuum polarization data with twisted boundary conditions using numerical derivatives. The study is based on CLS ensembles with two flavours of $O(a)$ improved Wilson fermions. We extrapolate the lattice data for the Adler function to the continuum limit and to the physical pion mass and analyze its dependence on the momentum transfer. We discuss the application of this method to the extraction of the $u,d$ contribution to $a_\mu^{\mathrm{HLO}}$.
118378992
The leading disconnected contribution to the anomalous magnetic moment of the muon
The hadronic vacuum polarization can be determined from the vector correlator in a mixed time-momentum representation. We explicitly calculate the disconnected contribution to the vector correlator, both in the $N_f = 2$ theory and with an additional quenched strange quark, using non-perturbatively $O(a)$-improved Wilson fermions. All-to-all propagators are computed using stochastic sources and a generalized hopping parameter expansion. Combining the result with the dominant connected contribution, we are able to estimate an upper bound for the systematic error that arises from neglecting the disconnected contribution in the determination of $(g-2)_\mu$.
122000156
Hadronic contribution to the lepton anomalous magnetic moment and pion form factor in lattice QCD
Abstract The Mainz lattice QCD group is currently carrying out simulations of lattice QCD with the aim of making predictions for a wide range of phenomenologically relevant Standard Model properties. Here we present progress in understanding and controlling systematic effects in the computation of the pion vector form factor and the leading hadronic contribution to the lepton anomalous magnetic moment.
119161844
Next-to-leading order QCD corrections to photon production via weak-boson fusion
We present a calculation of next-to-leading order QCD corrections to γjj production via weak-boson fusion at a hadron collider in the form of a flexible parton-level Monte Carlo program which allows us to study cross sections and distributions within experimentally relevant selection cuts. The radiative corrections are found to be moderate with residual scale uncertainties being considerably improved beyond tree level. The sensitivity of the reaction to anomalous W+W−γ couplings is investigated.
118421429
Photoproduction of single inclusive jets at future ep colliders in next-to-leading order QCD
A next-to-leading order QCD calculation for single-inclusive jet photoproduction in unpolarized and longitudinally polarized lepton-hadron collisions is presented which consistently includes 'direct' and 'resolved' photon contributions. The computation is performed within the 'small-cone approximation' in a largely analytical form. Phenomenological aspects of jet production at future ep colliders such as the CERN Large Hadron electron Collider and the polarized Brookhaven National Laboratory eRHIC are discussed, placing particular emphasis on the perturbative stability of the predictions and the possibility to constrain the parton content of the photon.
15230077
Hard exclusive photoproduction of Phi and J/Psi mesons
We calculate the leading-order perturbative contribution to gamma p -> M(V) p, with M(v) being a Phi or J/Psi meson, in the kinematic region of large energy and scattering angle.
118533381
Release Note -- Vbfnlo-2.6.0
Vbfnlo is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), double and triple vector boson (plus jet) production in hadronic collisions at next-to-leading order (NLO) in the strong coupling constant, as well as Higgs boson plus two jet production via gluon fusion at the one-loop level. This note briefly describes the main additional features and processes that have been added in the new release ‐ Vbfnlo Version 2.6.0. At NLO QCD diboson production (W , WZ, ZZ, Z and ), same-sign W pair production via vector boson fusion and the process Wj have been implemented (for which oneloop tensor integrals up to six-point functions are included). In addition, gluon induced diboson production can be studied separately at the leading order (oneloop) level. The diboson processes WW, WZ and W can be run with anomalous gauge boson couplings, and anomalous couplings between a Higgs and a pair of gauge bosons is included in WW, ZZ, Z and diboson production. The code has also been extended to include anomalous gauge boson couplings for single vector boson production via VBF, and a spin-2 model has been implemented for diboson pair production via vector boson fusion.
18008767
Next-to-leading order QCD corrections to W+W? production via vector-boson fusion
Vector-boson fusion processes constitute an important class of reactions at hadron colliders, both for signals and backgrounds of new physics in the electroweak interactions. We consider what is commonly referred to as W+W− production via vector-boson fusion (with subsequent leptonic decay of the Ws), or, more precisely, e+νe μ−μ + 2 jets production in proton-proton scattering, with all resonant and non-resonant Feynman diagrams and spin correlations of the final-state leptons included, in the phase-space regions which are dominated by t-channel electroweak-boson exchange. We compute the next-to-leading order QCD corrections to this process, at order α6αs. The QCD corrections are modest, changing total cross sections by less than 10%. Remaining scale uncertainties are below 2%. A fully-flexible next-to-leading order partonic Monte Carlo program allows to demonstrate these features for cross sections within typical vector-boson-fusion acceptance cuts. Modest corrections are also found for distributions.