119193746
Computing the Adler function from the vacuum polarization function
We use a lattice determination of the hadronic vacuum polarization tensor to study the associated Ward identities and compute the Adler function. The vacuum polarization tensor is computed from a combination of point-split and local vector currents, using two flavours of O($a$)-improved Wilson fermions. Partially twisted boundary conditions are employed to obtain a fine momentum resolution. The modifications of the Ward identities by lattice artifacts and by the use of twisted boundary conditions are monitored. We determine the Adler function from the derivative of the vacuum polarization function over a large region of momentum transfer $q^2$. As a first account of systematic effects, a continuum limit scaling analysis is performed in the large $q^2$ regime.
118474947
Lattice QCD Studies of the Leading Order Hadronic Contribution to the Muon g 2
The anomalous magnetic moment of the muon, g 2, is one of the most promising observables to identify hints for physics beyond the Standard Model. QCD contributions are currently responsible for the largest fraction of the overall theoretical uncertainty in g 2. The possibility to determine these hadronic contributions from first principles through lattice QCD calculations has triggered a number of recent studies. Recent proposals to improve the accuracy of lattice determinations are reported. We present an update of our studies of the leading-order hadronic contribution to g 2 with improved Wilson fermions.
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.
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 $(g-2)_\mu$.
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.
118394113
The leading hadronic contribution to (g-2) of the muon: The chiral behavior using the mixed representation method
We extend our analysis of the leading hadronic contribution to the anomalous magnetic moment of the muon using the mixed representation method to study its chiral behavior. We present results derived from local-conserved two-point lattice vector correlation functions, computed on a subset of light two-flavor ensembles made available to us through the CLS effort with pion masses as low as 190 MeV. The data is analyzed also using the more standard four-momentum method. Both methods are systematically compared as the calculations approach the physical point.
119231041
Higgs boson production in association with a photon via weak boson fusion
We present next-to-leading order QCD corrections to Higgs production in association with a photon via weak boson fusion at a hadron collider. Utilizing the fully flexible parton level Monte-Carlo program VBFNLO, we find small overall corrections, while the shape of some distributions is sensitive to radiative contributions in certain regions of phase-space. Residual scale uncertainties at next-to-leading order are at the few-percent level. Being perturbatively well under control and exhibiting kinematic features that allow to distinguish it from potential backgrounds, this process can serve as a valuable source of information on the $Hb\bar{b}$ Yukawa coupling.
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.
16880281
Next-to-leading-order QCD corrections to W(+)Z and W(-)Z production via vector-boson fusion
We present the calculation of the next-to-leading-order QCD corrections to electroweak pp{yields}e{sup +}{nu}{sub e}{mu}{sup +}{mu}{sup -}jj and pp{yields}e{sup -}{nu}{sub e}{mu}{sup +}{mu}{sup -}jj production at the CERN LHC in the form of a fully flexible parton-level Monte Carlo program. The QCD corrections to the total cross sections are modest, changing the leading-order results by less than 10%. At the Born level, the shape of kinematic distributions can depend significantly on the choice of factorization scale. This theoretical uncertainty is strongly reduced by the inclusion of the next-to-leading-order QCD corrections.
54521266
LONGITUDINAL GLUON POLARIZATION IN RHIC DOUBLE-SPIN ASYMMETRIES.
The longitudinally polarized gluon density is probed sensitively in hard collisions of polarized protons under the condition that the dominant dynamics are perturbative and of leading twist origin. First data have recently been presented by PHENIX on the double-spin asymmetry A{sub LL}{sup {pi}} for {pi}{sup 0} production at moderate transverse momentum p {perpendicular} {approx_equal} 1 {divided_by} 4 GeV and central rapidity. By means of a systematic investigation of the relevant degrees of freedom we show that the perturbative QCD framework at leading power in p{perpendicular} produces an asymmetry that is basically positive definite in this kinematic range, i.e. A{sub LL}{sup {pi}} {approx}> {Omicron}(-10{sup -3}).