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}).
11547130
Longitudinally polarized photoproduction of inclusive hadrons at fixed-target experiments
Abstract.We present a detailed phenomenological study of spin-dependent single-inclusive high- pT hadron photoproduction with particular emphasis on the kinematics relevant for the Compass and Hermes fixed-target experiments. We carefully examine the theoretical uncertainties associated with the only moderate transverse momenta accessible in such measurements and analyze the sensitivity of the relevant spin asymmetries to the gluon polarization in the nucleon as well as to the completely unknown parton content of circularly polarized photons.
118888006
NLO QCD corrections to processes with multiple electroweak bosons
The VBFNLO program package is a collection of Monte Carlo programs for the calculation of NLO QCD corrections to vector boson fusion cross sections, double and triple vector boson production, or the production of two electroweak bosons in association with an additional jet. An overview is given of the processes and features implemented in VBFNLO. WWγ and Wγ j production are discussed as examples.
118535972
Next-to-leading order QCD corrections to Higgs boson production in association with a photon via weak-boson fusion at the LHC
Higgs boson production in association with a hard central photon and two forward tagging jets is expected to provide valuable information on Higgs boson couplings in a range where it is difficult to disentangle weak-boson fusion processes from large QCD backgrounds. We present next-to-leading order QCD corrections to Higgs production in association with a photon via weak-boson fusion at a hadron collider in the form of a flexible parton-level Monte Carlo program. The QCD corrections to integrated cross sections are found to be small for experimentally relevant selection cuts, while the shape of kinematic distributions can be distorted by up to 20% in some regions of phase space. Residual scale uncertainties at next-to-leading order are at the few-percent level.
119301305
NLO corrections to electroweak and QCD production of W+W+ plus two jets in the POWHEG BOX
A bstractWe present the matching of the next-to-leading order QCD calculation for W+W+jj production via vector-boson fusion in hadronic collisions to parton-shower MonteCarlo programs according to the POWHEG method. Our implementation complements existing code for QCD-induced W+W+jj production in the POWHEG BOX package, thereby providing a platform for the complete Standard Model production of W+W+jj events via QCD and electroweak interactions. The impact of parton-shower effects is discussed for various distributions and found to be small in most cases. However, few observables that are relevant for analyses using a central jet veto, are modified significantly when they are interfaced to a parton shower program.
119196699
Weak boson scattering at the Large Hadron Collider
Weak boson scattering processes provide particularly prom ising means for gaining insight into the mechanism of electroweak symmetry breaking at hadron co lliders. Being very sensitive to interactions in the weak gauge boson sector, they will help t o distinguish the Standard Model from various new physics scenarios such as extra-dimensional Hi ggsless models. To unambiguously identify signatures of new physics, precise predictions fo r experimentally accessible observables within realistic selection cuts are crucial, including nex t-to-leading order QCD corrections. Here, we review how flexible Monte-Carlo methods can be employed fo r precision analyses of weak boson scattering reactions within the Standard Model and be yond.
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.
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 $(g-2)_\mu$.
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 $a_\mu^{\mathrm{HLO}}$.
59145986
Exploring the phase diagram of QCD with complex Langevin simulations
I Real Langevin simulations converge to the expected result. For gauge theories simulations with complexified degrees of freedom are no longer in a compact group, SU(3)→ SL(3,C), and convergence is no longer guaranteed and needs to be checked [2]. I Empirical studies and theoretical arguments show that convergence is achieved, if the distribution is localised (compact) in the imaginary part. I We use gauge-invariance to get gauge-links to the proximity of the SU(3) manifold, this method is known as gauge cooling [3] Uμ(x)→ V (x)Uμ(x)V(x + aμ) U ,V ∈ SL(3,C).
119208157
Wilson fermions at fine lattice spacings: scale setting, pion form factors and (g-2)_mu
We present an update on our on-going project to compute hadronic observables for Nf=2 flavours of O(a) improved Wilson fermions at small lattice spacings. The procedure to determine the lattice scale via the mass of the Omega baryon is described. Furthermore we present preliminary results for the pion form factor computed using twisted boundary conditions, and report on the implementation of a novel approach to determine the contribution of the hadronic vacuum polarisation to the anomalous magnetic moment of the muon.