119295352
QCD at nonzero chemical potential: Recent progress on the lattice
We summarise recent progress in simulating QCD at nonzero baryon density using complex Langevin dynamics. After a brief outline of the main idea, we discuss gauge cooling as a means to control the evolution. Subsequently we present a status report for heavy dense QCD and its phase structure, full QCD with staggered quarks, and full QCD with Wilson quarks, both directly and using the hopping parameter expansion to all orders.
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 $a_\mu^{\mathrm{HLO}}$.
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.
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.
18085138
Next-to-leading order QCD corrections to Z boson pair production via vector-boson fusion
Vector-boson fusion processes are an important tool for the study of electroweak symmetry breaking at hadron colliders, since they allow to distinguish a light Higgs boson scenario from strong weak-boson scattering. We here consider the channels WW{yields}ZZ and ZZ{yields}ZZ as part of electroweak Z boson pair production in association with two tagging jets. We present the calculation of the NLO QCD corrections to the cross sections for pp{yields}e{sup +}e{sup -}{mu}{sup +}{mu}{sup -}+2 jets and pp{yields}e{sup +}e{sup -}{nu}{sub {mu}}{nu}{sub {mu}}+2 jets via vector-boson fusion at order {alpha}{sub s}{alpha}{sup 6}, which is performed in the form of a NLO parton-level Monte Carlo program. The corrections to the integrated cross sections are found to be modest, while the shapes of some kinematical distributions change appreciably at NLO. Residual scale uncertainties typically are at the few percent level.
119280529
Gluons and the quark sea at high energies: distributions, polarization, tomography
This report is based on a ten-week program on Gluons and the quark sea at high-energies, which took place at the Institute for Nuclear Theory (INT) in Seattle in Fall 2010. The principal aim of the program was to develop and sharpen the science case for an Electron-Ion Collider (EIC), a facility that will be able to collide electrons and positrons with polarized protons and with light to heavy nuclei at high energies, offering unprecedented possibilities for in-depth studies of quantum chromodynamics (QCD). This report is organized around the following four major themes: (i) the spin and flavor structure of the proton, (ii) three dimensional structure of nucleons and nuclei in momentum and configuration space, (iii) QCD matter in nuclei, and (iv) Electroweak physics and the search for physics beyond the Standard Model. Beginning with an executive summary, the report contains tables of key measurements, chapter overviews for each of the major scientific themes, and detailed individual contributions on various aspects of the scientific opportunities presented by an EIC.
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}).
18093432
QCD Corrections to Vector Boson Pair Production via Weak Boson Fusion
NLO-QCD corrections to vector boson pair production via weak boson fusion have recently been calculated and implemented into flexible parton-level Monte-Carlo programs. These allow for the computation of cross sections and kinematical distributions within realistic experimental cuts. We summarize the basic elements of the calculation and review phenomenological results for the LHC.