Stefano Pozzorini

Electroweak corrections to hadronic production of W bosons at large transverse momenta

Abstract To match the precision of present and future measurements of W-boson production at hadron colliders electroweak radiative corrections must be included in the theory predictions. In this paper we consider their effect on the transverse momentum ( p T ) distribution of W bosons, with emphasis on large p T . We evaluate the full electroweak O ( α ) corrections to the processes p p → W + jet and p p ¯ → W + jet including virtual and real photonic contributions. We present the explicit expressions in analytical form for the virtual corrections and provide results for the real corrections, discussing in detail the treatment of soft and collinear singularities. We also provide compact approximate expressions which are valid in the high-energy region, where the electroweak corrections are strongly enhanced by logarithms of s ˆ / M W 2 . These expressions describe the complete asymptotic behaviour at one loop as well as the leading and next-to-leading logarithms at two loops. Numerical results are presented for proton–proton collisions at 14 TeV and proton–antiproton collisions at 2 TeV . The corrections are negative and their size increases with p T . At the LHC, where transverse momenta of 2 TeV or more can be reached, the one- and two-loop corrections amount up to −40% and +10%, respectively, and will be important for a precise analysis of W production. At the Tevatron, transverse momenta up to 300 GeV are within reach. In this case the electroweak corrections amount up to −10% and are thus larger than the expected statistical error.

Two-loop electroweak angular-dependent logarithms at high energies

Abstract We present results on the two-loop leading and angular-dependent next-to-leading logarithmic virtual corrections to arbitrary non-mass-suppressed processes at energies above the electroweak scale. In the ‘txa0Hooft–Feynman gauge the relevant Feynman diagrams involving soft and collinear gauge bosons γ , Z, W ± coupling to external legs are evaluated in the eikonal approximation in the region where all kinematical invariants are much larger than the electroweak scale. The logarithmic mass singularities are extracted from massive multi-scale loop integrals using the Sudakov method and alternatively the sector-decomposition method in the Feynman-parameter representation. The derivations are performed within the spontaneously broken phase of the electroweak theory, and the two-loop results are in agreement with the exponentiation prescriptions that have been proposed in the literature based on a symmetric SU(2)×U(1) theory matched with QED at the electroweak scale.

Electroweak corrections to hadronic photon production at large transverse momenta

We study the impact of electroweak radiative corrections on direct production of photons with high transverse momenta at hadron colliders. Analytic results for the weak one-loop corrections to the parton scattering reaction q→γg and its crossed variants are presented. For the high-energy region, where the corrections are strongly enhanced by logarithms of /MW2, we derive simple asymptotic expressions which approximate the exact one-loop results with high precision. The dominant two-loop electroweak contributions are also calculated. Numerical results are presented for the LHC and the Tevatron. The corrections are negative and their size increases with transverse momentum. For the LHC, where transverse momenta of 2 TeV or more can be reached, the size of the one- and two-loop effects amounts up to −17% and +3%, respectively. At the Tevatron, with transverse momenta up to 400 GeV, the one-loop corrections do not exceed −4% and the two-loop effects are negligible. Finally we compare the cross sections for hadronic production of photons and Z bosons and find that the electroweak corrections have an important impact on their ratio.

Logarithmic electroweak corrections to hadronic Z+1 jet production at large transverse momentum

Abstract We consider hadronic production of a Z boson in association with a jet and study one- and two-loop electroweak logarithmic corrections in the region of high Z-boson transverse momentum, p T ≫ M Z , including leading and next-to-leading logarithms. Numerical results for the LHC and Tevatron colliders are presented. At the LHC these corrections amount to tens of per cent and will be important for interpretation of the measurements.

Next-to-leading mass singularities in two-loop electroweak singlet form factors

Abstract We consider virtual electroweak corrections to the form factors for massless chiral fermions coupling to an SU(2)×U(1) singlet gauge boson in the asymptotic region s ⪢ M W 2 ∼ M Z 2 , where the invariant mass s of the external gauge boson is much higher than the weak-boson mass scale. Using the sector-decomposition method we compute mass singularities, which arise as logarithms of s / M W 2 and 1/ ϵ poles in D =4−2 ϵ dimensions, to one- and two-loop next-to-leading-logarithmic accuracy. In this approximation we include all contributions of order α l ϵ k log j + k ( s / M W 2 ), with l =1,2 and j =2 l ,2 l −1. We find that the electroweak two-loop leading- and next-to-leading-logarithmic mass singularities can be written in a form that corresponds to a generalization of Catanis formula for massless QCD.

An Algorithm for the high-energy expansion of multi-loop diagrams to next-to-leading logarithmic accuracy

Abstract We present an algorithm to compute arbitrary multi-loop massive Feynman diagrams in the region where the typical energy scale Q is much larger than the typical mass scale M , i.e., Q ≫ M , while various different energy and mass parameters may be present. In this region we perform an asymptotic expansion and, using sector decomposition, we extract the leading contributions resulting from ultraviolet and mass singularities, which consist of large logarithms ln ( Q 2 / M 2 ) and 1 / ɛ poles in D = 4 − 2 ɛ dimensions. To next-to-leading accuracy, at L loops all terms of the form α L ɛ − k ln j ( Q 2 / M 2 ) with j + k = 2 L and j + k = 2 L − 1 are taken into account. This algorithm permits, in particular, to compute higher-order next-to-leading logarithmic electroweak corrections for processes involving various kinematical invariants of the order of hundreds of GeV and masses M W ∼ M Z ∼ M H ∼ m t of the order of the electroweak scale, in the approximation where the masses of the light fermions are neglected.

Two-loop electroweak corrections at high energies

Abstract We discuss two-loop leading and angular-dependent next-to-leading logarithmic electroweak virtual corrections to arbitrary processes at energies above the electroweak scale. The relevant Feynman diagrams involving soft-collinear gauge bosons γ, Z, W ± have been evaluated in eikonal approximation. We present results obtained from the analytic evaluation of massive loop integrals. To isolate mass singularities we used the Sudakov method and alternatively the sector decomposition method in the Feynman-parameter representation.

New NLOPS predictions for tt¯+btt¯+b -jet production at the LHC.

Measurements of

t \bar{t} b \bar{b}

t bar{t} H