Searcharxiv⌕ Search

arXiv subjects

S. Weinzierl

Publications and source records attributed to S. Weinzierl.

34 records · Page 2Linked to original sources
arXiv2004

Top quark pair + jet production at next-to-leading order: NLO QCD corrections to gg -> t tbar g

The reaction pp/pbar p -> t tbar jet+X is an important background process for Higgs boson searches in the mass range below 200 GeV. Apart from that it is also an ideal laboratory for precision measurements in the top quark sector. Both applications require a solid theoretical prediction, which can be achieved only through a full next-to-leading order (NLO) calculation. In this work we describe the NLO computation of the subprocess gg -> t tbar g.

hep-ph↗
arXiv2004

Les Houches 'Physics at Tev Colliders 2003' QCD/SM Working Group: Summary Report

This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop.

hep-ph↗
arXiv2002

Two-loop amplitudes for e+ e- -> q qbar g: the nf-contribution

We discuss the calculation of the nf-contributions to the two-loop amplitude for e+ e- -> q qbar g. The calculation uses an efficient method based on nested sums. The result is presented in terms of multiple polylogarithms with simple arguments, which allow for analytic continuation in a straightforward manner.

hep-ph↗
arXiv2002

The fully differential single-top-quark cross section in next-to-leading order QCD

We present a new next-to-leading order calculation for fully differential single-top-quark final states. The calculation is performed using phase space slicing and dipole subtraction methods. The results of the methods are found to be in agreement. The dipole subtraction method calculation retains the full spin dependence of the final state particles. We show a few numerical results to illustrate the utility and consistency of the resulting computer implementations.

hep-ph↗
arXiv2000

Helicity Amplitudes for Single-Top Production

Single top quark production at hadron colliders allows a direct measurement of the top quark charged current coupling. We present the complete tree-level helicity amplitudes for four processes involving the production and semileptonic decay of a single top quark: W-gluon fusion, flavor excitation, s-channel production and W-associated production. For the first three processes we study the quality of the narrow top width approximation. We also examine momentum and angular distributions of some of the final state particles.

hep-ph↗
arXiv2000

Predictions on $B \to π\bar{l} ν_l$, $D \to π\bar{l} ν_l$ and $D\to K \bar{l} ν_l$ from QCD Light-Cone Sum Rules

The $f^+$ form factors of the $B\to π$, $D\to π$ and $D\to K$ transitions are calculated from QCD light-cone sum rules (LCSR) and used to predict the widths and differential distributions of the exclusive semileptonic decays $B\to π\bar{l}ν_l$, $D \toπ\bar{l}ν_l$ and $D \to K \bar{l}ν_l$, where $l=e,μ$. The current theoretical uncertainties are estimated. The LCSR results are found to agree with the results of lattice QCD calculations and with experimental data on exclusive semileptonic D decays. Comparison of the LCSR prediction on $B\to π\bar{l} ν_l$ with the CLEO measurement yields a value of |V_{ub}| in agreement with other determinations.

hep-ph↗
arXiv2000

QCD Sum Rules for Heavy Flavors

We give a short review of QCD sum rule results for B and D mesons and Lambda_Q and Sigma_Q baryons. We focus mainly on recent developments concerning semileptonic B->pion and D->pion transitions, pion couplings to heavy hadrons, decay constants and estimates of the b quark mass from a baryonic sum rule, and the extraction of the pion distribution amplitude from CLEO data.

hep-ph↗
arXiv1999

Reduction of multi-leg loop integrals

I give an efficient algorithm for the reduction of multi-leg one-loop integrals of rank one. The method combines the basic ideas of the spinor algebra approach with the dual vector approach and is applicable to box integrals or higher point integrals, if at least one external leg is massless. This method does not introduce Gram determinants in the denominator. It completes an algorithm recently given by R. Pittau.

hep-ph↗
arXiv1999

Perturbative QCD Correction to the Light-Cone Sum Rule for the $B^*Bπ$ and $D^*Dπ$ Couplings

The $B^*Bπ$ and $D^*Dπ$ couplings have previously been derived from a QCD light-cone sum rule in leading order. Here, we describe the calculation of the $O(α_s)$ correction to the twist 2 term of this sum rule. The result is used for a first next-to-leading order analysis. We obtain $g_{B^*Bπ}= 22\pm 7$ and $g_{D^*Dπ}=10.5\pm 3$, where the error indicates the remaining theoretical uncertainty.

hep-ph↗
arXiv1997

Perturbative QCD Correction to the $B\toπ$ Transition Form Factor

We report on the perturbative $O(α_s)$ correction to the light-cone QCD sum rule for the $B\to π$ transition form factor $f^+$. The correction to the product $f_Bf^+$ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding $O(α_s)$ correction in the two-point sum rule for $f_B$. The resulting cancellation of large QCD corrections in $f^+$ eliminates one important uncertainty in the sum-rule prediction for this form factor.

hep-ph↗
arXiv1996

One-Loop Amplitudes for e^+ e^- to q-bar q Q-bar Q

We present the one-loop helicity amplitudes for processes involving a vector boson V (V=W,Z, or gamma^*) and four massless quarks, 0 to V q-bar q Q-bar Q, where V couples to a massless lepton pair. These amplitudes are required for next-to-leading order O(alpha_s^3) numerical programs for four-jet production at e^+ e^- colliders, for W, Z or Drell-Yan production in association with two jets at hadron colliders, and for three-jet production in deeply inelastic scattering experiments. We obtained the amplitudes presented here by using their analytic properties to constrain their form.

hep-ph↗