The study of collider physics is nowadays the main tool to study and deeply understand the most accredited theory describing particles and their interactions: the Standard Model.
The Standard Model is a quantum field theory with local gauge symmetry: SU(3) × SU(2) × U(1). Matter is composed of fermions, half-spin particles, which interact through the exchange of bosons, spin-1 particles. An additional spin-0 boson, the Higgs boson, is introduced to explain the generation of masses via the Higgs mechanism.
The main focus of this talk is the production, at hadron colliders such as the LHC and Tevatron, of the Z and W bosons, which mediate the weak interaction. Among the various kinematic distributions, a special role is played by the transverse-momentum distribution (i.e. momentum perpendicular to the beam axis).
The corresponding cross sections are obtained through the factorization theorem, which expresses them as the convolution of the parton distribution functions (PDFs)—universal functions—with the partonic cross section, calculable within quantum chromodynamics (QCD) and quantum electrodynamics (QED) and object of our theoretical study.
QCD provides the dominant contributions, and in the region where the transverse momentum is of the order of the weak-boson mass, standard perturbative expansions can be applied. However, at small transverse-momentum values, large logarithmic terms, arising from soft and/or collinear parton emission, spoil the convergence of the series. To restore the predictive power of perturbation theory, these terms must be evaluated and resummed to all orders. Resummation, in turn, can be performed to different levels of accuracy, much like a standard perturbative expansion.
Although QCD radiative corrections dominate, the inclusion of QED corrections is necessary to achieve high precision, since the two coupling constants are related by α² ~ αs. In this case, we consider photon emission that can be soft and/or collinear.
In this talk I will discuss the combined QCD+QED resummation formalism, focusing on (i) the case of W-boson production, and (ii) the impact of QED corrections. In particular, we obtain all numerical predictions using the Fortran code DYqT, and we find that QED effects range from the per-mille to the percent level.
Rebeca Beltrán y Nicolás Loayza