Predictions for the LHC: from fixed-order theory to resummation calculations, via Monte Carlo generators

par Benjamin Fuks (IPHC Strasbourg)

lundi 23 nov. 2009, 14:30 → 15:30 Europe/Paris

Salle Master, batiment 20 (IPHC/DRS)

When studying the transverse-momentum (pT) distribution of some final state, it is convenient to separate the large- and small-pT regions. For the large values of pT the use of the fixed-order perturbation theory is fully justified, but in the small-pT region, the coefficients of the perturbative expansion are enhanced by powers of large logarithmic terms. Furthermore, at the production threshold, the mismatch between virtual corrections and phase-space suppressed real-gluon emission leads also to the appearance of large logarithmic terms. Accurate calculations of pT-spectrum and invariant mass distribution must then include soft-gluon resummation in order to obtain reliable perturbative predictions and properly take these logarithmic terms into account. We present resummation calculation for various Beyond the Standard Model theories, and also confront them with predictions obtained using the traditional approach of Monte Carlo generators, including matrix element-based calculations matched to parton showering.We particularly emphasize the differences between the various methods. The impact of theoretical uncertainties, such as scale and parton densities dependences, as well as non-perturbative effects, is also studied.

Slides fuks.pdf