Factorization at the LHC: From PDFs to Initial State Jets

by Dr Frank Tackmann

Thursday 23 Apr 2009, 11:00 → 12:00 Europe/Zurich

1/1-025 (CERN)

Factorization is one of the most basic concepts for understanding the data at the Tevatron or soon the LHC. I will discuss a new factorization theorem for the production of N energetic jets in pp collisions, where the relevant values of the partonic momentum fractions are away from the limit x -> 1. The factorization at the hard scale Q of the interaction does not yield the standard parton distribution functions (PDFs). Instead, at an intermediate scale \mu_b, initial-state soft radiation causes the incoming proton to break apart, producing an incoming jet and this initial-state jet requires a new ``beam function'' to be properly described. I will show that at the scale \mu_b, the beam function factorizes into a convolution of a calculable Wilson coefficient and the standard parton distribution function. At scales \mu < \mu_b, the evolution of the initial state is correctly described by the usual PDF evolution, which stops at \mu_b, much below the hard interaction scale Q. The remaining initial-state evolution for \mu_b < \mu < Q is described by the evolution of the beam function, which is given in terms of the virtuality of the initial-state jet.