High Energy / Nuclear Theory / RIKEN Seminars

[HET seminar] Precision Physics & Proton Structure at the LHC

by Johannes Michel (MIT)




The LHC precision program critically relies on precise theory predictions for Standard-Model baseline rates to identify possible deviations due to New Physics. In this talk, I will present third-order QCD predictions for Higgs, Z, and W boson production at the LHC, with a particular focus on their transverse-momentum (qT) distributions, and including fully realistic fiducial acceptance cuts on their decay products. I will discuss how the resummation of large logarithms of qT, which is governed by the factorization of the cross section in terms of transverse-momentum dependent (TMD) PDFs, gives rise to a net resummation effect even in total cross sections in the presence of fiducial cuts. I compare our predictions for the Z boson transverse-momentum spectrum to high-precision measurements by the ATLAS and CMS experiments, discussing in turn the estimation of residual perturbative uncertainties, parametric uncertainties from the strong coupling and collinear PDF, and uncertainties arising from the nonperturbative transverse dynamics of the proton as encoded in TMD PDFs and their evolution. I present intriguing early evidence that the ATLAS and CMS Z qT spectra may prefer a lower strong coupling than the PDG value, with important implications for the extraction of TMD physics and precision EW parameters from LHC data.