l+l-bbbar associated production and the W mass measurement

by Dr Emanuele A. Bagnaschi (DESY)

Thursday 3 May 2018, 15:15 → 16:15 Europe/Stockholm

HUB (Institutionen för teoretisk fysik)

The W mass measurement is one of the most important items of the SM research-program of the LHC. It is a difficult measurement both from the experimental and theoretical points of view. Among the theoretical issues currently under discussion in the community, a prominent place is held by the so-called "heavy-quark effects”. Different problematics are collected under this name. In this talk we focus on the impact of neglecting the mass of the bottom quark in the simulations of the Neutral Current (NC) Drell Yan (DY) process used to tune the MCs which are used in the W mass measurement. The structure of the talk is the following. In a first part, I will initially review the current theoretical status of the NC-DY process in the five-flavor scheme (5FS) and of the process l+l-bbbar in the four-flavor scheme (4FS). Afterwards, I will discuss the results of our study of l+l-bbbar predictions at NLO+PS using both the Madgraph5_aMC@NLO and the POWHEG-BOX frameworks and then present our prescription to build a combined prediction of the 5FS and 4FS processes to account for the bottom mass effects in the transverse momentum distribution (pT) of the Z boson. We have found a non-trivial distortion of at most O(1%) in the shape of pTZ. In a second part, I will first introduce and discuss the basics of the W-mass measurement process using the template-fitting procedure and then discuss the impact of the MC tune-modification due to the effects that I have discussed in the first part of the talk. We have found a shift in MW which is small but still visibile, of at most O(5 MeV). Reference: E. Bagnaschi et al., "Lepton-pair production in association with a bb¯ pair and the determination of the W boson mass", arXiv:1803.04336.