# How can you explain the shape of the W mass peak in a transverse mass plot in the case of WZ production

I'm looking for events where a W and a Z boson is produced from collision of two protons, with backgrounds coming from top-antitop production, production of 2 Z bosons and Drell-Yann processes (production of 1 Z boson). Selections have been made to reduce these backgrounds.

Plotted here is the transverse mass of the missing transverse momentum (i.e. the neutrino from W decay) and the lepton associated with the W boson. I'm unsure how to explain the shape of the WZ component. Why is there a flat, somewhat constant part in the beginning and a 'normal' but fairly wide resonance at the W boson mass? The transverse mass is an intuitively difficult concept for me so it's a hard to draw conclusions myself... I've tried looking it up online but I mostly find plots with a Jacobian peak, which looks nothing what I have. I also see a very slight increase of the ttbar background around 80 GeV (which I've confirmed on another plot). Is this an anomaly or can it be explained?

• You have to compare it with the equivalent monte carlo data. If you want to search deeper reasons check the monte carlo data. – anna v Sep 26 '18 at 3:18
• The coloured parts are the Monte Carlo simulations – Joshua Sep 26 '18 at 18:16
• so what is your problem then? if the monte carlo fits the data,? It means that the physics model used is correct, and you can go to the event generator and see what is the physics model used if you are that interested. – anna v Sep 26 '18 at 18:35
• This plot (and the others) are simply reproductions I've made from an existing paper to get started with ROOT. I had access to data and MC simulations that were created for me. I'm writing a report on it and I'd like to explain the various features of the graphs. – Joshua Sep 26 '18 at 20:13
• imo the only explanation lies in looking at the basic physics formulas inputs to the montecarlo. It is a multiparameter problem that needs the monte carlo. There one can see which interactions dominate where, and how they might add in order to give the observed peak. I think the monte carlo fit itself is the explanation. – anna v Sep 27 '18 at 4:33