search

GeorgeCocks-01 / URSS

0 stars 0 forks source link

Looking at W boson candidates in the data #2

Closed mvesteri closed 2 years ago

mvesteri commented 2 years ago

Hi @GeorgeCocks-01,

I copied another file to /tmp/13TeV_2018_34_Up_EW.root. This one will be too big to put in your home area so I suggest to just read it directly from that location. Once you are in the epp group you will be able to see this file from its normal location in epp storage.

Inside that file there is a TTree at WpIso/DecayTree. This tree contains candidate W boson decays to muons. Unlike the Z events that you were looking at, these events will contain a lot of background.

First task is to plot the mu_PT column. Do you see evidence of any signal?

Then you can look at the mu_PTSUMCONE040 column. This is the sum of the pT of all particles within a Lorentz-invariant "cone" around the muon. The cone radius is defined by delta_R = sqrt(delta_eta**2 + delta_phi**2). In this column the cone radius is delta_R = 0.4.

We refer to variables like this as "isolation". Can you think how this might discriminate between W -> mu nu events and background from QCD (jets)?

GeorgeCocks-01 commented 2 years ago

I was thinking it might be something to do with the particles moving faster with higher pT and so the measurements become worse due to that, but that's not the simulation failing.

The simulation seems to lose the peak at 0GeV as pT increases, but I'm not too sure why that would be.

mvesteri commented 2 years ago

The momentum resolution does indeed degrade at higher momentum (and pT), because what we measure is a deflection (or curvature) in a magnetic field. The resolution is constant in the curvature.

However, the main effect that I see in those plots is that at higher pT there is an excess of low isolation events in the data. I think that is due to contamination from real electroweak W, Z boson signals.

It would be good to check if any of the particles in the real data are actually identified as muons. If you look at the variables in the trees there should be one with "ISMUON" which is a bool flag saying whether we reconstructed the charged particle as a muon.

GeorgeCocks-01 commented 2 years ago

Ah I see. I've got the ISMUON array, and there are some muons in it. I was unsure if you wanted me to plot this or something similar to be able to see the data.

mvesteri commented 2 years ago

How often is ISMUON true? It may be that there is some real W->munu signal mixed in there.

GeorgeCocks-01 commented 2 years ago

1.345% of all interactions are muons

mvesteri commented 2 years ago

Can you see if the excess (of data over simulation) at low isolation values and higher "muon" pT is mostly from these identified muons?

mvesteri commented 2 years ago

With the excess I'm referring to e.g. these figures

GeorgeCocks-01 commented 2 years ago

For 65-70 muon pT and between 0-40 isolation, we had 1.944% muons.

GeorgeCocks-01 commented 2 years ago

Checking more values for the same isolation range (of 0-40) and ranging muon pT values: 3.276% for 35-40pT, 3.94% for 40-45, 3.02% for 45-50, 2.885% for 50-55, 2.66% for 55-60, 1.67% for 60-65, 1.944% for 65-70, 1.75% for 70-75, 1.27% for 75-80, 1.32% for 80-85.

There doesn't seem to be a distinct "higher pT gives higher %" trend. It seems like there's a peak around 35-45.

GeorgeCocks-01 commented 2 years ago

@mvesteri do those numbers seem right? Are there any other tasks I could start?