Cleaning for lepton jets

[Bryan]

I am trying to place constraints on a model using the ATLAS search for prompt lepton-jets (​arXiv:1212.5409). To identify the lepton-jets from the QCD background, multiple cuts are made. Some of these are easy to do in Delphes, using the EhadOverEem variable for each jet. I was wondering about some of the other variables, and if you have suggestions to move forward.

ATLAS defines an electron cluster energy concentration as the ratio of total energy in 3x7 cells to the total energy in 7x7 cells in eta-phi in the second sampling layer of the ecal.

Next, they use the electron cluster lateral shower width which uses the energy and pseudorapidity for cells in a 3x5 eta-phi window in the second sampling layer of the ecal.

After that, they define a variable called f_{HT} chichis the ratio of the number of high-threshold hits to the total number of hits from the TRT associated with each track. This is a very important variable as it greatly cuts out the background from pion jets. Of the variables, this is the one that I least know how to tackle in Delphes.

Lastly, a scaled isolation variable is defined as the transverse energy within a 0.1<DeltaR < 0.4 around the closure divided by the cluster E_T.

My question is then two-fold.
1) When I do the EventDisplay, I clearly see bins of eta and phi with clusters of the lego stacked ecal and hcal, along with the Delphes/fastjet defined jets. If I select one of these jets, how can I go about getting the energy in the ecal cells around it to form the first two variables?

2) Is there a variable in Delphes that I could use to help with f_{HT}? I could ignore this cut for my signals, as the cut barely affects the signal cross section, but as I extend the search strategy, this would cause problems when running on background samples.

Thank you for any help you can provide!

-Bryan

[Michele Selvaggi]

Hi Bryan,

the delphes calorimeter model is much simpler than the true ATLAS detector. It is strictly 2 dimensional (hence no longitudinal segmentation). Therefore I hardly see how you can define variables 1 and 2 using Delphes, given also that there is no lateral shower in Delphes (actually there is not even a shower, a cell is either hit, or it is not). Also, a track is purely a trajectory propagated with some efficiency and resolution from the vertex to the calorimeters. There is no such thing as tracker hits in Delphes.

I am afraid that in order to define such variables you'll need a much more elaborate detector model that the one provided by Delphes, some kind of full simulation. As a workaround, I can only suggest you to parameterise the background rejection efficiencies from the ATLAS paper and apply them a posteriori on your MC samples.

Cheers,
Michele