Understanding Interesting Isolation Variable Plot

Hi everyone,
Me and my lab partner are doing an undergraduate lab using the 13 TeV ATLAS open dataset.

We have been using the monte carlo data for the Higgs decaying into 2 photons (all 4 production processes combined). We produce the following 2D histogram, with the etcone and ptcone variables for the highest transverse momentum photons on the x and y axis respectively, with MeV units:


Note the empty region - does anybody know why this occurs? Are jets associated with Higgs production guaranteed to have high transverse energies/momenta? Is there reasoning for the diagonal boundaries of this region?

Here is real data, with a 2 photon selection cut applied, for comparison:


Any insight is appreciated, even if that’s telling us a better place to ask this question :slight_smile:


See “Questions or comments?” in: ATLAS Experiment → Resources → ATLAS Open Data