False Drell Yan results and lots of zero transverse momentum warnings

[Aimane]

Hello,

I am studying Higgs decays to mumu in e+e- collisions and I'm getting unexpected results when plotting background data.
I need to generate a few background processes (Z,ZZ,bbbar,mumu,...) and right now, I am doing some tests with e+e- -> gamma/Z -> mu+mu- as a part of the whole Drell Yan background. When I plot the distribution of muon pairs invariant mass, I get an enormous peak at the Z mass and nothing comparable in the rest of the spectrum, while I am expecting a Drell Yan-like continuum in the distribution starting at lower masses.

Does it mean that processes passing through a photon and not Z are negligible ? And why ?
Could it be a problem with my cards ?

I am using Pythia for generation and Delphes to simulate data acquisition. I specify the process in main03.cmnd and make a HepMC using main41.cc which calls upon main03.cmnd (attached to this ticket along with Delphes card)

I was also wondering if you could help me understand why I get too much warnings of the type :
Warning in <TVector3::PseudoRapidity>: transvers momentum = 0! return +/- 10e10
I know it means a zero transverse momentum but which one could it be ? Does it have anything to do with the fact that the system transverse momentum is zero, in which case the warnings would be normal ?

I am sorry for my numerous questions. I wish you could help me out with this.

Thank you very much in advance,

Aimane

[Pavel Demin]

When I plot the distribution of muon pairs invariant mass, I get an enormous peak at the Z mass and nothing comparable in the rest of the spectrum, while I am expecting a Drell Yan-like continuum in the distribution starting at lower masses.

I'd suggest to have a look at the distribution of muon pairs invariant mass that are generated by Pythia before running Delphes. If the distribution doesn't look as you expect, then something should probably be changed in the Pythia configuration.

I was also wondering if you could help me understand why I get too much warnings of the type :
Warning in <TVector3::PseudoRapidity>: transvers momentum = 0! return +/- 10e10

This warning is generated by the TVector3 class from ROOT. If the number of particles with zero transvers momentum is greater than you expect, then again something should probably be changed in the Pythia configuration.