[Comphep-common] uncertainty on 2l invariant mass distributions of ZZ production

[Pedro Ribeiro]

Dear CompHEP team


We are studying UED signal in 4 lepton final state for which the main
background is ZZ->4l. We have been using ZZ->4l samples produced with
Comphep.

In order to discriminate signal from background we have been looking at
the distribution of dilepton invariant mass, which has a triangular
shape and a endpoint between 20-60 GeV (depending on the model)  for the
signal due to the presence of a "neutralino" like particle. As expected,
the same distribution for the ZZ background shows a peak at the Z mass.

We wish to use the Z peak of the dilepton invariant mass distribution to
normalize the distribution when data is available. Then we would rely on
the shape as given my MC to extrapolate the event yield in our signal
region which is located at lower mass scale (10-60GeV) .

Two questions:

- Does compHep includes interference between Z and virtual gamma ?

- Which are the most relevant sources of uncertainty in the shape of
dilepton invariant mass distribution between 10 and 60 GeV, that is,
which parameters in CompHEP should we vary to get a estimate of the
uncertainty ?

Best Regards

Pedro