Low charged lepton efficiencies

[Marc Thomas]

Hi,

I'm running Delphes via MG5_v2.2.1, having installed pythia-pgs and Delphes3 via the "install" command. The installed versions are,
pythia-pgs: PyPGSVersion, 2.4.0
Delphes: VERSION, 3.1.2

When I generate 10,000 Standard Model events of the process
p p > z, z > e+ e-, with PT_lepton > 10. |eta_lepton| < 2.5,
and analyse in Delphes3 using the /examples/delphes_card_ATLAS.tcl as my delphes_card.dat, only 7797 of the events contain an electron, giving an electron efficiency of 78%.

When I analyse the event with pgs and Delphes 2 I get efficiencies of,
Delphes2 - efficiency = 95%
pgs - efficiency = 88%

This 78% efficiency for such a clean event seems very low, both given the Delphes2/pgs results, and looking at the electron efficiencies in the delphes_card, (of 95% for central hard electrons which most of my electrons are, and 85% for larger rapidity up to 2.5).

As a check, I altered both the "electron tracking efficiency" and the "electron efficiency" to 100% in all regions. This increases the efficiency to 94%, which again seems low given the 100% efficiency in the card.

This looks like a bug to me, or am I missing something. Are the isolation cuts in the default ATLAS card too harsh?

(For p p > z > mu+ mu- I also get a low efficiency of 83%.)

Any advice would be welcome.

Cheers,
Marc

[Michele Selvaggi]

Hi Marc,

this is not a bug, because the efficiency module is applied twice: the first time on tracks, and the second time on individual objects (electrons, muons). We kept it this way so that users would modify only the latter and not change the former.

In case you need higher electron efficiency you can always increase the tracking efficiency.

Michele

[Marc Thomas]

Thanks Michele,
It was the combination of electron efficiencies and the tight isolation cuts that was leading to the low efficiency.

Cheers,
Marc