Practical Pythia Event Filter (Jan)

Filtering of Pythia events preserving those which may fire HT trigger in the Endcap.

Motivation
In order to develop efficient e/h discrimination algo for reco of electrons from Ws it is necessary to generate sizable sample of QCD physics background events with 1e5 or more events triggering Endcap HT >10 GeV. The brute force approach (run PYTHIA+GSTAR+BFC long enough) is investigated by my not succeed due to low yield of events of interests.

Therefore, we are working on the in-fly Pythia events filtering. It must be more complex than accepting events with a single Pythia track above certain threshold because multiple tracks from jet (also hadrons) may deposit in a single tower cumulative energy exceeding the HT threshold even if all tracks have energy below this threshold.

The tricky part is to decide if EEMC response may be large before GSTAR does very time consuming simulation of EM & hadronic showers for the whole event.


Proposed Method (2-stage Pythia filtering)

  • Define : eta range [0.9,2.1], partonPTthres of 5 GeV, jetPTthres of 5 GeV (to be tuned later)
  • Inspect lines 7 & 8 of Pythia record (counting from 1) and drop event if none of partons is within eta range and above parton PT threshold.
    For survived events
  • Define 2D eta-phi grid covering eta [0.9,2.1] and 2pi in phi. Divide it in to cells of size 0.1x0.1. Clear grid for every event.
  • Loop over Pythia record 9..max and drop: partons, gluons, unstable particles, neutrino, muons.
    Retain all stable hadrons, e+, e- within eta range, project particle ET in to the eta-phi grid.
  • find seeds all cells with ET above 1/2 of jetThreshold.
  • for every seed from 8 pairs using every of its neighbors. If any pair ET sum is above jetThreshold event will be accepted and passed to GSTAR and eventually to BFC.

Additional comments:
* for Barrel eta range should be [-0.2,1.2] and cell size 0.05x0.05 in eta x phi.
* the code should be written in F77.
* at any step priority should be given to processing speed vs. program size. E.g. use lookup tables when reasonable.
* provide few QA histos generated with Pythia using HBOOK + kumac to display them

Content of Pythia record

1 proton 1
2 proton 2
3 parton from proton1
4 parton from proton2
5 parton from proton 1 after intial state radiation
6 parton from proton 2 after intial state radiation
7 parton 1 after scatter
8 parton 2 after scatter
9 ... intermediate and final partons/particles
....