Filtered Simulations For The Development of Electron/Hadron Discrimination Algorithms

Critical to the upcoming flavor physics at STAR is efficient electron identification in the endcap, particularly amongst the dominant charged hadron/meson background.  The development of such discrimination algorithms, however, requires extensive simulations.  To reduce the computational burden of these simulations to a practical level we must modify starsim, reconstructing only those events of interest.

In this case we require electrons and charged hadrons/mesons in the endcap, and by adding a filter to PYTHIA we can ensure that only events matching the this criteria are reconstructed.  Below is a small study showing the significant reduction in computing time gained with this filtering.

The filtered simulations required a charged hadron or meson in the endcap with pT > 15 GeV before GSTAR was allowed to reconstruct the event.  Candidate refers to an event meeting the above requirements in the PYTHIA record, and projected refers to an extrapolation estimate for 80 pb-1.

Hadrons/Mesons Filtered Filtered (Projected) Unfiltered Unfiltered (Projected)
Candidates 10 18,604 10 18,604
Reconstructed GEANT Events 10 18,604 2863 5,326,325
Integrated Luminousity (pb-1) 0.043 80 0.043 80
Starsim Running Time (hours) 0.274 509  7.42  13,817
BFC Running Time (hours) 0.845 1572  24.2  45,023

Looking at the tracks in the GEANT record we see that the filtering worked as described.  Here every charged hadron/meson in every reconstructed event is shown, and in the Filtered sample we see a sharp cutoff at 15 GeV exactly as expected. 

The same analysis can be done for the W boson simulations, here instead requiring an electron(positron) from a W decay in the endcap with pT > 15 GeV.

Ws Filtered Filtered (Projected) Unfiltered Unfiltered (Projected)
Candidates 10  672 10  672
Reconstructed GEANT Events 10 10 357  24,020
Integrated Luminousity (pb-1)  1.189 80  1.189 80
Starsim Running Time (hours)  0.0361  2.42  0.822  55.3
BFC Running Time (hours)  0.0882  5.93  2.807  188.8

Again, comparing the two files shows the desired effects

In both cases the computational demands seem impractical, but one has to remember that this extrapolation is based on the use of a single processor.  Real jobs will be run in parallel, significantly reducing the projected times to more reasonable levels.  Despite the reduction, however, it might still be necessary to reduce the desired integrated luminousity slightly.