Q6: How to overlap background events with signal events ?

A class JSFMergeEvent can be used for such purpose.

Let's consider the case to generate 10000 two-photon events and overlap these events to the signal event, $e^+e^-\rightarrow \mu^+\mu^-$.

First we need to generate two-photon event data. A sample JSF Configuration file, twogam.conf, is as follows.

JSFGUI.Pythia.Process.ZH:0
JSFGUI.Pythia.Process.twophoton:1
JSFGUI.RunMode:1
JSFGUI.OutputFileName: twogam.root
JSFGUI.OutputEventData:1

You can set these parameters from JSF Control Panel or use editor to edit directory. We use Pythia to generate two-photon events. Then do,

  jsf -b -q -conf=twogam.conf --maxevt=10000 gui.C

This will create a root file, twogam.root, containing 10000 events of two-photon process and cross section data.

Secondly, you generate the signal events, $e^+e^-\rightarrow \mu^+\mu^-$overlaying two-photon background events. A sample JSF configuration file is,

JSFGUI.Pythia.Process.ZH:0
JSFGUI.MergeEvent:1
JSFGUI.Pythia.Decay.Z:13
JSFGUI.Pythia.Process.gammaZ:1
JSFMergeEvent.DataFile:twogam.root
JSFMergeEvent.LumPerTrain:0.06

where, LumPerTrain specifies the integrated luminosity per beam crossing in unit of 1/nb. The value of 0.06 corresponds to the instantaneous luminosity of $9\times 10^{33}/cm^2/s$ operated at RF pulse frequency of 150Hz. There are about 100 bunches per pulse, but we assumed that we can not distinguish events from different bunch collisions happened in the same RF pulse. The average number of events in signal events is calculated as a product of LumPerTrain anda cross sections of background events. The number of background events in particular events is determined from Poisson distribution, and events are randomly selected from the background file, twogam.root, and their data are appended to the signal events.