What is "Weight" in TGenPhaseSpace Generate function

Hi all,

I’m glad there is a noobie section, because I’m sure I am missing something trivial here…

I am playing with my first simulation using TGenPhaseSpace. I am generating events and then I am going to subsequently weight them with x-sects which have been kindly provided by a theorist for the channel I am looking at.

I noticed in the TGenPhaseSpace example that a double ‘weight’ is returned when generating an event, and the example fills the hist with these weights.

How is this weight being calculated? Is this just statistical probability within the phase space? I am seeing absolutely nothing about this in the user guide – any help would be deeply appreciated!

@moneta can you give a hand with this question?


Would be amazing if anyone could shed any light on this!! :pray:

Hi Paul,

See the original implementation: http://cernlib.web.cern.ch/cernlib/mc/genbod.html

GENBOD generates a multi-particle weighted event according to Lorentz-invariant Fermi phase space. It is a modification of the routine GENEV (in FOWL (W505)) and uses the method of Raubold and Lynch (see Ref. 1). The total CM energy as well as the number and masses of the outgoing particles are specified by the user, but may be changed from event to event. GENBOD generates the CM vector momenta (and energies) of the outgoing particles and gives the weight which must be associated with each event. The weight may then be multiplied by any ‘matrix element’ or geometrical detection function calculated by the user.

That should help, right? :slight_smile:

Cheers, Axel.