MadGraph5_aMC@NLO

Madgraph VTIMUP field fill

Asked by Sara Vanini

I've generated BSM signals with Madgraph.

Looking at the lhe files, the field: VTIMUP (invariant lifetime -
distance from production to decay in mm) is not filled with the proper
value (0.0 is always there).

I'd need to know the distribution of this variable (distance from
production to decay, or, combined with the directional information from
the momentum, the vertex locations) of my exotic particles, so my
question is:
 is there a way to force Madgraph to fill the VTIMUP field ?

thanks
Sara

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Johan Alwall (johan-alwall) said : 		#1

Hello Sara,

The VTIMUP field is only relevant when you have a decaying particle in your events with lifetime over one micrometer or so (i.e., width < 2e-10). The value of the field can also be selected without any relation to the kinematics of the event. So it is safer and easier to implement this in a separate script (e.g. in the addmasses.py script) which can be run on the events after the run. What you need is just to pick a random number according to an exponential with width 1.973269718e-13/\Gamma (where \Gamma is the width of the particle in GeV).

Cheers,
Johan

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