MadGraph5_aMC@NLO

ISR with MadWeight

Asked by Juan Pablo Gomez

Dear all,
I am trying to use MadWeight to include the effects of ISR. I have seen that in the Madweight_card.dat there is an option for such purpose, which says:
isr 0 # isr=0 : ignore ISR effect (except if all FS particles are visible)
                                # isr=1 : correct kinematic based on reconstructed Pt(isr)
                                # isr=2 : correct kinematic based on reconstructed Pt(isr)
                                # + boost the weight to the CMS frame

My questions are:
1. In MadWeight the effects of ISR are managed substracting the total Pt of the ISR from the IS particles?
2. What is the difference between option 1 and 2?.
3. Which jets in the LHCO file are taken as the ISR?

Thanks in advance for your help,

JP

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Pierre Artoisenet Edit question
Solved by:
Juan Pablo Gomez
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Revision history for this message
Pierre Artoisenet (partois) said : 		#1

Hi Juan Pablo,

The different ISR modes are rahter simple and ad-hoc prescriptions to correct
for the kinematical effects of ISR:

ISR=0: no correction, EXCEPT that if all particles are visible, then the
       transverse momentum of ISR is estimated from the LHCO information as

       PT(ISR) = -PT(jets, leptons)

       During the phase-space integration, the PT of the parton-level final state
       is forced to counter-balance PT(ISR)

ISR=1: The transverse momentum if ISR is read from the LHCO event as follows:

       PT(ISR) = -PT(all jets, leptons) - PT(missing particle)

       During the phase-space integration, the PT of the parton-level final state
       is forced to counter-balance PT(ISR)

ISR=2: Same as for ISR=1, except that the value of the weight is not given in the lab frame.
       Point-by-point in the phase-space, the weight contribution is evaluated in a frame
       where the PT of the parton-level final state is zero. This option is there mainly for historical
       reasons, its usefullness is not clear anymore.

ISR=3: this mode has been implemented for very specific processes.
       One of them is p p >Z > mu+ mu-.
       In that case, no contraint is applied on pT(mu+mu-) point-by-point in the phase-space:
       the phase-space generation of pT(mu+mu-) only depends on the transfer function.
       Note that this changes the dimension of the weight, because it amounts to remove
       the delta function on PT in the definition of the weight.
       The weight contribution is translated to a frame where pT(mu+mu-)=0 point-by-point in the
       phase-space.

Le me know if you have further questions,

Pierre

Revision history for this message
Juan Pablo Gomez (djp) said : 		#2

Thanks a lot Pierre for your very clear answer!!!
Cheers,

JP