MadGraph5_aMC@NLO

how to merge two jets at parton level analysis

Asked by sudesh gupta

Hi,

I'm generating process e- p > e- b b~ j j. I'm interested to do analysis at parton level. To merge two jets of final state so that they are identified as one jet, I apply cuts
0.0 drjj
0.4 drjjmax
But madgraph is taking huge time and giving cross section in thounds pb (with a large error) due to divergences caused by this hard cut, right? How can I resolve this problem if I want to apply this cut which can act like merging at parton level analysis?

Thanks

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

The matrix-element is divergent when jet are colinear and therefore your cross-section is theoritically infinite.
In such limit, you need to resum the radiation and the description of collinear jet should be done by the parton-shower.

one suggestion would be to use a multiple multiplicity sample and use MLM (or CKKW-L) method to remove the double counting between the various sample.

Cheers,

Olivier

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sudesh gupta (sudesh12) said : 		#2

Thank you olivier.