QCUT value for ttll process
Dear experts,
I want to generate a ttll/vv sample using a LO EFT model, with an extra parton (to better reproduce NLO predictions). The process is generated in the 5FS, with a cut inv_mll > 10.
Excerpt from proc card:
=============
define p = p b b~
define j = p
define l+ = e+ mu+ ta+
define l- = e- mu- ta-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
import model dim6top_LO_UFO
generate p p > t t~ l+ l- / h FCNC=0 DIM6=1 @0
add process p p > t t~ vl vl~ / h FCNC=0 DIM6=1 @1
add process p p > t t~ l+ l- j / h FCNC=0 DIM6=1 @2
add process p p > t t~ vl vl~ j / h FCNC=0 DIM6=1 @3
=============
Excerpt from run card:
=============
#******
# Matching parameter (MLM only)
#******
1 = ickkw ! 0 no matching, 1 MLM
1.0 = alpsfact ! scale factor for QCD emission vx
False = chcluster ! cluster only according to channel diag
5 = asrwgtflavor ! highest quark flavor for a_s reweight
False = auto_ptj_mjj ! Automatic setting of ptj and mjj if xqcut >0
30.0 = xqcut ! minimum kt jet measure between partons
...
10.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
...
5 = maxjetflavor ! Maximum jet pdg code
=============
The addition of the extra parton (@2 and @3) requires matching, and I am unsure what would be the most relevant choice for the QCUT scale in this scenario.
From the matching doc [0], I read that a value QCUT=30 is suggested for tt~, which suggests that I should use QCUT >= 30 in my case.
I already produced DJR plots for 3 QCUT values (using 30K LHE events each):
a) QCUT=20 (xqcut=10) [1]
b) QCUT=40 (xqcut=30) [2]
c) QCUT=50 (xqcut=30) [3]
Scenario b) does not exhibit a smooth transition, and c) does not look too satisfying neither. I may retry with QCUT=60 to see if it works better.
However I am surprised that the scenario a) I was using initially, which corresponds to a small QCUT value, seems to provide the smoothest transition, whereas I was expecting that a higher value is required for this kind of processes.
Could you please let me know what are your thoughts on this ? In particular, what do you think would be the most sensible QCUT choice for such a process, and are there figures of merits other than the DJR plot to assess the correctness of the matching procedure ?
Thank you, cheers,
Nicolas
[0] https:/
[1] https:/
[2] https:/
[3] https:/
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