Dear Madgraph experts, I've been trying to generate EFT contributions to VBS WV semileptonic process using MG and reweighting. This is a simplified version of the process i'm using for testing purposes: [proc_card.dat] set group_subprocesses Auto set ignore_six_quark_processes False set loop_optimized_output True set complex_mass_scheme False import model SMEFTsim_U35_MwScheme_UFO-cqq1_massless define p = g u c d s b u~ c~ d~ s~ b~ define j = u u~ d d~ define l+ = e+ mu+ ta+ define l- = e- mu- ta- define vl = ve vm vt define vl~ = ve~ vm~ vt~ generate j j > w- z j j QED=4 QCD=0 SMHLOOP=0 NP=1, w- > j j NP=1, z > l+ l- NP=1 @0 NP=1 output WmTo2JZToLL_MG267 --nojpeg launch set nevents 100 The first question is: - Following previous threads [1], i understand that not all MG5 versions will work properly with the syntax above. Which version would you suggest to use in order to generate this process with decay chains reliably? I need LO weights for 15 operators (136 reweight points). One way is to turn on all the 15 operators in the param card and use the reweight module to turn on and off the operators such as [reweight_card.dat] change helicity False change rwgt_dir rwgt launch set SMEFT 2 1.0 set SMEFT 3 0.0 This procedure works fine for simple processes however, MG will take into consideration all diagrams involving the 15 operators even if their EFT coupling is set to 0. This leads to an unfeasible computational time. A solution would be to load a param card with just the operators we need at that point, reducing significantly the number of diagrams used to compute the "new" and "old" squared matrix elements. An example reweight_card is the following [reweight_card.dat] change helicity False change rwgt_dir rwgt launch set SMEFT 31 0.0 #as we only imported cqq1 originally, we set it to 0 to get SM x-sec weight change model SMEFTsim_U35_MwScheme_UFO-cHbox_massless launch models/SMEFTsim_U35_MwScheme_UFO/restrict_cHbox_massless.dat # only cHbox turned on with value 1 change model SMEFTsim_U35_MwScheme_UFO-cHbox_m1_massless launch models/SMEFTsim_U35_MwScheme_UFO/restrict_cHbox_m1_massless.dat # only cHbox turned on with value -1 I tried to generate events with the following MG5 versions and with cards reported above: MG5_aMC_v2_6_5 MG5_aMC_v2_6_7 MG5_aMC_v2_7_2 MG5_aMC_v2_7_3 MG5_aMC_v3_1_1. For all the versions except v3_1_1 the weights for different param cards are all identical [2]. Inspecting the reweight banner in the produce lhe events, it seems like new param cards are not loaded properly as the only operator appearing is cqq1 (the original one from the proc card) and not cHbox as imposed in the reweight card. For v3_1_1 the output reports different cross sections for the 3 hypothesis [4] as expected but the reweight field in the produce lhe banner still reports cqq1 operator only instead of cHbox [5] as for previous MG versions. I do not know if that's expected. Is this behaviour expected for old MG5 versions? If not, is there a patch i can apply to those versions in order to make them work (i'd really like to stick to older versions of MG5 e.g. MG_2_6_5 if possible and reliable)? You can find the UFO model with the restriction cards needed in [6]. Thank you for any help. Best, Giacomo -------------------------------------------------------------------------------------------------------------- [1] https://answers.launchpad.net/mg5amcnlo/+question/694807 [2] INFO: Original cross-section: 0.01231331 +- 0.0003383918 pb (cross-section from sum of weights: 0.012313305) INFO: Computed cross-section: INFO: rwgt_1 : 0.00370013995355 +- 0.00162138309569 pb INFO: rwgt_2 : 0.00369904505108 +- 0.0016211053997 pb INFO: rwgt_3 : 0.00369904505108 +- 0.0016211053997 pb [3] set param_card smeft 31 0.0 # orig: 1.0 change model SMEFTsim_U35_MwScheme_UFO-cHbox_massless ###################################################################### ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 #### ###################################################################### ... BLOCK SMEFT # 31 1.000000e+00 # cqq1 ... change model SMEFTsim_U35_MwScheme_UFO-cHbox_m1_massless ###################################################################### ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 #### ###################################################################### ... BLOCK SMEFT # 31 1.000000e+00 # cqq1 ... [4] INFO: Original cross-section: 0.0131389 +- 0.0004696784 pb (cross-section from sum of weights: 0.013138903) INFO: Computed cross-section: INFO: rwgt_1 : 0.00453341698314 +- 0.00198597459329 pb INFO: rwgt_2 : 0.00452848682598 +- 0.00198243881966 pb INFO: rwgt_3 : 0.00454112370342 +- 0.00199124229674 pb [5] set param_card smeft 31 0.0 # orig: 1.0 change model SMEFTsim_U35_MwScheme_UFO-cHbox_massless ###################################################################### ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 #### ###################################################################### ... BLOCK SMEFT # 31 1.000000e+00 # cqq1 ... change model SMEFTsim_U35_MwScheme_UFO-cHbox_m1_massless ###################################################################### ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 #### ###################################################################### ... BLOCK SMEFT # 31 1.000000e+00 # cqq1 ... Where we still see only cqq1 operator set to 1 which makes me think that things are not working properly. [6] http://gboldrin.web.cern.ch/gboldrin/generators/SMEFTsim_U35_MwScheme_UFO.tar.gz

When	Who	Action	New State
2021-12-17	Olivier Mattelaer	Answer	Answered
2021-12-17	Giacomo	Comment	Answered
2021-12-17	Olivier Mattelaer	Answer	Answered
2021-12-21	Giacomo	Confirm	Solved
2022-01-13	marco zaro	Comment	Solved
2022-01-13	Olivier Mattelaer	Comment	Solved

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