MadGraph5_aMC@NLO

Missing decays with bottom quarks after upgrading to v2.3

Asked by Inês Ochoa

Dear aMC@NLO team,

We noticed that by changing from version v2.2 to v2.3 of aMC@NLO, the Z->bb decay went missing from our final state, as evidenced by this line on the log file:
> Pass the definition of 'j' and 'p' to 4 flavour scheme.

We know this is triggered by the fact that we’re using a massive b in our proton definition. We understand that v2.3 fixes this inconsistency by forcing 4FNS for the proton, but we would like to understand if the change to the jets (“j”) is intended and if so, why. Unfortunately, this update between versions resulted in missing decays (e.g. z > j j). Can you please provide more information?

I am pasting the relevant portion of the card below:

set group_subprocesses Auto
set ignore_six_quark_processes False
set gauge unitary
set complex_mass_scheme False
import model sm

# Define multiparticle labels
define p = g u c d s u~ c~ d~ s~ b b~
define j = g u c d s u~ c~ d~ s~ b b~

define l+ = e+ mu+ ta+
define l- = e- mu- ta-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~

import model Vector_Triplet_UFO

generate p p > vz / a, (vz > z h / a, h > j j, z > l+ l- / a) @1 QED=99 QCD=99

Best
Inês

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Inês Ochoa
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Yes this is done on purpose. The reason is multi jet sample ( w plus jet, top plus jet,...) where you do not want to include b jet where you want to include in the jet definition only the massless quark. This is also consistent with the running of alphas.

Now you can use other multi particle name or you can set the define command after the import one as well.

I’m sorry for the time lost on this.

Cheers,

Olivier

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________________________________
From: <email address hidden> on behalf of Inês Ochoa <email address hidden>
Sent: Friday, May 24, 2019 6:02 PM
To: Olivier Mattelaer
Subject: [Question #681050]: Missing decays with bottom quarks after upgrading to v2.3

New question #681050 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/681050

Dear aMC@NLO team,

We noticed that by changing from version v2.2 to v2.3 of aMC@NLO, the Z->bb decay went missing from our final state, as evidenced by this line on the log file:
> Pass the definition of 'j' and 'p' to 4 flavour scheme.

We know this is triggered by the fact that we’re using a massive b in our proton definition. We understand that v2.3 fixes this inconsistency by forcing 4FNS for the proton, but we would like to understand if the change to the jets (“j”) is intended and if so, why. Unfortunately, this update between versions resulted in missing decays (e.g. z > j j). Can you please provide more information?

I am pasting the relevant portion of the card below:

set group_subprocesses Auto
set ignore_six_quark_processes False
set gauge unitary
set complex_mass_scheme False
import model sm

# Define multiparticle labels
define p = g u c d s u~ c~ d~ s~ b b~
define j = g u c d s u~ c~ d~ s~ b b~

define l+ = e+ mu+ ta+
define l- = e- mu- ta-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~

import model Vector_Triplet_UFO

generate p p > vz / a, (vz > z h / a, h > j j, z > l+ l- / a) @1 QED=99 QCD=99

Best
Inês

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Revision history for this message
Inês Ochoa (inesochoa) said : 		#2

Hi Olivier,

Thanks a lot for the quick reply!

Inês