Decay using madspin in aQGC model

Asked by Yannis Maznas

Dear experts,

I'm using the SM_LT0_UFO aQGC model in order to produce pp > l+ l- j j with the following process card:
set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model /cvmfs/
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
generate p p > j j z z QCD=0 QED=4 NP==1
output VBS_nb_ZZ_NP_1_SM_LT0_UFO


Since I realized from previously opened tickets that it's not possible to ask for signal (NP==1) including the z > l+ l- decay I removed it from the process card and tried to decay Z into leptons using madspin with basic commands

> decay z > l+ l-
> launch

but it exits with the following error message:

INFO: decay channels for z : ( width = 2.444616 GeV )
INFO: BR d1 d2
INFO: 1.521096e-01 b~ b
INFO: 1.521096e-01 s~ s
INFO: 1.521096e-01 d~ d
INFO: 1.185885e-01 c~ c
INFO: 1.185885e-01 u~ u
INFO: 6.785578e-02 vt~ vt
INFO: 6.785578e-02 vm~ vm
INFO: 6.785578e-02 ve~ ve
INFO: 3.433465e-02 e+ e-
INFO: 3.433465e-02 mu+ mu-
INFO: 3.425739e-02 ta+ ta-
INFO: generating the production square matrix element
INFO: generate p p > j j z z QCD=0 QED=4 NP==1;
INFO: Done 20.25
INFO: generating the full matrix element squared (with decay)
INFO: generate p p > j j z z QCD=0 QED=4 NP==1, z > l+ l- QCD=99, z > l+ l- QCD=99 --no_warning=duplicate;
Command "launch" interrupted with error:
MadGraph5Error : Decay processes cannot specify squared orders constraints.
Please report this bug to developers

           More information is found in 'MS_debug'.

           Please attach this file to your report.
MadSpin>Traceback (most recent call last):
  File "./MadSpin/madspin", line 57, in <module>[sys.executable] + ['-O'] + sys.argv)
  File "/usr/lib64/python2.6/", line 481, in call
    return p.wait()
  File "/usr/lib64/python2.6/", line 1307, in wait
    pid, sts = _eintr_retry_call(os.waitpid,, 0)
  File "/usr/lib64/python2.6/", line 462, in _eintr_retry_call
    return func(*args)
Any idea what's the problem about and if I can bypass it?

Thank you in advance


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Olivier Mattelaer (olivier-mattelaer) said :

Hi yannis,

The first question is if you can use a "simpler" syntax like:
generate p p > j j z z QCD=0 QED<=3 NP<=1

If the decay chain syntax is not allowed in madgraph it will not be allowed in MadSpin, since MadSpin needs the full matrix-element from MadGraph in order to be able to run.

Now if you are ok to not have the full spin-correlation and not have off-shell effect, you can use madspin with the option
set spinmode=none. (or rely on the parton-shower for such decay).



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