Loop induced gg->H->ZZ with Z decay by Madspin

Hi,

MadSpin does not work for loop induced processes (since we are not able to evaluate the associated matrix element).
If you do not care about full spin correlation then you can use the shower to do the decay.
Otherwise, the solution is to replace the header of the file to make it identical to a sample generated with the heft theory.
Then you can run MadSpin on that event sample without any problem.

Cheers,

Olivier

> On Mar 30, 2016, at 16:22, Lailin Xu <email address hidden> wrote:
>
> New question #289572 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/289572
>
> Hi,
>
> When I generate process p p > h > z z [QCD] and use MadSpin for Z boson decay, it crashed during decay with the following error:
>
> Command "generate_events run_01" interrupted with error:
> ValueError : need more than 1 value to unpack
>
> I'm using version 2.3.3.
> The detailed log file for debug can be found at: http://lxu.web.cern.ch/lxu/public/MG/run_01_tag_1_debug.log
>
> When I use the HEFT model, p p > h > z z, the decay with Madspin just works very well.
>
> Could you let me know what could be wrong?
>
> Thanks,
> Lailin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Many thanks for your reply.
I'll try to change the header file and run madspin
( I guess changing the model in madspin card should also work, eg, sm instead of loop_qcd_qed_sm).

Can I ask another question, which is not related with the MadSpin issue?
I understand that by using pp>h>zz [QCD], I can only get off-shell Higgs, and if I do
pp>h>e+ e- mu+ mu- [QCD], then I get only on-shell Higgs.
Is there a way to generate both on-shell and off-shell Higgs in one process, so that I can get the whole Higgs lineshape?

Thanks!
Lailin

Hi Olivier,

So I changed the model in MadSpin parameter card, but it then it got stuck when running the decay:

=======
...
generate 03:45:43 INFO: Extracting the banner ...
generate 03:45:43 INFO: process: p p > h > z z
generate 03:45:43 INFO: options:
generate 03:45:43 INFO: detected model: loop_qcd_qed_sm. Loading...
generate 03:45:45 import model heft --bypass_check # Madspin does not work for loop-induced process
generate 03:45:45 WARNING: No param_card defined for the new model. We will use the default one but this might completely wrong.
generate 03:45:45 INFO: detected model: heft. Loading...
generate 03:45:45 INFO: Restrict model heft with file ../../../models/heft/restrict_default.dat .
generate 03:45:45 INFO: Run "set stdout_level DEBUG" before import for more information.
generate 03:45:45 Kept definitions of multiparticles l- / j / vl / l+ / p / vl~ unchanged
generate 03:45:45 Defined multiparticle all = g u c d s u~ c~ d~ s~ a ve vm vt e- m- ve~ vm~ vt~ e+ m+ t b t~ b~ z w+ h h1 w- tt- tt+
generate 03:45:45 set BW_cut 1000000 # off-shell
generate 03:45:45 set max_weight_ps_point 400 # number of PS to estimate the maximum for each event
generate 03:45:45 decay t > w+ b, w+ > all all
generate 03:45:45 decay t~ > w- b~, w- > all all
generate 03:45:45 decay w+ > all all
generate 03:45:45 decay w- > all all
generate 03:45:45 decay z > l+ l-
generate 03:45:45 decay z > j j
generate 03:45:46 launch
....

generate 03:48:10 INFO: MadSpin: Decaying Events
generate 03:48:10 INFO:
generate 03:48:10 INFO: Decaying the events...
=======

From my previous experience, the decay with MadSpin is quite fast. But here it got stuck for a few hours.
It seems stuck with a command "check", though I'm sure where this command is.

Could you help me with this problem?
Thanks,
Lailin

Hi,

I understand that by using pp>h>zz [QCD], I can only get off-shell Higgs, and if I do
pp>h>e+ e- mu+ mu- [QCD], then I get only on-shell Higgs.

No this is not correct,
 pp>h>zz [QCD] gives only off-shell Higgs simply due to the requirement of the two z to be onshell (as final state)
pp>h>e+ e- mu+ mu- [QCD] includes both on-shell and off-shell Higgs.

the > X > syntax only requires to have at least one particle X to be in S-channel.

Cheers,

Olivier

Thanks Olivier Mattelaer, that solved my question.