Higgs decay to charm quark pairs

Hi,

By default the c mass is set at zero (and accordingly the Higgs do not couple to the c quark)
In oder to have this to work, you need to use the following model:
import model sm-full

Cheers,

Olivier

> On Feb 14, 2016, at 17:12, Inês Ochoa <email address hidden> wrote:
>
> New question #285512 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/285512
>
> Hi,
>
> I've tried generating ZH,H->cc events with aMC@NLO but the program crashes while trying to run Madspin with the following message:
>
> Command "generate p p > z h , h > c c~ , z > mu- mu+ " interrupted in sub-command:
> "generate p p > z h , h > c c~ , z > mu- mu+" with error:
> InvalidCmd : No amplitudes generated from process Process: h > c c~ WEIGHTED=4. Please enter a valid process
> Please report this bug on https://bugs.launchpad.net/madgraph5
> More information is found in 'MG5_debug'.
> Please attach this file to your report.
> Command "add process p p > z h pert_QCD, h > c c~ , z > mu- mu+ " interrupted in sub-command:
> "add process p p > z h pert_QCD, h > c c~ , z > mu- mu+" with error:
> InvalidCmd : No amplitudes generated from process Process: h > c c~ WEIGHTED=4. Please enter a valid process
> Please report this bug on https://bugs.launchpad.net/madgraph5
> More information is found in 'MG5_debug'.
> Please attach this file to your report.
> Command "launch --only_generation" interrupted with error:
> InvalidCmd : No processes generated. Please generate a process first.
> Please report this bug on https://bugs.launchpad.net/madgraph5
> More information is found in '/unix/atlas2/ines/software/MG5_aMC_v2_1_0/ZHcc_14TeV_2/run_08_tag_1_debug.log'.
> Please attach this file to your report.
>
>
> I have however the following information on the parameter card:
> DECAY 23 2.441404e+00
> DECAY 24 2.047600e+00
> DECAY 6 1.508336e+00
> DECAY 25 7.46830432e-03 # H width
> 6.64015055E-02 2 4 -4 # BR( H -> c cbar )
>
> Is there an additional step for this decay channel? It works fine with bb.
>
> Thanks!
> Ines
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Thanks for the prompt reply.

Loading this model causes a crash at the integration stage:

WARNING: A compilation Error occurs when trying to compile /unix/atlas2/ines/software/MG5_aMC_v2_1_0/ZHcc_14TeV_3/SubProcesses/P0_dxd_zh.
The compilation fails with the following output message:
    gfortran -O -fno-automatic -ffixed-line-length-132 -c -I. symmetry_fks_test_ME.f
    gfortran -O -fno-automatic -ffixed-line-length-132 -c -I. parton_lum_1.f
    run.inc:75.21:
        Included at parton_lum_1.f:51:

          common/to_rwgt/ do_rwgt_scale, rw_Fscale_down, rw_Fscale_up, rw_Rscale_do
                         1
    Warning: Padding of 4 bytes required before 'rw_fscale_down' in COMMON 'to_rwgt' at (1); reorder elements or use -fno-align-commons
    gfortran -O -fno-automatic -ffixed-line-length-132 -c -I. parton_lum_2.f
(...)

The version I'm using is v2.1.0. If it helps I can send the entire error message.

Thanks!
Ines

Dear Ines,

It is likely that this is already fixed since 2.1.0 is a very old version. So could you try with the latest version?

Cheers,

Olivier

Hi Olivier,

I've tried running with 2.3.3 instead, with the same parameter and run cards.

I still get a crash, a different one:
Error detected in "launch auto --parton"
write debug file /unix/atlas2/ines/software/MG5_aMC_v2_3_3/ZHcc_14TeV/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
aMCatNLOError : An error occurred during the collection of results.
 Please check the .log files inside the directories which failed:
       (...)

Looking into one of the log files there is this error messsage at the end:

 ---- POLES CANCELLED ----
 Error #6 in fks_Sij Infinity
Time in seconds: 1

As a reminder, the mg5 file I'm running looks like this:
import model sm-full
generate p p > z h [QCD]
output ZHcc_14TeV
launch -p
   MyParamCardFixedZBR.dat
   MyRunCard14.dat

cheers
Ines

Hi,
generating processes where particles decay into colored states is not 100% safe.
For this, I would suggest you to
1) create a restriction of the loop_sm where you keep the bottom and charm yukawa !=0, but you set their kinematic mass to 0
2) generate p p > mu+ mu- h [QCD] ; output

3)decay the higgs into cc~ with madspin
That should work without any problem...
Let me know if anything is unclear...
Cheers,

Marco

Hi Marco,

Thanks for your reply.

Regarding option 3), this is already what I'm doing. This error is occurring at the integration stage (while producing a grid pack), before any decay.

I found that running with 3FNS and loop_sm-c_mass runs smoothly but this is not exactly what I want.

I will try the first option, but can you give some pointers on how to do this? The parameter card I am using already has all the masses set to zero:
  1 0.000000 # d : 0.0
  2 0.000000 # u : 0.0
  3 0.000000 # s : 0.0
  4 0.000000 # c : 0.0

Cheers
Ines

Hi Ines,
so, the problem is that if you generate a process with a model which has a mass !=0, you cannot set it to 0 afterwards from the param_card.
So you need to use a model which starts with a zero charm mass.

So go into
models/loop_sm

cp restrict_c_mass.dat restrict_yc.dat
and set the kinematic mass for the charm and the bottom to 0, not the yukawa

Then, launch MG5_aMC@NLO

./bin/mg5_aMC
import model loop_sm-yc
p p > mu+ mu- h [QCD] ; output

edit the madspin card with h > c c~

and that should work OK.

The only problem is that now, in the folders with cc~ and bb~ in the initial state, you will include also diagrams with a hbb/ hcc vertex, because the corresponding yukawas are zero. Their contribution should be anyway rather small...

Another simpler solution would be to generate
p p > mu- mu+ h [QCD] with the usual loop_sm / loop_sm-no_b_mass, and do the h> c c~ decay within Pythia (there are no spin correlations in this case, so you do not lose anything doing this...)
Let me know if you need anything else...

Cheers,

Marco

Hi Marco,

Thanks for the details - this now runs smoothly. I have kept the generation as p p > z h [QCD] as I am cutting on the pT of the Z-boson. Can you just elaborate on the problem you mentioned? I guess it is not a problem if I generate explicitly zh instead of mumu h.

Finally, regarding your last suggestion: can you remind me / point me to instructions on how to set up the shower card so as to specify the decays? (I am using Herwig++).

Cheers
Ines

Thanks marco zaro, that solved my question.

Sorry, just one last question: I haven't touched the maxjetflavour parameter (always set to 4). Is there any consideration to be made here? I assume this is correct given that the charm kinematic mass was set to zero.

Thanks!

Hi Ines,
In ZH the higgs only couples to the Z boson. If you introduce a bottom and charm yukawa !=0, the higgs will also couple to b and c quarks in the initial state. This contributions should be anyway small.
Generating
p p > mu+ mu- h should run fine as well. The difference with Z h is in the fact that in the former case, you also integrate on the mu+mu- invariant mass (which is anyway dominated by regions close to the z mass), and you include spin correlations at the matrix element level.
If you generate p p > z h and then decay the z with madspin, you should get distributions which are very similar to p p > mu+ mu- h

For the shower card syntax, add a line
DM1 = 25 > -4 4 @ 1 @ 100

Finally, maxjetflavour from the run_card should not have any effect on this process (you don't have jets at the born).
Let me know if you need anything else...

Cheers,

Marco

Hi Marco,
Thanks!

Ines