higgs decay problem

[setesami@cern.ch]

Dear Expert,

I am producing a process with the higgs in the final state. But when i am trying to add the higgs decay it dose not work and gives me "NO hard process found" . I am wondering if the higgs decay is included in the sherpa.

Thanks Mohsen

[Frank Siegert]

Dear Mohsen,

Yes, Higgs decays are possible in Sherpa. There are two different options for enabling decays, one directly in the matrix element, cf. our manual at ​https://sherpa.hepforge.org/doc/SHERPA-MC-2.1.1.html#Decay , and one via a decay afterburner, cf. our manual at ​https://sherpa.hepforge.org/doc/SHERPA-MC-2.1.1.html#Hard-decays .

If you encounter any specific problems with one of these options we need your run card to see what went wrong.

Cheers, Frank

[anonymous]

Dear Frank, Thank you very much for your quick reply. Actually i have tried both options you mentioned me but it dose not work. I have used one of the online manual examples which is "Associated t anti-t H production at the LHC" and then adding the decay as follow.

Process 93 93 -> 25[a] 6 -6; Decay 25[a]-> 25[b] 25[c] Decay 25[b] -> 5 -5 Decay 25[c] -> 4 -4

but i am getting the " No hard process found" message. this Run.dat it works before i start to decay 2 higgs as below but as i said did not work for up decay scheme.

Process 93 93 -> 25[a] 6 -6; Decay 25[a]-> 25 25

the data card is in the attachment.

Thank you very much. Mohsen

[Frank Siegert]

Hi Mohsen,

By default the c and b quarks are treated as massless in Sherpa's matrix elements, and thus they don't couple to the Higgs. To allow for h->cc and h->bb decays you have to switch the quarks to massive by adding MASSIVE[4]=1 and MASSIVE[5]=1 such that their Yukawa couplings become non-zero, cf. http://sherpa.hepforge.org/doc/Sherpa.html#Model-Parameters .

Cheers, Frank

[setesami@cern.ch]

Dear Frank,

I have added MASSIVE option and did not work again. if you use Z boson instead which is not zero by default is also the same issue. have you tried to re-run my Run.dat to see if this is the case.

Thanks Mohsen

[Frank Siegert]

Yes, I have tested your run card with these two additional options (in the run section), this fixes the "no hard process found" message. You might instead get a different message now, "Couldn't find virtual ME for this process"? This appears if you have not compiled the corresponding loop library plugin (cf. http://sherpa.hepforge.org/doc/Sherpa.html#LHC_005fHTTBar ). I think for your process no loop matrix elements are available yet, so you probably want to run it in LO mode, in which case you have to adjust your run card according to our manual (mainly remove the NLO_QCD_Mode MC@NLO line). I'm attaching a thus modified run card, but obviously you want to check whether this is really what you want according to our manual.

Cheers, Frank

[setesami@cern.ch]

Sorry you were right . now it is working

Cheers Mohsen

[setesami@cern.ch]

Dear Frank,

Thank you very much for your answer now it is working on SM but i have to add that the same issue is happening when you are using the non standard model assumption for example the ADD model then final higgs decay gives you "No hard process found message".

Cheers Mohsen

[setesami@cern.ch]

Dear Frank,

Should i open a new ticket for my previous question or it could be included in this ticket as well.

Regards, Mohsen

[setesami@cern.ch]

Just kindly to ask if i get the answer from my previous question.

Thank you very much for your cooperation. Mohsen

[Frank Siegert]

Dear Mohsen,

Thanks for reporting this issue. I have now looked into it, and indeed the ADD model implementation has a bug of not enabling the Higgs-couplings, which is why your process is not found. I am attaching a patch which fixes this issue, you can apply it with:

cd SHERPA-MC-2.1.1 patch -p0 < add-higgs.patch make -C MODEL install

Can you try it with this patch?

Cheers, Frank

[setesami@cern.ch]

Dear Frank,

Sure. I have Sherpa 2.1.1 on the MacOS installed and applying your first command "patch -p0 < add-higgs.patch" gives this error patch: Only garbage was found in the patch input. should this command work on MAc as well?

Cheers, Mohsen

[Frank Siegert]

Yes, it should. Are you sure you downloaded the raw patch file ("Original format" at the bottom of the page you get to from the link above)? Please check the file you downloaded.

[setesami@cern.ch]

Dear Frank,

Sorry to reply late as i did something to my sherpa and it was destroyed so i had to re-install it. Yes you are right i download the patch correctly now and Yes it knows the process now.i still need to see if it gives me the cross section as well. i will let you with the result. Thank you very much

Cheers, Mohsen

[setesami@cern.ch]

Dear Frank,

Thank you very much now it completely works.

Cheers, Mohsen

[setesami@cern.ch]

Dear Frank,

As in my previous post. now the decaing of higgs to bbar tautau and etc is ok but it seems sherpa still did not know the higgs->gamma gamma for this model. do you think this also need to be fixed or am i missing something here.

Cheers, Mohsen

[Frank Siegert]

The Higgs -> gamma gamma couplings do not exist at tree level in the Standard Model, and are thus not automatically generated. They are implemented as effective vertices in the SM+EHC model, cf. http://sherpa.hepforge.org/doc/Sherpa.html#EHC

But it is not possible to combine ADD and EHC out of the box, you would need to write your own model implementation for that if you have a bit of experience in C++. The general steps are described in http://sherpa.hepforge.org/doc/Sherpa.html#Exotic-physics and you could use the building blocks from ADD and SM+EHC for that.

[setesami@cern.ch]

Thank you very much for the instruction. i will try to implement it.

Cheers, Mohsen