Problem in running Sherpa for generating Multijet files

[Stefan Hoeche]

Dear Sherpa Experts,

I am trying to generate the gamma+njet events in Sherpa. I was successful in generating gamma+1jet events but when I increase the multiplicity to 2 (for example) I was stuck in an error. I have tried this on standalone Sherpa. I am putting all my cards and files on this link

​http://www.hepforge.org/~sudha/SherpaFiles/

There is also a log file which has the output of running Sherpa for gamma+2jet event.

Could anyone please have a look and let me know where could I be going wrong?

Thanks & Regards, Sudha.

[Stefan Hoeche]

Dear Sudha,

Sherpa syntax does not allow to start from a 2->1 process. However, your input file assumes exactly this case, as the curly bracket notation means 'up to 2 extra partons'. Also, you cannot generate METS-merged samples and restrict both EW and QCD order at the same time. Could you please try the following instead:

(beam){
 BEAM_1 = 2212; BEAM_ENERGY_1 = 3500;
 BEAM_2 = 2212; BEAM_ENERGY_2 = 3500;
}(beam)

(processes){
  Process 93 93 -> 22 93 93{1}
  Order_EW 1
  CKKW sqr(20.0/E_CMS)
  End process;
}(processes)

(selector){
 NJetFinder 1 10 0 1
}(selector)

(shower){
  CSS_EW_MODE = 1
}(shower)

(me){
  ME_SIGNAL_GENERATOR   = Comix
}(me)

We always strongly encourage usage of the most recent Sherpa release, which, as of today, is version 1.2.2. As you are running a standalone Sherpa, it should be no problem at all to switch. Otherwise you will not automatically benefit from all bugfixes and updates which might (and in your case will!) affect the physics results. Note that there are no interface changes when upgrading to version 1.2.2, and apperently you are referring to the manual of version 1.2.2 anyway. Also, you will find working examples for prompt photon production in Examples/Tevatron_Photons/ of the Sherpa-1.2.2 package. These setups are described in the online manual, for more information please refer to arXiv:0912.3501.

Best

Stefan

[Stefan Hoeche]

Dear Stefan,

Thanks for the reply. Could you please explain me what do you mean by "Also, you cannot generate METS-merged samples and restrict both EW and QCD order at the same time."

I made the changes as directed by you. Now I do not get any error but it is taking a lot of time for generating 100 events only. I have put some part of the log into a file named "out" (attached with the mail). If you see in the end it says - integration time: ( 1h 35m 23s elapsed / 2d 6h 11m 12s left ) which is the time left for it to complete. Does it take so much time to generate 100 events?

Regards, Sudha.

[Stefan Hoeche]

Dear Sudha,

the setup I sent you is not optimal for event generation. I was merely trying to show how the (processes) and (selector) section have to be modified to get Sherpa running at all. For your physics analysis, please do upgrade to version 1.2.2 and use the setups provided in Examples/Tevatron_Photons, which will simply have to be adjusted for LHC beam types and energies. Note that events will be weighted when using these inputs.

Best

Stefan

[Stefan Hoeche]

In case of further questions regarding this issue, please reopen the ticket.