first attempt to run SHERPA

[lorenzo]

Hi,

I have installed and compiled - I think correctly - SHERPA-MC-2.1.0. Just tried to run on the Examples/V_plus_Jets/LHC_ZJets example. By trying to do so I get the following error:

174:loop_pi=(0x7fff4745eb60){

cls = sum, hls = sum oew = 2, oqcd = 1, maxoew = 99, maxoqcd = 99 ckkw = 1, nlo = 3, mhv = 1 scale = 'METS{1.*MU_F2}{1.*MU_R2}{1.*MU_Q2}', kfactor = 'NO' megenerator = 'Amegic', loopgenerator = 'BlackHat' selectorfile = , mpi process = 0 gpath = , min t-channels = 0', max t-channels = 99 no_particle (2), NLO{,}: {

d db

} no_particle (2), NLO{V,}{2,7}: {

e- e+

}

} Sherpa: Single_Virtual_Correction::SelectLoopProcess throws not implemented:

Couldn't find virtual ME for this process.

Exception_Handler::GenerateStackTrace(..): Generating stack trace {

0x7fb0b5914840 in 'ATOOLS::Terminate()' (Exception_Handler.C:135) 0x402b02 in 'main' (Main.C:71)

}

Do you have any idea about what went wrong?

Cheers, lorenzo

[marek]

Hi Lorenzo,

did you link Sherpa against Blackhat, which is asked to compute the one-loop matrix elements (see the Loop_Generator setting for your process and the example's description in the manual ​https://sherpa.hepforge.org/doc/SHERPA-MC-2.1.0.html#LHC_005fZJets)?

Alternatively, Sherpa can also be linked to other one-loop codes to provide these corrections, such as OpenLoops. Once done, simply change the setting for Loop_Generator for the relevant processes, and the other code is used.

Hope this helps, Marek

PS: You might want to use the most recent Sherpa-2.1.1 as it contains bugfixes wrt. 2.1.0.

[Frank Siegert]

Also, if you simply want to try out Sherpa without going to NLO accuracy and without installing any additional tools, you can set LJET:=0 in the run card (and potentially also lower NJET, i.e. the number of partons in the multi-leg MEs).

Sherpas, are there any objections for our next release to simplify the V+jets example setups to NJET:=2; LJET:=0 to make them more beginner-friendly?

[Jovan.Mitrevski@cern.ch]

Are there instructions on how to link against Blackhat? I did:

./configure --prefix=/data/jmitrevs/sherpa_try2

and saw

config.status: creating AddOns/BlackHat/Makefile

I followed with make, but I see:

Making all in BlackHat make[3]: Entering directory `/data/jmitrevs/SHERPA-MC-2.1.1/AddOns/BlackHat' make[3]: Nothing to be done for `all'. make[3]: Leaving directory `/data/jmitrevs/SHERPA-MC-2.1.1/AddOns/BlackHat'

So it seems like nothing is done. I tried running the same Z+jets test and ran into the same problem.

[anonymous]

Please have a look at http://sherpa.hepforge.org/doc/SHERPA-MC-2.1.1.html#BlackHat-Interface You may also follow the instructions in Sec.9 of ​http://www.hepforge.org/archive/blackhat/BHpublic_draft.pdf. However, please do not use --enable-sherpaplugin when installing BlackHat. Instead, install BlackHat first, then use --enable-blackhat in Sherpa, as described in item 1 on page 14.