Interfacing Sherpa with GoSam

[Generic User (don't modify these fields)]

Hi,

I'm trying to interface Sherpa-2.2.0 with GoSam-2.0 for QCD (and ultimately EW) corrections. I've been using the manual and the Z + jet example but have been unsuccessful. Could you give me some advice on what I'm doing wrong?

My Run.dat file is attached and copied below.

(run){

% general settings EVENTS 1000;

% tags and settings for scale definitions FSF:=1.0; RSF:=1.0; QSF:=1.0;

% tags and settings for ME generators ME_SIGNAL_GENERATOR Amegic LHOLE; LHOLE_OLP GoSam SHERPA_LDADD golem_olp; LHOLE_CONTRACTFILE OLE_order.olc; EVENT_GENERATION_MODE Weighted; RESULT_DIRECTORY Results.FSF.RSF.QSF

% model parameters MODEL SM; MASSIVE[15] 1; % collider setup BEAM_1 2212; BEAM_ENERGY_1 3500; BEAM_2 2212; BEAM_ENERGY_2 3500;

}(run);

(processes){

Process 1 -1 -> 11 -11 21; Order (*,2); NLO_QCD_Mode MC@NLO; Loop_Generator LHOLE; Scales FASTJET[A=antikt,PT=20.,ET=0,R=0.4,M=0]{FSF*H_T2}{RSF*H_T2}{QSF*PPerp2(p[4])} RS_Enhance_Factor 10; End process;

}(processes);

(selector){

Mass 11 -11 66. 116. NJetFinder 1 20. 0. 0.4 -1

}(selector);

To attempt to interface with GoSam, what I do is, 1) Install sherpa with config --enable-lhole, -- enable-fastjet="to dir"

2) Run the Run.dat above

• This gives the message

" ME_Generators::ME_Generators(): Try loading 'LHOLE' from 'libSherpaLHOLE'.

ME_Generators::ME_Generators(): ME generator 'LHOLE' not found. Ignoring it."

but produces an OLE_order.lh file.

3) I run gosam with the OLE_order.lh file, which produces a OLE_order.olc and a libgolem_olp.so file.

4) I copy the OLE_order.olc file to my Sherpa run directory and make a symbolic link from the Sherpa directory to libgolem_olp.so.

5) I ./makelibs and then Run sherpa again. The gosam logo appears, but I'm suspicious that it isn't used as later I get the message "You are using OneLOop-3.5". Amegic runs but eventually fails with the message

"Sherpa: CS_Gamma::TrialWeight throws fatal error: ep 07 10:50

Invalid amplitude for 2_4dGe-e+Gd

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

0x7f6fba4ac330 in 'ATOOLS::Terminate()' (Exception_Handler.C:135) 0x400fe3 in 'main' (Main.C:33)

}"

I've attached the tarred status directory.

Any advice/help would be welcome. Thank you.

[Generic User (don't modify these fields)]

tarred/zipped status directory

[Generic User (don't modify these fields)]

Run.dat file

[marek]

Hi,

not having tested your setup in detail here a few comments:

to 2) Please ignore this output, the LHOLE interface is nonetheless used, internally it simply is not a ME Generator but a one loop ME interface.

to 5) As far as I can tell GoSam is at least initialised, as the banner indicates. OneLOop is a library for scalar integrals only and thus might be used by GoSam to compute those (please check with the GoSam authors). The crash you are experiencing does not come from Amegic but from our MC@NLO and originates in the fact that you only specified one Born flavour combination, something that is ill defined at the level of a full NLO calculation. Here, the indicated splitting function is tried to be generated by the MC@NLO but not present in your setup, hence the crash. Please try again with 93 93 -> 11 -11 93.

Hope this helps, please reopen if the problem persists. Marek