Photon process

[dirkzerwas]

Hi @apricePhy,

I added PhotonProduction to the examples for Sherpa and gave Babayaga a try (runs awkwardly).

One thing I noticed:

• Babayaga wants thetaMin and thetaMax in degrees
• I added a conversion to the Selector class so that we can transform theta to eta (useful for the sherpa selector at least)
• we should probably agree on which unit we want for the angles? (degree or rad)
• the executable (called babayaga_fcc.exe) refuses all sqrts greater the 91.0GeV :(

Babayaga provides an lhe file, but the line for cross sections is empty, I will check with Fulvio if he knows,.....

There is a problem in the definition of the finalstate for whizard.py:

• the finalstate is generated from get_final_pdg_lis()
• which is list(_finfo)
• _finfo is filled in a loop as _finfo[p] = particle.,....
  This usually works, but if we have two equal particles in the final state (gamma, gamma) or ZZ, the list(_finfo) will return only a single particle.
  Need to look at this....

[dirkzerwas]

After some work on the Selectors (need to add units and a conversion from deg->rad->eta etc:

Photon91.0 sqrts= 91:
Madgraph 51.941 +- 0.027225 pb
Babayaga 0 +- 0 pb
Sherpa 52.1944 +- 0.00260813 pb

Correcting by had the .sin for whizard:
Whizard: 51.9975302 +- 0.0890507272 pb

Running by hand Babayaga (with the script):
::::::>>>>>> weighted events <<<<<<::::::
2 photons: 8.31194160 +- 0.19358241 ( 16.9165 %)
3 photons: 40.82313177 +- 1.12056181 ( 83.0835 %)
total: 49.13507337 +- 1.10691870 pb

Not bad, I would say :)

-> it could be that only the "unweighted" cross section is transmitted to LHE, however even requesting only 100 events unweighted (changed as the only parameter) leads to a minutes long processing without result.

I will check with Fulvio?

[apricePhy]

Hi @dirkzerwas,

Regarding the choice of deg or rad, I would follow the experimental convention i.e if they set the resolution of the detector in degrees we use degrees. I am not aware if this is universal though between the experiments. I would vote for radians and if people complain we can always add an option to specify

[dirkzerwas]

Hi @apricePhy,

sounds good in LHC world it's eta, in ALEPH it was degrees in analysis (mostly for 180. and avoiding to rounding effects due to pi in analyses), but also rad for the angular acceptance of forward lumi-cals.

I tried to do something (see main branch) for angles:
-> if "deg", "rad" or "eta" (the last does not have a unit)
-> at object creation all three alternatives are calculated and saved as attribute "min"+"unit" (mineta, mindeg, minrad)
-> get_Min gets an optional argument (default), so that min+unit is returned, either the original or the derived ones.
-> I adapted it through in the "one_particle_selector"

I have used it in Whizard, Madgraph, Babyaga to ensure a consistent setting according to the generator (Babayaga needs degrees, Whizard accepts degrees, but the default is rad, so we would need to write out the unit as well, breaking the nice logic you implemented.
Could you have a look?

One thing I noticed: current the "name" in the selector class is the process name, it could be helpful to add the name of the selector key (currently not transmitted), then it is easier to steer the unit (eg if "selector name == theta or rap or pseudorapidity or..... do the "deg,rad,eta" conversion. Just a thought....

Dirk

Hi @dirkzerwas,

Regarding the choice of deg or rad, I would follow the experimental convention i.e if they set the resolution of the detector in degrees we use degrees. I am not aware if this is universal though between the experiments. I would vote for radians and if people complain we can always add an option to specify

[dirkzerwas]

Carlo provided an upgrade to Babayaga to write the cross section to the LHEF. The two files are now in the hands of Gerri and Juan to update the KEY4HEP version. Once it's in the nightlies and we have checked, we can close this issue.

[dirkzerwas]

Juan implemented Carlo's changes, the fix works (tested on alma).
Rounding issue: need to implement a fixed format in conversions f16.8 (inspired by SLHA)