How to select ISR photons in cuts/expressions

Hi Tabira,
if you a beam statement that cotains ISR or CIRCE+ISR in the form
beams = e1, E1 => isr
or
beams = e1, E1 => circe2 => isr
two additional photons from the ISR will be two photons in the (sub)events in additional to possible (hard) ME=matrix element photons., e.g. in radiative Bhabha:

process rad_bab = e1, E1 => e1, E1, A

You can then restrict your subevent in the following way:

cuts = let @me_photons = select if Index > 2 [A] in
     all E > 10 GeV [@me_photons] and all Theta > 10 degree [@me_photons]

In the first line a subevent @me_photons is defined restricting to indices > 2 (so here only the 3rd, i.e. matrix element photon) to which then the energy and angular cuts in the second line are applied (but not the ISR photons).
Best,
    JRR

Thanks a lot.

I would like to make a check. With these cuts, I get a cross section an order of magnitude lower for the process ee->vvXXA (~0.56fb, isr on) as compared to just ee->vvXX (~10 fb, isr off).

My code,

model = z2btype2UFO (ufo)

Ma = 50 GeV
betaH = 1.40564765
process eevvaaA = e1 , e1bar => nu1:nu2:nu3, nu1bar:nu2bar:nu3bar, a, a, A

beams = e1 , e1bar => isr
Wh2 = 4 MeV
sqrts = 250 GeV

compile
?fatal_beam_decay = false

isr_q_max = 20 GeV
isr_alpha = 1./137.
epa_q_min = 5 GeV
epa_x_min = 0.01

cuts = let subevt @meA = select if Index > 2 [A] in
  all E > 10 GeV [@meA] and all Theta > 10 degree [@meA]

integrate (eeaaA)

simulate (eeaaA)
show (results)

output,

| ------------------------------------------------------------------------
| Phase space: 201 channels, 11 dimensions
| Phase space: found 201 channels, collected in 41 groves.
| Phase space: Using 434 equivalences between channels.
| Phase space: wood
| Beam structure: isr, none => none, isr
| Beam structure: 1 channels, 2 dimensions
| Applying user-defined cuts.
| Starting integration for process 'eeaa'
| Integrate: iterations not specified, using default
| Integrate: iterations = 10:20000:"gw", 5:50000:""
| Integrator: 41 chains, 201 channels, 13 dimensions
| Integrator: Using VAMP channel equivalences
| Integrator: 20000 initial calls, 20 bins, stratified = T
| Integrator: VAMP
|=============================================================================|
| It Calls Integral[fb] Error[fb] Err[%] Acc Eff[%] Chi2 N[It] |
|=============================================================================|
| VAMP: parameter mismatch, discarding grid file 'eeaa.m1.vg'
   1 19899 3.4254508E-01 6.05E-02 17.67 24.93* 1.80
   2 19759 1.1077369E+00 8.12E-01 73.28 103.00 0.26
   3 19613 4.1354438E-01 9.38E-02 22.69 31.77* 0.24
   4 19472 7.2171293E-01 2.74E-01 38.02 53.06 0.11
   5 19336 3.5393179E-01 2.37E-02 6.69 9.30* 0.93
   6 19210 5.6186507E-01 1.03E-01 18.26 25.31 0.29
   7 19100 4.2440681E-01 3.34E-02 7.88 10.89* 0.54
   8 18991 4.8988865E-01 4.52E-02 9.22 12.71 0.48
   9 18884 5.3256700E-01 2.60E-02 4.89 6.72* 1.24
  10 18788 5.3691332E-01 1.84E-02 3.43 4.70* 1.59
|-----------------------------------------------------------------------------|
  10 193052 4.7291882E-01 1.11E-02 2.35 10.32 1.59 5.79 10
|-----------------------------------------------------------------------------|
  11 49976 5.4062312E-01 1.72E-02 3.17 7.09 0.62
  12 49976 5.5813105E-01 1.76E-02 3.15 7.04* 0.40
  13 49976 5.5768946E-01 1.71E-02 3.07 6.86* 0.37
  14 49976 5.6744811E-01 1.97E-02 3.47 7.76 0.37
  15 49976 6.7984786E-01 1.41E-01 20.69 46.25 0.10
|-----------------------------------------------------------------------------|
  15 249880 5.5569956E-01 8.88E-03 1.60 7.99 0.10 0.48 5
|=============================================================================|
| Time estimate for generating 10000 events: 0d:02h:12m:11s
| Starting simulation for process 'eeaa'
| Simulate: using integration grids from file 'eeaa.m1.vg'
| RNG: Initializing TAO random-number generator
| RNG: Setting seed for random-number generator to 11366
| Simulation: requested number of events = 0
| corr. to luminosity [fb-1] = 0.0000E+00
| Events: reading from raw file 'eeaa.evx'
| Events: parameter mismatch, discarding old event set
| Events: closing raw file 'eeaa.evx'
| Events: generating new events
| Events: writing to raw file 'eeaa.evx'
| Events: generating 0 unweighted, unpolarized events ...
| Events: event normalization mode '1'
| ... event sample complete.
| Events: closing raw file 'eeaa.evx'
eeaa:
   5.5569956E-01 +- 8.88E-03 fb ( 1.6 %)
| There were no errors and 18 warning(s).
| WHIZARD run finished.

Could you kindly tell me if I am missing something? or is this a sensible result for this process? Thanks a lot for all your help!

Hi Tabira,
one genereal remark: the adaptation of the integration looks ok, but not overwhelmingly good. This is a 2->5 process with beam structure, so the number of calls per iteration is clearly to small. I would raise this to 100k or 200k. On the other hand, maybe 8+3 iterations are enough.
Regarding the size of cross sections, you can calibrate this by comparing
1) ee->vvXX vs. ee->vvXXA without ISR
2) ee ->vvXX with and without ISR.
This should give you a feeling whether cross sections have the correct order of magnitude.
Best,
    JRR

Thank you! I increased the calls per iteration and it appears to be converging fine now but still with the same order of magnitude, ~ 0.30 fb

I also made the comparisons:

1) ee->vvXX w/o ISR ~11.2 fb
    ee->vvXXA w/o ISR ~ 0.38 fb

2) ee ->vvXX w ISR ~10.2 fb and w/o ~ 11.2 fb

It seems just the addition of the photon reduces the x section by a lot.. I also checked for ee -> ZXX and ee->ZXXA (w/o ISR) where it also largely reduces from ~80fb to ~3.1 fb. So maybe it is fine. I am marking this problem as solved as the original question was already answered and I have no more for the time being. Thanks a lot for helping me out!