beamstrahlung effect for 1TeV ILC

Hi Saumyen,
first of all replace the beam spectrum by
$circe2_file = "1000_B1b_ws_ee018.circe"
which you can download from the WHIZARD Hepforge page:
https://whizard.hepforge.org/circe_files/ILC/
Secondly, I wouldn't use RAMBO as phase space method, it is not the most efficient one, just erase the line with $phs_method and WHIZARD will take its default phase space parameterization, called wood.
Some more remarks: you need cuts to get a finite cross section. This example has been discussed in the Snowmass software tutorial on Monday, cf. slide 22:
https://indico.fnal.gov/event/45413/contributions/196321/attachments/135130/167437/WHIZARD_Snowmass_tutorial_v2.pdf
Note that in the event records you will then see 5 photons, 4 collinear ones which are the beam remnants from beamstrahlung and ISR, and the matrix element photon. There is a possibility to generate finite pT for the ISR photons, search in the WHIZARD manual for the topic ISR handler.
Best,
    JRR (Juergen)

Thanks a lot for the response and valuable suggestions.
I downloaded the circe file. But where to put that in? I put that in home and edited the script like in below:
#-----------------------------------------
model = SM
process Bhaba = "e-", "e+" => "e-","e+", "A"
sqrts = 1 TeV
beams = e1, E1 => circe2 => isr
beams_pol_density = @(+1), @(+1)
beams_pol_fraction = 80%, 30%
$circe2_file = "/home/pdas/1000_B1b_ws_ee018.circe"
$circe2_design = "ILC"
?circe_polarized = false
cuts = all E > 8 GeV [photon]
 and all 174.5 degree > Theta > 5.5 degree [photon]
 and all Pt < 500 GeV [photon]
 and all 174.5 degree > Theta > 5.5 degree [lepton]
 and all Dist < 0.4 [electron, positron]
n_events = 1000
sample_format = lhef
simulate (Bhaba)
#-----------------------------------------

It showed an error saying,
*** FATAL ERROR: Variable '?circe_polarized' set without declaration

Then I edited the line to (although, the manual says without quotation marks)
?circe_polarized = "false"

Then I got this error:
*** FATAL ERROR: Syntax error (at or before the location indicated above)

This, I can't figure out what's wrong with. Could you guide me to resolve this issue?
Another thing . I went through the slides you share (would have been great if I could join). There in slide 22 (or page 48), I found different types (genres) of cuts. Can you explain how they important? Or, may be where can I find more detail on them.

Regards,
Saumyen

The variable is ?circe2_polarized not just ?circe_polarized.
Regarding the cuts, I consider relatively self-explanatory. To fully grasp the kinematic importance of cuts depends on the considered
process and physics behind this. Probably you should look into some of the LEP II articles on (radiative) Bhabha scattering to check on the cuts, or on similar analysis for ILC.

Okay, the first problem is resolved. I changed the line
?circe_polarized = false
to
?circe2_polarized = false
Sorry!

But using that too, I got an error as the following:
******************************************************************************
*** ERROR: Simulate: sum of process integrals must be positive; skipping.
******************************************************************************
and there's no .lhe file.
But, removing the lines with ISR and beamstrahlung, I'm getting the no error and also the .lhe file.

Can you give me some idea what's going wrong?

Regards,
Saumyen

Yes, okay I will surely look at some literatures on radiative Bhaba...
Thank you so much. (actually I saw your reply a bit late)

Regards,
Saumyen

The error message tells you that the integrated cross section is zero. Probably you applied cuts on photons that affected also
the collinear photons. You need to define a subevent where you exclude the ISR etc. photons by means of
let cuts =
 let subevt @non_isr_photon = [ select if Index > 2 [A] ] in
   all ....... [@non_isr_photon]

Thanks a lot Juergen. That worked.
But how can I used polarised beam option with this circe files? When I'm giving the commands for polarised beam
beams_pol_density = @(+1), @(+1)
beams_pol_fraction = 80%, 30%
with
?circe2_polarized = true

I'm getting the error message:
******************************************************************************
*** FATAL ERROR: CIRCE2: Beam polarization can't be set for polarized data file
******************************************************************************

But giving the polarisation options for the beam but setting
?circe2_polarized = false

it's running fine. Is this way to run? Because I don't know if setting
?circe2_polarized = false
the beam polarisation will be implemented or not...

Regards,
Saumyen

Hi Saumyen,
indeed the Sec. 5.5.7 of the manual on beamstrahlung is not totally up-to-date, and the question is an obvious one to ask. When setting ?circe2_polarized to true the assumption is that there are helicity luminosities available in the CIRCE2 beam spectra, i.e. that these spectra are exclusive in the four electron/positron helicity combinations. This has to based on a helicity exclusive simulation done with the machine simulation tool GuineaPig which to my knowledge has not been done since the days of the TESLA project in the early 2000s. In such a case the polarization fractions are encoded in the beam spectra themselves and WHIZARD rightfully won't let you set the polarization fractions yourself. That said, all the beam spectra for ILC and CLIC (as well as those for CEPC as well) are unpolarized or polarization averaged. So the assumption is made that the squeezing of the beams to nanometer sizes in the interaction region of the collider leaves the polarization of the original beams unchanged. The latter are set within WHIZARD (as you did) via beams_pol_fraction, and the mandatory flag for CIRCE2 is the
?circe2_polarized = false.
Cheers,
    JRR

Thank you so much Juergen for the explanation. I'll follow that.
In the meantime I wanted to know how can I link my Pythia8 package with Whizard. How do I re-configure this with Pythia8 and HepMC? Also if possible with Delphes (But this is not critically important). Do I have to reinstall this ?
Another thing, I was trying to get plots of a couple of variables with the following commands:
n_events = 1000
analysis = record e_photon (eval E [A]) ;
    record pt_photon (eval Pt [A])
histogram e_photon (0 GeV, 500 GeV, 10 GeV)
histogram pt_photon (0 GeV, 500 GeV, 10 GeV)
plot e_photon
sample_format = lhef
simulate (Bhaba)
compile_analysis {$out_file = "test.dat"}

But no plots are coming. What might be the probable reason? Is some package missing in my system? I am though getting the .dat file and some files in .dvi, .ps, .pdf format. Also .mp file is there. But in the PDF or PS files no istogram is there. Only the following things are written.:

Data within bounds:
hObservablei = 18.3 ± 0.90 [n entries = 1000]
All data:
hObservablei = 18.3 ± 0.90 [n entries = 1000]

Would have been good if could see the Histos.

Anyway, thanks a lot for the help.

Regards,
Saumyen

That is a totally different question, please open another question.

Original part around beamstrahlung answered.