A problem when using isr

Hi Dayun,
Discontinuities are usually caused by insufficient statistics. 50 iterations are nonsensical, normally 5+3 are fine for these processes, but the number of calls is clearly way too low. 20-50k for a process with ISR should be taken here.
cheers,
    JRR

Hi Juergen,
Thank you for your reply. I tried to take 50k calls, but the problem still exists. It seems that the statistics are not the cause.
I found this problem when I was doing Z-lineshape. When the center of mass energy is less than the pole mass of Z, the curve is normal. However, When the center of mass can be at the position of the Z pole mass, the curve jumps, and at this point the curve becomes very rough. I want to show you it, but I don't know what to do.
My code:

model = SM
alias prt = e1:E1:e2:E2
process bornproc = e1, E1 => e2, E2
compile
cuts = all E >= 100 MeV [prt]
   and all abs (cos(Theta)) <= 0.99 [prt]
   and all M2 >= (1 GeV)^2 [prt, prt]
$description = "A WHIZARD Example"
$x_label = "$\sqrt{s}$/GeV"
$y_label = "$\sigma(s)$/pb"
$title = "The Z Lineshape in $e^+e^-\to\mu^+\mu^-$"
plot lineshape_born { x_min = 90 GeV x_max = 93 GeV }
scan sqrts = (90 GeV => 93 GeV /+ 0.01 GeV) {
  beams = e1, E1 => isr
  integrate (bornproc) { iterations = 5:50000:"gw", 3:50000 }
  record lineshape_born (sqrts, integral (bornproc) / 1000)
}
compile_analysis { $out_file = "Z-lineshape.dat" }

And my data:
   9.114000000000E+01 1.472923003720E+03 0.000000000000E+00 0.000000000000E+00
   9.115000000000E+01 1.476899188626E+03 0.000000000000E+00 0.000000000000E+00
   9.116000000000E+01 1.477983239766E+03 0.000000000000E+00 0.000000000000E+00
   9.117000000000E+01 1.481813179215E+03 0.000000000000E+00 0.000000000000E+00
   9.118000000000E+01 1.484049177708E+03 0.000000000000E+00 0.000000000000E+00
   9.119000000000E+01 1.555117112793E+03 0.000000000000E+00 0.000000000000E+00
   9.120000000000E+01 1.590738926303E+03 0.000000000000E+00 0.000000000000E+00
   9.121000000000E+01 1.611577924023E+03 0.000000000000E+00 0.000000000000E+00
   9.122000000000E+01 1.590749636476E+03 0.000000000000E+00 0.000000000000E+00
   9.123000000000E+01 1.599954907264E+03 0.000000000000E+00 0.000000000000E+00

Hi Juergen,
Thank you for your last reply. I tried to take 50k calls, but the problem still exists. It seems that the statistics are not the cause.
I found this problem when I was doing Z-lineshape. When the center of mass energy is less than the pole mass of Z, the curve is normal. However, when the pole mass of Z is located, the curve jumps, and at this point the curve becomes very rough. The results are shown in the attached pdf file.
My code:

model = SM
alias prt = e1:E1:e2:E2
process bornproc = e1, E1 => e2, E2
compile
cuts = all E >= 100 MeV [prt]
   and all abs (cos(Theta)) <= 0.99 [prt]
   and all M2 >= (1 GeV)^2 [prt, prt]
$description = "A WHIZARD Example"
$x_label = "$\sqrt{s}$/GeV"
$y_label = "$\sigma(s)$/pb"
$title = "The Z Lineshape in $e^+e^-\to\mu^+\mu^-$"
plot lineshape_born { x_min = 90 GeV  x_max = 93 GeV }
scan sqrts = (90 GeV => 93 GeV /+ 0.01 GeV) {
  beams = e1, E1 => isr
  integrate (bornproc) { iterations = 5: 50000:"gw", 3: 50000 }
  record lineshape_born (sqrts, integral (bornproc) / 1000)
}
compile_analysis { $out_file = "Z-lineshape.dat" }

> Your question #703485 on WHIZARD changed:
> https://answers.launchpad.net/whizard/+question/703485
>
>     Status: Open => Answered
>
> Juergen Reuter proposed the following answer:
> Hi Dayun,
> Discontinuities are usually caused by insufficient statistics. 50 iterations are nonsensical, normally 5+3 are fine for these processes, but the number of calls is clearly way too low. 20-50k for a process with ISR should be taken here.
> cheers,
>     JRR
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/whizard/+question/703485/+confirm?answer_id=0
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/whizard/+question/703485
>
> You received this question notification because you asked the question.
>

Indeed, it looks like a jump when Whizard exceeds the Z pole and the phase space switches from a single channel (massless photon exchange) to two channels (massless photon + massive Z boson) which takes place between collider energies of 91.18 and 91.19 GeV. We still have to check whether the uncertainty above the threshold is reliable, it might not. We will investigate and come back to you.

You said that the phase space switches from a single channel (massless photon exchange) to two channels (massless photon + massive Z boson) which takes place between collider energies of 91.18 and 91.19 GeV. I don't understand it. For our process e+e-=>mu+mu-, isn't there always these two channels?

Thanks!
> Your question #703485 on WHIZARD changed:
> https://answers.launchpad.net/whizard/+question/703485
>
> Juergen Reuter posted a new comment:
> Indeed, it looks like a jump when Whizard exceeds the Z pole and the
> phase space switches from a single channel (massless photon exchange) to
> two channels (massless photon + massive Z boson) which takes place
> between collider energies of 91.18 and 91.19 GeV. We still have to check
> whether the uncertainty above the threshold is reliable, it might not.
> We will investigate and come back to you.
>
> --
> You received this question notification because you asked the question.
>

Indeed, sorry, that might have been confusing. I didn't mean Feynman diagrams, they are of course always present. However, the parameterization of the phase space which is a mapping from the (in your case 4-dim. phase space, 3n-4 = 2 for n=2 final state particles plus two fractions from the electron PDFs a.k.a. ISR structure functions ("Bjorken-x's") to the 4-d unit hypercube. An s-channel particle exchange from a massless particle and a massive particle below threshold (or very far away from threshold) have the very similar functional properties and can be described within the same parameterization. Once you exceed the Z-pole the on-shell/Breit-Wigner resonance is within kinematical reach and needs to be accounted for by a different phase-space mapping. Hence, above the Z-pole there are two different phase-space channels (in the language of topology or differential geometry the atlas describing the phase-space manifold now has two charts and not only one). The (squared) matrix element is of course always the same.

Clicked wrong button, no user info requested.

Sorry, I'm still a little confused. From your description, I guess what you meant was that the Whizard calculate the e+ e-->Z and Z->X X processes separately by regarding the mediator Z as a real particle? But once we directly write down the e+ e- -> X X, shouldn't the generated diagrams include all the on-shell and off-shell contributions of the Z-boson so that considering the two processes separately will elicit a double-counting? Or would you like to provide us with some references？
> Your question #703485 on WHIZARD changed:
> https://answers.launchpad.net/whizard/+question/703485
>
>     Status: Open => Needs information
>
> Juergen Reuter requested more information:
> Indeed, sorry, that might have been confusing. I didn't mean Feynman
> diagrams, they are of course always present. However, the
> parameterization of the phase space which is a mapping from the (in your
> case 4-dim. phase space, 3n-4 = 2 for n=2 final state particles plus two
> fractions from the electron PDFs a.k.a. ISR structure functions
> ("Bjorken-x's") to the 4-d unit hypercube. An s-channel particle
> exchange from a massless particle and a massive particle below threshold
> (or very far away from threshold) have the very similar functional
> properties and can be described within the same parameterization. Once
> you exceed the Z-pole the on-shell/Breit-Wigner resonance is within
> kinematical reach and needs to be accounted for by a different phase-
> space mapping. Hence,  above the Z-pole there are two different phase-
> space channels (in the language of topology or differential geometry the
> atlas describing the phase-space manifold now has two charts and not
> only one). The (squared) matrix element is of course always the same.
>
> --
> To answer this request for more information, you can either reply to
> this email or enter your reply at the following page:
> https://answers.launchpad.net/whizard/+question/703485
>
> You received this question notification because you asked the question.
>

No, as I said the matrix element is _always_ the one for the full process e+e- -> mu+ mu- with s-channel photon and Z exchange (in your case only with Z exchange as you put a restriction on the matrix element). All the things about channels is only and really only about the functional form how Whizard parameterizes the phase space, i.e. the integration measure over the final state momenta.

Hi Juergen,

We would like to ask about the problem about isr we talked about last time, that is, when Whizard exceeds&nbsp;the Z pole, lineshape become unsmooth. Is&nbsp; any solution now？

Thank you for your help.

 ----------Reply to Message----------
 On Sat, Oct 22, 2022 01:20 AM Juergen Reuter<<email address hidden>&gt; wrote:

  Your question #703485 on WHIZARD changed:
https://answers.launchpad.net/whizard/+question/703485

Juergen Reuter posted a new comment:
Indeed, it looks like a jump when Whizard exceeds the Z pole and the
phase space switches from a single channel (massless photon exchange) to
two channels (massless photon + massive Z boson) which takes place
between collider energies of 91.18 and 91.19 GeV. We still have to check
whether the uncertainty above the threshold is reliable, it might not.
We will investigate and come back to you.

--
You received this question notification because you asked the question.

Hi Dayun,
as you have noticed we flagged this as a bug, after having definitely confirmed your findings. We are looking for the root cause of this issue at the moment. For the time being, we think that you can use the setting
?phs_s_mapping = false
in the SINDARIN input file. This option should give a correctly normalized cross section in the threshold region (it will also give the correct normalization far away from threshold, but there without this kinematic mapping, integration and event generation become poor and inefficient.
Cheers,
    JRR

A fix for this has been committed and is available from the nightly builds from tomorrow on. It will be released with version 3.1.1 of WHIZARD within the next couple of weeks.

A bug fix for this bug was released with v3.1.1. In that new version, everything works as expected without the need for the user to set any special parameter. Closing.

It looks like you are using the WHIZARD event generator to simulate a process involving initial-state radiation (ISR) in the context of the Standard Model. In your code, you define a process eemm representing electron-positron annihilation into a muon-antimuon pair with ISR.

The output shows the integrated cross-section (s18 and s19) for two different center-of-mass energies (sqrts). The cross-section with ISR (s19) is higher than the one without ISR (s18), which is expected since ISR increases the available energy for the process.

If you are observing unexpected behavior or "jumping" in the mass of the propagator, you may need to check your model, input parameters, or consider increasing the number of iterations for a more accurate result. Furhter You can read articles for troubleshooting such as https://chatgptlogindeutsch.com/chatgpt-deutsch/