pythia in ee final state

Parton shower is a unitarity calculation. simply put, the chance for particle to shower further "P(shower)" and the chance for particle to particle to stop showering "P(no-shower)" sums up into 1, P(shower) + P(no-shower) = 1.
Your cross section is first defined from matrix element level and when particle propagates during the showering process, P(shower) + P(no-shower) is every time 1 and thus cross section does not change through showering. This is the same for "pp > xx" process, this is not only something that happens for "ee > ee"

what do you mean? can you say it more simple?

It means that the parton-shower does not modify the cross-section. So what you obseverve is the correct behavior (and it does not mean that the parton-shower is useless).

so do you mean that pythia can only deal with final state ? in fact what we care about is Initial state ee, we want to study ISR radiation in ee Initial state.

No pythia can handle both ISR and FSR. Now you need to know what pythia is doing for you (and how).

From your last question, I guess that your "real" question is how to simulate electron beam with PDF such that one can recover resonance below the beam energy. This is indeed something that require the full matrix-element and therefore something that the parton-shower can not do.

For that you can run madgraph with setting
lpp1 and lpp2 to electron beam
and pdlabel to isronlyll

Cheers,

Olivier

"real question", lol
yeah, i want to calculate the influence of radiation in initial ee state, and at the direction of beam it will have an analytical solution like log(me).
so which file can lpp and isronlyll be set?

Those parameters are in the run_card.dat

Cheers,

Olivier

a little weird,,, after set lpp=+-3, pdlabel= isronlyll, it gives this information:

ERROR: Parton-Shower are not yet ready for such proton component definition. Parton-shower will be switched off
Survey return zero cross section.
   Typical reasons are the following:
   1) A massive s-channel particle has a width set to zero.
   2) The pdf are zero for at least one of the initial state particles
      or you are using maxjetflavor=4 for initial state b:s.
   3) The cuts are too strong.
   Please check/correct your param_card and/or your run_card.
Zero result detected: See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14

Are you sure that you did not setup the beam type in the wrong order (i.e. asking for an electron from the positron beam making the cross-section to drop to zero)

Concerning the pythia8 support, you will need a very recent version of the code (3.5.4 might be the only option here).

For reference/test, I have use the following script in (not yet releaesed) 3.6.0 (the script will not work in 3.5.x):
 import model sm
 generate e+ e- > e+ e-
 output
 launch
 analysis=OFF
 shower=Pythia8
 set lpp1 -3
 set lpp2 3
 set ebeam scan1:[i*100 for i in range(1,11)]
 set pdlabel isronlyll

and the scan output file returns:

#run_name run_card#ebeam1 run_card#ebeam2 cross
run_01_01 1.000000e+02 1.000000e+02 9.603350e+02
run_01_02 2.000000e+02 2.000000e+02 2.399605e+02
run_01_03 3.000000e+02 3.000000e+02 1.079482e+02
run_01_04 4.000000e+02 4.000000e+02 6.126767e+01
run_01_05 5.000000e+02 5.000000e+02 3.983391e+01
run_01_06 6.000000e+02 6.000000e+02 2.797483e+01
run_01_07 7.000000e+02 7.000000e+02 2.079831e+01
run_01_08 8.000000e+02 8.000000e+02 1.603293e+01
run_01_09 9.000000e+02 9.000000e+02 1.265626e+01
run_01_10 1.000000e+03 1.000000e+03 1.031228e+01

I have also check that without the scan command (new in 3.6.0) the same script does work in 3.5.4 but crashes with zero cross-section if you flip beam identity.

Cheers,

Olivier

oh ,I see.
after flipping back it works.but the shower will be closed automaticallly, and ISR effect seems very small.
At a CM energy of 380 GeV, the cross section without ISR is 268pb, while with ISR I got 266 pb. Do you know why it is so small?
----------
set lpp1=-3;lpp2=3;pdlabel=isronlyll

Your guess is at good at mine, since I also only start to learn such type of physics.

Looks like the Z channel contribution is not the dominant one for ee>ee (while it is for ee>mumu)
and therefore the effect is less relevant than for ee > mumu. Since the main contribution (t-channel photon) will not present such gain. Comparing result from ee>mumu to ee>ee is a clear indication that such effect is not relevant (this off course also depends of course of the cuts that you apply/....)

result with ee > ee
   1 #run_name run_card#lpp1 run_card#lpp2 run_card#ebeam1 run_card#ebeam2 cross
   2 run_01_01 0.000000e+00 0.000000e+00 5.000000e+01 5.000000e+01 2.375548e+03
   3 run_01_02 0.000000e+00 0.000000e+00 1.000000e+02 1.000000e+02 9.637497e+02
   4 run_01_03 0.000000e+00 0.000000e+00 1.500000e+02 1.500000e+02 4.285444e+02
   5 run_01_04 0.000000e+00 0.000000e+00 2.000000e+02 2.000000e+02 2.415246e+02
   6 run_01_05 0.000000e+00 0.000000e+00 2.500000e+02 2.500000e+02 1.557015e+02
   7 run_01_06 0.000000e+00 0.000000e+00 3.000000e+02 3.000000e+02 1.090681e+02
   8 run_01_07 0.000000e+00 0.000000e+00 3.500000e+02 3.500000e+02 8.046772e+01
   9 run_01_08 0.000000e+00 0.000000e+00 4.000000e+02 4.000000e+02 6.206864e+01
  10 run_01_09 0.000000e+00 0.000000e+00 4.500000e+02 4.500000e+02 4.932609e+01
  11 run_01_10 0.000000e+00 0.000000e+00 5.000000e+02 5.000000e+02 4.021187e+01
  12 run_01_11 3.000000e+00 -3.000000e+00 5.000000e+01 5.000000e+01 2.412919e+03
  13 run_01_12 3.000000e+00 -3.000000e+00 1.000000e+02 1.000000e+02 9.610369e+02
  14 run_01_13 3.000000e+00 -3.000000e+00 1.500000e+02 1.500000e+02 4.256381e+02
  15 run_01_14 3.000000e+00 -3.000000e+00 2.000000e+02 2.000000e+02 2.390728e+02
  16 run_01_15 3.000000e+00 -3.000000e+00 2.500000e+02 2.500000e+02 1.554745e+02
  17 run_01_16 3.000000e+00 -3.000000e+00 3.000000e+02 3.000000e+02 1.080540e+02
  18 run_01_17 3.000000e+00 -3.000000e+00 3.500000e+02 3.500000e+02 8.007069e+01
  19 run_01_18 3.000000e+00 -3.000000e+00 4.000000e+02 4.000000e+02 6.166274e+01
  20 run_01_19 3.000000e+00 -3.000000e+00 4.500000e+02 4.500000e+02 4.898676e+01
  21 run_01_20 3.000000e+00 -3.000000e+00 5.000000e+02 5.000000e+02 3.970561e+01
result with ee > mumu:
   1 #run_name run_card#lpp1 run_card#lpp2 run_card#ebeam1 run_card#ebeam2 cross
   2 run_01_01 0.000000e+00 0.000000e+00 5.000000e+01 5.000000e+01 5.131200e+01
   3 run_01_02 0.000000e+00 0.000000e+00 1.000000e+02 1.000000e+02 2.789000e+00
   4 run_01_03 0.000000e+00 0.000000e+00 1.500000e+02 1.500000e+02 1.186350e+00
   5 run_01_04 0.000000e+00 0.000000e+00 2.000000e+02 2.000000e+02 6.590700e-01
   6 run_01_05 0.000000e+00 0.000000e+00 2.500000e+02 2.500000e+02 4.192100e-01
   7 run_01_06 0.000000e+00 0.000000e+00 3.000000e+02 3.000000e+02 2.906200e-01
   8 run_01_07 0.000000e+00 0.000000e+00 3.500000e+02 3.500000e+02 2.131000e-01
   9 run_01_08 0.000000e+00 0.000000e+00 4.000000e+02 4.000000e+02 1.631400e-01
  10 run_01_09 0.000000e+00 0.000000e+00 4.500000e+02 4.500000e+02 1.288610e-01
  11 run_01_10 0.000000e+00 0.000000e+00 5.000000e+02 5.000000e+02 1.042790e-01
  12 run_01_11 3.000000e+00 -3.000000e+00 5.000000e+01 5.000000e+01 1.124890e+02
  13 run_01_12 3.000000e+00 -3.000000e+00 1.000000e+02 1.000000e+02 5.905300e+00
  14 run_01_13 3.000000e+00 -3.000000e+00 1.500000e+02 1.500000e+02 2.337700e+00
  15 run_01_14 3.000000e+00 -3.000000e+00 2.000000e+02 2.000000e+02 1.240140e+00
  16 run_01_15 3.000000e+00 -3.000000e+00 2.500000e+02 2.500000e+02 7.473100e-01
  17 run_01_16 3.000000e+00 -3.000000e+00 3.000000e+02 3.000000e+02 4.936600e-01
  18 run_01_17 3.000000e+00 -3.000000e+00 3.500000e+02 3.500000e+02 3.431600e-01
  19 run_01_18 3.000000e+00 -3.000000e+00 4.000000e+02 4.000000e+02 2.506200e-01
  20 run_01_19 3.000000e+00 -3.000000e+00 4.500000e+02 4.500000e+02 1.885430e-01
  21 run_01_20 3.000000e+00 -3.000000e+00 5.000000e+02 5.000000e+02 1.463630e-01