[Comphep-common] COMPHEP for excited leptons - confirmation about the checks before production

[Eduard Boos]

Dear Jian,
If you have a resonance in the intermediate state you have to put the
width of the resonance. Make sure, you did that and also introduce the
corresponding "Regularization". You have 4-fermion interactions which
violate unitary behaviour, so one should not be surprise with growing
energy or pt distributions. Yes, the errors are in %.  If you put cuts,
the cross section is the one from the corresponding kinematic area.

Please, have a look into the CompHEP manual for details.

Best, Edward


> Dear Experts,
>
> I am running COMPHEP for the following process:
> qqbar->e*e->e,E,E,e
> i.e. e* decaying to 3 leptons via contact interaction.
>
> Just as a check I tried running for:
> u+U->e,E,E,e
>
> (1) I got two feynman diagrams.
> Please find attached feynmanDiag.png
> I understand that these two diagrams correspond to
> e*+ in one and e*- in the other.
> Do you think this is correct?
>
>
> (2) The kinematic scheme showed by COMPHEP (also attached:
> kinematic_scheme.png) is as follows:
> u,U->e,e,E,E
> =========================================================
> in=12   -> out1=3  out2 =456
> in=456 -> out1=4  out2=56
> in=56  ->  out1=5  out2=6
> =========================================================
> I am not sure about how the naming of the particles is done.
> I understand that 456 always refer to the particles coming out from e* and
> 3 refers to the
> one which is produced in conjunction with e*.
> This scheme is valid for both the feynam diagrams
> Do you think this understanding is correct?
>
>
> (3) After putting Itmax=10 ; ncalls = 9720,
> Please find the result of numerical calculation attached (please find
> comphepNumericalSession.ng attached).
> The final xsec is: 3.035e-3 with an error of 4.59e-1. Is this error in %?
> So the final error is
> 4.59e-1 times 3.035e-3?
>
> Do you think the results are fine?
>
> (4) I get the following distributions for E4, M456 (please find pt4.png
> and M456.png attached)
> I see that:
> (a) cross-section is increasing with E4. Shouldn't it start decreasing
> after some point?
> (b) M456 should have peaked at 400 since I understand that 456 are coming
> from the decay of e*.
> It is peaking but it is not sharply peaked.
>
> All these distributions are done for pT of the outgoing particles > 15 GeV
> and |eta| < 3.1
>
> Do you think something is wrong going here?
>
> Please let me know if you require more input from my side.
>
> Thanks for your help,
> Best Regards,
> Shilpi Jain
>
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