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

[Shilpi Jain]

Dear Edward,

Thanks for your response.

(1) I put the width of resonance (0.0002173 GeV for 800 GeV mass e*)
Since the process is:

u(1) +U (2) -> e (3) + e* -> e (3) + e(4) + E(5) + E(6)

whereas number in the bracket denotes the number of the particle 
in COMPHEP as I understand.
I am still not sure about the particle numbering.
In the manual, it is written that 
"It is assumed that particles are numerated in the same order as they are written down in
the (sub)process name"

Does this mean that if I put the process as u,U -> E, e, E, e while preparing
my process (as shown in process.png)
then the numbering will be like this:
u(1), U(2) -> E(3), e(4), E(5), e(6) 

(2) I put the regularization as follows (also shown in attached regularization.png):
==========================================
momentum | Mass | Width | power
312             | Mex  | wex    | 2
==========================================

[ since P(e*) = P(e) - P(u) - P(U) ]

But I get the error of "Bad precision" during vegas. This is shown in the attached vegas.png file.

I think I am doing something wrong somewhere. Could you please help me
in correcting this?

Thanks a lot for your help,
Best Regards,
Shilpi


________________________________________
From: Eduard Boos [boos at theory.sinp.msu.ru]
Sent: 30 September 2012 17:42
To: Shilpi Jain
Cc: comphep-common at theory.sinp.msu.ru
Subject: Re: [Comphep-common] COMPHEP for excited leptons - confirmation about the checks before production

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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> Comphep-common mailing list
> Comphep-common at theory.sinp.msu.ru
> http://theory.sinp.msu.ru/mailman/listinfo/comphep-common
>

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