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

[Mikhail Dubinin]

Dear Shilpi,

besides the manual, you can find two examples with many details
(particle numbering, regularizations, kinematical scheme, etc)

CMS twiki

https://twiki.cern.ch/twiki/bin/viewauth/CMS/Regularization

Survey in Uspekhi (example somewhere in the middle)

Edward Boos, Mikhail Dubinin, Problems of automatic calculation for
collider physics, Phys.Usp. 53 (2010) 1039-1051 

Please look through these practical materials, hope a number of useful
recommendations can be found there. 

Regards       Mikhail



On Sun, 2012-09-30 at 22:45 +0000, Shilpi Jain wrote:
> 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
> >
> > _______________________________________________
> > Comphep-common mailing list
> > Comphep-common at theory.sinp.msu.ru
> > http://theory.sinp.msu.ru/mailman/listinfo/comphep-common
> >
> 
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