Negative Crosssection is the output and no events are getting generated.

Hello,
without kinematical cut on the electron, this process is divergent. This
is the reason of your problem. You should apply, for example pt >20 cut
on the photon.
Alexander

On Mon, 20 Jul 2020, 06:35 Atanu Guha, <email address hidden>
wrote:

> New question #691965 on CalcHEP:
> https://answers.launchpad.net/calchep/+question/691965
>
> Dear Sir,
>
> I am getting a strange problem while incorporating polarization by the
> following code (only relevant parts I am giving). Without the polarization
> option the code s working perfectly fine. But for the given polarization
> choice (+80,+30) it yields negative crossection and no events are being
> generated.
>
> Please suggest me if I am doing anything wrong.
>
> ##################################
> Model: SM
> Model changed: False
> Gauge: Feynman
> Process: e%,E%->n,N,A
>
> Composite: n=ne,nm
> Composite: N=Ne,Nm
>
> Kinematics : 12 -> 34 , 5
> Kinematics : 34 -> 3 , 4
>
> pdf1: ISR & Beamstrahlung
> pdf2: ISR & Beamstrahlung
>
> Bunch x+y sizes (nm) : 480
> Bunch length (mm) : 0.3
> Number of particles : 2E+10
>
> Polarization1:0.8
> Polarization2:0.3
>
> p1: 500
> p2: 500
> ##################################
>
> --
> You received this question notification because your team CalcHEP is an
> answer contact for CalcHEP.
>

P.S.

I meant
"without kinematical cut on the PHOTON this process is divergent. "
PT>20GeV cut on the poton
i.e.
T(A)>20
will solve the problem just put this instruction (see example in the batch template which comes with CalcHEP)

Alexander

Ok. I put

########
Cut parameter: T(A)
Cut invert: False
Cut min: 10
Cut max: 500

Cut parameter: E(A)
Cut invert: False
Cut min: 10
Cut max: 500

Cut parameter: Y(A)
Cut invert: False
Cut min: -2.5
Cut max: +2.5
#########

Ok, I am checking the modification.

T(A) is enough

On Mon, 20 Jul 2020, 11:11 Atanu Guha, <email address hidden>
wrote:

> Question #691965 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/691965
>
> Status: Answered => Solved
>
> Atanu Guha confirmed that the question is solved:
> Ok. I put
>
> ########
> Cut parameter: T(A)
> Cut invert: False
> Cut min: 10
> Cut max: 500
>
> Cut parameter: E(A)
> Cut invert: False
> Cut min: 10
> Cut max: 500
>
> Cut parameter: Y(A)
> Cut invert: False
> Cut min: -2.5
> Cut max: +2.5
> #########
>
>
> Ok, I am checking the modification.
>
> --
> You received this question notification because your team CalcHEP is an
> answer contact for CalcHEP.
>

Ok. But including these also did not solve the problem. If I remove the polarization, then only the problem is solved.

Hii.. I modified my code... and this is the modified version now. Still I am facing the same issue.

##############################################################
Model: SM
Model changed: False
Gauge: Feynman
Process: e%,E%->n,N,A

Composite: n=ne,nm
Composite: N=Ne,Nm

Kinematics : 12 -> 34 , 5
Kinematics : 34 -> 3 , 4

pdf1: ISR & Beamstrahlung
pdf2: ISR & Beamstrahlung

Bunch x+y sizes (nm) : 480
Bunch length (mm) : 0.3
Number of particles : 2E+10

Polarization1:0.8
Polarization2:0.3

p1: 500
p2: 500

Cut parameter: T(A)
Cut invert: False
Cut min: 20
Cut max: 500

Number of events (per run step): 10000
Filename: ee_neNeA

NTuple: False
Cleanup: False
Max number of cpus: 8

nSess_1: 5
nCalls_1: 100000
nSess_2: 5
nCalls_2: 100000
##########################################

Hi.... Sorry.....

Hi...

I found my problem...

Polarization1:0.8
Polarization2:0.3

This choice is making the problem. Maximum polarization is 0.5, so if I need to use 80% porlaized beam, I should set the value 0.5*0.8... right?

P.S.
You can cross check your results with zero polarization

for
Process: e%,E%->n,N,A
and
Polarization1:0.0
Polarization2:0.0

you should get the same cross section as for
Process: e,E->n,N,A

Alexander

Thanks Alexander Belyaev, that solved my question.