total proton proton scattering cross section computation

Asked by Kim Berghaus on 2019-12-03

I want to compute the total hadronic proton proton cross-section at 7 TeV COM energy.

I generated the process:
p p > j j
and changed the run card to, keeping the default pdf settings:
> set no_parton_cut
> set ptl -1

I get the following note and am not sure if it is a problem or if I may ignore it:
Note: The following floating-point exceptions are signalling: IEEE_INVALID_FLAG_IEEE_DIVIDE_BY_ZERO IEEE_OVERFLOW_FLAG IEEE_UNDERFLOW_FLAG IEEE_DENORMAL

The computed total cross section is: 5.68*10^11 pb, which disagrees with measurements of the total proton proton cross-section by about a factor of 5 (according to this paper https://arxiv.org/pdf/1110.1395.pdf fig 5 the cross section should be ~1.1*10^11 pb).

Do you understand why there is a disagreement between the madgraph output and the experimental measurements? Are there cuts that I should be applying?

Thanks a lot for your help.

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2019-12-03
Last reply:
2019-12-04

Hi,

If you really do not put any cut then this cross-section is infinite.
You do not hit such singularity since we cut event with scale lower than 4 GeV^2.
But this is obviously a too soft cut for doing ANY comparison with data.

Note that In order to compare with data, you have to apply the same jet algorithm and the same cut associated to it.
So you typically need loos cut at MG5amc level and then pass your event to the parton-shower and hadronization then cut on your observable to match your experiment.

Cheers,

Olivier

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