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goord / Camgen

A generic tree-level particle scattering Monte Carlo generator using recursive amplitude evaluation
GNU General Public License v2.0
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Total cross section depends on number of events #29

Open Paraseus opened 11 years ago

Paraseus commented 11 years ago

The cross section for non-trivial processes changes with the number of events. One gets different results for the cross section for 1e5, 1e6 and 1e7 events. Even without any cuts or adaptive grids.

For example for C C > A A A A where C and A are two new scalars with trivial couplings AAh0 and CCh0h0 and where h0 is the normal Higgs boson with a mass of 125 GeV. A and C are stable with a small mass.

(The reason for the new particles was to isolate any strange couplings causing the effect.)

I have sent an example code for this some times ago, I only list the bug so we don't forget about it ;)

goord commented 10 years ago

It may be the case that for narrow-width Higgs above the double-Higgs threshold the error on the cross section is somewhat underestimated. A 'real' dependence on N seems unlikely because the number of generated events is nowhere in the generation/weight calculation. So I suspect the xsec fluctuating more than the error suggests in the double-resonance region.

Paraseus commented 10 years ago

I am not sure what you mean by 'above the double-Higgs threshold'. The increase in cross-section is there over the whole sqrt(s-hat) range, not just above ~250 GeV. I have a plot of this (not sure if I ever sent it to you though).

goord commented 10 years ago

I watched that plot yesterday: it seems that below the single-Higgs threshold the difference is much smaller than above the 250 GeV.

2013/12/3 Wouter van den Wollenberg notifications@github.com

I am not sure what you mean by 'above the double-Higgs threshold'. The increase in cross-section is there over the whole sqrt(s-hat) range, not just above ~250 GeV. I have a plot of this (not sure if I ever sent it to you though).

— Reply to this email directly or view it on GitHubhttps://github.com/goord/Camgen/issues/29#issuecomment-29697042 .