n_passed is too small

Asked by Jui-Lin Kuo on 2019-09-11


When I simulate some longer target-detector distance experiments (e.g. DUNE) with certain models, it happens that the number of dark matter accepted by detector is not enough to start the simulation of the interaction part, and the code reports "Exception : Error: numbers of events entering the detector too small!".
It might be due to the model I used does not produce dark matter flux focusing on the beam axis.

I've tried several possibilities to increase n_passed and I found only increasing nevents (the requested unweight event in production) can effectively increase n_passed.
In the end, I tried setting the nevents to be 1M which seems to be the maximum value allowed by the code but the n_passed is still too small.
I'm wondering is there any other possible ways except increasing nevents to have enough n_passed for successfully performing the simulation, and still get the correct estimation of number of final signal events.

Many thanks,

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Launchpad Janitor (janitor) said : #1

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

Luca (lbuono) said : #2

Dear Jui-Lin,

sorry I missed your message.

You are right, when the production mechanism is handled by maddump itself, the basic thing to do to enlarge n_passed is to increase nevents.

Can you provide an example of the processes you are interested in?

In principle, one can use the cuts framework provided by madgraph, to build event samples enriched in some particular region of the phase space. For example, for a very forward detector, one could ask to generate the DM particles at very large rapidity values.

I would avoid the possibility to lower the minimum number of passed events (and overcome in this way the issue) since the fit might be then unreliable.


Jui-Lin Kuo (juilinkuo) said : #3

Dear Luca,

Sorry for the late response and thanks for the explanation.

I'm interested in p p > chi chi~, where chi is a dark fermion which couples to photon via electromagnetic form factors (now I consider dim-5 operators, please see https://arxiv.org/pdf/1811.04095.pdf). The detection process is chi e scattering. It seems that for dim-5 operators the cross section is p-wave, thus the resulting DM distribution might have a larger angular spread.


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