# Neutrino flux measurents?

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kimmm
How does the neutrio flux can be measured by a near detector of the accelerator neutrio experiments,such as T2K?
As I know neutrino interactions with the matter in the near detector is too low,and so how they can count the neutrino flux by counting the produced particle from the interaction?

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## Answers and Replies

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Have you tried to do the maths? The rate is not too low. In fact, it is typically higher than in the far detector as the near detector is much closer and the flux decreases as ##1/L^2## with the distance ##L## from the source.

kimmm
Have you tried to do the maths? The rate is not too low. In fact, it is typically higher than in the far detector as the near detector is much closer and the flux decreases as ##1/L^2## with the distance ##L## from the source.

yeah as you said in the near detector the rate is higher, do you know the way of calclating the flux in the near detector?

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yeah in as you said in the near detector the rate is high
So why do you claim it is not?

Typically you would compute the flux by simulations of the target station. You can make a reasonable proxy by assuming an amount of produced pions and finding the corresponding flux in the forward direction - unless what you have is an off-axis beam in which case you would need an off-axis direction.

Edit: You can also look at the simulations already done by the experiments, e.g., https://arxiv.org/pdf/1211.0469.pdf

kimmm
So why do you claim it is not?

Typically you would compute the flux by simulations of the target station. You can make a reasonable proxy by assuming an amount of produced pions and finding the corresponding flux in the forward direction - unless what you have is an off-axis beam in which case you would need an off-axis direction.
can I sum it up like this,although may be I am still a bit confused about that,
well as the pions produced,then they will decay to neutrinos and the neutrinos go through the detector,but still the problem is that just 1 in 10 to power 20 of the neutrios do the interaction with the target,so can we do the proportional relations to compute the neutrino flux?

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Yes, why wouldn't you? The interaction rate is proportional to the flux multiplied by the cross section. Obviously you will have related statistical and systematic uncertainties, but a priori the rate is a direct proxy for the flux.

kimmm
So why do you claim it is not?

Typically you would compute the flux by simulations of the target station. You can make a reasonable proxy by assuming an amount of produced pions and finding the corresponding flux in the forward direction - unless what you have is an off-axis beam in which case you would need an off-axis direction.

Edit: You can also look at the simulations already done by the experiments, e.g., https://arxiv.org/pdf/1211.0469.pdf

thanks for the paper

kimmm
Yes, why wouldn't you? The interaction rate is proportional to the flux multiplied by the cross section. Obviously you will have related statistical and systematic uncertainties, but a priori the rate is a direct proxy for the flux.
thank you soooo much, it was really a huge struggle in my mind.