3 ms·

Yes, when neutrinos do react (rare though that is) it produces electrons that move in the same direction as the neutrino, and which move at extremely high speed

by jjk166 4y ago

Yes, when neutrinos do react (rare though that is) it produces electrons that move in the same direction as the neutrino, and which move at extremely high speed, faster than the speed of light in the medium in fact, which produces cherenkov radiation. This radiation is what the sensors actually detect. Essentially they are giant cameras looking for brief streaks of light. By seeing how long and in what direction the streak is, you can determine both the direction and energy of the incoming neutrino.

snophysics 4y ago
In this case they are detecting inverse beta decay events. The antineutrino interacts with a proton producing a positron and a neutron. The positron annihilates with an electron producing two gamma rays and the neutron then captures on a proton and releases a 2.22 MeV gamma ray. I think the only realistic way to determine the direction is by looking at the direction of the neutron by comparing the position of the positron annihilation with the neutron capture, but typically the neutron scatters so much in these detectors that it is not possible to do on an event by event basis (although see [0] for a possible detector that could). What you're talking about is elastic scattering and I think this may be possible (see [1]), but I don't know of anyone who is able to do this at these low energies. As a side note, the WATCHMAN collaboration has been studying the ability to monitor nuclear reactors using these sorts of detectors for a while. [0] https://arxiv.org/pdf/1410.8530.pdf https://arxiv.org/pdf/1410.8530.pdf [1] https://www.osti.gov/servlets/purl/1332127 https://www.osti.gov/servlets/purl/1332127
- jjk166 4y ago
  No, I'm not referring to elastic scattering. It's the positron that they are tracking, and it moves in approximately the same direction as the neutrino to conserve linear momentum. It's exactly the same process, the only difference is anti-neutrinos produce positrons, neutrinos produce electrons.
  - snophysics 4y ago
    I don't think that's true. The energies of the neutrinos they are looking at are relative low (less than 15 MeV), and according to https://journals.aps.org/prd/pdf/10.1103/PhysRevD.60.053003 https://journals.aps.org/prd/pdf/10.1103/PhysRevD.60.053003 the positron is isotropic around 15 MeV and is only forward pointing at much higher energies.

by jjk166 4y ago

snophysics 4y ago

In this case they are detecting inverse beta decay events. The antineutrino interacts with a proton producing a positron and a neutron. The positron annihilates with an electron producing two gamma rays and the neutron then captures on a proton and releases a 2.22 MeV gamma ray. I think the only realistic way to determine the direction is by looking at the direction of the neutron by comparing the position of the positron annihilation with the neutron capture, but typically the neutron scatters so much in these detectors that it is not possible to do on an event by event basis (although see [0] for a possible detector that could). What you're talking about is elastic scattering and I think this may be possible (see [1]), but I don't know of anyone who is able to do this at these low energies. As a side note, the WATCHMAN collaboration has been studying the ability to monitor nuclear reactors using these sorts of detectors for a while. [0] https://arxiv.org/pdf/1410.8530.pdf https://arxiv.org/pdf/1410.8530.pdf [1] https://www.osti.gov/servlets/purl/1332127 https://www.osti.gov/servlets/purl/1332127

jjk166 4y ago
No, I'm not referring to elastic scattering. It's the positron that they are tracking, and it moves in approximately the same direction as the neutrino to conserve linear momentum. It's exactly the same process, the only difference is anti-neutrinos produce positrons, neutrinos produce electrons.
- snophysics 4y ago
  I don't think that's true. The energies of the neutrinos they are looking at are relative low (less than 15 MeV), and according to https://journals.aps.org/prd/pdf/10.1103/PhysRevD.60.053003 https://journals.aps.org/prd/pdf/10.1103/PhysRevD.60.053003 the positron is isotropic around 15 MeV and is only forward pointing at much higher energies.