Question

4 Neutrinos The nature of the neutrinos is an urgent issue in modern physics. Big detectors are operated or are being set up to detect neutrinos. Among them are the ICE-CUBE in Antartica and the KM3 in the Mediterranian Sea. Both use either 1 km³ of antarctic ICE respectively sea water as active detector medium. For this, photomultipliers are deployed in the ice, respectively the water. Those detect Cherenkov light from reaction products of the neutrinos. (a) $\bullet$ Give an example of a reaction that could be used to detect a muon neutrino ($\nu_{\mu}$) and $\bullet$ a muon antineutrino ($\bar{\nu}_{\mu}$), respectively. $\bullet$ Which interaction or which interactions can cause neutrino reactions? [3 pts] (b) The incoming neutrinos have energies well above 50 GeV. Photomultipliers are used to detect the signal. $\bullet$ Do you think, that one can find back the direction from where the neutrinos came and thereby do neutrino astronomy? Give reasoning for your judgment? [3 pts] (c) At the highest up to date observed energies (about $10^{20}eV$) the cross section for neutrino reactions is estimated to be of order $10^{-31} cm^2$ to $10^{-34}cm^2$. $\bullet$ How high must the flux of neutrinos at these energies be at minimum in order to be able to observe at least one event per day in one of these detectors with 1 km³ active volume each? (water/ice are H2O, use density 1 g/cm³, $n_p$ =10 protons per molecule, $n_n$=8 neutrons per molecule.) [4 pts]

          4
Neutrinos
The nature of the neutrinos is an urgent issue in modern physics. Big detectors are operated or
are being set up to detect neutrinos. Among them are the ICE-CUBE in Antartica and the KM3
in the Mediterranian Sea. Both use either 1 km³ of antarctic ICE respectively sea water as active
detector medium. For this, photomultipliers are deployed in the ice, respectively the water. Those
detect Cherenkov light from reaction products of the neutrinos.
(a) \(\bullet\) Give an example of a reaction that could be used to detect a muon neutrino ($\nu_{\mu}$) and \(\bullet\)
a muon antineutrino ($\bar{\nu}_{\mu}$), respectively. \(\bullet\) Which interaction or which interactions can cause
neutrino reactions?
[3 pts]
(b) The incoming neutrinos have energies well above 50 GeV. Photomultipliers are used to detect
the signal. \(\bullet\) Do you think, that one can find back the direction from where the neutrinos
came and thereby do neutrino astronomy? Give reasoning for your judgment?
[3 pts]
(c) At the highest up to date observed energies (about $10^{20}eV$) the cross section for neutrino
reactions is estimated to be of order $10^{-31} cm^2$ to $10^{-34}cm^2$. \(\bullet\) How high must the flux of
neutrinos at these energies be at minimum in order to be able to observe at least one event
per day in one of these detectors with 1 km³ active volume each? (water/ice are H2O, use
density 1 g/cm³, $n_p$ =10 protons per molecule, $n_n$=8 neutrons per molecule.)
[4 pts]

4
Neutrinos
The nature of the neutrinos is an urgent issue in modern physics. Big detectors are operated or
are being set up to detect neutrinos. Among them are the ICE-CUBE in Antartica and the KM3
in the Mediterranian Sea. Both use either 1 km³ of antarctic ICE respectively sea water as active
detector medium. For this, photomultipliers are deployed in the ice, respectively the water. Those
detect Cherenkov light from reaction products of the neutrinos.
(a) ∙ Give an example of a reaction that could be used to detect a muon neutrino (νμ) and ∙
a muon antineutrino (ν̅μ), respectively. ∙ Which interaction or which interactions can cause
neutrino reactions?
[3 pts]
(b) The incoming neutrinos have energies well above 50 GeV. Photomultipliers are used to detect
the signal. ∙ Do you think, that one can find back the direction from where the neutrinos
came and thereby do neutrino astronomy? Give reasoning for your judgment?
[3 pts]
(c) At the highest up to date observed energies (about 10^20eV) the cross section for neutrino
reactions is estimated to be of order 10^-31 cm^2 to 10^-34cm^2. ∙ How high must the flux of
neutrinos at these energies be at minimum in order to be able to observe at least one event
per day in one of these detectors with 1 km³ active volume each? (water/ice are H2O, use
density 1 g/cm³, np =10 protons per molecule, nn=8 neutrons per molecule.)
[4 pts]

Added by Mark G.

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