1 | \subsection {Supernovae} |
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2 | |
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3 | The core collapse supernovae are spectacular events which have been |
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4 | theoretically studied for more than three decades. After explosion the star |
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5 | loses energy, mainly by neutrino emission, and cools down, ending as a |
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6 | neutron star or a black hole. Many features of the collapse mechanism are |
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7 | indeed imprinted in the neutrinos released during the explosion. |
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8 | |
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9 | At the same time, a galactic supernova would give particle physicists the |
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10 | occasion to explore the neutrino properties on scales of distance up to |
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11 | $10^{17}$ km and of time up to $\sim 10^{5}$ years and at very high density. |
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12 | The detected signal from a supernova explosion depends on the |
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13 | structure of the neutrino mass spectrum and lepton mixing. Therefore, in |
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14 | principle, studying the properties of a supernova neutrino burst one |
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15 | can get information about the values of parameters relevant for the |
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16 | solution of the solar neutrino problem, the type of the mass |
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17 | ordering (the so-called mass hierarchy), |
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18 | the mixing parameter $\sin^2\theta_{13}$, the |
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19 | presence of sterile neutrinos and new neutrino interactions. |
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20 | |
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21 | It is generally believed that |
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22 | core-collapse supernovae have occurred throughout the |
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23 | Universe since the formation of stars. Thus, there should |
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24 | exist a diffuse background of neutrinos originating from |
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25 | all the supernovae that have ever occurred. Detection |
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26 | of these diffuse supernova neutrinos (DSN) would offer |
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27 | insight about the history of star formation and supernovae |
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28 | explosions in the Universe. |
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29 | |
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30 | Now the requirements for a detector are to be very massive, located |
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31 | underground, to stay in operation for at least 20 years and to be equipped |
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32 | with a real time neutrino detection electronics with a threshold around |
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33 | 10 MeV. For those reasons a megaton water \v{C}erenkov detector with a |
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34 | fiducial volume around 450 kt is a good choice. Such a detector would |
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35 | detect $\sim 10^{5}$ |
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36 | events from a galactic stellar collapse, and of the order of 20 events from a |
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37 | supernova in Andromeda galaxy, which is one of the closest to our Milky way. |
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38 | The large mass of such a detector compared to other proposed and existing |
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39 | facilities means that the sample collected will outnumber that of all other |
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40 | detectors combined. |
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41 | The general and relative performances are summarized in section \ref{sec:SN}. |
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42 | |
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43 | %As an example for an explosion at the center of our galaxy, we expect |
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44 | %$\sim 300$ events per kiloton of water. A megaton water \v{C}erenkov detector |
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45 | %would be sensitive to three main neutrino signals |
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46 | |
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47 | All types of neutrinos and anti-neutrinos are emitted |
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48 | from a core-collapse supernova, but not all are equally |
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49 | detectable. |
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50 | The $\bar{\nu_e}$ is most likely to interact in a water \v{C}erenkov detector. |
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51 | Three main neutrino signals would be detected, each one yielding unique |
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52 | information: |
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53 | \begin{enumerate} |
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54 | \item Inverse beta decay events (89\%) allowing for a good |
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55 | determination of the time evolution and energy distribution of the neutrino |
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56 | burst. The potentials would be enhanced by the detection of the neutron |
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57 | with the addition of a small mount of Gadolinium \cite{Beacom:2003nk}. |
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58 | \item Neutral current events involving $^{16}O$ (8\%), which are sensitive |
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59 | to the temperature of the neutrino spectrum. |
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60 | \item Directional elastic scattering events from $\nu_{x}$ + $e^{-}$ and |
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61 | $\bar{\nu}_{x}$ + $e^{-}$ ($\sim$ 3\%). These events provide the direction |
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62 | of the supernova within $\pm 1$ degree. |
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63 | \end{enumerate} |
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64 | %Each one of these modes will yield unique information. |
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65 | |
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66 | |
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67 | |
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68 | |
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69 | |
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70 | |
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