[387] | 1 | \subsection {Supernovae} |
---|
| 2 | |
---|
| 3 | The core collapse supernovae are spectacular events which have been |
---|
| 4 | theoretically studied for more than three decades. After explosion the star |
---|
| 5 | loses energy, mainly by neutrino emission, and cools down, ending as a |
---|
| 6 | neutron star or a black hole. Many features of the collapse mechanism are |
---|
| 7 | indeed imprinted in the neutrinos released during the explosion. |
---|
| 8 | |
---|
| 9 | At the same time, a galactic supernova would give particle physicists the |
---|
| 10 | occasion to explore the neutrino properties on scales of distance up to |
---|
| 11 | $10^{17}$ km and of time up to $\sim 10^{5}$ years and at very high density. |
---|
| 12 | The detected signal from a supernova explosion depends on the |
---|
| 13 | structure of the neutrino mass spectrum and lepton mixing. Therefore, in |
---|
| 14 | principle, studying the properties of a supernova neutrino burst one |
---|
| 15 | can get information about the values of parameters relevant for the |
---|
| 16 | solution of the solar neutrino problem, the type of the mass |
---|
| 17 | ordering (the so-called mass hierarchy), |
---|
| 18 | the mixing parameter $\sin^2\theta_{13}$, the |
---|
| 19 | presence of sterile neutrinos and new neutrino interactions. |
---|
| 20 | |
---|
| 21 | It is generally believed that |
---|
| 22 | core-collapse supernovae have occurred throughout the |
---|
| 23 | Universe since the formation of stars. Thus, there should |
---|
| 24 | exist a diffuse background of neutrinos originating from |
---|
| 25 | all the supernovae that have ever occurred. Detection |
---|
| 26 | of these diffuse supernova neutrinos (DSN) would offer |
---|
| 27 | insight about the history of star formation and supernovae |
---|
| 28 | explosions in the Universe. |
---|
| 29 | |
---|
| 30 | Now the requirements for a detector are to be very massive, located |
---|
| 31 | underground, to stay in operation for at least 20 years and to be equipped |
---|
| 32 | with a real time neutrino detection electronics with a threshold around |
---|
| 33 | 10 MeV. For those reasons a megaton water \v{C}erenkov detector with a |
---|
| 34 | fiducial volume around 450 kt is a good choice. Such a detector would |
---|
| 35 | detect $\sim 10^{5}$ |
---|
| 36 | events from a galactic stellar collapse, and of the order of 20 events from a |
---|
| 37 | supernova in Andromeda galaxy, which is one of the closest to our Milky way. |
---|
| 38 | The large mass of such a detector compared to other proposed and existing |
---|
| 39 | facilities means that the sample collected will outnumber that of all other |
---|
| 40 | detectors combined. |
---|
| 41 | The general and relative performances are summarized in section \ref{sec:SN}. |
---|
| 42 | |
---|
| 43 | %As an example for an explosion at the center of our galaxy, we expect |
---|
| 44 | %$\sim 300$ events per kiloton of water. A megaton water \v{C}erenkov detector |
---|
| 45 | %would be sensitive to three main neutrino signals |
---|
| 46 | |
---|
| 47 | All types of neutrinos and anti-neutrinos are emitted |
---|
| 48 | from a core-collapse supernova, but not all are equally |
---|
| 49 | detectable. |
---|
| 50 | The $\bar{\nu_e}$ is most likely to interact in a water \v{C}erenkov detector. |
---|
| 51 | Three main neutrino signals would be detected, each one yielding unique |
---|
| 52 | information: |
---|
| 53 | \begin{enumerate} |
---|
| 54 | \item Inverse beta decay events (89\%) allowing for a good |
---|
| 55 | determination of the time evolution and energy distribution of the neutrino |
---|
| 56 | burst. The potentials would be enhanced by the detection of the neutron |
---|
| 57 | with the addition of a small mount of Gadolinium \cite{Beacom:2003nk}. |
---|
| 58 | \item Neutral current events involving $^{16}O$ (8\%), which are sensitive |
---|
| 59 | to the temperature of the neutrino spectrum. |
---|
| 60 | \item Directional elastic scattering events from $\nu_{x}$ + $e^{-}$ and |
---|
| 61 | $\bar{\nu}_{x}$ + $e^{-}$ ($\sim$ 3\%). These events provide the direction |
---|
| 62 | of the supernova within $\pm 1$ degree. |
---|
| 63 | \end{enumerate} |
---|
| 64 | %Each one of these modes will yield unique information. |
---|
| 65 | |
---|
| 66 | |
---|
| 67 | |
---|
| 68 | |
---|
| 69 | |
---|
| 70 | |
---|