1 | \subsection{Solar neutrinos} |
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2 | |
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3 | Water \v{C}herenkov detectors have measured the high energy tail |
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4 | of the solar $^{8}$B neutrino flux using electron-neutrino |
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5 | elastic scattering \cite{Smy:2002rz}. |
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6 | Since such detectors could record the time of an interaction and reconstruct |
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7 | the energy and direction of the recoiling electron, unique information |
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8 | of the spectrum and time variation of the solar neutrino flux was extracted. |
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9 | This provided further insights into the ``solar neutrino problem'', |
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10 | the deficit of the neutrino flux (measured by several experiments) |
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11 | with respect to the flux expected by the standard solar models. |
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12 | It also constrained the neutrino flavor oscillation solutions in a fairly |
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13 | model-independent way. |
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14 | |
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15 | The recoiling electrons from solar neutrino interactions are low in energy |
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16 | and produce few \v{C}herenkov photons. However, if at least 20 \% of the |
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17 | detection surface is photo-sensitive then solar neutrinos above 10 MeV |
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18 | could be detected even with a modest photo-sensor efficiency. |
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19 | A detector with larger size than any existing Water \v{C}erenkov has |
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20 | the potential to measure spectrum and time-variation of the high-energy |
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21 | solar neutrino flux more precisely, if systematic uncertainties can be |
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22 | kept small. |
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23 | For example, Super-Kamiokande's measurements obtained from 1258 days |
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24 | of data could be repeated in about half a year (the seasonal flux variation |
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25 | measurement requires of course a full year). In particular, a first |
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26 | measurement of the flux of the rare hep neutrinos may be possible. |
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27 | Elastic neutrino-electron scattering is strongly forward peaked. |
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28 | To separate the solar neutrino signal from background events, this |
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29 | directional correlation is exploited. Angular resolution is limited |
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30 | by multiple scattering. The reconstruction algorithm first reconstructs |
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31 | the vertex from the PMT times and then the direction assuming a single |
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32 | Cherenkov cone originating from the reconstructed vertex. |
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33 | Reconstructing 7 MeV events in a 400 kton |
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34 | fiducial volume water \v{C}erenkov (UNO,MEMPHYS,...) seems not to be a problem. |
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35 | |
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36 | This means we are able to make improvements in solar neutrino detection |
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37 | with a megaton-scale \v{C}erenkov |
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38 | detector: even if it is not the main goal of such a detector |
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39 | it could be an excellent by-product. |
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40 | |
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