[386] | 1 | |
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| 2 | \section{Monte Carlo Generators} |
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| 3 | |
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| 4 | |
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| 5 | |
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| 6 | Accurate measurements of neutrino oscillation parameters by future experiments could be significantly hampered |
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| 7 | |
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| 8 | by the large uncertainties in neutrino cross-section in the sub-GeV range. Neutrino interactions with nucleon in |
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| 9 | |
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| 10 | nuclei are not well understood from a theoretical point of view, especially at low energies, and experimental |
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| 11 | |
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| 12 | data are sparse. Futhermore, most of available data come from Bubble chamber experiments made in the late 70s and have |
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| 13 | |
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| 14 | large systematic errors induced by the determination of the neutrino flux. Calulations for charged current $\nu_\mu$ are |
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| 15 | |
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| 16 | shown in Fig \ref{fig:neutrinoxsection}. \\ |
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| 17 | |
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| 18 | |
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| 19 | |
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| 20 | New generation of high intensity and well controlled neutrino beams allow to collect much precised data that will |
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| 21 | |
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| 22 | attend to futher understand interactions and better constrain models.\\ |
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| 23 | |
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| 24 | |
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| 25 | |
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| 26 | \begin{figure}[hbt] |
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| 27 | |
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| 28 | \begin{center} |
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| 29 | |
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| 30 | \vspace{0.1cm} |
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| 31 | |
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| 32 | \includegraphics[width=85mm]{./figures/neutrinoXsection.epsf} |
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| 33 | |
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| 34 | \vspace{0.5cm} |
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| 35 | |
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| 36 | \caption{ $\nu_\mu$ charged current cross-section calculations compared with experimental data} |
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| 37 | |
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| 38 | \label{fig:neutrinoxsection} |
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| 39 | |
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| 40 | \end{center} |
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| 41 | |
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| 42 | \end{figure} |
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| 43 | |
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| 44 | |
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| 45 | |
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| 46 | Many Monte-carlo generator codes exist but are optimised for a dedicated experiment, ${\it{e.g.}}$ tuned for specific |
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| 47 | |
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| 48 | target materials. The GENIE collaboration\footnote{http://hepunx.rl.ac.uk/~candreop/generators/GENIE/} \cite{genie} gathers |
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| 49 | |
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| 50 | experimentalists from major neutrino experiments as well as theorits and proposes a Universal neutrino generator |
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| 51 | |
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| 52 | that will work for all nuclear targets in all energies. |
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| 53 | |
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| 54 | The code of the framework is developped in Object-Oriented language to ease the interface with standard libraries like |
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| 55 | |
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| 56 | the CERNLIB or CLHEP packages, with other existing simulation softwares (Geant4, Pythia7, $\ldots$) and with standard |
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| 57 | |
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| 58 | analysis tools such as ROOT.\\ |
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| 59 | |
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| 60 | An additional feature that is included in the GENIE framework is an interface with a database containing the |
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| 61 | |
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| 62 | world's neutrino data \cite{xsectiondata} for model validation.\\ |
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| 63 | |
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| 64 | |
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| 65 | |
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| 66 | \section{Background rejection in large water Cerenkov} |
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| 67 | |
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| 68 | |
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| 69 | |
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| 70 | Large underground water Cherenkov detectors can measure $\nu_{\rm{e}}$ appearance as well as $\nu_\mu$ |
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| 71 | |
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| 72 | disappearance. Projects have different configurations in neutrino flux and energy spectrum, although with |
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| 73 | |
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| 74 | a similar overall shape with a the dip from oscillation minimum in the oscillated $\nu_\mu$ distribution. |
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| 75 | |
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| 76 | |
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| 77 | |
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| 78 | \par |
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| 79 | |
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| 80 | For a $\nu_\mu$ disapearance experiment, the signal is muons from charged current quasi elestic interactions, |
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| 81 | |
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| 82 | $\nu_\mu + n \rightarrow p + \mu^-$. |
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| 83 | |
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| 84 | |
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| 85 | |
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| 86 | \par |
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| 87 | |
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| 88 | For a $\nu_{\rm{e}}$ appearance experiment, the signal comes from oscillated $\nu_{\rm{e}}$ neutrinos, |
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| 89 | |
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| 90 | $\nu_\mu \rightarrow \nu_{\rm{e}}$, $\nu_{\rm{e}} + n \rightarrow p + e^-$ and is detected as a fully |
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| 91 | |
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| 92 | contained single electron-ring event.\\ |
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| 93 | |
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| 94 | |
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| 95 | |
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| 96 | \par |
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| 97 | |
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| 98 | Realistic monte-carlo studies for background rejection in $\nu_{\rm{e}}$ appearance experiments are |
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| 99 | |
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| 100 | the essential groundwork for the quest for the last unknown mixing angle of the mixing matrix and |
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| 101 | |
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| 102 | precise measurement of $\theta_{13}$. Main background sources are the $\nu_{\rm{e}}$ contamination in |
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| 103 | |
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| 104 | the beam and neutral current events with one pion decaying into two photons, $\nu + N \rightarrow N' + \nu + \pi^0 (\gamma\gamma)$. |
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| 105 | |
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| 106 | The latter can be reduced by the reconstruction of the second fainter photon-ring. Indeed, it is likely that |
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| 107 | |
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| 108 | one of the photon will carry away most of the energy, and when the energy fraction of one photon is very small, |
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| 109 | |
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| 110 | the event closely resembles electron signal. Algorthims for $\pi^0$ identification have thus been developped |
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| 111 | |
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| 112 | both at T2K \cite{dunmore} and at a megaton class detector on a Very Long Base Line neutrino beam \cite{yanagisawa}. |
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| 113 | |
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| 114 | Background can be subtracted for values of $\theta_{13}$ at the CHOOZ limit, understanding of systematic uncertainties becomes yet crucial |
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| 115 | |
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| 116 | as $\theta_{13}$ gets smaller. \\ |
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| 117 | |
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| 118 | |
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| 119 | |
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| 120 | Estimated performances can be further improved with a better energy reconstruction for all charged |
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| 121 | |
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| 122 | current events. |
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| 123 | |
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| 124 | |
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| 125 | |
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| 126 | |
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| 127 | |
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| 128 | |
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| 129 | |
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| 130 | \section{Photodetection} |
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| 131 | |
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| 132 | |
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| 133 | |
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| 134 | The remarkable successes of SuperK, Kamland, and SNO experiments have triggered |
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| 135 | |
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| 136 | future extrapolated projects aiming the improvement on the accuracy of the |
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| 137 | |
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| 138 | actual neutrinos family parameters, the exploration of the other ones as well as |
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| 139 | |
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| 140 | the search for proton lifetime; sensitive volumes should reach the megaton |
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| 141 | |
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| 142 | scale, |
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| 143 | |
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| 144 | which is an extrapolation by a factor 10-20 of the SK size. In the same |
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| 145 | |
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| 146 | inflatory direction, the detection of very high energy cosmic neutrinos in ice |
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| 147 | |
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| 148 | or water Cerenkov-based detectors will also lead to large numbers of |
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| 149 | |
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| 150 | photomultipliers. It exists then a strong motivation for R\&D trying to decrease |
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| 151 | |
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| 152 | the price of photo-sensitive $cm^2$, which is a major component of projects |
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| 153 | |
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| 154 | budgets. Note that for the calculation of these "surface unit prices", HV, |
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| 155 | |
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| 156 | front-end electronics and cables have of course to be included. |
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| 157 | |
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| 158 | |
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| 159 | |
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| 160 | In another hand, the use of Cerenkov light requires conflicting qualities |
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| 161 | |
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| 162 | concerning the single photoelectron sensitivity, the fast time response |
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| 163 | |
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| 164 | needed for a good vertex determination, the best photodetection efficiency for |
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| 165 | |
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| 166 | setting lower energy thresholds and a robust water pressure resistant |
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| 167 | |
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| 168 | envelop able to work at 10 atmospheres pressure without fatal implosion. The |
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| 169 | |
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| 170 | process of fabrication should also take account of the time needed to built |
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| 171 | |
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| 172 | large quantities ( scale: 100000 u). Clearly common R\&D with industry are |
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| 173 | |
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| 174 | needed. |
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| 175 | |
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| 176 | |
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| 177 | |
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| 178 | Price lowering can follow one or several recepices: |
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| 179 | |
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| 180 | \begin{itemize} |
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| 181 | |
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| 182 | \item |
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| 183 | |
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| 184 | Remove the glass blowing (\cite{ferenc}) |
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| 185 | |
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| 186 | |
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| 187 | |
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| 188 | This leads to a very elegant development using sealed glass planes (\cite{ferenc}) |
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| 189 | |
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| 190 | \item |
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| 191 | |
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| 192 | Simplify the electron multiplicative element (\cite{ferenc},\cite{sk},\cite{photonis}) |
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| 193 | |
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| 194 | |
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| 195 | |
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| 196 | The basic idea is to accelerate photoelectrons from photocathode with a large |
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| 197 | |
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| 198 | potential (10-20 KV); for shaped field, it exists a small surface of |
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| 199 | |
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| 200 | convergence where can be placed either scintillator+small pm (\cite{photonis}), |
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| 201 | |
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| 202 | or an APD ( \cite{sk}). The total gain is then the product of the acceleration gain ( |
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| 203 | |
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| 204 | $\sim$ 4500) followed by the detecting device gain ( $\sim$ 30 or more for an APD). |
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| 205 | |
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| 206 | Such system disposes of a fast time response even for large size photocathods |
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| 207 | |
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| 208 | and of an impressive single |
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| 209 | |
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| 210 | p.e performance. The main drawbacks are the problems brought with the isolation of |
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| 211 | |
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| 212 | the very high voltage and a |
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| 213 | |
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| 214 | frontend fast amplification needed for the APD case. |
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| 215 | |
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| 216 | \item |
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| 217 | |
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| 218 | Optimize the unit size (\cite{photonis}) |
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| 219 | |
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| 220 | |
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| 221 | |
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| 222 | For classical big pmts, there is a not obvious relation between size, price/$cm^2$ |
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| 223 | |
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| 224 | ,time performance, total efficiency and investments for production tools. |
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| 225 | |
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| 226 | Photonis (\cite{photonis}) evaluated this and found as the best candidate a 12 |
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| 227 | |
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| 228 | inches tube, compared to bigger ones. |
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| 229 | |
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| 230 | \item |
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| 231 | |
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| 232 | Increase the photocathode efficiencies (\cite{ferenc},\cite{photonis}) |
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| 233 | |
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| 234 | |
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| 235 | |
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| 236 | The use of $\sim$ 20 KV hv permits an excellent collection efficiency. Improvement |
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| 237 | |
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| 238 | of photocathode QE efficiency can be found in the use of reflective photo-cathod |
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| 239 | |
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| 240 | (30-44 $\%$ instead of $\sim 20 \%$) |
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| 241 | |
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| 242 | \end{itemize} |
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| 243 | |
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| 244 | |
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| 245 | |
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| 246 | \begin{thebibliography}{99} |
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| 247 | |
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| 248 | |
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| 249 | |
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| 250 | \bibitem{genie} C. Andreopoulos and H. Gallagher, "Tools for Neutrino Interaction Model Validation", Nucl.Phys.Proc.Suppl.139:247-252,2005 |
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| 251 | |
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| 252 | \bibitem{xsectiondata} Mike Whalley, "A New Neutrino Cross Section Data Resource", Nucl.Phys.Proc.Suppl.139:241-246,2005 |
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| 253 | |
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| 254 | |
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| 255 | |
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| 256 | \bibitem{costas} Neutrino Interactions and MC Event Generators |
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| 257 | |
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| 258 | Presented by C. Andreopoulos (Rutherford Lab) |
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| 259 | |
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| 260 | |
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| 261 | |
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| 262 | \bibitem{dunmore} Analysis and background aspects in large water Cherenkov detectors |
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| 263 | |
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| 264 | Presented by J. Dunmore (Irvine) |
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| 265 | |
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| 266 | \bibitem{yanagisawa} Background understanding and suppression in Very Long Baseline Neutrino Oscillation experiments with water Cherenkov detectors |
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| 267 | |
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| 268 | Presented by C. Yanagisawa (Stony Brook) |
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| 269 | |
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| 270 | |
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| 271 | |
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| 272 | \bibitem{ferenc} |
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| 273 | |
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| 274 | Development of new large-aera photosensors in the USA |
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| 275 | |
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| 276 | |
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| 277 | |
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| 278 | Presented by D. Ferenc (Davis) |
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| 279 | |
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| 280 | |
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| 281 | |
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| 282 | \bibitem{sk} |
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| 283 | |
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| 284 | R\&D of a large format hybrid photo-detector (HPD) for a next |
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| 285 | |
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| 286 | generation water Cherenkov detector. |
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| 287 | |
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| 288 | |
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| 289 | |
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| 290 | Presented by H. Aihara ( Tokyo) |
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| 291 | |
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| 292 | |
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| 293 | |
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| 294 | \bibitem{pouthas} |
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| 295 | |
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| 296 | Large photodetector developments in Europe |
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| 297 | |
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| 298 | |
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| 299 | |
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| 300 | Presented by J. Pouthas (Orsay) |
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| 301 | |
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| 302 | |
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| 303 | |
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| 304 | \bibitem{photonis} |
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| 305 | |
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| 306 | Revisiting the optimum PMT size for water Cherenkov megaton detectors |
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| 307 | |
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| 308 | |
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| 309 | |
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| 310 | Presented by C. Marmonier (Photonis) |
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| 311 | |
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| 312 | |
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| 313 | |
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| 314 | \bibitem{hama} |
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| 315 | |
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| 316 | Large formats PMTs from Hamamatsu Photonics |
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| 317 | |
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| 318 | |
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| 319 | |
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| 320 | Presented by M.A. Birkel (Hamamatsu) |
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| 321 | |
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| 322 | |
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| 323 | |
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| 324 | \bibitem{burle} |
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| 325 | |
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| 326 | Burle Indistries: Recent photomultiplier and device developments |
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| 327 | |
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| 328 | |
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| 329 | |
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| 330 | Presented by R. Caracciolo (Burle) |
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| 331 | |
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| 332 | |
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| 333 | |
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| 334 | \bibitem{etube} |
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| 335 | |
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| 336 | Electron Tubes: Detector considerations for neutrino physic |
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| 337 | |
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| 338 | |
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| 339 | |
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| 340 | Presented by T. Wright (Electron Tubes) |
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| 341 | |
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| 342 | \end{thebibliography} |
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| 343 | |
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| 344 | |
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| 345 | |
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