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