[387] | 1 | \subsection{Proton decay sensitivity} |
---|
| 2 | For proton decay, no specific simulation for MEMPHYS has been carried out yet. |
---|
| 3 | We therefore rely on the study done by UNO, adapting the results to MEMPHYS |
---|
| 4 | (which has an overall better coverage) when possible. |
---|
| 5 | \subsubsection{$p \rightarrow e^+\pi^0$} |
---|
| 6 | |
---|
| 7 | Following UNO study, |
---|
| 8 | the detection efficiency of $p \rightarrow e^+\pi^0$ |
---|
| 9 | (3 showering rings event) is $\epsilon=$43\% |
---|
| 10 | for a 20 inch-PMT coverage of 40\% or its equivalent, as envisioned for |
---|
| 11 | MEMPHYS. The corresponding estimated |
---|
| 12 | atmospheric neutrino induced background is at the level of 2.25 events/Mt.yr. |
---|
| 13 | From these efficiencies and background levels, |
---|
| 14 | proton decay sensitivity as a function of detector exposure can be |
---|
| 15 | estimated (see Fig. \ref{pdk1}). |
---|
| 16 | |
---|
| 17 | \begin{figure}[htb] |
---|
| 18 | \begin{minipage}[c]{0.44\textwidth} |
---|
| 19 | \epsfig{figure=./figures/epi0-WC-Shiozawa.eps,width=\textwidth,angle=0} |
---|
| 20 | \caption{\it \label{pdk1} Sensitivity for $e^+\pi^0$ proton decay |
---|
| 21 | lifetime, as determined by UNO \cite{uno}. MEMPHYS corresponds to case (A).} |
---|
| 22 | \end{minipage} |
---|
| 23 | \begin{minipage}[c]{0.05\textwidth} |
---|
| 24 | ~ |
---|
| 25 | \end{minipage} |
---|
| 26 | \begin{minipage}[c]{0.44\textwidth} |
---|
| 27 | \epsfig{figure=./figures/Knu-WC-Shiozawa.eps,width=\textwidth,angle=0} |
---|
| 28 | \caption{\it \label{pdk9_jbz} |
---|
| 29 | Expected sensitivity on $\nu K^+$ proton decay as a function of MEMPHYS |
---|
| 30 | exposure \cite{uno} (see text for details).} |
---|
| 31 | \end{minipage} |
---|
| 32 | \end{figure} |
---|
| 33 | |
---|
| 34 | $10^{35}$ years partial |
---|
| 35 | lifetime could be reached at the 90\% CL for a 5 Mt.yr exposure with MEMPHYS |
---|
| 36 | (similar to case A in figure~\ref{pdk1}). |
---|
| 37 | |
---|
| 38 | |
---|
| 39 | \subsubsection{$p \rightarrow \overline{\nu}K^+$} |
---|
| 40 | |
---|
| 41 | Since the $K^+$ is below the \v{C}erenkov threshold, this channel is |
---|
| 42 | detected via the decay products of the kaon: a 256 MeV/c muon and |
---|
| 43 | its decay electron (type I) or a 205 MeV/c $\pi^+$ and $\pi^0$ |
---|
| 44 | (type II), with the possibility of a delayed (12 ns) coincidence |
---|
| 45 | with the 6 MeV nuclear de-excitation prompt $\gamma$ (Type III). |
---|
| 46 | In Super-Kamiokande, the efficiency for the reconstruction of |
---|
| 47 | $p \rightarrow \overline{\nu}K^+$ is $\epsilon=$ 33\% (I), 6.8\% (II) |
---|
| 48 | and 8.8\% (III), |
---|
| 49 | and the background is at the 2100, 22 and 6/Mt.yr level. For the |
---|
| 50 | prompt $\gamma$ method, the background is dominated by |
---|
| 51 | mis-reconstruction. As stated by UNO, there are good |
---|
| 52 | reasons to believe that this |
---|
| 53 | background can be lowered at the level of 1/Mt.yr corresponding |
---|
| 54 | to the atmospheric neutrino interaction $\nu p \rightarrow \nu |
---|
| 55 | \Lambda K^+$. In these conditions, and using Super-Kamiokande performances, |
---|
| 56 | a 5 Mt.yr MEMPHYS exposure would |
---|
| 57 | allow to reach the $2\times10^{34}$ years partial lifetime |
---|
| 58 | (see Fig. \ref{pdk9_jbz}). |
---|
| 59 | |
---|
| 60 | %\subsubsection{Comparison with liquid argon detectors} |
---|
| 61 | %Comparisons have been done between megaton scale \v{C}erenkov detectors |
---|
| 62 | %and liquid argon TPC's with a mass of 100 kilotons. The main results show an |
---|
| 63 | %advantage to \v{C}erenkov detectors for the $e^+ \pi^0$ channel, due to their |
---|
| 64 | %higher mass, while liquid argon TPC's get better results for the |
---|
| 65 | %$\bar\nu K^+$ channel, due to a much better detection efficiency. |
---|
| 66 | %The two techniques look therefore quite complementary. |
---|
| 67 | |
---|