source: Backup NB/Talks/MEMPHYSetal/ISS KEK WC/session3.tex @ 386

The session was organized around :
Water Cerenkov detectors in the three regions of the world - USA-Asia-Europa.
Other detectors in the same regions.

\section{Megaton class Water Cerenkov detectors}

There are three projects in the world with the same goals but with different schedules and political priority. So the situation for each " region " has been shown.

\subsection{Japan with Hyper-Kamiokande}

Japan has a wide experience in using water Cerenkov detector since the experiments done with Kamiokande and Superkamiokande and it is not very  surprising that the concept of a Megaton water Cherenkov detector dates back to 1992 in this country. 

\begin{table}
\begin{center}
\begin{tabular}{|*{4}{c|}}
\hline
        & Kamiokande &  Super Kamiokande & Hyper Kamiokande \\
\hline
Mass & 3,000 t (+1,500 t) & 50,000 t & 1,000,000 t\\
\hline
PM's Coverage & 20\% & 40\% (SK-I and SK-III) & ? \\
&&20\% (SK-II)&\\
\hline
Observation Started & 1983 & 1996 & 2023? \\
\hline
Cost (Oku-Yen)\footnote{1 Oku-Yen $\approx$ 1M\$} & 5 & 100 & 500? \footnote{target cost, no realistic estimation yet} \\
\hline
\end{tabular}
\end{center}
\caption{Comparison is done between old and future water Cerenkov in Japan}
\label{tab:kam_detectors}
\end{table}

On table \ref{tab:kam_detectors} a comparison is done between old and future water Cerenkov in Japan.


\begin{figure}
\centerline{\epsfig{figure=./figures/HK.epsf,height=7.cm}}
\caption{\it Artistic view of a possible scenario for the futur Hyper-Kamiokande detector}
\label{fig:hk}
\end{figure}


The next detector HyperKamiokande (fig. \ref{fig:hk}) will have characteristics such as :
Water depth < 50m (If the present  20-inch 
PMT are used), and linear dimensions for 
light path has to be less than 100m. 
According to optimization of Fid/total, 
rock stability, no sharp edges the best
 compromise looks to be two twin cavities
-       tunnel shaped - and two twin cylindrical
-        detectors.

-Two detectors are independent.
 One detector is alive when the other 
is calibrated or maintained.

-Both cavities should be excavated at 
the same time. But staging scenario is 
possible for the later phase of the 
detector construction.
                                                                                                     
 Precise measurements of $^{8}B$ solar neutrino spectrum and day/night asymmetry by Mega-ton detectors are still important for further study of solar neutrino oscillation. 
Quite high statistics of supernova events is expected for galactic supernova (fig \ref{fig:snhk_1}).
 It enables us to measure:
\begin{itemize}
\item    Precise anti$\nu_e$ spectrum and time variation
\item    $\nu_e$ and $\nu_x$ spectrum measurement by $\nu_e$ scattering
\end{itemize}

\begin{figure}
\centerline{\epsfig{figure=./figures/nakahata_1.epsf,height=7.cm}}
\caption{\it Supernovae events from galaxies}
\label{fig:snhk_1}
\end{figure}


\begin{figure}
\centerline{\epsfig{figure=./figures/nakahata_2.epsf,height=7.cm}}
\caption{\it SRN event rate in Megaton detector}
\label{fig:snhk_2}
\end{figure}


Expected number of supernova relic neutrino (SRN) event is ~250/5yr/Megaton (fig. \ref{fig:snhk_2}). Delayed coincidence method to tag ne bar is important to discover SRN neutrinos but it needs to fill the water tank with Gd  (see Gadzooks)
Hyper-K could be  installed  in Tochibora Mine (close to kamioka). Some years after start-up of T2K- the construction could last for 10 years, hopefully from 2013 - 2022. And followed by a T2-HK experiment.
  
\subsection{DUSEL and UNO in USA}

The DUSEL (Deep Underground Science and Engineering Laboratory) process is in three parts :
\begin{itemize}
\item{Solicitation 1 } Community wide study of 
\begin{itemize}
\item Scientific roadmap : from Nuclear/Particle/Astro-Physics to Geo Physics/Chemistry/Microbiology/Engineering
\item Generic infrastructure requirements
\item Proposal supported by all 8 sites 
                Approved by NSF (January 05)
                PI's went to Washington 28 February to 2 March 
                to clarify goals and time scale
\end{itemize}

\item{Solicitation 2}
  Preselection of 3 sites
Þ       Solicitation 3
Þ       Selection of initial site(s)
Þ       MRE and Presidential Budget (09) -> 2012-2015

The main requirements for a good site are :

Multidisciplinary from the start
Not only physics. astrophysics but also Earth sciences, biology, engineering
Internal strategy inside NSF : interest many directorates ->MRE line
NSF=lead agency but involvement of other agencies: DOE (HEP/Nuclear, Basic Sciences) , NASA (Astrobiology), NIH, USGS + industry
Flexibility
This is an experimental science facility, not an observatory
Specifically adaptive  strategy to take into account :
\begin{itemize}
\item         The evolution of science
\item   International environment ( available facilities -e.g. SNOLAB, MegaScience coord.)
\item   Budgetary realities
\end{itemize}
Excavate as we go ? LN Gran Sasso
Potentially multi-sites 
Although some advantages of a single site in terms of technical infrastructure and visibility 
not necessary provide we have a common management (multi-campus concept)
variety of rock type and geological history 
closer to various  universities (important for student involvement

\item DUSEL aims at a selection of major questions in physics , astrophysics, biology:
\begin{enumerate}
\item What are the properties of the neutrinos?
Are neutrinos their own antiparticle?  
                3rd generation of neutrinoless double beta decay. (1 ton)
                key ingredient in the formulation of a new ``Standard Model'', and can only be obtained by the study of :
What is the remaining, and presently unknown, parameters of the neutrino mass matrix?  $\theta_{13}$
        What is the hierarchy of masses? 
        Is there significant violation of the CP symmetry among the neutrinos?

\item Do protons decay? 
The lifetime for proton decay is a hallmark of theories beyond the Standard Model. Strong dependence on theory may allow a spectacular discovery! 

These questions relate immediately to :

                - the completion of our understanding of particle and nuclear physics
                - the mystery of matter-antimatter asymmetry

\item What is the nature of the dark matter in the universe? 
Is it comprised of weakly interacting massive particles (WIMPs) of a type not presently known, but predicted by theories such as Supersymmetry? 
  
\item What is the low-energy spectrum of neutrinos from the sun?  
Solar neutrinos have been important in providing new information not only about the sun but also about the fundamental properties of neutrinos.

\item Important by-products
-       Neutrinos from Supernovae: Long term enterprise for galactic SN!
-       Underground accelerator (cf. Luna)
-       Nuclear cross sections important for astrophysics and cosmology

\item What can we learn on evolution and genomics? 
Isolated from the surface gene pool for very long periods of time.
Does the deep subsurface harbor primitive life processes today?  
How different are they from microbes on the surface? A reservoir for unexpected and biotechnologically useful enzymes? Potential biotechnology and pharmaceutical applications!
How do these microbes evolve with very low population density, extremely low metabolism rate and high longevity, no predators? Phage? 
The role of the underground in the life cycle
Did life on the earth's surface come from underground?
Can has the subsurface acted as refuge during extinctions.
What signs of subsurface life should we search for on Mars?
Is there dark life as we don't know it?
Does unique biochemistry, e.g. non-nucleic acid based, and molecular signatures exist in isolated subsurface niches? 
                Same requirements as geomicrobiology
        + sequencing and DNA/protein synthetic facilities
\end{enumerate}
\end{itemize}

{\bf  Since august 2005 the National Science Foundation (NSF) selected two sites for its "Deep Underground Science and Engineering Laboratory (DUSEL) Site and Conceptual Design." {\it Homestake (South Dakota) and Henderson (Colorado) } will receive 0.5M\$ to produce a conceptual design for a possible DUSEL. The awards result from the 2nd stage of a 3-stage process that is providing input for NSF's future decision on DUSEL.}

\subsubsection{ UNO  R\&D Proposal}

UNO has been proposed in September 99 at the conference NNN99 first one of the series.
Since there a lot of questions arose :
\begin{description}
\item[-] Is it feasible to excavate a UNO size cavern? 
\item[-] Can it be stable for  more than 30 years?
\item[-] Can it be done economically?
\item[-] Can the water containment be done using liners?
\item[-] Can the PMT mounting system be built economically?
\item[-] Can the photo-detection be done more economically?
\item[-] Cheaper PMTs? Or  New photo-detectors?
\end{description}

Among the recommandations from US comittees at the APS meeting:

 
-       
The Henderson mine is the UNO preferred site 
\begin{itemize}
\item  Owned by Climax Molybdenum Company, a subsidiary of Phelps Dodge Corporation
\item  Established in 1970's
-Henderson is a modern mine developed under strict environmental regulation
and self imposed high standards
\item  One of the 10 largest underground hard rock mines operating in the
world w/ a vast infrastructure
\item Mine Product: Molybdenum (Moly) ore
\item Mining Method: Panel Caving (Block Caving)
\item Mining Capacity: ~40,000 - 50,000 ton/day
- Actual operation: ~20,000 - 30,000 ton/day
? under-utilized infrastructure
\item Expected Mine Life: another ~20 years
\end{itemize}

On the physics motivations :

\begin{itemize}
\item  Promote the science case of proton decay research further
\item Proton decay: a Giant Orphan of Particle Physics
\item  Need serious assistance of theoretical community  e.g. writing letters to funding agencies

\item  Do rigorous R\&D
\item  Establish feasibility and reduce detector cost
\item Engage private industry
\item Develop full simulation/analysis software
\end{itemize}
 
\subsection{The MEMPHYS at Fr\'ejus Project}

Historically the idea of using a Superbeam (proton beam on a target with a magnetic horn to focus a neutrino beam) on a large water cerenkov detector was first developed in Japan with K2K and T2K, and now the T2HK project, and in the US with the UNO project. In the nineties some people begin to think in a competitive European project of megaton water cerenkov class detector for proton decay, neutrino oscillation and astroparticle physics. CERN is the most potential neutrino beam site in Europe. The idea to go cheap and fast lead tp think of reused the superconducting LEP cavities to boost a 4MW proton beam at 2.2GeV, giving a $\nu_\mu$ beam of 270MeV as mean energy. The ideal baseline for a far detector is then around 135km. By case the Frejus underground laboratory is located at this exact distance and because of the Mont-Blanc tragedy it was planned to drill a new safety gallery before the end of 2010. The convergence of this two facts leads naturally people to propose the CERN-Frejus project, also known as the MEMPHYS project. Since this time two main things have changed in this basic proposition.\\
The first one is due to the fact that the use of LEP cavities is not foreseen anymore. It let the opportunity of optimising the superbeam scenario in energy and intensity. This work, done by J.E.Campagne and A.Cazes \cite{ref:campcaz} shows that a 3.5GeV proton energy improve greatly the physics sensitivity with a superbeam at 130km from its detector.
The second point is the new idea developed by P.Zucchelli \cite{ref:zuc} to use a beta beam, produced by radioactive is stored in a decay ring, to produce $\nu_e$ and anti$\nu_e$ beams of very high purity with a perfectly known spectrum and intensity. The required in energy is achievable with the SPS at CERN, increasing greatly the synergy between CERN and Frejus laboratory. Beta beams profits also from a strong synergy with nuclear physicists using radioactive ions produced from the ISOL technique : the neutrino beta beams is now a part of the design study funded by Europe of the future EURISOL facility. After some iterations it seems that the best scenario for a CERN beta beam is to run with $He^6$ (for anti-$\nu_e$ production) and $Ne^{18}$ (for $\nu_e$ production), both with a gamma factor of 100.
Physics case for the CERN-Frejus project will be developed in this paper in session 2, but as a preliminary result figure \ref{fig:schedule} show the $\theta_{13}$ limits of sensitivity for different future experiments as a function of the year including some realistic schedules and figure \ref{fig:sensitivity} show the $\theta_{13}$ sensitivity in function of the CP phase for different experiments, scenarios and combinations of super and beta beams.
  
\begin{figure}
\centerline{\epsfig{figure=./figures/schedule.epsf,height=7.cm}}
\caption{\it A possible schedule baseline of the $\theta_{13}$ sensitivity for the future detectors}
\label{fig:schedule}
\end{figure}

\begin{figure}
\centerline{\epsfig{figure=./figures/sensitivity.epsf,height=7.cm}}
\caption{\it $\theta_{13}$ sensitivity in fonction of the CP violation phase for different scenarios}
\label{fig:sensitivity}
\end{figure}

Super and beta beams can be ready before 2020 but the physics case of a large Water Cerenkov in the Frejus site includes a large part of non accelerator physics : proton decay and super nova observation are at least as reach as the neutrino beam physics. This leads people to prefer to build a cavity and a detector taking benefit of the safety gallery, start non accelerator physics right away and design neutrino oscillation study as soon as beams are available.
A prestudy of the feasibility of the cavity has been launched and funding for a more detailed study will be requested to UE in 2007. A collaboration with Photonis has started around a R\&D on photodetection. Finally a closer inter-regional (North-America, Japan, Europe) cooperation around this project is wished.

 
\subsection{GADZOOKS!}

One can imagine how powerful would be a large water cerenkov able to differenciate the anti-neutrino spectroscopy with the specific $\nuebar p \rightarrow e + n$ reaction through n tagging. This is the proposition of GADZOOKS! (Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!)\cite{ref:gadzook}.
Beyond the kT scale one can forget to use liquid scintillator, $^{3}He$ counters or NaCl. In this last case for example, only 50\% of n capture on Cl is possible with 6\% of NaCl by mass water, which means 60 kilotons of salt in a megaton detector! The
solution is perhaps contained in gadolinium trichloride, GdCl3, which is highly soluble, newly inexpensive and transparent
in solution.\\

\begin{figure}
\centerline{\epsfig{figure=./figures/gadzooks.epsf,height=7.cm}}
\caption{\it The expected coincident signals in Super-K with 100 tons of $GdCl_3$. Detector energy resolution is properly taken in account. The upper supernova curve is the current SK relic limit, while the lower curve is the thoretical lower bound.}
\label{fig:gadzook}
\end{figure}


Neutrons in water quickly lose energy by collisions with free protons (and oxygen nuclei); once thermal energies are reached, the neutron continues to undergo collisions, changing its direction, but on average not its energy, until it is captured. The cross section for thermal neutron capture on natural Gd is 49000 barns, compared to 0.3 barns on free protons. With the proposed 0.2\% admixture by
mass of GdCl3 in water, 90\% of neutron captures are on Gd (8 MeV gamma cascade), 0.2\% on Cl (8.6 MeV gamma cascade), and the rest on H (2.2 MeV gamma, not detectable in SK). After thermalization, capture occurs in about 20 µs (about 10 times faster than in pure water) and about 4 cm; both are slightly increased by the pre-thermalization phase. Compared to typical time and distance separations between events in SK, as well as the position resolution, these are exceedingly small. For 1\% of the total cost of a Mton detector assuming 40\% PM coverage, this kind of new detector is achievable.
In such a detector backgrounds have to be studied in details. The goal is to not compromise an antineutrino single signal by making background neutron capture visible. Neutron from cosmic ray muon spallation in the detector walls, the U/Th/Rn decay chains, or also the $^{152}Gd$ which alpha decay can produce 17O(a,n) or 18O(a,n) reactions, are backgrounds which have to be deeply studied.\\
Under this background conditions many goals of physics are achievable. Detection of Diffuse Supernova Neutrino Background (noted DSNB later) would be the first detection of neutrinos from significant redshifts. Rate and shape of DSNB spectrum (see fig. 1) are important inputs for cosmology. Of course a galactic supernovae would be more than easily visible in a GdCl3 megaton class detector producing almost 300000 events ! Speacking of reactor neutrinos, a megaton detector with GdCl3 to maintain a threshold as low as 3 MeV would collect six Kamland years of data in one day. The spread on Dm212 value fron 10\% to 1\% with three monthes of data. For accelerator neutrinos, neutrino-neutron elastic scattering will be a significant neutral current channel. For proton decay, neutron detection may reduce atmospheric backgrounds.\\
This summer the near detector of K2K experiment will be used as a large R\&D to improve some hardware aspects as Gd filtering, light attenuation and material effects. If this one year R\&D is positive a possible improvement of super-K with GdCl3 is in 2006.

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