A. Ceres

The Data Acquisition and Transport Design for NEMO Phase 1

The NEMO collaboration proposes to build an underwater neutrino telescope located South-East off the Sicily coast. This paper describes the concepts underlying the communication link design going over the whole data acquisition and transport from the front-end electronics to the module sending data on-shore through a fiber optic link which relies on Dense Wavelength Division Multiplexing. An on-shore board, plugged into a PC, extracts and distributes data both to first-level trigger and control systems. Underwater apparatus monitoring and controls are guaranteed by oceanographic instruments and dedicated sensors, whose data are packed and sent back to shore using the same optical link. The communication is fully bidirectional, allowing transmission of timing and control commands. The architecture described here provides a complete real-time data transport layer between the onshore laboratory and the underwater detector. During winter 2006 a first prototype of the apparatus has been deployed: calibration results from the currently working system are here reported.

NEMO: A PROJECT FOR A KM3 UNDERWATER DETECTOR FOR ASTROPHYSICAL NEUTRINOS IN THE MEDITERRANEAN SEA

The status of the project is described: the activity on long term characterization of water optical and oceanographic parameters at the Capo Passero site candidate for the Mediterranean km3 neutrino telescope; the feasibility study; the physics performances and underwater technology for the km3; the activity on NEMO Phase 1, a technological demonstrator that has been deployed at 2000 m depth 25 km offshore Catania; the realization of an underwater infrastructure at 3500 m depth at the candidate site (NEMO Phase 2).

Status and first results of the NEMO Phase-2 tower

In March 2013, the NEMO Phase 2 tower has been successfully installed in the Capo Passero site, at a depth of 3500 m and 80 km off from the southern coast of Sicily. The unfurled tower is 450 m high; it is composed of 8 mechanical floors, for a total amount of 32 PMTs and various instruments for environmental measurements. The tower positioning is achieved by an acoustic system. The tower is continuously acquiring and transmitting all the measured signals to shore. Data reduction is completely performed in the Portopalo shore station by a dedicated computing facility connected to the persistent storage system at LNS, in Catania. Results from the last 9 months of acquisition will be presented. In particular, the analyzed optical rates, showing stable and low baseline values, are compatible with the contribution mainly of 40K light emission, with a small percentage of light bursts due to bioluminescence. These features reveal the optimal nature of the Capo Passero abyssal site to host a km3-sized Neutrino Telescope.

The optical modules of the phase-2 of the NEMO project

A 13-inch Optical Module (OM) containing a large-area (10-inch) photomultiplier was designed as part of Phase-2 of the NEMO project. An intense R&D activity on the photomultipliers, the voltage supply boards, the optical coupling as well as the study of the influences of the Earths magnetic field has driven the choice of each single component of the OM. Following a well-established production procedure, 32 OMs were assembled and their functionality tested. The design, the testing and the production phases are thoroughly described in this paper.

The NOE scintillating fiber calorimeter prototype test results

Abstract An intense R&D program has been carried out by the NOE Collaboration during the last years, to develop a massive fine grain scintillating fiber calorimeter, to be used, in combination with an appropriate target, in a Long Base Line experiment at the CERN to Gran Sasso (CNGS) neutrino beam. The performance of a 4 ton NOE calorimeter prototype exposed to a test beam at CERN PS is shown. Results on the linearity, electromagnetic and hadronic energy resolution are reported and compared with the Monte Carlo predictions.

A transition radiation detector interleaved with low-density targets for the NOE experiment

Abstract The NOE Collaboration has proposed a transition radiation detector (TRD) interleaved with marble targets to tag the electron decay channel of τ leptons produced by ν τ , eventually originated by ν μ oscillations in a long base line experiment. A reduced scale TRD detector prototype has been built and exposed to an electron/pion beam at the CERN PS. Discrimination capabilities between electrons and both charged and neutral pions, representing the main source of background for our measurement, have been determined obtaining rejection factors of the order of the tenth of percent for charged pions, and of a few percent for the neutral pion, matching the experiment requirements. The capabilities of this detector to measure the energy released by particles that start showering inside the targets are shown. A momentum resolution σ p / p ≤40% is found for muons in the range of 1– 7 GeV /c .

The trigger and data acquisition for the NEMO-Phase 2 tower

In the framework of the Phase 2 of the NEMO neutrino telescope project, a tower with 32 optical modules is being operated since march 2013. A new scalable Trigger and Data Acquisition System (TriDAS) has been developed and extensively tested with the data from this tower. Adopting the all-data-to-shore concept, the NEMO TriDAS is optimized to deal with a continuous data-stream from off-shore to on-shore with a large bandwidth. The TriDAS consists of four computing layers: (i) data aggregation of isochronal hits from all optical modules; (ii) data filtering by means of concurrent trigger algorithms; (iii) composition of the filtered events into post-trigger files; (iv) persistent data storage. The TriDAS implementation is reported together with a review of dedicated on-line monitoring tools.

Long-term optical background measurements in the Capo Passero deep-sea site

In March 2013, the Nemo Phase-2 tower has been successfully installed at 100 km off-shore Capo Passero (Italy) and 3500 m depth. This 8-floor tower hosts 32 10-inch PMTs. Results from optical background measurements are presented. In particular, the analyzed rates show stable and low baseline values, compatible with the contribution of 40K light emission, with a small percentage of light bursts due to bioluminescence. All these features are a confirmation of the stability and good optical nature of the site.

Evaluation of candidate photomultiplier tubes for the NOE scintillating fiber calorimeter

Several measurements have been made on different phototubes in order to select the type to be used for the readout system of the NOE magnetized scintillating fiber calorimeter. Characteristics such as gain, linearity, time resolution and cathode uniformity have been examined on several PMT types with standard, fine mesh or channel multiplier structure. The PMT response in the presence of the magnetized calorimeter fringe fields has also been studied. Here we report on the results of these measurements and of the comparisons between the different PMT types.

Wavelength-shifting fibers for calorimetric measurements in a long base line neutrino oscillation experiment

Abstract The NOE Collaboration has proposed a calorimeter to measure the energy of the final states of ν interaction events. The properties of long scintillator bars with wavelength-shifting fiber readout have been studied to develop a calorimeter design option. Various prototypes have been exposed to a cosmic rays stand. The total measured light yield in the middle of a 6 m -long fiber is about 15 photoelectrons. With this photon collection performance, it has been simulated that the calorimeter can achieve 17%/ E and 50%/ E resolutions for electrons and pions, respectively.