Solar Neutrino Detector Research Articles

GEM operation in helium and neon at low temperatures

We study the performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne and Ne+H 2 at temperatures in the range of 2.6–293 K. In He, at temperatures between 62 and 293 K, the triple-GEM structures often operate at rather high gains, exceeding 1000. There is an indication that this high gain is achieved by the Penning effect in the gas impurities released by outgassing. At lower temperatures, the gain–voltage characteristics are significantly modified probably due to the freeze-out of impurities. In particular, the double- and single-GEM structures can operate down to 2.6 K at gains reaching only several tens at a gas density of about 0.5 g/l; at higher densities the maximum gain drops further. In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in Ne at low temperatures can be reestablished in Penning mixtures of Ne+H 2: very high gains, exceeding 10 4, have been obtained in these mixtures at 50–60 K, at a density of 9.2 g/l corresponding to that of saturated Ne vapor near 27 K. The results obtained are relevant in the fields of two-phase He and Ne detectors for solar neutrino detection and electron avalanching at low temperatures.

Solar neutrino day-night effect and θ13

We consider the possibility of probing the leptonic mixing angle θ13 through day–night asymmetry measurements at future water Cherenkov solar neutrino detectors. It is shown that, depending on the measured value of the asymmetry, the current upper bound on θ13 may be improved, or even a lower bound on this mixing parameter may be obtained.

Development of In-loaded liquid scintillators for solar neutrino detectors

Development of In-loaded liquid scintillators for solar neutrino detectors

Ideas for future liquid Argon detectors

We outline a strategy for future experiments on neutrino and astroparticle physics based on the use, at different detector mass scales (100 ton and 100 kton), of the liquid Argon Time Projection Chamber (LAr TPC) technique. The LAr TPC technology has great potentials for both cases with large degree of interplay between the two applications and a strong synergy. The ICARUS R&D programme has demonstrated that the technology is mature and that one can built a large ($\sim$ 1 kton) LAr TPC. We believe that one can conceive and design a very large mass LAr TPC with a mass of 100 kton by employing a monolithic technology based on the use of industrial, large volume cryogenic tankers developed by the petro-chemical industry. We show a potential implementation of a large LAr TPC detector. Such a detector would be an ideal match for a Superbeam, Betabeam or Neutrino Factory, covering a broad physics program that could include the detection of atmospheric, solar and supernova neutrinos, and search for proton decays, in addition to the rich accelerator neutrino physics program. In parallel, physics is calling for another application of the LAr TPC technique at the level of 100 ton mass, for low energy neutrino physics and for use as a near station setup in future long baseline neutrino facilities. We present here the main physics objectives and outline the conceptual design of such a detector.

A large liquid scintillator detector for low-energy neutrino astronomy

The potential of a large liquid scintillator detector in an underground laboratory for supernova neutrino detec- tion, solar neutrino detection, and the search for proton decay p → K+ν is discussed.

Update on HERON

A brief report is presented on the status of the HERON R&D project. The goal of the project is to create a superfluid helium-based detector of low-energy solar neutrinos.

Cryogenic Low Energy Astrophysics with Neon

The unique properties of liquid neon make possible a large fiducial target with ultra-low background and energy threshold for the simultaneous detection of low-energy solar neutrinos and WIMP dark matter.

Results from KamLAND

KamLAND demonstrated the reactor ν ¯ e disappearance at long baselines and high confidence level (99.95%) for the first time. The ν ¯ e flux from the sun was also searched and no candidates events were found, allowing for the most stringent upper limit. The present status of the geoneutrino search and the 7Be solar neutrino detection are presented.

Neutrino detection with CLEAN

This article describes CLEAN, an approach to the detection of low-energy solar neutrinos and neutrinos released from supernovae. The CLEAN concept is based on the detection of elastic scattering events (neutrino–electron scattering and neutrino–nuclear scattering) in liquified noble gases such as liquid helium, liquid neon, and liquid xenon, all of which scintillate brightly in the ultraviolet. Key to the CLEAN technique is the use of a thin film of wavelength-shifting fluor to convert the ultraviolet scintillation light to the visible, thereby allowing detection by conventional photomultipliers.Liquid neon is a particularly promising medium for CLEAN. Because liquid neon has a high scintillation yield, has no long-lived radioactive isotopes, and can be easily purified by use of cold traps, it is an ideal medium for the detection of rare nuclear events. In addition, neon is inexpensive, dense, and transparent to its own scintillation light, making it practical for use in a large self-shielding apparatus. The central region of a full-sized detector would be a stainless steel tank holding approximately 135 metric tons of liquid neon. Inside the tank and suspended in the liquid neon would be several thousand photomultipliers.Monte Carlo simulations of gamma ray backgrounds have been performed assuming liquid neon as both shielding and detection medium. Gamma ray events occur with high probability in the outer parts of the detector. In contrast, neutrino scattering events occur uniformly throughout the detector. We discriminate background gamma ray events from events of interest based on a spatial maximum likelihood method estimate of event location. Background estimates for CLEAN are presented, as well as an evaluation of the sensitivity of the detector for p–p neutrinos. Given these simulations, the physics potential of the CLEAN approach is evaluated.

The photomultiplier tube testing facility for the Borexino experiment at LNGS

A facility to test the photomultiplier tubes (PMTs) for the solar neutrino detector Borexino was built at the Gran Sasso laboratory. Using the facility 2200 PMTs with optimal characteristics were selected from the 2350 delivered from the manufacturer. The details of the hardware used are presented.

Online monitoring system and data management for KamLAND

In January 22, 2002, KamLAND started the data-taking. The KamLAND detector is a complicated system which consists of liquid scintillator, buffer oil, spherical balloon and so on. In order to maintain the detector safety, we constructed monitoring system which collected detector status information such as balloon weight, liquid scintillator oil level and so on. In addition, we constructed continuous Rn monitoring system for the 7Be solar neutrino detection. The KamLAND monitoring system consists of various network, LON, 1-Wire, and TCP/IP, and these are indispensable for continuous experimental data acquisition.

EFFECTIVE FIELD THEORY IN NUCLEAR ASTROPHYSICS

In this talk I review some general ideas of effective field theory and give examples of high precision calculations which have astrophysical applications. The examples are np→dγ for big-bang nucleosynthesis and νd inelastic scattering relevant for the solar neutrino detection processes employed by the Sudbury Neutrino Observatory.

A simple analytic three-flavour description of the day-night effect in the solar neutrino flux

In the 3-flavour framework we derive a simple approximate analytic expression for the day-night difference of the flux of solar $\nu_e$ at terrestrial detectors which is valid for an arbitrary Earth density profile. Our formula has the accuracy of a few per cent and reproduces all the known analytic expressions for the Earth matter effects on the solar neutrino oscillations obtained under simplifying assumptions about the Earth's density profile (matter of constant density, 3 layers of constant densities, and adiabatic approximation). It can also be used for studying the Earth matter effects on the oscillations of supernova neutrinos. We also discuss the possibility of probing the leptonic mixing angle $\theta_{13}$ through day--night asymmetry measurements at future water Cherenkov solar neutrino detectors. We show that, depending on the measured value of the asymmetry, the current upper bound on $\theta_{13}$ may be improved, or even a lower bound on this mixing parameter may be obtained.

Ar and Kr concentrations in nitrogen as a measure of the 39Ar and 85Kr activities in connection with the solar neutrino experiment Borexino

Among other radionuclides, 39Ar and 85Kr are potential background sources in the solar neutrino detector Borexino. The expected low event rate requires that the nitrogen used in the experiment needs to have lower concentrations than 0.5 μBq/m 3 for 39Ar and 0.2 μBq/m 3 for 85Kr, corresponding to volume concentrations in N 2 of 0.4×10 −6 m 3/m 3 for Ar and 0.2×10 −12 m 3/m 3 for Kr. Applying gas mass spectrometry and special care in the sampling technique we succeeded in finding the required purity. In addition, we studied the possibility to purify nitrogen from Kr by the adsorption method.

Neutrinos and our sun — Part 2

In this part we describe the chain of nuclear reactions that fuse protons into helium nuclei in the centres of stars. Neutrinos play an important role in the proton-proton chain and detection of these neutrinos is important for a direct insight into the processes taking place at the centre of the sun. Experiments for the detection of solar neutrinos and the emerging result from them, known as the Solar Neutrino Puzzle, are described. The puzzle refused to go away even with very carefully designed experiments. Its solution came from physics, by reviving the idea of neutrino oscillations, speculated many decades ago. Recent experiments have confirmed these ideas and have enriched our knowledge of these fundamental particles.

LOW ENERGY NEUTRINO PHYSICS AFTER SNO AND KamLAND

In the recent years important discoveries in the field of low energy neutrino physics (Eν in the ≈ MeV range) have been achieved. Results of the solar neutrino experiment SNO show clearly flavor transitions from νe to νμ,τ. In addition, the long standing solar neutrino problem is basically solved. With KamLAND, an experiment measuring neutrinos emitted from nuclear reactors at large distances, evidence for neutrino oscillations has been found. The values for the oscillation parameters, amplitude and phase, have been restricted. In this paper the potential of future projects in low energy neutrino physics is discussed. This encompasses future solar and reactor experiments as well as the direct search for neutrino masses. Finally the potential of a large liquid scintillator detector in an underground laboratory for supernova neutrino detection, solar neutrino detection, and the search for proton decay p→K+ν is discussed.

Cryogenic avalanche detectors based on gas electron multipliers

We study the performances of gaseous and two-phase (liquid-gas) cryogenic detectors of ionizing radiation based on gas electron multipliers (GEMs) and operated in an avalanche mode in pure noble gases. The gas amplification in He, Ar and Kr is systematically studied at low temperatures, using triple-GEM multipliers. High gains, exceeding 10 4, were obtained in these gases in the range of 120–300 K. Stable electron avalanching was demonstrated in a saturated Kr vapor in the two-phase mode. These results are relevant for understanding basic mechanisms of electron avalanching at low temperatures and for applications in cryogenic particle detectors, in particular in dark matter and solar neutrino detectors.

Solar neutrinos from CNO electron capture

The neutrino flux from the sun is predicted to have a CNO-cycle contribution as well as the known pp-chain component. Previously, only the fluxes from beta+ decays of 13N, 15O, and 17F have been calculated in detail. Another neutrino component that has not been widely considered is electron capture on these nuclei. We calculate the number of interactions in several solar neutrino detectors due to neutrinos from electron capture on 13N, 15O, and 17F, within the context of the Standard Solar Model. We also discuss possible non-standard models where the CNO flux is increased.

Development of a gadolinium-loaded liquid scintillator for solar neutrino detection and neutron measurements

A high flashpoint, low-toxicity liquid scintillator based on α-hydroxytoluene and containing 10 wt% Gd has been developed for solar neutrino detection and neutron measurements. Dissolution of the gadolinium compound into the scintillator was facilitated by the use of the extractant triethylphosphate. Preliminary investigation has shown the attenuation length of the loaded scintillator to be 1.42 m at 420 nm and the light collection to be 30% of that produced by an unloaded sample.

Detection of a single electron produced inside bulk superfluid helium

The HERON project is an effort to develop a detector for low-energy solar neutrinos in real time by observing their elastic scattering from electrons using superfluid helium as the target material. By applying appropriate electric fields, the recoil electron can be separated from the positive ion, drifted upward to the liquid–vacuum interface, transmitted through the surface with the aid of a vortex ring, and detected using a calorimeter. By studying the correlation of the 16eV photon signal produced by scintillation and the single-electron signal, we can locate a neutrino event in a large detector and distinguish it from the background events involving multiple Compton scattering.