Geoneutrinos in Borexino

This paper describes the Borexino detector and the high-radiopurity studies and tests that are integral part of the Borexino technology and development. The application of Borexino to the detection and studies of geoneutrinos is discussed.Comment: Conference: Neutrino Geophysics Honolulu, Hawaii December 14-16, 200

Maximal νe→νs\nu_e \to \nu_s solution to the solar neutrino problem: just-so, MSW or energy independent?

We examine the maximal $\nu_e \to \nu_s$ solution to the solar neutrino problem. This solution can be motivated by the exact parity model and other theories. The $\nu_e$ survival probability exhibits one of three qualitatively different behaviours depending on the value of $\Delta m^2$, viz. approximately energy independent, just-so or MSW. By the last of these we mean an enhanced night-time event rate due to regeneration in the Earth. We study all of these possibilities in the context of the recent SuperKamiokande data.Comment: minor changes to text and fig.

Coupling of energy conversion systems and wellbore heat exchanger in a very deep oil well

The conventional geothermal power plants use the reinjection wells mostly to avoid the depletion of the geothermal reservoir gathering in the underground of the produced brine. Nevertheless, reinjection operations entail high economic costs and some risks. An alternative is the extraction of the heat without geothermal fluids production, the wellbore heat exchanger. The goal of the present paper is the analysis of the power production of the wellbore heat exchanger (WBHX) in time and the comparison between two different conversion systems of the thermal energy into electrical: the organic ranking cycle (ORC) plant and the Stirling motor. The selected case study is the oil field of Villafortuna Trecate, a medium enthalpy geothermal resource. The simulation results show a substantial decrease of the wellhead temperature in the first 6 months. After 1 year, the thermal power extracted with the WBHX is greater than 1.3 MW. The design parameters are 20 m3/h for the flow rate, outlet temperature 100.38 °C and the inlet temperature is 40 °C. The R-C318 has been selected as working fluid in the ORC plant: the net electrical power is 121 kW. The air is the working fluid in the Stirling motor: the evaluated net electrical power is 152 kW. The Stirling engine has an efficiency greater than 41 % compared to a system ORC

Optical properties of bialkali photocathodes

The optical properties of the `bialkali' KCsSb and RbCsSb photomultiplier cathodes have been experimentally investigated in the visible range. The measurements carried out include the absolute reflectance at near-normal incidence, the polarization-dependent relative reflectance at various angles and the change in polarization upon reflection from the photocathode. These experimental inputs have been combined with a theoretical model to determine the complex refractive index of the photocathodes in the wavelength range 380 to 680 nm and their thickness. As a result of this work, we derive a model which predicts the fraction of light impinging on a photomultiplier tube that is reflected, absorbed or transmitted, as a function of wavelength and angle, and dependent on the medium to which the photomultiplier is coupled.Comment: 51 pages (double spacing), 16 figures, submitted for publication in NIM

Solar and Reactor Neutrinos: Upcoming Experiments and Future Projects

Sub-MeV solar neutrino experiments and long-baseline reactor oscillation experiments toe the cutting edge of neutrino research. The upcoming experiments KamLAND and BOREXINO, currently in their startup and final construction phase respectively, will provide essential information on neutrino properties as well as on solar physics. Future projects, at present under development, will measure the primary solar neutrino fluxes via electron scattering and neutrino capture in real time. High precision data for lepton mixing as well as for stellar evolution theory will become available in the future. This paper aims to give an overview of the upcoming experiments and of the projects under development.Comment: 11 pages, 14 figures, LATEX (espcrc2.sty). Contribution to the proceedings of "TAUP2001 - Topics in Astroparticle and Underground Physics", LNGS, Italy (September 8-12, 2001

Fast algorithms for min independent dominating set

We first devise a branching algorithm that computes a minimum independent dominating set on any graph with running time O*(2^0.424n) and polynomial space. This improves the O*(2^0.441n) result by (S. Gaspers and M. Liedloff, A branch-and-reduce algorithm for finding a minimum independent dominating set in graphs, Proc. WG'06). We then show that, for every r>3, it is possible to compute an r-((r-1)/r)log_2(r)-approximate solution for min independent dominating set within time O*(2^(nlog_2(r)/r))

On Approximating Restricted Cycle Covers

A cycle cover of a graph is a set of cycles such that every vertex is part of exactly one cycle. An L-cycle cover is a cycle cover in which the length of every cycle is in the set L. The weight of a cycle cover of an edge-weighted graph is the sum of the weights of its edges. We come close to settling the complexity and approximability of computing L-cycle covers. On the one hand, we show that for almost all L, computing L-cycle covers of maximum weight in directed and undirected graphs is APX-hard and NP-hard. Most of our hardness results hold even if the edge weights are restricted to zero and one. On the other hand, we show that the problem of computing L-cycle covers of maximum weight can be approximated within a factor of 2 for undirected graphs and within a factor of 8/3 in the case of directed graphs. This holds for arbitrary sets L.Comment: To appear in SIAM Journal on Computing. Minor change

The Nylon Scintillator Containment Vessels for the Borexino Solar Neutrino Experiment

Borexino is a solar neutrino experiment designed to observe the 0.86 MeV Be-7 neutrinos emitted in the pp cycle of the sun. Neutrinos will be detected by their elastic scattering on electrons in 100 tons of liquid scintillator. The neutrino event rate in the scintillator is expected to be low (~0.35 events per day per ton), and the signals will be at energies below 1.5 MeV, where background from natural radioactivity is prominent. Scintillation light produced by the recoil electrons is observed by an array of 2240 photomultiplier tubes. Because of the intrinsic radioactive contaminants in these PMTs, the liquid scintillator is shielded from them by a thick barrier of buffer fluid. A spherical vessel made of thin nylon film contains the scintillator, separating it from the surrounding buffer. The buffer region itself is divided into two concentric shells by a second nylon vessel in order to prevent inward diffusion of radon atoms. The radioactive background requirements for Borexino are challenging to meet, especially for the scintillator and these nylon vessels. Besides meeting requirements for low radioactivity, the nylon vessels must also satisfy requirements for mechanical, optical, and chemical properties. The present paper describes the research and development, construction, and installation of the nylon vessels for the Borexino experiment

Spectroscopy of Solar Neutrinos

In the last years, liquid-scintillator detectors have opened a new window for the observation of low-energetic astrophysical neutrino sources. In 2007, the solar neutrino experiment Borexino began its data-taking in the Gran Sasso underground laboratory. High energy resolution and excellent radioactive background conditions in the detector allow the first-time spectroscopic measurement of solar neutrinos in the sub-MeV energy regime. The experimental results of the Beryllium-7 neutrino flux measurements as well as the prospects for the detection of solar Boron-8, pep and CNO neutrinos are presented in the context of the currently discussed ambiguities in solar metallicity. In addition, the potential of the future SNO+ and LENA experiments for high-precision solar neutrino spectroscopy will be outlined.Comment: 6 pages, 5 figures, highlight talk at the annual fall meeting of the German Astronomische Gesellschaft in Potsdam (Sep 2009

Self-Calibration of Neutrino Detectors using characteristic Backgrounds

We introduce the possibility to use characteristic natural neutrino backgrounds, such as Geoneutrinos (\bar{\nu}_e) or solar neutrinos (\nu_e), with known spectral shape for the energy calibration of future neutrino detectors, e.g. Large Liquid Scintillator Detectors. This "CalEffect" could be used without the need to apply any modifications to the experiment in all situations where one has a suitable background with sufficient statistics. After deriving the effect analytically using \chi^2 statistics, we show that it is only tiny for reactor neutrino experiments, but can be applicable in other situations. As an example, we present its impact on the identification of the wiggles in the power spectrum of supernova neutrinos caused by Earth matter effects. The Self-Calibration Effect could be used for cross checking other calibration methods and to resolve systematical effects in the primary neutrino interaction processes, in particular in the low energy cross sections.Comment: 6 pages, 4 figure