Direct evidence for neutrino flavor transformation from neutral-current interactions in the Sudbury Neutrino Observatory

Observations of neutral-current nu interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the nu(e) component of the 8B solar flux is phis(e) = 1.76(+0.05)(-0.05)(stat)(+0.09)(-0.09)(syst) x 10(6) cm(-2) s(-1) for a kinetic energy threshold of 5 MeV. The non-nu(e) component is phi(mu)(tau) = 3.41(+0.45)(-0.45)(stat)(+0.48)(-0.45)(syst) x 10(6) cm(-2) s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(+0.44)(-0.43)(stat)(+0.46)(-0.43)(syst) x 10(6) cm(-2) s(-1), consistent with solar models.     

Proposal to build a neutrino observatory in Sudbury, Canada

Summary The proposal to build a heavy-water Čerenkov detector deep underground is discussed. The main physics objectives are to measure the⁸B solar neutrino flux, to identify neutrino oscillations and to watch for gravitational collapse. The measurements of the sources of background and the optical properties of heavy water, which are necessary to prove the feasibility of the detector, are reported. The present status of the project is indicated.

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Riassunto Si discute il progetto di costruire un rivelatore Čerenkov ad acqua pesante a grande profondità. Gli obiettivi fisici principali sono quelli di misurare il flusso di neutrini solati di⁸B, d'identificare le oscillazioni neutriniche e di osservare il collasso gravitazionale. Si riportano le misure delle sorgenti di background e le proprietà ottiche dell'acqua pesante, che sono necessarie per provare la fattibilità del rivelatore. Si indica lo stato attuale del progetto.

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Резюме Обсуждается преложение о строительстве черенковского детектора на тяжелойводе. Основные физические задачи—измерение потока⁸B солнечных нейтрино, идентификация нейтринных осцилляций и наблюдение гравитационного коллапса Сообщаются результаты измерений источников фона и оптических свойств тяжелой воды, необходимые для вьшолнения этого детектора. Описывается состояние проекта в настоящее время.

     

Analysis of the neutral-current interaction in the inclusive neutrino reactions

We attempt a general phenomenological analysis of the neutral weak current in the inclusive neutrino reactions using the parton model as a tool. From the recently reported data on these processes we determine the strengthH of the neutral-current interaction as well as the amount of theVA interference. We find (H/G)²=0·54±0·06 whereG is the Fermi coupling constant and theVA interference contribution turns out to be 33±23%. We also discuss the comparison of the data with various models for the neutral hadronic current. An erratum to this article is available at .     

Model-independent analysis of the neutral-current interaction in the inclusive neutrino reactions

On the basis of some general assumptions on the deep inelastic structure functions, such as scaling and chiral symmetry we determine the values of {(H _V ³)²+(H _A ³)²}+η{(H _V ⁰)²+(H _A ⁰)²} andH _V ³ H _A ³+ηH _V ⁰ H _A ⁰ whereH _V ^3,0 andH _A ^3,0 are the four coupling constants characterizing the hadronic neutral current andη is the ratio of the isoscalar to isovector structure functions. General expressions are given for the kinematical averages 〈v〉 and 〈Q ²〉 for the neutral-current reactions in terms of the coupling constants. This analysis does not depend on the validity of the quark-parton model.     

Experimental study of neutral-current and charged-current neutrino cross sections

Samples of 9200 muon-neutrino and 3800 muon-antineutrino interactions on nuclei were obtained with the fine-grain calorimeter of the CHARM Collaboration at the CERN 200 GeV narrow-band neutrino beam. The interactions were classified as either neutral-current or charged-current processes on an event-by-event basis. Neutral-current and charged-current cross sections in neutrino and antineutrino interactions are presented. From these results we deduce a statistically significant contribution of right-handed coupling to the neutral hadronic current, and a value of the electroweak mixing angle corresponding to sin²θ = 0.220 ± 0.014.     

Neutrino observations from the sudbury neutrino observatory

Neutrino observations from the Sudbury Neutrino Observatory are presented from preliminary analyses. Based on energy, direction and location, the data in the region of interest appear to be dominated by ⁸B solar neutrinos, detected by the charged current reaction on deutrium and elastic scattering from electrons, with very little background. Measurements of radioactive backgrounds indicate that the measurement of all active neutrino types via the neutral current reaction on deuterium will be possible with small systematic uncertainties. Results for the fluxes observed with these reactions will be provided when further calibrations have been completed.     

Active to sterile neutrino mixing limits from neutral-current interactions in MINOS

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10(20) protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754 ± 28(stat) ± 37(syst) for oscillations among three active flavors. The fraction f(s) of disappearing ν(μ) that may transition to ν(s) is found to be less than 22% at the 90% C.L.     

Variables for probing neutrino oscillation at super-Kamiokande and the Sudbury Neutrino Observatory

We propose several new variables, insensitive to the absolute flux of the incident solar or supernova neutrino beam, which probe the shape of the observed spectrum at super-Kamiokande and Sudbury Neutrino Observatory experiments and can sensitively signal neutrino oscillations. One class of such variables involve moments of the distributions recorded at the two facilities while another variable, specific to SNO, utilises the integrated charged and neutral current signals. The utility of these variables in the context of supernova neutrinos both from the collapse epoch and the post-bounce era is also discussed.     

Effect of gluons on neutral-current interactions in deep inelastic neutrino scattering

The contribution of neutral spin-1 gluons to the deep inelastic neutral-current processesv(v)+N→v(v)+ hadrons is worked out in the parton model. Such a contribution violates Bjorken scaling strongly.     

NESTOR: An underwater neutrino observatory in the Ionian sea

Deep underwater high energy neutrino detection is a very promising field in both elementary particle physics and astrophysics. On one side, the energy range of ground based accelerators cannot be extended much more respect to the present, leaving only astronomical sources for future investigations. In the astrophysics field, neutrinos are the tool to explore further in the universe due to their low interactions. By the same token, the experimental problems for a neutrino detector are enormous. The Cherenkov effect is practically the only possible tool, because it uses sea water both as shield and as detector. NESTOR is the first step toward a full fledged deep underwater neutrino experiment. While its area, of the order of 10000 m^**2, cannot hope to identify all possible celestial sources, it is nevertheless a necessary step toward the “Km^**3” experiment. The first deployment tests have already been performed, proving the feasibility of the mechanical design, and the electronics is almost completely ready. Additional tests are scheduled for this autumn and next year will see a relevant part of the experiment installed at the bottom of the Ionian sea.     

Muon response in ICAL detector at India-based neutrino observatory

The magnetized iron calorimeter (ICAL) detector, proposed to be built in the India-based neutrino observatory (INO) laboratory, aims to study atmospheric neutrino oscillations. A simulations study of response of muons to the ICAL detector is presented in the form of momentum reconstruction, angle resolution and reconstruction, and charge identification efficiency (CID).     

Solar neutrino oscillation diagnostics at SuperKamiokande and Sudbury Neutrino Observatory

Results for solar neutrino detection from the SuperKamiokande collaboration have been presented recently while those from the Sudbury Neutrino Observatory are expected in the near future. These experiments are sensitive to the⁸B neutrinos from the sun, the shape of whose spectrum is well-known but the normalization is less certain. We propose several variables, insensitive to the absolute flux of the incident beam, which probe the shape of the observed spectrum and can sensitively signal neutrino oscillations. They provide methods to extract the neutrino mixing angle and mass splitting from the data and also to distinguish oscillation to sequential neutrinos from those to a sterile neutrino.     

The km Mediterranean neutrino observatory - the NEMO.RD project

The NEMO.RD Project is a feasibility study of a km³ underwater telescope for high energy astrophysical neutrinos to be located in the Mediterranean Sea. Results on various issues of this project are presented on: i) Monte Carlo simulation study of the capabilities of various arrays of phototubes in order to determine the detector geometry that can optimize performance and cost; ii) oceanographic survey of various sites in search of the optimal one; iii) feasibility study of mechanics, deployment, connections and maintenance of such a detector. Parameters of a site near Capo Passero, Sicily, where depth, transparency and other water parameters seem optimal are shown.     

New ideas in neutrino detection

What is new in the field of neutrino detection? In addition to new projects probing both the low and high ends of the neutrino energy scale, an inexpensive, effective technique is being developed to allow tagging of antineutrinos in water Cherenkov (WC) detectors via the addition to water of a solute with a large neutron cross-section and energetic γ daughters. Gadolinium is an excellent candidate since in recent years it has become very inexpensive, now less than $8 per kilogram in the form of commercially available gadolinium trichloride. This non-toxic, non-reactive substance is highly soluble in water. Neutron capture on gadolinium yields an 8.0 MeV gamma cascade easily seen in detectors like Super-Kamiokande. The uses of GdCl₃ as a possible upgrade for the Super-Kamiokande detector — with a view toward improving its performance as an antineutrino detector for supernova neutrinos and reactor neutrinos — are discussed, as are the ongoing R&;D efforts which aim to make this dream a reality within the next two years.