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R. G. H. Robertson

Publications and source records attributed to R. G. H. Robertson.

125 records · Page 7Linked to original sources
arXiv2007

KATRIN: an experiment to measure the neutrino mass

KATRIN is a very large scale tritium-beta-decay experiment to determine the mass of the neutrino. It is presently under construction at the Forschungszentrum Karlsruhe, and makes use of the Tritium Laboratory built there for the ITER project. The combination of a very large retarding-potential electrostatic-magnetic spectrometer and an intense gaseous molecular tritium source makes possible a sensitivity to neutrino mass of 0.2 eV, about an order of magnitude below present laboratory limits. The measurement is kinematic and independent of whether the neutrino is Dirac or Majorana. The status of the project is summarized briefly in this report.

nucl-ex↗
arXiv2007

Search for the second forbidden beta decay of 8B to the ground state of 8Be

A significant decay branch of 8B to the ground state of 8Be would extend the solar neutrino spectrum to higher energies than anticipated in the standard solar models. These high-energy neutrinos would affect current neutrino oscillation results and also would be a background to measurements of the hep process. We have measured the delayed alpha particles from the decay of 8B, with the goal of observing the two 46-keV alpha particles arising from the ground-state decay. The 8B was produced using an in-flight radioactive beam technique. It was implanted in a silicon PIN-diode detector that was capable of identifying the alpha-particles from the 8Be ground state. From this measurement we find an upper limit (at 90% confidence level) of 7.3 x 10^{-5} for the branching ratio to the ground state. In addition to describing this measurement, we present a theoretical calculation for this branching ratio.

nucl-ex↗
arXiv2007

An array of low-background $^3$He proportional counters for the Sudbury Neutrino Observatory

An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active flux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and November 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters filled with a mixture of $^3$He and CF$_4$ gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral current reaction in the D$_2$O, and four strings filled with a mixture of $^4$He and CF$_4$ gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.

nucl-ex↗
arXiv2006

Multi-layer scintillation detector for the MOON double beta decay experiment: Scintillation photon responses studied by a prototype detector MOON-1

An ensemble of multi-layer scintillators is discussed as an option of the high-sensitivity detector Mo Observatory Of Neutrinos (MOON) for spectroscopic measurements of neutrino-less double beta decays. A prototype detector MOON-1, which consists of 6 layer plastic-scintillator plates, was built to study the sensitivity of the MOON-type detector. The scintillation photon collection and the energy resolution, which are key elements for the high-sensitivity experiments, are found to be 1835+/-30 photo-electrons for 976 keV electrons and sigma = 2.9+/-0.1% (dE/E = 6.8+/-0.3 % in FWHM) at the Qbb ~ 3 MeV region, respectively. The multi-layer plastic-scintillator structure with good energy resolution as well as good background suppression of beta-gamma rays is crucial for the MOON-type detector to achieve the inverted hierarchy neutrino mass sensitivity.

nucl-ex↗
arXiv2006

Solar Neutrinos

Experimental work with solar neutrinos has illuminated the properties of neutrinos and tested models of how the sun produces its energy. Three experiments continue to take data, and at least seven are in various stages of planning or construction. In this review, the current experimental status is summarized, and future directions explored with a focus on the effects of a non-zero theta-13 and the interesting possibility of directly testing the luminosity constraint. Such a confrontation at the few-percent level would provide a prediction of the solar irradiance tens of thousands of years in the future for comparison with the present-day irradiance. A model-independent analysis of existing low-energy data shows good agreement between the neutrino and electromagnetic luminosities at the +/- 20 % level.

nucl-ex↗
arXiv2004

emiT: an apparatus to test time reversal invariance in polarized neutron decay

We describe an apparatus used to measure the triple-correlation term (\D \hatσ_n\cdot p_e\times p_ν) in the beta-decay of polarized neutrons. The \D-coefficient is sensitive to possible violations of time reversal invariance. The detector has an octagonal symmetry that optimizes electron-proton coincidence rates and reduces systematic effects. A beam of longitudinally polarized cold neutrons passes through the detector chamber, where a small fraction beta-decay. The final-state protons are accelerated and focused onto arrays of cooled semiconductor diodes, while the coincident electrons are detected using panels of plastic scintillator. Details regarding the design and performance of the proton detectors, beta detectors and the electronics used in the data collection system are presented. The neutron beam characteristics, the spin-transport magnetic fields, and polarization measurements are also described.

nucl-ex↗
arXiv2003

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.

hep-ph↗
arXiv2002

Comment on "Evidence for Neutrinoless Double Beta Decay"

We comment on the recent claim for the experimental observation of neutrinoless double-beta decay. We discuss several limitations in the analysis provided in that paper and conclude that there is no basis for the presented claim.

hep-ex↗
arXiv2002

The Majorana Ge-76 Double-Beta Decay Project

The Majorana Experiment is a next-generation Ge-76 double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in Ge-76, in the form of 200 detectors in a close-packed array for high granularity. Each crystal will be electronically segmented, with each region fitted with pulse-shape analysis electronics. A half-life sensitivity is predicted of 4.2e27 y or < 0.02-0.07 eV, depending on the nuclear matrix elements used to interpret the data.

hep-ex↗
arXiv2000

New Limit on the D Coefficient in Polarized Neutron Decay

We describe an experiment that has set new limits on the time reversal invariance violating D coefficient in neutron beta-decay. The emiT experiment measured the angular correlation J . p_e x p_p using an octagonal symmetry that optimizes electron-proton coincidence rates. The result is D=[-0.6+/-1.2(stat)+/-0.5(syst)]x10^(-3). This improves constraints on the phase of g_A/g_V and limits contributions to T violation due to leptoquarks. This paper presents details of the experiment, data analysis, and the investigation of systematic effects.

nucl-ex↗
arXiv2000

Spectroscopy of Double-Beta and Inverse-Beta Decays from 100Mo for Neutrinos

Spectroscopic studies of two beta-rays from 100Mo are shown to be of potential interest for investigating both the Majorana neutrino mass by neutrinoless double beta-decay and low energy solar neutrino's by inverse beta-decay. With a multi-ton 100Mo detector, coincidence studies of correlated beta-beta from neutrinoless double beta-decay, together with the large Q value, permit identification of the neutrino-mass term with a sensitivity of ~ 0.03 eV. Correlation studies of the inverse beta and the successive beta-decay of 100Tc, together with the large capture rates for low energy solar neutrino's, make it possible to detect in realtime individual low energy solar neutrino in the same detector.

nucl-ex↗
arXiv2000

A Compact 3H(p,gamma)4He 19.8-MeV Gamma-Ray Source for Energy Calibration at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) is a new 1000-tonne D2O Cerenkov solar neutrino detector. A high energy gamma-ray source is needed to calibrate SNO beyond the 8B solar neutrino endpoint of 15 MeV. This paper describes the design and construction of a source that generates 19.8-MeV gamma rays using the 3H(p,gamma)4He reaction (``pt''), and demonstrates that the source meets all the physical, operational and lifetime requirements for calibrating SNO. An ion source was built into this unit to generate and to accelerate protons up to 30 keV, and a high purity scandium tritide target with a scandium-tritium atomic ratio of 1:2.0+/-0.2 was included. This pt source is the first self-contained, compact, and portable high energy gamma-ray source (E>10 MeV).

physics.ins-det↗
arXiv2000

Neutrino Detection using Lead Perchlorate

We discuss the possibility of using lead perchlorate as a neutrino detector. The primary neutrino interactions are given along with some relevant properties of the material.

nucl-ex↗
arXiv2000

Neutrino Mass and Oscillations

Current evidence for neutrino oscillation is reviewed, some areas for closer investigation are suggested, and a plausible future experimental program is summarized.

hep-ex↗
arXiv1998

Solar Neutrino Interactions with 18O in SuperKamiokande

The ratio of 18O nuclei to electrons in SuperKamiokande is quite small, about 1:5000. However this nucleus provides two unpaired neutrons and a low threshold for solar neutrino absorption, resulting in an unusually large cross section. The 18O nuclei, together with 17O and deuterium, will produce in excess of 460 scattered electrons per year with energies above the initial SuperKamiokande threshold of 6.5 MeV, or about 6.7% of the total solar neutrino signal, for an electron neutrino flux scaled to the current SuperKamiokande counting rate. We explore whether this might complicate efforts to extract the neutrino spectrum from elastic scattering events and whether there might be any prospect of combining 18O and elastic scattering events to separate charged and neutral current interactions. Under current operating conditions the answers are no, as the Fermi, Gamow Teller, and forbidden contributions to the 18O cross section conspire to produce a nearly isotropic cross section. Thus most of the events are indistinguishable from background. This result is relevant to SuperKamiokande detection of solar antineutrinos, which arise in certain oscillation scenarios.

nucl-th↗
arXiv1996

Probability of a Solution to the Solar Neutrino Problem Within the Minimal Standard Model

Tests, independent of any solar model, can be made of whether solar neutrino experiments are consistent with the minimal Standard Model (stable, massless neutrinos). If the experimental uncertainties are correctly estimated and the sun is generating energy by light-element fusion in quasi-static equilibrium, the probability of a standard-physics solution is less than 2%. Even when the luminosity constraint is abandoned, the probability is not more than 4%. The sensitivity of the conclusions to input parameters is explored.

nucl-th↗