T. Daily

Measurement of the solar electron neutrino flux with the Homestake chlorine detector

The Homestake Solar Neutrino Detector, based on the inverse beta-decay reaction νe +37Cl →37Ar + e-, has been measuring the flux of solar neutrinos since 1970. The experiment has operated in a stable manner throughout this time period. All aspects of this detector are reviewed, with particular emphasis on the determination of the extraction and counting efficiencies, the key experimental parameters that are necessary to convert the measured 37Ar count rate to the solar neutrino production rate. A thorough consideration is also given to the systematics of the detector, including the measurement of the extraction and counting efficiencies and the nonsolar production of 37Ar. The combined result of 108 extractions is a solar neutrino-induced 37Ar production rate of 2.56 ± 0.l6 (statistical) ± 0.16 (systematic) SNU.

Measurement of the response of the Russian-American gallium experiment to neutrinos from a Cr-51 source

The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low energy neutrinos, a 517 kCi source of 51Cr was produced by irradiating 512.7 g of 92.4% enriched 50Cr in a high flux fast neutron reactor. This source, which mainly emits monoenergetic 747 keV neutrinos, was placed at the center of a 13.1 tonne target of liquid gallium and the cross section for the production of 71Ge by the inverse beta decay reaction Ga(νe, e −)71Ge was measured to be (5.55 ± 0.60 (stat.) ± 0.32 (syst.)) × 10−45 cm2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 ± 0.12 (exp.) +0.035 −0.027 (theor.) and to the cross section of Haxton is 0.87 ± 0.11 (exp.) ± 0.09 (theor.). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement. PACS codes: 26.65.+t, 13.15.+g, 95.85.Ry Typeset using REVTEX

Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a [Formula Presented] source

The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low energy neutrinos, a 517 kCi source of 51Cr was produced by irradiating 512.7 g of 92.4% enriched 50Cr in a high flux fast neutron reactor. This source, which mainly emits monoenergetic 747 keV neutrinos, was placed at the center of a 13.1 tonne target of liquid gallium and the cross section for the production of 71Ge by the inverse beta decay reaction Ga(νe, e −)71Ge was measured to be (5.55 ± 0.60 (stat.) ± 0.32 (syst.)) × 10−45 cm2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 ± 0.12 (exp.) +0.035 −0.027 (theor.) and to the cross section of Haxton is 0.87 ± 0.11 (exp.) ± 0.09 (theor.). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement. PACS codes: 26.65.+t, 13.15.+g, 95.85.Ry Typeset using REVTEX

Recent results from sage

A radiochemical {sup 71}Ga-{sup 71}Ge experiment to determine the primary flux of neutrinos from the Sun began measurements of the solar neutrino flux at the Baksan Neutrino Observatory in 1990. The number of {sup 71}Ge atoms extracted from initially 30 and later 57 tons of metallic gallium was measured in fifteen runs during the period of January 1990 to May 1992. The observed capture rate is 70{plus_minus}19 (stat){plus_minus}10 (syst) SNU. This is to be compared with 132 SNU predicted by the Standard Solar Model.

Solar neutrino observations with the Homestake 37Cl detector

The continuous twenty year record of these measurements of the solar neutrino flux with the Homestake chlorine detector, indicates that the average solar neutrino flux is 2.2±0.3 SNU and that this νe flux appears to vary with the 11 year solar activity cycle. Higher νe fluxes are observed during solar quiet periods and lower νe fluxes during solar active periods. When the Homestake data is combined with the Kamiokande results, the region of overlap between the two experiments is for an observed to predicted 8B neutrino flux ratio of about 0.4 and very little low energy neutrino flux. If the Kamiokande results are corrected for MSW effects, neutral current scatterings by non‐electron neutrinos, then both the 8B and the 7Be fluxes are about 1/3 of the Standard Solar Model predictions.

Neutrino bursts from collapsing stars-results from the Homestake burst search

The 300 ton water Cerenkov detector located at a depth of 4.2 km water equivalent in the Homestake gold mine has been searching for bursts of neutrinos since late 1978. The detector has sensitivity sufficiently high to observe 10 MeV neutrinos and antineutrinos from collapsing stars releasing 1053 erg of neutrino energy at a distance of 10 kpc. No neutrino bursts have been seen over a running time of 384 days.

Preliminary results from the Russian-American gallium experiment Cr-neutrino source measurement

The Russian-American Gallium Experiment has been collecting solar neutrino data since early 1990. The flux measurement of solar neutrinos is well below that expected from solar models. We discuss the initial results of a measurement of experimental efficiencies by exposing the gallium target to neutrinos from an artificial source. The capture rate of neutrinos from this source is very close to that which is expected. The result can be expressed as a ratio of the measured capture rate to the anticipated rate from the source activity. This ratio is 0.93 + 0.15, {minus}0.17 where the systematic and statistical errors have been combined. To first order the experimental efficiencies are in agreement with those determined during solar neutrino measurements and in previous auxiliary measurements. One must conclude that the discrepancy between the measured solar neutrino flux and that predicted by the solar models can not arise from an experimental artifact. 17 refs., 3 figs., 1 tab.

First results from SAGE II

The Russian‐American Gallium solar neutrino Experiment (SAGE) began the second phase of operation (SAGE II) in September of 1992. Monthly measurements of the integral flux of solar neutrinos have been made with 55 tonnes of gallium. The K‐peak results of the first five runs of SAGE II give a capture rate of 76+21−18(stat)+5−7(sys) SNU. Combined with the SAGE I result, the capture rate is 74+13−12(stat)+5−7(sys) SNU. This represents only 56%–60% of the capture rate predicted by different Standard Solar Models.

Search for Nucleon Decay: The Deep Underground Water Cerenkov Detector and the Homestake Tracking Spectrometer

We report the initial result of a search for nucleon decay using a 300-ton water Cerenkov detector located 1480 m underground in the Homestake gold mine at Lead, South Dakota. We find TN > 2.4 × 1031 B μ y, where TN is the nucleon total lifetime and where B μ is the model-dependent probability of production and detection of a stopping and decaying muon following a nucleon decay event. In the SU(5) grand unified model, calculations of B μ vary from approximately 5 to 10%, thereby yielding nucleon total lifetime limits ranging from 1 to 2 × 1030 y.