Chlorine Solar Neutrino Experiment Research Articles

The homestake chlorine solar neutrino experiment—past, present and future

The Homestake chlorine solar neutrino detector has measured the total flux of electron neutrinos from the Sun above 0.814 MeV as 2.56±0.16(stat)±0.16(syst) SNU compared to the predicted flux of 7.5 SNU. When combined with the recent SNO measurement of the electron neutrino flux from 8 B decays, the Homestake measurement gives 0.55 ± 0.27 SNU for the “1 MeV” electron neutrino flux ( 7 Be, PeP and CNO) compared to the prediction of 1.83 SNU, assuming no neutrino flavor transitions.

The goodness of fit of radioactive counting data with application to the data of the chlorine solar neutrino experiment

A procedure is given for determining the goodness of fit between an observed time series of events from radioactive decay and the model that is presumed to have produced these events. This procedure is applied to the data from the chlorine solar neutrino experiment at Homestake and it is found that the goodness of fit probability is high for both single experiments and for the entire data set. The spectrum of individual experiment production rates is then compared to the expected distribution based on the assumption of a constant production rate and good agreement is also found.

Standard solar neutrinos

Abstract The 8B solar neutrino flux predicted by the standard solar model (SSM) is consistent within the theoretical and experimental uncertainties with that observed at Super-Kamiokande. The combined results from the Super-Kamiokande and the Chlorine solar neutrino experiments do not provide a solid evidence for neutrino properties beyond the minimal standard electroweak model. The results from the Gallium experiments and independently the combined results from Super-Kamiokande and the Chlorine experiment imply that the 7Be solar neutrino flux is strongly suppressed compared with that predicted by the SSM. This conclusion, however, is valid only if the neutrino absorption cross sections near threshold in Gallium and Chlorine do not differ significantly from their theoretical estimates. Such a departure has not been ruled out by the Chromium source experiments in Gallium. Even if the 7Be solar neutrino flux is suppressed compared with that predicted by the SSM, still it can be due to astrophysical effects not included in the simplistic SSM. Such effects include spatial and/or temporal variations in the temperature in the solar core, rotational mixing in the solar core, and dense plasma effects which may strongly enhance p-capture by 7Be relative to e-capture. The new generation of solar observations, which already look non stop deep into the sun, like Super-Kamiokande through neutrinos, and SOHO and GONG through acoustic waves, may be able to point at the correct solution; astrophysical solutions if they detect unexpected temporal and/or spatial behaviour, or particle physics solutions if Super-Kamiokande detects characteristic spectral distortion or temporal variations (e.g., the day-night effect) of the 8B solar neutrino flux. If Super-Kamiokande will not discover spectral distortions or time dependence of the 8B solar neutrino flux then, only future solar neutrino experiments such as SNO, BOREXINO and HELLAZ, will be able to find out whether the solar neutrino problem is due to neutrino properties beyond the minimal standard electroweak model or whether it is just a problem of the too simplistic standard solar model.

Helium diffusion in the sun

We calculate improved standard solar models using the new Livermore (OPAL) opacity tables, an accurate (exportable) nuclear energy generation routine which takes account of recent measurements and analyses, and the recent Anders-Grevesse determination of heavy element abundances. We also evaluate directly the effect of the diffusion of helium with respect to hydrogen on the calculated neutrino fluxes, on the primordial solar helium abundance, and on the depth of the convective zone. Helium diffusion increases the predicted event rates by about 0.8 SNU, or 11 percent of the total rate, in the chlorine solar neutrino experiment, by about 3.5 SNU, or 3 percent, in the gallium solar neutrino experiments, and by about 12 percent in the Kamiokande and SNO solar neutrino experiments. The best standard solar model including helium diffusion and the most accurate nuclear parameters, element abundances, and radiative opacity predicts a value of 8.0 SNU +/- 3.0 SNU for the C1-37 experiment and 132 +21/-17 SNU for the Ga - 71 experiment, where the uncertainties include 3 sigma errors for all measured input parameters.

The neutrino electromagnetic moments and charge radius confront Kamiokande II and Homestake experimental results

An analysis is done comparing the main results from the Kamiokande II and chlorine solar neutrino experiments to test the possible existence of a neutrino electric or magnetic moment and charge radius. We find an upper bound on the charge radius of 5.9×10 −11 MeV −2 at 90% CL, an improvement with respect to the previous experimental value by a factor greater than 2. We show that the maximum permissible range for the proper combination of electromagnetic moments has a mild dependence on the theoretical solar model and is reached at the experimental lower bound of the charge radius. Within experimental errors, the apparent discrepancy observed between the data of the two experiments is consistent both with a vanishing magnetic moment and charge radius, and with a Dirac magnetic moment as large as 5.4±1.4×10 −10 μ B for zero charge radius.

Statistical analysis of time variations of 37Ar production rate in chlorine solar neutrino experiment

Fourier analysis of the R. Davis group data has been carried out. A method of signal selection at small signal/noise ratio was suggested and significance levels of individual peaks in the spectrum were determined. The correlation coefficients of neutrino fluxes and some characteristics of solar activity were calculated. The analysis conducted allowed us to reveal three significant peaks in the spectral density of 37Ar production rate in Cl detector: 113.8, 55.6, and 26.6 months (with a ratio of ∼ 4∶2∶1). The probability of a random origin of these peaks is less than 4%.

Solar-cycle modulation of event rates in the chlorine solar neutrino experiment

The time dependence of the event rates in the Homestake chlorine solar neutrino experiment are reexamined using new Ar-37 production data covering the period from late 1986 to mid-1989. The data span almost two complete solar cycles. A careful statistical analysis using nonparametric rank-order statistics is used to calculate quantitative significance levels that do not depend on experimental errors. The results show that the Ar-37 production rate in the experiment is anticorrelated with solar activity for approximately 1977-1989. The shape of the Ar-37 production rate is different from the inverted sunspot activity curve. The Ar-37 production rate is better descrbed by a skewed sawtooth function than by the sunspot number. The best-fitting sawtooth function with sunspot period has a slow rise and a rapid decline. The Ar-37 maximum occurs about 12.5 yr after the solar sunspot minimum, while minimum Ar-37 production is more nearly simultaneous with the sunspot maximum. 42 refs.

Neutrino oscillations and the solar neutrino problem

The theory of neutrino oscillations is reviewed. Vacuum mixing of two neutrinos is considered in detail. Experiments aimed at detecting neutrino oscillations at reactors, accelerators and meson facilities are presented, as well as the chlorine solar neutrino experiment, in which fewer neutrinos than predicted by the solar standard model are detected. Also the phenomenon of neutrinos changing flavour as they travel through matter and its application to the solar neutrino problem are described.

“Just so” neutrino oscillations

We examine in detail the possibility that the low rates observed in the chlorine solar neutrino experiment are due to vacuum oscillations between just two neutrino species — a possibility which remains viable over a finite mass range. We calculate the expected signals, seasonal variations, and effects of time-averaging for both chlorine and gallium based solar neutrino detectors. These provide unique signals for such oscillations, and thus also allow them to be distinguished from the recently proposed resonant neutrino conversion process, as well as from other possible causes of the observed suppression. Finally we display several striking signatures of oscillations relevant to future experiments which may be sensitive to the incident neutrino energy spectrum.

Limits on neutrino oscillation parameters from the chlorine solar-neutrino experiment

MSW regeneration of solar ν e in the earth can lead to a seasonal variation in the capture rate in the chlorine solar-neutrino experiment. The absence of such an effect in the data allows us to set a limit on the neutrino oscillation parameters for Δm 2 near 3 × 10 −6 eV 2. The limit thus obtained is only weakly dependent on solar-model inputs.