Solar Neutrino Measurements Research Articles

Cornering solar radiative-zone fluctuations with KamLANDand SNO salt

We update the best constraints on fluctuations in the solarmedium deep within the solar radiative zone to include the newSNO salt solar neutrino measurements. We find that these newmeasurements are now sufficiently precise that neutrino-oscillation parameters can be inferred independently of anyassumptions about fluctuation properties. Constraints onfluctuations are also improved, with amplitudes of 5% nowexcluded at the 99% confidence level for correlation lengths inthe range of a few hundred kilometres. Because they are sensitive tocorrelation lengths which are so short, these solar neutrinoresults are complementary to constraints coming fromhelioseismology.

Summary of solar neutrino measurements

Summary of solar neutrino measurements

Solar neutrino measurements from Super-Kamiokande I

The status of phase 1 of Super-Kamiokande (SK I) is discussed. The accident of November 12, 2001 is described, and its impact on the future of solar neutrino physics at Super-Kamiokande is discussed. The performance of SK I as a solar neutrino detector is reviewed. Data analysis procedures and results from 1496 days of SK I data are presented.

THE SOLAR NEUTRINO PROBLEM AND ITS OSCILLATION SOLUTION

The current status of solar neutrino measurements and their oscillation interpretation is reviewed.

Solar Neutrino measurements

This paper discusses present results and future measurements of solar neutrinos by experiments presently in operation, including Homestake, Sage, Gallex, Kamiokande, Superkamiokande and SNO. The results to date, including both solar model dependent and independent measurements indicate that solar electron neutrinos are changing to other active types and that transitions solely to sterile neutrinos are disfavored. The initial flux of 8 B solar neutrinos is found to be in very good agreement with solar model calculations. Future measurements will focus on greater accuracy for experiments sensitive to low neutrino energies as well as charged current and neutral current sensitive reactions to provide more accurate measurements of neutrino flavour change and further studies of day-night flux differences and spectral shape. These future results are expected to define the parameters for solar neutrino flavor change and initial solar fluxes with much better accuracy.

Solar 8B and hep neutrino measurements from 1258 days of Super-Kamiokande data.

Solar neutrino measurements from 1258 days of data from the Super-Kamiokande detector are presented. The measurements are based on recoil electrons in the energy range 5.0-20.0 MeV. The measured solar neutrino flux is 2.32+/-0.03(stat)+0.08-0.07(syst)x10(6) cm(-2) x s(-1), which is 45.1+/-0.5(stat)+1.6-1.4(syst)% of that predicted by the BP2000 SSM. The day vs night flux asymmetry (Phi(n)-Phi(d))/Phi(average) is 0.033+/-0.022(stat)+0.013-0.012(syst). The recoil electron energy spectrum is consistent with no spectral distortion. For the hep neutrino flux, we set a 90% C.L. upper limit of 40x10(3) cm(-2) x s(-1), which is 4.3 times the BP2000 SSM prediction.

Solar neutrino results (from radio-chemical and water cherenkov detectors)

Recent results on solar neutrino measurements are discussed. The results from radio-chemical experiments are briefly summarized. The new data from 1117 effective days of Super-Kamiokande shows that the spectrum shape agrees with that expected from the convoluted effect of the 8B-neutrino spectrum, the recoil electron spectrum of neutrino electron scattering and the detector responses and that there is a 3.4% difference between the day- and night-time fluxes, but statistically not significant. There is no strong smoking gun evidence for oscillation yet, however those precise measurements of the spectrum shape and day/night fluxes have given a constraint on the oscillation parameters, indicating at 95% confidence level that the large mixing angles solutions (MSW LMA and LOW) are preferable.

Neutrino mass and mixing measurements at Super-Kamiokande

The latest atmospheric and solar neutrino measurements from over 1100 live days of the Super-Kamiokande detector are presented. Atmospheric results continue to strongly support the hypothesis of ν μ oscillations via the measured deficit of μ - like interactions and the strong dependence of the deficit on neutrino flight distance. Analysis of the data gives best fit 2-component oscillation parameters (sin 2 2θ, δ m 2) = (1.00, 3.2 × 10 −3 ev 2) with χ 2/ DOF = 124.7/135. In contrast, the no-oscillation hypothesis gives χ 2/ DOF = 296.5/139. For solar neutrinos, no evidence of neutrino oscillations is seen in the spectral shape or expected day/night enhancement effect. The Small Mixing Angle (SMA) and Vacuum Oscillation (VO) allowed regions from flux deficit alone are excluded at the 95% c.l.

Study of solar neutrinos with the 600 t liquid argon ICARUS detector

The ICARUS time projection chamber can yield sound information on 8B solar neutrinos. Owing to the high-energy resolution and the good capability of event reconstruction it can make a contribution to our understanding of neutrino intensities and their energy spectrum. Moreover, the MSW oscillation probability for sterile and active neutrinos can be well studied because both elastic scattering by electrons and absorption reaction on argon nuclei can be measured independently. The main problem in detecting the low-energy neutrino interactions arises from the environmental radioactivity. In the present work we study by Monte Carlo simulation the topology and the rates of the events, induced by neutrinos and background neutrons, in a 470 t (fiducial mass) liquid-argon TPC detector. For neutrino interactions we use the standard solar model BP98 and the recent experimental confirmation of the shell model computation of absorption cross section. The noise is estimated from new data on natural neutron background, collected in the hall C of the Gran Sasso laboratory. It is confirmed that, with a relatively modest neutron shielding and particular off-line event triggers, the weight of spurious events can be made to have little influence on the ICARUS solar neutrino measurement. Indeed, we expect 6 (26) background events per year in the 212 (759) elastic scattering (absorption reaction) sample.

Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a51Crsource

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 was measured to be (5.55 +/- 0.60 (stat.) +/- 0.32 (syst.)) x 10^(-45) cm^2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 +/- 0.12 (exp.) +/- 0.03 (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 for the solar neutrino measurements is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement.

Calibration of Super-Kamiokande using an electron LINAC: The Super-Kamiokande Collaboration

In order to calibrate the Super-Kamiokande experiment for solar neutrino measurements, a linear accelerator (LINAC) for electrons was installed at the detector. LINAC data were taken at various positions in the detector volume, tracking the detector response in the variables relevant to solar neutrino analysis. In particular, the absolute energy scale is now known with less than 1% uncertainty.

Naturally light sterile neutrinos in gauge mediated supersymmetry breaking

Moduli are generic in string (M) theory. In a large class of gauge-mediated Supersymmetry breaking models, the fermionic components of such fields have very light masses, around the eV scale, and non-negligible mixing with active neutrinos, of order $10^{-4}$. Consequently, these fermions could play the role of sterile neutrinos to which active neutrinos oscillate, thus affecting measurements of solar neutrinos or of atmospheric neutrinos. They could also provide warm dark matter, thus affecting structure formation.

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, − 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.

Model-independent determination of the solar neutrino spectrum with and without the MSW effect.

Besides the opportunity for discovering new neutrino physics, solar neutrino measurements provide a sensitive probe of the solar interior, and thus a rigorous test of solar model predictions. We present model independent determinations of the neutrino spectrum by using relevant flux components as free parameters subject only to the luminosity constraint. (1) Without the Mikheyev-Smirnov-Wolfenstein (MSW) effect, the best fit for the combined data is poor. Furthermore, the data indicate a severe suppression of the $^7$Be flux relative to the $^8$B, contradicting both standard and nonstandard solar models in general; the $pp$ flux takes its maximum value allowed by the luminosity constraint. This pathology consistently appears even if we ignore any one of the three data. (2) In the presence of the two-flavor MSW effect, the current constraint on the initial $^8$B flux is weak, but consistent with the SSM and sufficient to exclude nonstandard models with small $^8$B fluxes. No meaningful constraint is obtained for the other fluxes. In the future, even allowing MSW, the $^8$B and $^7$Be fluxes can be determined at the $\pm$(15 -- 20)\% level, making competing solar models distinguishable. We emphasize that the neutral current sensitivity for $^7$Be neutrinos in BOREXINO, HELLAZ, and HERON is essential for determining the initial fluxes. The constraints on the MSW parameters in the model independent analysis are also discussed.

Kamiokande solar neutrino results

The results on the solar neutrino measurement covering over 7 years in the Kamiokande detector are explained, and their systematic errors are briefly reviewed. The time averaged flux assuming the shape of the 8 B beta decay is (2.89 −0.21 +0.22 ±0.35) × 10 6 cm 2 / sec and the ratio of the flux to the standard solar model of Bahcall and Pinsonnault is 0.51 ± 0.04 ± 0.06. Model independent approaches to the solar neutrino problem that we can conduct by the future solar neutrino experiment, Superkamiokande, are also presented.

Kamiokande results on atmospheric neutrinos and solar neutrinos

The recent results on the atmospheric neutrinos and solar neutrinos are summarized. The double ratio, (μ/e) data/(μ/e) MC, of the fully contained atmospheric neutrino events for 6.18ktonyr is (0.59∼0.60)±0.06±0.05. The solar neutrino measurement extended till the end of July in 1993 gives almost entire coverage of the solar maximum in solar cycle 22. The observation gives the almost constant solar 8B-neutrino flux of Data/SSM = 0.05±0.04±0.06 on an average for the Kamiokande II and III data.

Solar neutrino measurement with the radiochemical gallium detector (GALLEX)

The GALLEX experiment for the detection of solar neutrinos by means of a radiochemical gallium detector is operated by groups from Italy, France, Germany, Israel and the USA in the Gran Sasso underground laboratory (LNGS) near L'Aquila (Italy). It consists of (i) the technical scale tank made of glass fiber reinforced polyester fabric containing 101 tonnes (54 m3) of a highly concentrated (8 moll−1) GaCl3 solution; (ii) a gas sparging system for desorption of GeCl4 which has been formed by interaction of the neutrinos with gallium according to71Ga +νe →71Ge + e− and by addition of ca. 1 mg of a stable Ge isotope; (iii) the absorption columns for concentration of GeCl4 into a volume of 1 l of water; (iv) the laboratory scale apparatus for conversion of GeCl4 to GeH4 and mixing with the counting gas Xe; (v) the counter filling station, and (vi) the low level proportional counters.

Solar neutrinos and solar oscillations

For solar neutrino measurements to contribute directly to particle physics it is essential that we know the structure of the Sun. Only then can we be sure both of the conditions under which the neutrinos are produced and of the state of the material through which they must pass before arriving at the detectors on Earth. Solar oscillations play at least one, and possibly two important roles: firstly, as passive carriers of information about density and sound speed, they provide important diagnostic information which has been used to set quite stringent constraints on the structure of the Sun’s interior; secondly, as active participants in the dynamics of the solar core, it is not out of the question that they induce motion that influences substantially the rates of the various thermonuclear reactions that em it the neutrinos. The basic processes of seismic inference will be discussed briefly, followed by a summary of those inferences that have a bearing on neutrino production. Finally, some of the uncertainties in our understanding of the Sun’s interior will be aired, to restrain the temptation to accept too hastily the details of the simple hydrostatic classical models of the Sun.

The Chemistry of GALLEX—Measurement of Solar Neutrinos with a Radiochemical Gallium Detector

AbstractIn the GALLium Experiment, GALLEX, low‐energy solar neutrinos produced in the main hydrogen fusion reaction inside the Sun are being counted for the first time in a radiochemical gallium detector. In this way, the theories about stellar structure may be verified and the question of the existence of a neutrino rest mass be brought closer to a solution. The experiment is being carried out with international collaboration at the Gran Sasso underground laboratory (LNGS) in the Abruzzi mountains in Italy. In this paper we survey the planning, construction and initial experimental operation of the gallium detector, paying special attention to the chemical aspects of the experiment. The chemical problem to be solved is the separation of very few 71Ge atoms from 100 metric tons of a highly concentrated GaCl3 solution acidified with hydrochloric acid. In addition, these Ge atoms must be isolated and converted into germane, GeH4, for low‐level counting of 71Ge in a gas proportional counter. After extensive preparatory work to meet the extreme requirements of the experiment, the first results have now become available.

Implications of new GALLEX results for the Mikheyev-Smirnov-Wolfenstein solution of the solar neutrino problem.

We compare the implications for $^{7}\mathrm{Be}$ and pp neutrinos of the two Mikheyev-Smirnov-Wolfenstein fits to the new GALLEX solar neutrino measurements. Small-mixing-angle solutions tend to suppress the former as electron neutrinos, but not the latter, and large-angle solutions tend to reduce both by about a factor of 2. The consequences for BOREXINO and similar solar neutrino-electron scattering experiments are discussed.