Solar neutrino observation

While no direct, uncontested evidence for massive neutrinos or lepton mixing has been obtained, suggestive evidence has come from solar neutrino observations, from anomalies in the relative fractions of Ug and observed in energetic cosmic-ray air showers, and possibly from a Vg appearance experiment at Los Alamos. Sample limits are ... 

Anselmann P, Hampel W, Heusser G et al (1992a) Solar neutrinos observed by GALLEX at Gran Sasso. Phys Lett B 285 376... 

For some experiments, the solar neutrino flux and the rate of decay of the proton being extreme examples, tire count rate is so small that observation times of months or even years are required to yield rates of sufficiently small relative uncertainty to be significant. For high count rate experiments, the limitation is the speed with which the electronics can process and record the incoming infomiation. 

Neutrino deficit Subatomic particles predicted to be released by the nuclear reactions on the Sun and should be detected on Earth. The number of neutrinos observed on Earth is much less than predicted by the models of solar nuclear fusion. 

The solar neutrino problem was identified by the first results of Davis et al. using the Cl detector at the Homestake Mine. Davis et al. observed only about one-third of the expected solar neutrino flux as predicted by standard models of the sun, which assume 98.5% of the energy is from the pp chain and 1.5% of the energy is from the CNO cycle. The final result of the Cl detector experiment is that the observed solar neutrino flux is 2.1 + 0.3 SNU compared to the predicted 7.9 + 2.4 SNU, where the solar neutrino unit (SNU) is defined as 10-36 neutrino captures/second/target atom. The GALLEX and SAGE detectors subsequently reported solar neutrino fluxes of 77+10 SNU and 69+13 SNU, which are to be compared to the standard solar model prediction of 127 SNU for the neutrinos detected by these reactions. 

As we discussed, numerous neutrinos are produced by the proton-proton chain in the Sun. However, neutrinos interact only very weakly with matter. Every second over 100 billion neutrinos from the Sun pass through every square inch of our bodies and virtually none of them interact with us. Because neutrinos interact so weakly with matter, detecting them is very difficult. For example, in the first solar neutrino detection experiment, scientist Ray Davis used 100,000 gallons of cleaning fluid (for the chlorine the fluid contained) in a detector located in a South Dakota gold mine. Davis expected to detect on average of 1.8 solar neutrinos per day. Instead, Davis s observed rate has consistently been much lower than this. Also, the long-term rate, plotted as a function of time, shows an anticorrelation between neutrino rate and sunspot activity. 

An area that was pioneered by nuclear chemists is the search for solar neutrinos. Although main-sequence stars, of which the Sun is a typical representative, have for decades been believed to derive their energy from the series of fusion reactions mentioned above, there was no direct observational evidence for this until Raymond Davis in the 1960s undertook to measure the flux of neutrinos from the Sun which accompany these reactions (Davis et al. 1968 Cleveland et al. 1998). The experiment involved measuring the number of Ar atoms (35.0 d) formed by neutrino capture in Cl in a tank of perchloroethylene. With only a few atoms of Ar per month extracted from over 600 t of liquid, this was indeed the ultimate low-level radiochemical separation. Nevertheless, the experiment was successful in detecting the neutrinos, but ever since the first data appeared in 1968, the measured neutrino flux persisted in being only one third of what was expected from model calculations, and this so-called solar neutrino puzzle literally gave rise to a whole new field — neutrino astronomy. 

More recently, some direct evidence for hydrogen burning in the sun has become available through the study of solar neutrinos. K.S. Hirata et al.. Observation of Neutrino Burst from the Supernova SN1987A, Physical Review D, 44,2241-2260,1991. 

During the 10-year period in which the data in Tables V and VI were acquired, the electronic solar neutrino experiment in the Sudbury Neutrino Observatory (SNO) in Canada was completed and began data taking. The heart of SNO is a transparent acryclic sphere holding 1000 tons of heavy (deuterated) water with which to observe the reaction initiated by Ve from the in the sun. 

Fig. 6.10. Results of a dynamical calculation of the r-process in the hot neutrino bubble inside a 20 Mq supernova (continuous curve) compared to the observed Solar-System abundance distribution (filled circles). After Woosley etal. (1994). Courtesy Brad Meyer.

If further observational and associated theoretical work should confirm the current tension among the SBBN-predicted and observed primordial abundances of D, 4He, 7Li, what physics beyond the standard models of cosmology and particle physics has the potential to resolve the apparent conflicts Are those models which modify the early, radiation-dominated universe expansion rate consistent with observations of the CMB temperature fluctuation spectrum If neutrino degeneracy is invoked, is it consistent with the neutrino properties (masses and mixing angles) inferred from laboratory experiments as well as the solar and cosmic ray neutrino oscallation data ... 

Supernovae. All stars above an original mass of more than 8 solar masses are expected to explode at the end of their lifetime after they have exhausted nuclear burning the observable effect of such an explosion is called a supernova. When they explode, they emit about 3 x 10 ° ergs in neutrinos and also about 10 erg in visible energy, such as in shock waves in ordinary matter, the former stellar... 

The theoretical forecasts of the neutrino fluxes used to compare with experimental observations are those from the so-called standard solar model (SSM). This model relies on the values of the solar mass, radius, luminosity, and age (4.7 billion years) and on the best-considered values of the nuclear reaction cross sections. In addition, there are some special assumptions. It is presumed that the sun is not rotating, or differentially rotating, rapidly enough in its interior to affect its internal structure or dynamics. Processes that could mix the solar interior, such as diffusion or periodic hydrodynamic oscillation, are not taken into... 

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