Neutrino flux

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. 

The first reaction is a fusion of two protons to produce a 2H nucleus, a positron (e+) and a neutrino (ve). The second reaction is a proton capture with the formation of 3He and a y-ray. In the third reaction two 3He nuclei fuse to give 4He and two protons. The total energy released in one cycle is 26.8 MeV or 4.30 x 10-12 J. An important product of this process is the neutrino and it should provide a neutrino flux from the Sun that is measurable at the surface of the Earth. However, the measured flux is not as big as calculated for the Sun - the so-called neutrino deficit... 

Table 5.3. Outline of stellar structure and evolution Solar neutrino fluxes expected and detected in different experiments ... 

Table 5.4. Solar neutrino fluxes from heavy water experiments...

Neutrinos inform us almost instantaneously of what is happening in the Sun s core. However, the main interest of this solar cardiograph is hardly to detect some failure in the Sun s cycle. In capturing solar neutrinos, the aim of contemporary physics is rather to catch the Sun in the act of nuclear transmutation. By measuring the neutrino flux, we may check our understanding of the Sun as a whole and at the same time analyse the relationship between this strange particle and more commonplace forms of matter. 

But what does the Sun provide us with in the way of measurable quantities How can we guarantee the veracity of our model stars The key quantities all concern the surface intrinsic brightness, radius and effective temperature, that is, the temperature of the equivalent blackbody. But new constraints have now been added to this visible data, this time directly affecting the depths of our great star. These are the neutrino flux and global oscillations of the Sun s great body. 

Note added After this colloquium, we analyze the the probability of the long gap systematically. We find that the almost constant neutrino flux whose decay time of the event rate is longer than 10 seconds can caused the 7 seconds gap before 3 events with the probability of 1 2 percent. But it seems not very natural to consider the constant neutrino flux. 

The sun is a major source of neutrinos reaching the surface of Earth due to its close proximity. The sun emits 1.8 x 1038 neutrinos/second, which, after an 8-min transport time, reach the surface of Earth at a rate of 6.4 x 1010 neutrinos/s/cm2. The predictions of the standard solar model for the neutrino fluxes at the surface of Earth due to various nuclear reactions are shown in Table 12.3. 

TABLE 12.3 Predicted Solar Neutrino Fluxes (Bahcall and Pena-Garay)... 

Figure 12.18 Log-log plot of predicted neutrino fluxes from various solar nuclear reactions. The energy regions to which the neutrino detectors are sensitive are shown at the top. [From Bahcall (from Bahcall website).]...

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. 

The direct observational evidence for the occurrence of neutrino oscillations came from observations with the Cerenkov detectors. The SNO detector found one-third the expected number of electron neutrinos coming from the sun in agreement with previous work with the radiochemical detectors. The Super Kamiokande detector, which is primarily sensitive to electron neutrinos, but has some sensitivity to other neutrino types found about one-half the neutrino flux predicted by the standard... 

Stellar nucleosynthesis The reaction, 4He + JHe - 7Be + photon, happens at the center of the Sun and other stars. The 7Be decay thatfollows is an important factor in the so-called solar neutrino puzzle. Although 7Be is rather rare at the solar center, decaying to 7Li with its 8-week halflife, there is rather a huge mass of 7Be at any given time at the solar center because 7Be is stable against breakup into smaller nuclear particles. That mass of7Be can be reliably calculated. But evidence of neutrinos from the Sun shows that the neutrino flux expected from that mass of 7Be does not entirely arrive at the Earth. 

The lion s share of fluorine is produced by the intense burst of neutrinos that occurs when the Type II supernova core collapses. Although neutrinos interact only infrequently with matter, a tiny fraction of their intense flux during a 10-second burst drives a proton or neutron from the 20Ne nucleus, in either case resulting in 19F. This occurs where both 20Ne and the neutrino flux are most abundant, near the core of the exploding massive star. Much of this 19F is subsequently destroyed by nuclear reactions in the heated gas when the shock wave passes, but enough survives to account for the 19F/2°Ne abundance ratio in the Sun. 

The rarest of these proton-rich isotopes have a different and more exotic sources the immense neutrino flux from the forming hot neutron star can either convert a neutron into a proton (making,... 

Thermal SN explosion mechanism was proposed by Colgate and White [32], In this picture, part of the neutrino flux liberated in the core collapse is deposited to the stellar mantle to make it unbound ( 1051 ergs is needed). Specific mechanisms include neutrino-driven fluid instabilities, for example convection both above neutrinosphere and inside the proto-NS. Neutrino-driven convection, however, may not be as important as thought before, as follows from recent detailed 2D studies of convection [24], Instead, other fluid instabilities such as newly found double-diffusive instability (the so-called lepto-entropy fingers ) [23], may effectively increase neutrino luminosity to help successful explosion. Note here that process ve -I u(, e1 I e —>7 + 7... 

AMANDA has yet to observe an extraterrestrial neutrino source, but she has demonstrated the cost-effectiveness and robustness of the technique. The detector is very versatile it addresses many different neutrino physics subjects and sets the most stringent upper limits on Galactic and extragalactic neutrino fluxes. The improved search for diffuse fluxes, which has ruled out several predictions, along with the extended four-year search for point sources has started to constrain the enormous parameter space that exist in many models of neutrino production. The reported experimental limits on the diffuse neutrino flux are less than an order of magnitude above the Waxman-Bahcall bound ( Waxman and Bahcall, 1999). As more of the data on tape is analyzed, AMANDA sensitivities will continue to improve. This is a very exciting time in neutrino astronomy and we look forward to neutrino astrophysics with next generation of neutrino telescopes. 

Figure 2. Cosmogenic neutrino flux of the family for various models Protheroe-Johnson (dashed line), Engel-Seckel-Stanev (dotted line), and the minimal (solid line) flux. (From Ahn, Cavaglih, Olinto 2003.)...

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