Neutrino hypothesis

Enrico Fermi on his voyage to the new world postulated that a third particle was needed to balance the emission of the electron in 3 decay. However, the existing conservation laws also had to be satisfied, so there were a number of constraints on the properties of this new particle. Focusing on the decay of a neutron as a specific example, the reaction is already balanced with respect to electric charge, so any additional particle must be neutral. The electrons were observed with energies up to the maximum allowed by the decay Q value so the mass of the particle must be smaller that the instrumental uncertainties. Initially, this instrumental 

The general form of (3 decay of a heavy parent nucleus,71Z, can be written as  

Up to this point we have concentrated on the (3-decay process in which a neutron is converted into a proton. There are a large number of unstable nuclei that have more protons in the nucleus than the stable isobar and so will decay by converting a proton into a neutron. We can write an equation for (3+ decay that is exactly analogous to the previous equation  

To summarize, there are three types of decay, all known as 3 decay. They are 

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Italian physicist Enrico Eermi s (1901-1954) 1934 theory of beta decay used the neutrino hypothesis. (This theory, still used for approximate calculations, was only surpassed for more accurate calculations by theories developed in the 1970s.) But did neutrinos really exist In the 1930s, no experiments to detect them were possible. 

In the last decade, neutrino experiments have demonstrated that neutrinos are massive particles which may oscillate among three autostates. Such experiments [77-82] have evidenced the mass difference between the autostates, but not the neutrino mass scale value. The only way to determine the neutrino mass is the knowledge of the shape of the end point of energy spectrum in beta decays. In the hypothesis of the Majorana neutrino (neutrino coincides with antineutrino and its rest mass is different from zero), the measure of the decay half-life in the neutrinoless double-beta decay (DBD) would be necessary. A number of recent theoretical interpretations of neutrino oscillation experiments data imply that the effective Majorana mass of the electron neutrino (as measured in neutrinoless DBD) could be in the range 0.01 eV to the present bounds. 

In the years following Ya.B. returned several times to this topic. With the emergence of the hypothesis that a significant portion of the Universe s mass is concentrated in massive neutrinos, studies of higher-degree singularities which form in the process of pancake growth became very timely [64]. Analysis of the collisionless model, both theoretical and by means of... 

Open questions with respect to decay (e.g. conservation of energy and spin) led to Fermi s hypothesis of the existence of another elementary particle, the neutrino, in 1934. This particle should be neutral and have a mass of approximately zero. Due to these properties its detection was very difficult. The first successful experiment was... 

It is remarkable that Fermi introduced this essentially correct interaction only two years after the discovery of the neutron and one year after Pauli s hypothesis of the neutrino. Fermi modeled his interaction after QED, with = 7p, but the actual interaction has to be determined by experiment. After a confusing period in which experiments appeared to indicate tensor-type interactions, the so-called V-A theory was developed, which has the remarkable feature of breaking parity invariance. Specifically, one has Fp = 7 (1 — 75), in which the 7 75 part changes sign under a parity transformation. The V-A interaction creates particles with negative helic-ity, which means that, if they have velocities close to the speed of light, their spins are oriented against the direction of motion. 

In Figure 10 we make a two-dimensional plot of a and y, and show the area allowed by Eq. (43) and all atomic results from Table 3. Also shown in Figure 10 is the area allowed by the polarized electron scattering results [Eq. (42)], plus further restrictions imposed on a, y by neutrino experiments if the factorization hypothesis is included. One can see that the atomic PNC results significantly exclude values of the parameters that would otherwise be allowed. It is noteworthy, of course, that the Weinberg-Salam theory falls within all allowed regions. 

In 1960 it was proposed by several physicists, in order to explain a number of experimental observations in a simple way, that there are two neutrinos and two antineutrinos, with somewhat different properties. It was postulated that one neutrino (y) and one antineutrino (v) have a close relation of some sort to the electron and positron, and the other neutrino (y ) and antineutrino (y ) have a similar relation to the muon and antimuon. Experimental verification of this hypothesis was obtained in 1962 by a difficult experiment carried out by a group of Columbia University and Brookhaven National Laboratory scientists. As mentioned above, Reines and Cowan had shown that a neutrino produced by a reaction involving electrons reacts with a proton to produce a neutron and an electron. In the 1962 experiment it was shown that neutrinos produced by the decomposition of muons react with protons to produce only muons, and not electrons ... 

Other possibilities that have been considered in the literature are that T could be a new lepton with (i) the quantum numbers of either the electron or the muon (this has occasionally been referred to as the ortholepton hypothesis)—in this case the r neutrino, i>r would be identical with either i/g or (ii) with the quantum numbers of one of the light antileptons (the paralepton hypothesis)—in this case would be identical with either z7g or i. All these hjq>otheses have by now been dismissed on experimental grounds. 

This, in turn, combined with the LEP demonstration of three neutrino species, gives strong support to the hypothesis of three left-handed lepton... 

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