Neutrino's are very small particles with no electric charge and little or no mass. Neutrinos are elementary particles—that is, they cannot be broken into smaller particles. Neutrinos are so small that they pass right through most material. One important kind of neutrino is created in the nuclear reactions that give the Sun its energy. The Sun produces so many neutrinos that 70 billion neutrinos pass through every square centimeter (0.15 sq in) of the surface of Earth every second. Scientists study neutrinos to learn more about the reactions that give the Sun its energy. Similar reactions occur in radioactive substances, or materials made up of atoms that spontaneously change into other particles (Radioactivity). Neutrinos also help scientists understand these radioactive reactions. Neutrinos play an important part in the theory scientists have developed to explain the elementary particles that make up all matter and energy.

Neutrinos are members of a group of elementary particles called leptons. Leptons differ from other elementary particles in a property called spin. Spin is analogous to a measurement of a particle’s angular momentum. Scientists measure the spin of particles in units of a constant number. This constant is equal to a number called Planck’s constant (h) divided by two times the constant pi (p). Leptons have spins of +1/2 (times the unit h/2pi). All neutrinos have a spin of +1/2.

Leptons are part of a larger group of particles called fermions. Fermions are defined as particles that obey a rule called the Pauli exclusion principle (named after its developer, Austrian-born Swiss physicist Wolfgang Pauli). The Pauli exclusion principle states that two identical particles cannot occupy the same point in space. The two main types of leptons are those with electric charge and those without electric charge. Neutrinos are leptons without electric charge. Physicists know of three kinds of neutrinos and three kinds of leptons that are not neutrinos. The three nonneutrino leptons are electrons, muons, and taus. Each nonneutrino lepton has a neutrino partner. The three types of neutrinos are the electron neutrino (νe), muon neutrino (νµ), and tau neutrino (νt). All three of the neutrinos have no electric charge and very small masses (or maybe no mass at all). Despite their similarity, physicists have ways of telling the three types of neutrinos apart. When neutrinos interact with matter, the interactions produce new particles. Any reaction involving a neutrino will produce the neutrino’s charged lepton partner. Physicists can therefore deduce which neutrino was involved in a reaction by detecting the charged lepton that has been produced. If a tau lepton is present in the interaction result, physicists know that a tau neutrino interacted with matter. If a muon or electron is present, physicists know that a muon neutrino or an electron neutrino, respectively, was present before the interaction.

All three types of neutrinos have antiparticles. Antiparticles are opposites of the particles that make up ordinary matter. Particles with electric charge have antiparticles whose electric charges are opposite. The distinction between neutrinos (which have no electric charge) and antineutrinos is more complicated. The direction of a neutrino’s spin is always opposite to the direction of its velocity. The direction of the spin of an antineutrino is always the same as its velocity’s direction. This rule may not work if neutrinos do actually have mass, but physicists have not found a violation of the rule yet.

CERN is the European Organization for Nuclear Research, is one of the world's largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world's largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

From: CERN.

As promised in my article about Murphy's law I would like to introduce to you one of my favourtite scientist Wolfgang Pauli. Wolfgang Pauli was born on April 25th, 1900 in Vienna. He received his early education in Vienna before studying at the University of Munich under Arnold Sommerfeld. He obtained his doctor's degree in 1921 and spent a year at the University of Göttingen as assistant to Max Born and a further year with Niels Bohr at Copenhagen. The years 1923-1928 were spent as a lecturer at the University of Hamburg before his appointment as Professor of Theoretical Physics at the Federal Institute of Technology in Zurich. During 1935-1936, he was visiting Professor at the Institute for Advanced Study, Princeton, New Jersey and he had similar appointments at the University of Michigan (1931 and 1941) and Purdue University (1942). He was elected to the Chair of Theoretical Physics at Princeton in 1940 but he returned to Zurich at the end of World War II.

Pauli was outstanding among the brilliant mid-twentieth century school of physicists. He was recognized as one of the leaders when, barely out of his teens and still a student, he published a masterly exposition of the theory of relativity. His exclusion principle, which is often quoted bearing his name, crystallized the existing knowledge of atomic structure at the time it was postulated and it led to the recognition of the two-valued variable required to characterize the state of an electron. Pauli was the first to recognize the existence of the neutrino, an uncharged and massless particle which carries off energy in radioactive ß-disintegration; this came at the beginning of a great decade, prior to World War II, for his centre of research in theoretical physics at Zurich.

Pauli helped to lay the foundations of the quantum theory of fields and he participated actively in the great advances made in this domain around 1945. Earlier, he had further consolidated field theory by giving proof of the relationship between spin and"statistics" of elementary particles. He has written many articles on problems of theoretical physics, mostly quantum mechanics, in scientific journals of many countries; his Theory of Relativity appears in the Enzyklopaedie der Mathematischen Wissenschaften, Volume 5, Part 2 (1920), his Quantum Theory in Handbuch der Physik, Vol. 23 (1926), and his Principles of Wave Mechanics in Handbuch der Physik, Vol. 24 (1933).

Pauli was a Foreign Member of the Royal Society of London and a member of the Swiss Physical Society, the American Physical Society and the American Association for the Advancement of Science. He was awarded the Lorentz Medal in 1930. Wolfgang Pauli married Franciska Bertram on April 4th, 1934. He died in Zurich on December 15th, 1958.

From Nobel Lectures, Physics 1942-1962, Elsevier Publishing Company, Amsterdam, 1964

Further Readings on Sciennce : Maza's Weblog Science Pages....
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