The Lepton - By: Rabbit
“Why The Name Lepton”
Leptons: In 1897 the first lepton was discovered by J.J. Thomson and his team of British physicists. Physicists got the name “lepton” from the Greek language, meaning “slender”. It wasn’t until 1975 that Martin Lewis Perl and his colleagues at the SLAC LBL group discovered the tau through a series of experiments. Up until 1975, it was originally thought that leptons were the lightest subatomic particles, than came the tau in 1975. Although the name “lepton” is no longer appropriate, we still use it today. Now we use it to describe all spin-1/2 particles that are not affected by the strong force.
“The Muons & Carl David Anderson”
In 1936 an American Physicist named Carl David Anderson & Seth Neddermeyer discovered the muon (it’s former name, “mu-meson”), nearly 40 years after the discovery of the electron. In 1936 Carl David Anderson was awarded the Nobel Prize in Physics for his discovery of the positron in 1932, and also for the discovery of the muon, in 1936. He unexpectedly discovered the creation of a particle that had the same mass as the electron, but it had an opposite electrical charge, while experimenting with cosmic rays. This alone validated Paul Dirac’s theoretical prediction of the existence of the positron. Shortly after, Carl David Anderson would produce conclusive evidence by blasting gamma rays into other materials, resulting in the creation of the positron-electron pairs.
After they (Carl Anderson and Seth Neddermeyer) discovered the muon, they quickly noticed this subatomic particle was 207 times more massive than the electron, but it still had the same negative electric charge and the same spin ½ as the electron. Due to it’s shear mass (207 times that of the electron), it was categorized as a meson, rather than a lepton; but this was corrected when physicists noticed it shared more commonalities with electrons, rather than mesons. Since muons do not undergo the strong interaction, muons were reclassified into a new group of particles such as the electrons, muons, and the neutrino; in which they are now known as leptons. At first glance back in 1932, they thought they seen the pion, but they were mistaken. However, the muon was the first of a long list of other subatomic particles, so that alone was a great achievement.
“The Tau & Martin Lewis Perl”
The tau lepton is a superheavy cousin of the electron, and it’s also the carrier of electrical current in household appliances. Both particles are identical in all respects, except the fact that the tau is approximately 3,500 times heavier than the electron. However, the tau only survives for less than a trillionth of a second, while the electron remains stable. In the mid 1970’s Martin Lewis Perl and his team of colleagues at the SLCA-LBL group, conducted a series of experiments that detected the presents of the tau, and before that it was believed that only two quark-lepton families existed. Their equipment consisted of SLAC, a new type of colliding rings called SPEAR, and also the LBL magnetic detector.
With this equipment, they could also detect and distinguish between leptons, hadrons, and also photons. However, they did not detect the tau directly, but rather discovered anomalous events. After more than a year’s worth of careful analysis, Martin Lewis Perl was able to convince his research team that they were in fact observing a new and different type of elementary particle, in which he named it the “tau”. This was significant because the tau turned out to be a newly discovered member of a third quark-lepton family, the top quark. It wasn’t until 1995 that Fermi scientists discovered the top quark; the same year Martin Lewis Perl was awarded the Nobel Prize in Physics for his discovery of the tau lepton.
“How Important is The Tau”
The discovery of the tau was very important because it’s the only lepton that can decay into hadrons. Like the current decay models of the tau, the hadronic decay is through the weak interaction. Being the tauonic lepton number is conserved in weak decays, a tau neutrino is created when a tau decays to a muon or an electron.
The branching ratio of the common purely leptonic tau decays at:
-17.82% for decay into a tau neutrino, electron and electron antineutrino.
-17.39% for decay into a tau neutrino, muon and nuon antineutrino.
The similarity of values of the two branching ratios is a consequence of lepton universality. The tau lepton is also predicted to be able to form exotic atoms like other charged subatomic particles. One example is the tauonium, by the analogy to muonium, consists in antiauon and an electron. Another possibility is an onium atom called true tauonium; however, it’s very difficult to detect.
“Leptons & The 6 Different Flavors”
A lepton is a member of subatomic particles that only respond to electromagnetic force, weak force, and also the gravitational force. However, they are not affected by the strong force. The leptons appear to be point-like particles without an internal structure. Although leptons are considered to be elementary particles, they do not appear to be made up of smaller units of matter. Leptons can either have one unit of electric charge or be neutral.
Each charged lepton has an associated neutral partner, or neutrino that has no electric charge, along with no significant mass. There are six different flavors of leptons; the most familiar lepton is known as the electron. As for the five other leptons, they are known as the muon and the tau particle; and there are also three different types of neutrino associated with each of them, the electron neutrino, the muon neutrino, and of course the tau neutrino. In the six different flavors of leptons, three have an electrical charge (the electrons, muons, and taus); while the other three do not have an electrical charge. The muon and tau are charged like electrons, but they carry larger amounts of mass.
As for the other three types of neutrinos, they have no electrical charge and have very little mass; not to mention, they are very difficult to find. Electrons are the lightest leptons, and only carry a mass of 1/1,840, that of a proton. The muons are much heavier, and have more than 200 times as much mass as the electrons. As for the taus, they are approximately 3,700 times more massive than the electrons. Each charged lepton including the neutrinos have antiparticles, commonly known as, antileptons.
Although the mass of an antilepton, are in fact identical to that of leptons, all the other properties are reversed and each lepton has a corresponding antimatter antilepton. When talking about antimatter, please note that all elementary particles have corresponding antiparticles known as, antimatter. Where antimatter particles have opposite charges than their usual components. For example, positrons have a +1 charge and the electrons have a -1 electric charge. The protons have antiprotons, the neutrons have antineutrons, and the electrons have “anti-electrons”.
The “anti-electrons” are common enough to have their own special name, known as positrons. Mathematically speaking, the total lepton number L is constant. The number of leptons minus the number of antileptons always remains constant. Therefore a conservation law for leptons of each different type seems to hold; the number of electrons and electron-neutrinos, for example, is conserved separately from the number of muons and muon-neutrions. However, the current limit of violation concerning the conservation law is one part per million.
Leptons have other characteristic features in addition to their charge and mass properties, and it’s their intrinsic angular momentum, or spin. Leptons are actually classified within larger groups of subatomic particles; the fermions for example, are characterized by half-integer values of their spin. However, the total number of leptons; appear to be the same in every particle reaction.
“The Effects & Influence of The Lepton in Nuclear Physics”
What’s most intriguing about the leptons is they’re involved in several different processes, like beta decay in nuclear physics. In nuclear physics, beta decay is a type of radioactive decay, where the beta particle -- the electron or positron -- is emitted from an atomic nucleus. The process of beta decay allows an atom to obtain the optimal ratio of both protons and neutrons. There are actually two different types of beta decay, a decay that is mediated by what’s known as weak force: both beta minus and beta plus. When referring to beta minus, it’s a form of beta decay that produces an electron emission; while beta plus is the emission of the positron.
Sincerely,
Rabbit
