Antimatter

"Ionization and curvature measurements clearly showed this particle to have a mass much smaller than... a proton... a mass entirely consistent with an electron. ...[D]espite the strong admonitions of the Chief that upward-moving cosmic ray particles were very rare, this... was an example..."

"In the early 1950s... attention was focused on two new unstable, electrically neutral particles... tau and theta. ...[T]he tau and theta were 'strange'—they carried Gell-Mann's additional charge. They decayed in different ways, and had different parities... [T]he tau and theta had the same mass. ...Chen Ning ('Frank') Yang and , thought it was bizarre for two apparently different particles to have the same mass, and suspected... two faces of the same particle, despite... different parities. ...[They] had to throw overboard ...apparently solid ...assumptions about quantum behaviour: ...[1] it would not be basically altered by left-right mirror reflection... [2] behaviour would not be altered by a mirror that reflected particles as antiparticles and vice-versa... [They] re-examined the evidence for both mirror symmetries, which everyone had assumed ...watertight ...showing that for particle decays this had never been proved conclusively."

"Lee and Yang... suggested that the particle-antiparticle mirror could be flawed. ...[T]wo experiments—by , Leon Lederman and Marcel Weinrich... and by Jerome Friedman and Val Telegdi...—looked at multiple particle transformations in which a pion decays into a , which in turn decays into an electron. ...[These] found that ...[f]or a positively charged pion, the muon's spin points backwards, against its direction of motion. [When t]he antiparticle... a negatively charged pion... decays, the muon emerges with its spin pointing in the direction of its motion. Looking in a mirror that changes particles into antiparticles, the antismoke comes down the chimney."

"For the subnuclear world, the ordinary mirror has to be replaced by an extended mirror that carries out three reflections simultaneously—switching particle to antiparticle and vice-versa, changing left to right and vice-versa, and reversing the . ...[R]espectively C (for charge), P (for parity) and T (for time). The CPT mirror changes Alice into a mirror-image Anti-Alice going backward in time."

"Sakharov looked wryly at the composition of an average cubic metre of Universe. ...a billion quanta of radiation, one proton and no antiprotons. Tracking... to just after the Big Bang... [we] should have had... a billion antiprotons, and a billion and one protons. ...Why the odd proton? ...[A]ntimatter had slipped off the map of the Universe ...Sakharov put forward a three-point explanation."

"[1] Big Bang... particle-antiparticle creation briefly got out of hand, more pairs being created than were reabsorbed back into radiation. ...[T]he present Universe is much larger than a sphere of light rays which started out from the Big Bang... Sometime in the past, the Universe... expanded faster than light... Most of the Universe we have not yet seen, despite traveling at [c]... not yet having had time to reach us. ...In the first fraction of a second... the Universe must have 'inflated' faster than the speed of light and particle-antiparticle pairs were produced faster than they could be reabsorbed."

"[2] ...some mechanism had to tilt the balance in favor of matter. With Cronin and Fitch's... implications for the , Sakharov thought he had... the answer. But was the tiny subnuclear effect... enough..? Probably not... But... [h]eavier quarks, more exotic than strangeness, could show larger effects. Making B particles containing the 'beauty' (...'bottom') quark and manufacturing enough of them to probe the has become a major focus of... research."

"[3] The proton... has to be slightly unstable... Sitting still, the -filled proton would have to disintegrate into electrons and other light particles. ...But ...the level of ...instability needed was so small as to be almost undetectable. ...[E]xperiments are trying to capture this effect..."

"The Big Bang should have been matter-antimatter symmetric. But the visible Universe... shows little sign of this primordial antimatter."

"Paul Dirac, the spiritual father of antimatter, probably did not yet know very much about the Big Bang picture when he gave his Nobel lecture... and suggested that the Universe could contain both matter and antimatter without us knowing... If Dirac were right, the whole Universe should be a uniform mix... overall the two halves of the Universe should balance. Where is this antimatter?"

"Light antiparticles... as s, are common in cosmic rays. However, such... are usually from particle-antiparticle pairs produced... as primary cosmic ray particles collide with atmospheric gas or interstellar dust. ...'Fountains' of positrons... seen... peering into the center of our Galaxy... can be explained by violent cosmic processes spitting out... radiation..."

"Any antimatter stars... [w]hen such... died in explosions, their... antinuclei would have been flung out... But the cosmic rays arriving... have revealed no signs of antimatter heavier than s."

"[P]erhaps matter and antimatter are separated into distinct domains. Maybe... there is... an antidomain. ...Wherever and whenever the boundaries... briefly touched, pieces... would have mutually annihilated to give powerful bursts of... s. As the Universe... cooled these... would have... produced a dim but uniform... signal all over the sky."

"If the initial Universe had contained widely space clusters of matter and antimatter, these would have left their... imprint on the Cosmic Background Radiation. The tiny ripples seen by COBE and other detectors are not compatible with separate domains of matter and antimatter... The Universe we can see looks to have been eternally free of nuclear antimatter."

"It became apparent that in a hot early epoch of the big bang there would exist a fully mixed dense state of matter and antimatter in the form of ic and ic pairs in thermal equilibrium with radiation. As the universe expanded and cooled this situation would result in an almost complete annihilation of both matter and antimatter."

"Antinucleons "freeze out" of thermal equilibrium when the annihilation rate becomes smaller than the expansion rate of the universe. This would have occurred when the temperature of the universe dropped below ∼20 MeV. The predicted freeze out density of both matter and antimatter is only about 4×10-11 of the closure density of the universe..."

"Sakharov showed that three conditions are necessary in order to create the appropriately significant concentration of s in the early universe. They are: • Violation of Baryon Number, B • Violation of C and CP • Conditions in which Thermodynamic Equilibrium does not Hold"

"If CPV is predetermined, then only matter will remain in the present universe. We can refer to this case as a "global" matter-antimatter asymmetry. If... CPV is the result of spontaneous symmetry breaking, domains of positive and negative CPV may result. In the case of spontaneous CPV, the Lagrangian is explicitly CP invariant, but at the symmetry breaking phase transition a CP invariant high temperature vacuum state undergoes a transition to a state where the vacuum solutions break CP either way. This mechanism may be compared to the spontaneous formation of ferromagnetic domains when a piece of unmagnetized iron cools below the critical temperature in the absence of a magnetic field. Although there is no preferred direction of magnetization, individual domains acquire random local directions of magnetization."

"If the CP domain structure is stretched to astronomical size by a subsequent period of moderate inflation, then, following , s may survive as galaxies in some regions of the universe and antibaryons may survive as antigalaxies in other regions. In this case, we have a "local" matter-antimatter asymmetry instead of a global one. ...[i.e.,] a "locally asymmetric domain cosmology (LADC)." Following baryogenesis, the walls of the initially CP symmetric vacuum between the positive and negative CP domains must vanish because they are quite massive and could eventually dominate the evolution of the universe, in conflict with observations."

"Antimatter galaxies will look exactly the same as matter galaxies. This is because the photon is its own antiparticle. However, we can look for other clues. Searches have been made for antimatter in the cosmic radiation and for the indirect traces of cosmic matter-antimatter annihilation in the extragalactic γ-ray background radiation."

"properties can play a crucial role in determining the matter-antimatter asymmetry of the universe if thermal is the correct solution to the problem. Owing to this, the study of Neutrino models goes beyond the mere purpose of generating tiny neutrino masses, and it is natural to incorporate the puzzle of cosmic ."

"One of the most fundamental concepts in the study of physics is the idea of symmetry. Yet, Nature as we know it does not always seem to be perfectly symmetrical. ...[T]he principal theme for this current work is motivated by none other than the apparent between matter and antimatter in the universe. Therefore, along with the appeal of symmetry, a major topic of interest is the mechanism of symmetry breaking or asymmetry creation."

"[I]t is quite fascinating that two seemingly unrelated problems—the tiny masses of light neutrino and the matter-antimatter asymmetry—may be explained by the mere introduction of heavy RH [right-hand] neutrinos to the SM. ...[T]he former may be explained by the Type I seesaw mechanism while thermal leptogenesis provides an attractive solution to the later. This... means that an intricate link between neutrino properties and the baryon asymmetry can be established. Consequently, it has been the purpose of this work to explore the implications of several different neutrino models in the leptogenesis context."

"In the representative models... it has been found that successful leptogenesis is only possible in a very fine-tuned region of the parameter space. Specifically, one must select the f = u case, as well as certain combinations of Dirac and Majorana phases in UPMNS such that a lepton asymmetry can be generated via either resonant of flavoured N2-leptogenesis. Further, it has been shown that although the f = e case can yield a TeV scale RH neutrino, the probability of detecting it at the LHC or a next-generation collider such as the ILC is far too small."

"[W]e investigated the effects of introducing an effective transition electromagnetic dipole moment [EMDM] operator between the LH light and the RH heavy neutrinos. ...As a result, a new scenario for leptogenesis whereby the lepton asymmetry is solely generated by the EMDM-type (instead of the usual Yukawa-mediated) interactions is possible. By exploring the key ingredients leading to , we have shown by explicit computations of the relevant diagrams in a toy model that, in principle, electromagnetic leptogenesis is a viable alternative for creating a lepton asymmetry. ...[T]here is no doubt that transition EMDM interactions between light and heavy neutrinos can have far-reaching consequences in the early universe."

"Sakharov published other papers in cosmology. ...[T]he most far-reaching, innovative, and original... concerned "". "s"... denote collectively not only protons and neutrons but also... unstable particles... created when protons and neutrons collide at extraordinarily high speeds. "Antibaryons"... carry the opposite electrical charge. When baryons and antibaryons collide, they annihilate each other, producing... exotic, unstable particles, such as pi-mesons, which are lighter than baryons, as well as radiation... "quanta"... or photons, which have no mass at all. The "background radiation" cosmologists discovered in the mid-1960s is... a remnant of the... annihilation of baryons and antibaryons... when the universe was created or shortly afterward. Baryons and antibaryons, in other words, are one form of matter and antimatter, respectively; electrons... and their opposite, positrons, are another."

"Sakharov tried to explain why exists... how there came to be a surplus of baryons... The consensus... was that there had to be baryon symmetry when the universe began. But there was no consensus on how symmetry broke down. ...According to Sakharov, for baryon asymmetry... the universe at the quantum level... had to have, in Christopher Korda's words, "an intrinsic ." ...[P]hysicists ...refer to the sequence... Sakharov described as "the Sakharov conditions.""

"Sakharov's conclusion was that ""—the difference between baryons and antibaryons in the universe—was not constant, as most... believed. ...[B]aryons, and in particular protons, can decay, and it was Sakharov's concept of proton decay and how it comes about that proved to be perhaps the most remarkable of all his contributions to cosmology. ...D. S. Chernavski, went as far as to say that, by showing theoretically that the proton can disnintegrate, he revealed "the basis of the universe." Ironically, Sakharov's ideas on the subject did not attract much attention for about a decade. But the development of... gauge theories in the late 1970s sparked new interest... even though proton decay has yet to be confirmed experimentally."

"A nucleus contains two protons and two neutrons. Under suitable circumstances a proton can change into a neutron and emit energy some of which materializes as a positron, similar to what happens in the positron emitters of... medicine."

"The finds itself in the heart of the sun, where there are lots of electrons and is instantly destroyed, turned into s. These try to rush away... but are interrupted by the crowd of electrically charged particles, electrons and protons... [R]epeatedly absorbed by electrons and then emitted with less energy... it will take a hundred thousand years before gamma rays... reach the surface... In doing so the rays lose lots of energy... changing from s to ultra-violet and at last into the rainbow of colours that are visible... So daylight is the result of antimatter being produced in the heart of the sun and, in part, of its annihilation."

"The laws of electricity and magnetism that underlie the existence of bulk matter don't care which bits... carry negative charge, and which... are positive. If we swapped all positives to negative, and all negatives to positive... resulting forces would be the same and the structures they built would... be unchanged. ...[T]o all outward appearances, nothing would appear different. Such a swapping of charges would turn what we know as matter into... antimatter. An anti-atom of would consist of a negative encircled by a positively charged . Paul Dirac... first predicted that such a mirror image of matter should exist."

"[H]ow can an electron with negative electrical charge emerge from the energy in a puff of light, which has no... charge? This is where nature's two forms of matter enter the story. The negatively charged electron has a positively charged form... the . The energy of a photon, a particle of light, becomes trapped in these two complementary pieces of substance. This... can also happen in reverse: an electron and a positron can annihilate one another, their individual energies being taken by the photons that rush from the scene of destruction at the speed of light. The emergence of substance from pure energy... is almost biblical in scope. With antimatter... we make contact with the gods of creation."

"In 1923 ... was investigating s... using a . ...The ...rays would knock electrons out of atoms... whose trails he could see... [I]n addition to knocking electrons out of the gas, they were ejecting them out of the walls of the chamber ...which interfered with the measurements... He... came up with the... idea of sweeping away the unwanted electrons by putting the chamber between the poles of a large magnet. ...[T]he clearer view revealed ...the magnetic forces seemed to make some of the 'electrons' curve 'the wrong way'. Today we know he was seeing s, but... [the] anomalous trails were a distraction from what he was trying to do. ...News about these images spread ...and five years later Skobeltsyn decided to show them at an international conference in Cambridge. ...[N]o one could offer an explanation. It was ironic that [this was]... the same year and... place that Dirac came up with his theoretical prediction of positrons... [A]s no one at the time had any reason to expect... positrons existed, he missed the big prize."

"Blackett had been working with a in Rutherford's group... a chamber that was ready for action every ten seconds or so, and took photos on ordinary film. ...[H]e accumulated ...pictures of trails made by s—a product of radioactive nuclear decays— ...bombarding nitrogen gas in the chamber. ...[I]n 1931 arrived ...His specialty was detecting nuclear radiation using s. ...Their big idea ...put one Geiger counter above a cloud chamber, and another... below. ...By connecting the Geiger counters to a ...a flash of light [and the cinematograph] captured the tracks of the cosmic rays on film. ...They noticed that ...a few tracks that appeared at first sight to be electrons, were ...curved the wrong way in the magnetic field. Blackett talked to Dirac about them... neither aware of the precious truth. ...It was only when they heard of Anderson's discovery that Blackett and Occhialini ...realized what they had."

"[L]uckily... they had more... Many of the pictures showed up to twenty... tracks ...from a copper plate just above the chamber ...roughly half of the particles were negatively charged and the rest positively charged. Blackett and Occhialini realized... the appearance of equal numbers of positrons and electrons must be... the result of s hitting the metal."

"Albert Einstein's equation E = mc^2, implies that energy (E) can be converted into mass (m)—radiation into matter—and Blackett and Ochialini had for the first time demonstrated the creation of matter, and antimatter, from radiation; they had proved that Anderson's new particle was not some weird extraterrestrial interloper."

"An ambitious plan took hold at Berkeley... to build an accelerator that would speed s such that when smashed into a target, there would be enough energy to produce an . ...When energy turns into massive particles they emerge in pairs, a particle... matched with its antiparticle, so the BeVatron was built with enough power to produce an antiproton in conjunction with a proton... Several ideas on how to isolate the antiproton 'needle' from the particle 'haystack' were presented... A small team... of , Emilio Segre, , and won the competition ...their idea worked ...and in 1955 they announced their discovery. One of the other teams led by that had entered the competition also gained success... with the discovery of the in 1957. So thirty years after Dirac['s]... seminal prediction, the basic pieces of the antiworld were in place: , antiproton, and ."

"Since antimatter will destroy any material object, it must be kept in a cage without material walls. The solution... a vacuum that is better than in outer space with magnetic and electric fields that confine the antiparticles, positrons, or antiprotons, as circulating beams. That is in effect what is done at particle physics laboratories such as CERN..."

"Magnetic fields that had been able to focus positrons into stable orbits were unable to control the wild antiprotons... Budker's idea was to pass the antiprotons through clouds of cold electrons. Although electrons are matter and antiprotons are antimatter, they are in no danger to one another: electrons are destroyed by their antiparticle, the positron, while the antiproton is at risk only from protons or neutrons. ...By 1974 Budker... succeeded in making and cooling antiprotons, but not in sufficient numbers to make an intense beam."

"It is just like matter except with a reversal of charges. ...We make it and study it in our laboratories, but find little of it in nature. The laws of physics for antimatter are almost an exact mirror of those for matter."

"For each type of matter particle there is a matching type of antimatter particle. ...[W]e can convert energy from radiation into a matched pair..."

"[T]heories suggest that, at very early times... all possible types of particles and antiparticles, existed equally in a hot, dense, and very uniform . ...[A]s the Universe expanded and cooled... annihilation could still occur whenever a particle met an antiparticle, but the reverse... creation of a particle and an antiparticle, became... rare."

"[H]igh energy laboratories can produce particles with energies similar to those that prevailed in the [very early] Universe... allows us to model the primordial production of small nuclei from collisions starting with s and s, long before stars began to form. Because we know... what energies are required for collisions to take apart... light elements [ less than 11] into... protons and neutrons, we can identify... the time at which the Universe became cold enough that this destruction practically ceased, and... production of elements started in earnest."

"The fate of antimatter to disappear was sealed by the time the Universe was no older than a millionth of a second."

"[T]he mystery of the missing antimatter... What laws of nature, not yet manifest in experiments and not part of our current Standard Model, were active in the early Universe, allowing the observed amount of matter to persist while all antimatter disappeared from the Universe?"