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E Glossary and Acronyms Active galactic nuclei (AGN): Bright centers of some galaxies; they are thought to have huge black holes at the center. Very distant ones are called quasars. Background: False events or unwanted particles traversing the device, preventing useful data taking. Baseline: Typically the distance between the neutrino source and detector. Neutrino oscillation experiments are usually categorized as short or long baseline. Beta decay: In this context, the radioactive decay of a nucleus whereby a neutron is converted into an electron and a proton while emitting a neutrino. Double beta decay is a much rarer process with two electrons emitted either with or without two neutrinos. Big bang: The model of the initial phase of the universe in which all matter and energy were concentrated with high density and temperature 15 billion years ago. The present universe expanded from that epoch and is still expanding. Bottom: The second-heaviest quark. It has negative electric charge one-third that of the electron. Charged-current: Interaction between a neutrino and another particle involving the exchange of charged electroweak force carrier, the W particle. Charm: The third-heaviest quark. It carries positive electric charge two-thirds that of electron. CNO cycle: The carbon-nitrogen-oxygen cycle of stellar fusion that uses the heavier
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elements carbon, nitrogen, and oxygen to effectively convert hydrogen into helium. Cosmic microwave background (CMB) radiation: The residual light from the big bang. Cosmic rays: Protons, nuclei of heavy atoms, and possibly other particles that have been accelerated to high energies by astrophysical process and then impinge upon Earth. CP violation: The mechanism by which matter and antimatter evolve in time differently. The C and P, standing for charge conjugation and parity, refer to so-called symmetry operations in quantum physics. Dark energy: An as-yet-unknown form of energy that pervades the universe. Its presence is inferred from the discovery recently that the expansion of the universe is accelerating. Dark matter: Matter that does not emit or absorb enough light or other radiation to be observed directly. Dirac-like: A theoretical framework for the introduction of particles with mass into a modern quantum field theory (named for Paul A.M.Dirac). A key feature of this framework is that the particle is distinct from its antiparticle. Down: A low-mass quark of negative charge one-third that of the electron. The down quark is one of the two quarks that occur in everyday matter (neutrons, protons). Elastic scattering (interaction): In this context, the scattering of neutrinos by electrons via the electroweak interaction. The probability with which an electron neutrino scatters differs from that for the muon or tau neutrino. Electron-volt (eV): A measure of energy equal to that gained by an electron passing through a potential difference of 1 volt. Einstein’s relation between mass and energy (E=mc2) is often used to define a unit of particle mass when divided by the speed of light (c) squared. The electron volt, with its internationally recognized multipliers for milli, kilo, and mega (meV, keV, MeV), respectively, is a useful unit for discussing the variety of particle masses. Equivalence principle: A fundamental principle of Einstein’s theory of general relativity of which one consequence is that all objects (and light) behave in a gravitational field in the same way independent of the velocity, internal structure, or other properties. Gamma-ray burst (GRB): High-intensity burst of gamma rays from cosmic sources first observed by detectors on satellites. Most of the gamma-ray bursts
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come from objects at cosmological distances. Gamma-ray bursts are also visible in other parts of the electromagnetic spectrum. Gravitational lensing: A consequence of Einstein’s theory of general relativity in which the path of light can be bent by the presence of matter, giving rise to effects similar to those of light traveling through an optical lens. Gravitational wave: A ripple in the geometry of space-time propagating as a wave according to the theory of general relativity. Hadron: A particle such as a proton, neutron, or pi meson (pion) that can interact via the strong force, as well as the electroweak force. Jet (astrophysical): A stream of fast-moving material ejected outward from an object such as a young star or a massive black hole in the center of a galaxy. Large Magellanic Cloud: A dwarf galaxy, proximate to and orbiting our own Milky Way Galaxy. Left-handed, right-handed: A particle condition describing the relative orientation of its direction of motion and the sense in which its angular momentum is rotating (“spinning”). A right-handed particle has its rotation sense aligned with respect to its direction of motion as in the advance of a right-handed screw. Left-handed implies the opposite orientation. Left- and right-handed neutrinos have different interactions. Lepton: Any one of a group of six fundamental particles having electroweak interactions assigned in three families (the charged electron, muon, and tau, each with its associated neutrino). Majorana-like: Refers to that property of neutrino mass description in which the neutrino and its antiparticle are identical (named for E.Majorana). Mixing: In neutrino oscillations, refers to the possibility that a neutrino created as purely one type can at a later time or position be composed of a mixture with the other two types. Mixing angle: A parameter that gives a measure of the amount of mixing between any pair of neutrino types. Muon: The second-lightest lepton particle in the Standard Model. The muon is produced copiously in cosmic-ray interactions in the atmosphere and is deeply penetrating in matter. mwe: A designation of radiation-shielding depth in meters of water equivalent. Typically, 1 meter of rock is approximately 3 mwe.
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Neutral current: The interaction between a neutrino and another particle involving the exchange of a neutral electroweak force carrier, the Z particle. Neutralino: The term ascribed to the lightest supersymmetric particle, which is neutral and is expected to have the longest lifetime of all supersymmetric particles as there are no other supersymmetric partner particles into which it can decay. Neutrino oscillation: A process whereby neutrinos of one type change into those of another type (and even back again) if one or more of the types has mass. (See also mixing.) Neutron star: A star with such high density and pressure that its constituents have been completely crushed by gravity until most of the electrons have been squeezed into protons forming neutron-rich material. Nucleosynthesis: The process by which protons and neutrons fuse together to form the nuclei of the chemical elements. Big-bang nucleosynthesis refers to the time period 3 minutes after the big bang when the lightest elements (hydrogen, deuterium, helium, etc.) were formed. Pi mesons, pion: One of the many strongly interacting but unstable particles. Those that carry charge can decay into muons and neutrinos (or their antiparticles). pp reactions: In this context, refers to the principal, initiating fusion reaction in the Sun in which electron-type neutrinos are created. Quantum gravity: A modern theory for gravity attempting an appropriate description of physical processes that occur at very small length scales or over very short times. The Einstein theory of general relativity, as a classical theory, is inconsistent with the principles of quantum theory. Quark: The elementary constituents of matter, such as the proton and neutron, but also of the unstable particles created in very energetic interactions. There are six types of quarks in the Standard Model (up, down, charm, strange, top, and bottom). Relativity: A theoretical framework proposed by Einstein in the early part of the 20th century. There are two theories of relativity, the general (gravity) and special theories. Relic: In this context, particles created in and remaining currently from the big bang or other astrophysical events. Shock, shock wave: A very narrow region of high pressure and temperature formed in a fluid when the fluid flows supersonically over a stationary object or when a projectile flies supersonically through a fluid.
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Spin: An intrinsic property of particles. Defines a measure of the angular momentum they carry. Standard Model: The theory summarizing the current picture of elementary particle physics. It includes three families of quarks and leptons, the electroweak theory of the weak and electromagnetic forces, and the quantum chromodynamic theory of the strong force. Standard solar model: The modern theory of how the Sun produces energy from fusion, including a detailed description of the nuclear processes, abundances, and reaction rates. Strange: The fourth-heaviest quark. It carries a negative charge one-third that of the electron. Supernova: A powerful explosion of a star. Depending on the type of explosion, supernovae are categorized as Type Ia or Type II (more cataclysmic). θ13, θ12: The mixing angles for neutrino oscillations that measure the content of the electron neutrino into two of the mass states (see Figure 4.1). Tau: The heaviest and last-discovered charged lepton particle of the Standard Model. Top: The heaviest of the six quarks. It carries a positive charge two-thirds that of the electron. Unified theory, grand:A class of modern theories attempting to go beyond the current Standard Model of particle physics and account for the unification of all the forces of nature. Up:One of the lightest of the six quarks. It carries a positive charge two-thirds that of the electron. Water Cerenkov detection:A technique in which large volumes of water are instrumented with photon sensors (photomultiplier tubes). The photons are created when a charged particle’s speed exceeds the velocity of light in water. WIMP:Weakly interacting massive particle: a leading particle candidate for dark matter.
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