In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy. The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. For either electron or positron emission to be energetically possible, the energy release or Q value must be positive.
A neutrino is a fermion that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles excluding massless particles. The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.
The electron neutrino is an elementary particle which has zero electric charge and a spin of 1⁄2. Together with the electron, it forms the first generation of leptons, hence the name electron neutrino. It was first hypothesized by Wolfgang Pauli in 1930, to account for missing momentum and missing energy in beta decay, and was discovered in 1956 by a team led by Clyde Cowan and Frederick Reines.
In particle physics, the W and Z bosons are vector bosons that are together known as the weak bosons or more generally as the intermediate vector bosons. These elementary particles mediate the weak interaction; the respective symbols are
W+
,
W−
, and
Z0
. The
W±
bosons have either a positive or negative electric charge of 1 elementary charge and are each other's antiparticles. The
Z0
boson is electrically neutral and is its own antiparticle. The three particles each have a spin of 1. The
W±
bosons have a magnetic moment, but the
Z0
has none. All three of these particles are very short-lived, with a half-life of about 3×10−25 s. Their experimental discovery was pivotal in establishing what is now called the Standard Model of particle physics.
Jack Steinberger was a German-born American physicist noted for his work with neutrinos, the subatomic particles considered to be elementary constituents of matter. He was a recipient of the 1988 Nobel Prize in Physics, along with Leon M. Lederman and Melvin Schwartz, for the discovery of the muon neutrino. Through his career as an experimental particle physicist, he held positions at the University of California, Berkeley, Columbia University (1950–68), and the CERN (1968–86). He was also a recipient of the United States National Medal of Science in 1988, and the Matteucci Medal from the Italian Academy of Sciences in 1990.
In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move closer to the optimal ratio of protons and neutrons. As a result of this transformation, the nucleus emits two detectable beta particles, which are electrons or positrons.
The neutrinoless double beta decay (0νββ) is a commonly proposed and experimentally pursued theoretical radioactive decay process that would prove a Majorana nature of the neutrino particle. To this day, it has not been found.
Double electron capture is a decay mode of an atomic nucleus. For a nuclide with a number of nucleons A and atomic number Z, double electron capture is only possible if the mass of the nuclide is lower.
The Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) is an electron antineutrino detector at the Kamioka Observatory, an underground neutrino detection facility in Hida, Gifu, Japan. The device is situated in a drift mine shaft in the old KamiokaNDE cavity in the Japanese Alps. The site is surrounded by 53 Japanese commercial nuclear reactors. Nuclear reactors produce electron antineutrinos () during the decay of radioactive fission products in the nuclear fuel. Like the intensity of light from a light bulb or a distant star, the isotropically-emitted flux decreases at 1/R2 per increasing distance R from the reactor. The device is sensitive up to an estimated 25% of antineutrinos from nuclear reactors that exceed the threshold energy of 1.8 megaelectronvolts (MeV) and thus produces a signal in the detector.
In nuclear physics and chemistry, the Q value for a reaction is the amount of energy absorbed or released during the nuclear reaction. The value relates to the enthalpy of a chemical reaction or the energy of radioactive decay products. It can be determined from the masses of reactants and products. Q values affect reaction rates. In general, the larger the positive Q value for the reaction, the faster the reaction proceeds, and the more likely the reaction is to "favor" the products.
Inverse beta decay, commonly abbreviated to IBD, is a nuclear reaction involving an electron antineutrino scattering off a proton, creating a positron and a neutron. This process is commonly used in the detection of electron antineutrinos in neutrino detectors, such as the first detection of antineutrinos in the Cowan–Reines neutrino experiment, or in neutrino experiments such as KamLAND and Borexino. It is an essential process to experiments involving low-energy neutrinos such as those studying neutrino oscillation, reactor neutrinos, sterile neutrinos, and geoneutrinos. The IBD reaction can only be used to detect antineutrinos due to lepton conservation.
T2K is a particle physics experiment studying the oscillations of the accelerator neutrinos. The experiment is conducted in Japan by the international cooperation of about 500 physicists and engineers with over 60 research institutions from several countries from Europe, Asia and North America and it is a recognized CERN experiment (RE13). T2K collected data within its first phase of operation from 2010 till 2021. The second phase of data taking (T2K-II) is expected to start in 2023 and last until commencement of the successor of T2K – the Hyper-Kamiokande experiment in 2027.
The Enriched Xenon Observatory (EXO) is a particle physics experiment searching for neutrinoless double beta decay of xenon-136 at WIPP near Carlsbad, New Mexico, U.S.
Herwig Franz Schopper is a Czech-born experimental physicist and was the director general of CERN from 1981 to 1988.
Borexino is a particle physics experiment to study low energy (sub-MeV) solar neutrinos. The detector is the world's most radio-pure liquid scintillator calorimeter. It is placed within a stainless steel sphere which holds the photomultiplier tubes (PMTs) used as signal detectors and is shielded by a water tank to protect it against external radiation and tag incoming cosmic muons that manage to penetrate the overburden of the mountain above.
The Neutrino Ettore Majorana Observatory is an international collaboration of scientists searching for neutrinoless double beta decay (0νββ). The collaboration has been active since 1989. Observation of 0νββ would indicate neutrinos are Majorana particles and could be used to measure the neutrino mass. It is located in the Modane Underground Laboratory (LSM) in the Fréjus Road Tunnel. The experiment has had 3 detectors, NEMO-1, NEMO-2, NEMO-3 and is planning to construct a new detector SuperNEMO. The NEMO-1 and NEMO-2 prototype detectors were used until 1997. Latest experiment NEMO-3 was under design and construction from 1994 onwards, took data from January 2003 to January 2011 and the final data analysis was published in 2018. The NEMO-2 and NEMO-3 detectors produced measurements for double neutrino decays and limits for neutrinoless double-beta decay for a number of elements, such as molybdenum-100 and selenium-82. These double beta decay times are important contributions to understanding the nucleus and are needed inputs for neutrinoless decay studies, which constrain neutrino mass.
The Cryogenic Underground Observatory for Rare Events (CUORE[ˈkwɔːre], also Italian for 'heart') is a particle physics facility located underground at the Laboratori Nazionali del Gran Sasso in Assergi, Italy. CUORE was designed primarily as a search for neutrinoless double beta decay in 130Te, a process that has never been observed. It uses tellurium dioxide (TeO2) crystals as both the source of the decay and as bolometers to detect the resulting electrons. CUORE searches for the characteristic signal of neutrinoless double beta decay, a small peak in the observed energy spectrum around the known decay energy; for 130Te, this is Q = 2527.518 ± 0.013 keV. CUORE can also search for signals from dark matter candidates, such as axions and WIMPs.
The Germanium Detector Array experiment was searching for neutrinoless double beta decay (0νββ) in Ge-76 at the underground Laboratori Nazionali del Gran Sasso (LNGS). Neutrinoless beta decay is expected to be a very rare process if it occurs. The collaboration predicted less than one event each year per kilogram of material, appearing as a narrow spike around the 0νββ Q-value in the observed energy spectrum. This meant background shielding was required to detect any rare decays. The LNGS facility has 1400 meters of rock overburden, equivalent to 3000 meters of water shielding, reducing cosmic radiation background. The GERDA experiment was operated from 2011 onwards at LNGS.
When embedded in an atomic nucleus, neutrons are (usually) stable particles. Outside the nucleus, free neutrons are unstable and have a mean lifetime of 879.6±0.8 s. Therefore, the half-life for this process is 611±1 s. .
FASER is planned to be one of the eight particle physics experiments in 2022 at the Large Hadron Collider at CERN. It is designed to both search for new light and weakly coupled elementary particles, and to study the interactions of high-energy neutrinos.
