The Neutrino

Ettore Majorana Ettore Majorana (,, uploaded 19 April 2013, retrieved 14 December 2019 ; born on 5 August 1906 – possibly dying after 1959) was an Italian theoretical physicist who worked on neutrino masses. On 25 March 1938, he disappeared under mysteri ...

Observatory (NEMO experiment) is an international collaboration of scientists searching for

neutrinoless double beta decay 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. The discovery o ...

(0νββ). The collaboration has been active since 1989. Observation of 0νββ would indicate

neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...

s are

Majorana particles A Majorana fermion (, uploaded 19 April 2013, retrieved 5 October 2014; and also based on Ettore Majorana, the pronunciation of physicist's name.), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hy ...

and could be used to measure the neutrino mass. It is located in the

Modane Underground Laboratory The Modane Underground Laboratory (LSM) (french: Laboratoire Souterrain de Modane; also known as the Fréjus Underground Laboratory) is a subterranean particle physics laboratory located within the Fréjus Road Tunnel near Modane, France. It is jo ...

(LSM) in the

Fréjus Road Tunnel The Fréjus Road Tunnel is a tunnel that connects France and Italy. It runs under Col du Fréjus in the Cottian Alps between Modane in France and Bardonecchia in Italy. It is one of the major trans-Alpine transport routes between France and Ital ...

. The experiment has (as of 2018) had 3 detectors, NEMO-1, NEMO-2, NEMO-3 (and a demonstrator module of SuperNEMO-detector) and is planning (as of 2018) 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.http://www.rcnp.osaka-u.ac.jp/dbd18/Data/Prog/S0303_Patrick.pdf 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 Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

and are needed inputs for neutrinoless decay studies, which constrain neutrino mass. The NEMO collaboration remains active and is constructing an improved SuperNEMO detector. Planning of SuperNEMO and commissioning of SuperNEMO demonstrator module is on-going as of 2019.

Experiment

Other 0νββ experiments use the same material for the source of double beta decays and the detector. This allows a large mass of source material to be used and thereby maximizes the sensitivity of the experiment, but limits its flexibility. NEMO takes a different approach, using thin foils of source material surrounded by a separate tracking

calorimeter A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimete ...

. This allows the use of any source material which can be formed into a thin foil. Also, because its tracking is more accurate, it can reliably detect if two electrons come from the same place, thereby reducing false detections of double beta decays. The experiment has a cylindrical shape with 20 sectors that contain different

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...

s in the form of thin foils with a total surface of about 20 m². The main isotopes used for the neutrinoless double beta decay search are about 7 kg of enriched molybdenum-100 and about 1 kg of

selenium-82 Selenium (34Se) has six natural isotopes that occur in significant quantities, along with the trace isotope 79Se, which occurs in minute quantities in uranium ores. Five of these isotopes are stable: 74Se, 76Se, 77Se, 78Se, and 80Se. The last thr ...

. The experiment also contains smaller amounts of

cadmium-116 Naturally occurring cadmium (48Cd) is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decays have not been observed, due to extremely long half-lives. The tw ...

neodymium-150 Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes of ...

zirconium-96 Naturally occurring zirconium (40Zr) is composed of four stable isotopes (of which one may in the future be found radioactive), and one very long-lived radioisotope (96Zr), a primordial nuclide that decays via double beta decay with an observed h ...

and

calcium-48 Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so ...

foils.

Tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

and

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

foils are used for background measurements. A tracking detector on each side of the foil detects

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s and

positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...

s from the double beta decay. They are identified by their curvature in a magnetic field and particle energy is measured in a calorimeter. In 0νββ, the sum of the electron and positron energies will be the( ''Q'' value) released in double beta decay. For standard double beta decay the neutrinos, which cannot be observed directly, reduce the detected energy.

Results

Neutrinoless double beta decay (0νββ) has not been observed in 5 years of data taking and limits have been set for several isotopes. NEMO-2 reported 0νββ limits for

Majoron In particle physics, majorons (named after Ettore Majorana) are a hypothetical type of Goldstone boson that are conjectured to mediate the neutrino mass violation of lepton number or ''B'' − ''L'' in certain high energy collisions such as : ...

models of ¹⁰⁰Mo, ¹¹⁶Cd, ⁸²Se and ⁹⁶Zr. NEMO-3 reported precision 2νββ half-lives for its 7 isotopes and 0νββ limits for ⁹⁶Zr, ⁴⁸Ca, ¹⁵⁰Nd at Neutrino08. NEMO-3 reported 2νββ and more 0νββ limits at SUSY08. In 2014, NEMO-3 reported a search for 0νββ of molybdenum-100 yielded T_1/2 > . This can be translated into an upper limit on the effective neutrino mass: m_v < , depending on the nuclear model. NEMO 2νββ Half-life Measurements NEMO Highest 0νββ Decay Lower Limits The ⁹⁶Zr decay is particularly relevant because of its high Q and use in searches for time-dependence of the physical constants. Geochemical measurements of ZrSiO₄ allow comparison of its historic and present rates, by extracting the resultant ⁹⁶Mo. The final results of NEMO-3 were published in 2018.

SuperNEMO

A next generation experiment, SuperNEMO, is under construction. It is based on technology used by the NEMO-3 experiment, but will be more than a factor of ten bigger. The SuperNEMO detector will consist of 20 modules each containing approximately 5 kg of enriched double beta decay emitting isotope in the form of a thin foil. The installation of a first module (using selenium-82) in the LSM is under way, with data taking expected in the second half of 2015. As of 2019, the commissioning of the SuperNEMO demonstration module (basically one of the 20 modulus of the whole SuperNEMO) is underway, and the collaboration continues to plan to construct the whole 20-module SuperNEMO detector.

References

External links

NEMO Experiment's official Site
{{neutrino detectors Neutrino observatories