Mu3e is a

particle physics Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and ...

experiment at the

Paul Scherrer Institute The Paul Scherrer Institute (PSI) is a multi-disciplinary research institute for natural and engineering sciences in Switzerland. It is located in the Canton of Aargau in the municipalities Villigen and Würenlingen on either side of the ...

, searching for decays of

anti Anti may refer to: *Anti-, a prefix meaning "against" *Änti, or Antaeus, a half-giant in Greek and Berber mythology *A false reading of '' Nemty'', the name of the ferryman who carried Isis to Set's island in Egyptian mythology *Áńt’į, or ...

muon A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of , but with a much greater mass. It is classified as a lepton. As wi ...

s (''Mu'') to an

electron The electron (, or in nuclear reactions) 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 partic ...

and two

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 collide ...

s (''3e''). This decay is extremely unlikely in the

Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces ( electromagnetic, weak and strong interactions - excluding gravity) in the universe and classifying all known elementary particles. I ...

of particle physics, as it changes the

lepton number In particle physics, lepton number (historically also called lepton charge) is a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle reaction. Lepton number ...

. Several new theories, especially

supersymmetric In a supersymmetric theory the equations for force and the equations for matter are identical. In theoretical and mathematical physics, any theory with this property has the principle of supersymmetry (SUSY). Dozens of supersymmetric theorie ...

ones, predict a much more frequent decay. Searching for this decay allows a test of these theories, even if they cannot be tested directly in other experiments like at the

LHC The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundr ...

. It has also been shown the experiment is sensitive to probe new light dark sector particles such as dark photon. Mu3e is constructed at the Paul Scherrer Institute. It is planned to create the world's most intense muon beam which will allow to analyze two billion decays per second. This rate is necessary to study more than 10¹⁶ muon decays in total. Important backgrounds are the decays

\mu^+ \to e^+e^-e^+\bar\nu_e

and

\mu^+ \to e^+\bar\nu_e

. To distinguish between signal and background, the detector has a spatial resolution better than 200

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Uni ...

, a time resolution better than 100 ps and an energy resolution better than 0.5

MeV In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. ...

for the individual electrons. To minimize

multiple scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...

, the detector is built as light as possible.

Semiconductor detector A semiconductor detector in ionizing radiation detection physics is a device that uses a semiconductor (usually silicon or germanium) to measure the effect of incident charged particles or photons. Semiconductor detectors find broad applicati ...

s are used for the spatial and energy resolution,

scintillator A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbe ...

fibers provide a good timing resolution. The whole experiment is in a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

of 1

Tesla Tesla most commonly refers to: * Nikola Tesla (1856–1943), a Serbian-American electrical engineer and inventor * Tesla, Inc., an American electric vehicle and clean energy company, formerly Tesla Motors, Inc. * Tesla (unit) (symbol: T), the SI-d ...

to determine the energy of the particles based on their curvature radius. data taking is expected to begin in 2024. The full rate of two billion muons per second will not be reached before 2028. The experiment is expected to either find the decay or to set an upper limit of 10⁻¹⁶ on the

branching fraction In particle physics and nuclear physics, the branching fraction (or branching ratio) for a decay is the fraction of particles which decay by an individual decay mode or with respect to the total number of particles which decay. It applies to eithe ...

, a factor 10,000 better than previous experiments.SINDRUM-Kollaboration
Search for the Decay mu+ ---> e+ e+ e-
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External links

Description of the experiment at psi.ch

Research Proposal

Mu3e experiment record
on

INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970 ...

References

Particle experiments

See also

External links

References