question: What's the difference between a muonic atom and an electronic atom?
comment: Muons are particals that function like electrons, but where electrons ha e almost immeasurably small mass, muons have a bigger mass that is clearly measurable. It's still a stupid small number though and really hard to write. Anyway, a muonic atom has muons where one or more of it's electrons should be, so it winds up heavier overall. They're pretty rare though.
passages: In a "muonic atom" (previously called a "mu-mesic" atom, now known to be a misnomer as muons are not mesons), an electron is replaced by a muon, which, like the electron, is a lepton. Since leptons are only sensitive to weak, electromagnetic and gravitational forces, muonic atoms are governed to very high precision by the electromagnetic interaction. 
   Exotic atom
  
  An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons (muonic atoms) or pions (pionic atoms). Because these substitute particles are usually unstable, exotic atoms typically have very short lifetimes and all currently observed atoms cannot persist under normal conditions.
  
  Section::::Muonic atoms.
   Such muon beams are available at PSI (Swiss Muon Source SµS), TRIUMF, J-PARC, ISIS Neutron and Muon Source and RIKEN-RAL.
  
  Section::::How it works.:Muon production.:Low-energy muon beam.
   Section::::How it works.:Different types of muon sources: "continuous" vs. "pulsed".
  
  In addition to the above-mentioned classification based on energy, muon beams are also divided according to the time structure of the particle accelerator, i.e. continuous or pulsed.
   Muonium, despite its name, is "not" an onium containing a muon and an antimuon, because IUPAC assigned that name to the system of an antimuon bound with an electron. However, the production of a muon/antimuon bound state, which is an onium, has been theorized.
  
  Section::::Hypernuclear atoms.
  
  Atoms may be composed of electrons orbiting a hypernucleus that includes strange particles called hyperons. Such hypernuclear atoms are generally studied for their nuclear behaviour, falling into the realm of nuclear physics rather than atomic physics.
  
  Section::::Quasiparticle atoms.
   With this change in definition, the term "mu meson" was abandoned, and replaced whenever possible with the modern term "muon", making the term mu meson only historical. In the new quark model, other types of mesons sometimes continued to be referred to in shorter terminology (e.g., "pion" for pi meson), but in the case of the muon, it retained the shorter name and was never again properly referred to by older "mu meson" terminology.
   Normally in the nomenclature of particle physics, an atom composed of a positively charged particle bound to an electron is named after the positive particle with "-ium" appended, in this case "muium". The suffix "-onium" is mostly used for bound states of a particle with its own antiparticle. The exotic atom consisting of a muon and an antimuon is known as "true muonium". It is yet to be observed, but it may have been generated in the collision of electron and positron beams.
   Section::::Technical aspects.
  
  The apparatus is a muon-tracking device that consists of muon sensors and recording media. There are several different kinds of muon sensors used in muography apparatuses: plastic scintillators, nuclear emulsions, or gaseous ionization detectors. The recording medium is the film itself, digital magnetic or electronic memory. The apparatus is directed towards the target volume, exposing the muon sensor until the muon events required in order to form a statistically sufficient muogram are recorded, after which, (post processing) a muograph displaying the average density along each muon path is created.
   Section::::CMS by layers.:Layer 5 – The muon detectors and return yoke.
  
  As the name “Compact Muon Solenoid” suggests, detecting muons is one of CMS’s most important tasks. Muons are charged particles that are just like electrons and positrons, but are 200 times more massive. We expect them to be produced in the decay of a number of potential new particles; for instance, one of the clearest "signatures" of the Higgs Boson is its decay into four muons.
   PSI and TRIUMF host the two continuous muon sources available for µSR experiments.
   Because the muon is a lepton, the atomic energy levels of muonium can be calculated with great precision from quantum electrodynamics (QED), unlike in the case of hydrogen, where the precision is limited by uncertainties related to the internal structure of the proton. For this reason, muonium is an ideal system for studying bound-state QED and also for searching for physics beyond the standard model.
  
  Section::::Nomenclature.
   ISIS Neutron and Muon Source and J-PARC are the two "pulsed" muon sources available for µSR experiments.
  
  Section::::How it works.:The technique.
  
  Section::::How it works.:The technique.:Muon implantation.
   With two particles now known with the intermediate mass, the more general term "meson" was adopted to refer to any such particle within the correct mass range between electrons and nucleons. Further, in order to differentiate between the two different types of mesons after the second meson was discovered, the initial mesotron particle was renamed the "mu meson" (the Greek letter "μ" ("mu") corresponds to "m"), and the new 1947 meson (Yukawa's particle) was named the pi meson.
   "Negative" muons can, however, form muonic atoms (previously called mu-mesic atoms), by replacing an electron in ordinary atoms. Muonic hydrogen atoms are much smaller than typical hydrogen atoms because the much larger mass of the muon gives it a much more localized ground-state wavefunction than is observed for the electron. In multi-electron atoms, when only one of the electrons is replaced by a muon, the size of the atom continues to be determined by the other electrons, and the atomic size is nearly unchanged. However, in such cases the orbital of the muon continues to be smaller and far closer to the nucleus than the atomic orbitals of the electrons.
   Observation of such decay modes would constitute clear evidence for theories beyond the Standard Model. Upper limits for the branching fractions of such decay modes were measured in many experiments starting more than years ago. The current upper limit for the → + branching fraction was measured 2009–2013 in the MEG experiment and is 4.2 × 10.
  
  Section::::Muon decay.:Theoretical decay rate.
   Real-time muography requires muon sensors to convert the muon's kinetic energy into a number of electrons in order to process muon events as electronic data rather than as chemical changes on film. Electronic tracking data can be processed almost instantly with an adequate computer processor; in contrast, film muography data have to be developed before the muon tracks can be observed. Real-time tracking of muon trajectories produce real-time muograms that would be difficult or impossible to obtain with film muography.
  
  Section::::Invention of muography.:High-resolution muography.
   The first muogram was a matrix of the number of muon events produced in 1970 by the American physicist Luis Walter Alvarez. Alvarez installed his apparatus in the Belzoni Chamber to search for hidden chambers of the Pyramid of Chephren. He recorded the number of muons after they had passed through the Pyramid. With an invention of this particle tracking technique, he worked out the methods to generate the muogram as a function of muon's arriving angles. The generated muogram was compared with the results of the computer simulations, and he concluded that there were no hidden chambers in the Pyramid of Chephren after the apparatus was exposed to the Pyramid for several months.
   Section::::How it works.
  
  Section::::How it works.:Introduction.
   Muon spin rotation and relaxation are mostly performed with positive muons. They are well suited to the study of magnetic fields at the atomic scale inside matter, such as those produced by various kinds of magnetism and/or superconductivity encountered in compounds occurring in nature or artificially produced by modern material science.
   If no time dilation exists, then those muons should decay in the upper regions of the atmosphere, however, as a consequence of time dilation they are present in considerable amount also at much lower heights. The comparison of those amounts allows for the determination of the mean lifetime as well as the half-life of muons. formula_3 is the number of muons measured in the upper atmosphere, formula_4 at sea level, formula_5 is the travel time in the rest frame of the Earth by which the muons traverse the distance between those regions, and formula_6 is the mean proper lifetime of the muons:
   Section::::Muon radiography and tomography.
  
  Since muons are much more deeply penetrating than X-rays or gamma rays, muon imaging can be used with much thicker material or, with cosmic ray sources, larger objects. One example is commercial muon tomography used to image entire cargo containers to detect shielded nuclear material, as well as explosives or other contraband.
   In the laboratory frame the polarization of a high-energy muon beam is limited to about 80% and its energy is of the order of ~40-50MeV. Although such a high energy beam requires the use of suitable moderators and samples with sufficient thickness, it guarantees a homogeneous implantation of the muons in the sample volume. Such beams are also used to study specimens inside of recipients, e.g. samples inside pressure cells.
  
  Such muon beams are available at PSI, TRIUMF, J-PARC and RIKEN-RAL.
  
  Section::::How it works.:Muon production.:Surface beam.
   Since a muon is more massive than an electron, the Bohr orbits are closer to the nucleus in a muonic atom than in an ordinary atom, and corrections due to quantum electrodynamics are more important. Study of muonic atoms' energy levels as well as transition rates from excited states to the ground state therefore provide experimental tests of quantum electrodynamics.
  
  Muon-catalyzed fusion is a technical application of muonic atoms.
  
  Section::::Hadronic atoms.
   Section::::Research.:Physical science.
  
  The group aims to develop an ultra-sensitive device for measuring the physical properties of muons, and study the properties of new materials, including semiconductors, nano-magnetic materials, high-temperature superconductors, and topological insulators. 
  
  BULLET::::- Muon Spin Relaxation (μSR): Use muons to research superconductivity, nano-magnetism, and topological insulation through measuring local electromagnetic properties
  
  Section::::Research.:Atomic and molecular science.
  
  In these fields, they aim to precisely measure rare isotope mass and develop atomic manipulation technology, develop micro-measurement technology for atomic structures, and find the precise measurements of basic physical constants. 
   In all cases the information about the absorption of the muons was used as a measure of the thickness of the material crossed by the cosmic ray particles.
  
  Section::::Muon transmission imaging.
  