Elementary particle which moves close to the speed of light
Inparticle physics, arelativistic particle is anelementary particle with kinetic energy greater than or equal to its rest-mass energy given by Einstein's relation,, or specifically, of which the velocity is comparable to thespeed of light.[1]
This is achieved byphotons to the extent that effects described byspecial relativity are able to describe those of such particles themselves. Several approaches exist as a means of describing the motion of single and multiple relativistic particles, with a prominent example being postulations through theDirac equation of single particle motion.[2]
Since the energy-momentum relation of an particle can be written as:[3]
1
where is the energy, is the momentum, and is the rest mass,when the rest mass tends to be zero, e.g. for a photon, or the momentum tends to be large, e.g. for a large-speed proton, this relation will collapses into a linear dispersion, i.e.
2
This is different from the parabolic energy-momentum relation for classical particles. Thus, in practice, the linearity or the non-parabolicity of theenergy-momentum relation is considered as a key feature for relativistic particles. These two types of relativistic particles are remarked as massless and massive, respectively.
In experiments,massive particles are relativistic when their kinetic energy is comparable to or greater than the energy corresponding to their rest mass. In other words, a massive particle is relativistic when its total mass-energy is at least twice its rest mass. This condition implies that the speed of the particle is close to the speed of light. According to theLorentz factor formula, this requires the particle to move at roughly 85% of the speed of light. Such relativistic particles are generated inparticle accelerators,[a] as well as naturally occurring incosmic radiation.[b] Inastrophysics,jets ofrelativistic plasma are produced by the centers ofactive galaxies andquasars.[4]
Relativistic electrons can also exist in some solid state materials,[6][7][8][9] including semimetals such as graphene,[6] topological insulators,[10] bismuth antimony alloys,[11] and semiconductors such as transitional metal dichalcogenide[12] and black phosphorene layers.[13] These lattice confined electrons with relativistic effects that can be described using theDirac equation are also called desktop relativistic electrons or Dirac electrons.
^For example, at theLarge Hadron Collider operating with a collision energy of 13 TeV, a relativisticproton has a mass-energy 6,927 times greater than its rest mass and travels at 99.999998958160351322% of the speed of light.
^Stacy, J. Gregory; Vestrand, W. Thomas (2003)."Gamma-Ray Astronomy".Encyclopedia of Physical Science and Technology (Third ed.). Academic Press. p. 397-432.ISBN978-0122274107.
^Gibbons, Gary William."Relativstic mechanics". Encyclopaedia Britannica. RetrievedJune 6, 2021.
^Yuan, Luke C. L. (2000). "A novel transition radiation detector utilizing superconducting microspheres for measuring the energy of relativistic high-energy charged particles".Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.441 (3):479–482.Bibcode:2000NIMPA.441..479Y.doi:10.1016/S0168-9002(99)00979-1.
^Diaz, Horacio Coy (2015). "Direct Observation of Interlayer Hybridization and Dirac Relativistic Carriers in Graphene/MoS2 van der Waals Heterostructures".Nano Letters.15 (2):1135–1140.Bibcode:2015NanoL..15.1135C.doi:10.1021/nl504167y.PMID25629211.
