View source for Tests of relativistic energy and momentum

[[File:Rel-Newton-Kinetic.svg|thumb|300px|'''Kinetic energy in special relativity and Newtonian mechanics.''' Relativistic kinetic energy increases to infinity when approaching the speed of light, thus no massive body can reach this speed.]]
'''Tests of relativistic energy and momentum''' are aimed at measuring the [[Mass in special relativity|relativistic expressions]] for [[energy]], [[momentum]], and [[mass]]. According to [[special relativity]], the properties of [[particle]]s moving approximately at the [[speed of light]] significantly deviate from the predictions of [[Newtonian mechanics]]. For instance, the [[speed of light]] cannot be reached by [[mass]]ive particles.<ref>{{cite book |title=Introduction to Particle Cosmology: The Standard Model of Cosmology and its Open Problems |author1=Cosimo Bambi |author2=Alexandre D. Dolgov |edition=illustrated |publisher=Springer |year=2015 |isbn=978-3-662-48078-6 |page=24 |url=https://books.google.com/books?id=JYhgCgAAQBAJ}} [https://books.google.com/books?id=JYhgCgAAQBAJ&pg=PA24 Extract of page 24]</ref>

Today, those relativistic expressions for particles close to the speed of light are routinely confirmed in [[Undergraduate education|undergraduate]] laboratories, and necessary in the design and theoretical evaluation of collision experiments in [[particle accelerator]]s.<ref name=taylor /><ref name=plett /> See also [[Tests of special relativity]] for a general overview.

==Overview==
[[File:Rel-Newton-Momentum.svg|thumb|250px|Similar to kinetic energy, relativistic momentum increases to infinity when approaching the speed of light.]]
In [[classical mechanics]], [[kinetic energy]] and [[momentum]] are expressed as
:<math>E_{k}=\tfrac{1}{2}mv^{2} ,\quad p=mv . \,</math>

On the other hand, [[special relativity]] predicts that the speed of light is constant in all [[inertial frames of reference]]s. The relativistic [[energy–momentum relation]] reads:

:<math>E^{2}-(pc)^{2}=(mc^{2})^{2} \,</math>,

from which the relations for rest energy <math>E_{0}</math>, relativistic energy (rest + kinetic) <math>E</math>, kinetic energy <math>E_{k}</math>, and momentum <math>p</math> of [[mass]]ive particles follow:

:<math>E_{0}=mc^{2},\quad E=\gamma mc^{2},\quad E_{k}=(\gamma-1)mc^{2},\quad p=\gamma mv</math>,

where <math>\gamma=1/\sqrt{1-(v/c)^{2}}</math>. So relativistic energy and momentum significantly increase with speed, thus the speed of light cannot be reached by massive particles. In some  relativity textbooks, the so-called "[[relativistic mass]]" <math>M=\gamma m\,</math> is used as well. However, this concept is considered disadvantageous by many authors, instead the expressions of relativistic energy and momentum should be used to express the velocity dependence in relativity, which provide the same experimental predictions.

==Early experiments==
{{Main|Kaufmann–Bucherer–Neumann experiments}}

First experiments capable of detecting such relations were conducted by [[Walter Kaufmann (physicist)|Walter Kaufmann]], [[Alfred Bucherer]] and others between 1901 and 1915. These experiments were aimed at measuring the [[Deflection (physics)|deflection]] of [[beta ray]]s within a magnetic field so as to determine the [[mass-to-charge ratio]] of electrons. Since the charge was known to be velocity independent, any variation had to be attributed to alterations in the electron's momentum or mass (formerly known as transverse [[electromagnetic mass]] <math>m_{T}=m\gamma,</math> equivalent to the "relativistic mass" <math>M</math> as indicated above). Since relativistic mass is not often used anymore in modern textbooks, those tests can be described of measurements of relativistic momentum or energy, because the following relation applies:

:<math>\frac{M}{m}=\frac{p}{mv}=\frac{E}{mc^{2}}=\gamma</math>
 
Electrons traveling between 0.25–0.75c indicated an increase of momentum in agreement with the relativistic predictions, and were considered as clear confirmations of special relativity. However, it was later pointed out that although the experiments were in agreement with relativity, the precision was not sufficient to rule out competing models of the electron, such as the one of [[Max Abraham]].<ref>{{Citation |author1=Zahn, C. T.  |author2=Spees, A. A.  |name-list-style=amp | year=1938 | title= A Critical Analysis of the Classical Experiments on the Variation of Electron Mass | journal=Physical Review | volume=53|issue=7 | pages= 511–521 | doi=10.1103/PhysRev.53.511 | bibcode=1938PhRv...53..511Z}}</ref><ref name=farago>{{Citation |author1=P. S. Faragó  |author2=L. Jánossy  |name-list-style=amp | year=1957 | title= Review of the experimental evidence for the law of variation of the electron mass with velocity | journal=Il Nuovo Cimento |volume=5|  issue=6|pages= 379–383 | doi=10.1007/BF02856033|bibcode=1957NCim....5.1411F|s2cid=121179531 }}</ref>

Already in 1915, however, [[Arnold Sommerfeld]] was able to derive the [[Fine structure]] of [[Hydrogen spectral series|hydrogen-like spectra]] by using the relativistic expressions for momentum and energy (in the context of the [[Old quantum theory|Bohr–Sommerfeld theory]]). Subsequently, [[Karl Glitscher]] simply substituted the relativistic expressions for Abraham's, demonstrating that Abraham's theory is in conflict with experimental data and is therefore refuted, while relativity is in agreement with the data.<ref>{{Cite journal|author=Glitscher, Karl|year=1917|title= Spektroskopischer Vergleich zwischen den Theorien des starren und des deformierbaren Elektrons|journal=Annalen der Physik|volume=357|issue=6|pages= 608–630|doi=10.1002/andp.19173570603|bibcode = 1917AnP...357..608G |hdl=2027/uc1.b2637473|url=https://zenodo.org/record/1424320}}</ref>

== Precision measurements ==
[[File:RogersExpGraph2.svg|thumb|300px|Three data points of Rogers ''et al.'', in agreement with special relativity]]

In 1940, Rogers ''et al.'' performed the first electron deflection test sufficiently precise to definitely rule out competing models. As in the Bucherer-Neumann experiments, the velocity and the charge-mass-ratio of beta particles of velocities up to 0.75c was measured. However, they made many improvements, including the employment of a [[Geiger counter]]. The accuracy of the experiment by which relativity was confirmed was within 1%.<ref>{{Citation |author1=Rogers, Marguerite M. |author2=McReynolds, A. W. |author3=Rogers, F. T. | year=1940 | title= A Determination of the Masses and Velocities of Three Radium B Beta-Particles: The Relativistic Mass of the Electron | journal=Physical Review |volume=57| issue=5| pages= 379–383 | doi=10.1103/PhysRev.57.379 | bibcode=1940PhRv...57..379R|hdl=1911/18426 }}</ref>

An even more precise electron deflection test was conducted by Meyer ''et al.'' (1963). They tested electrons traveling at velocities from 0.987 to 0.99c, which were deflected in a static homogenous magnetic field by which ''p'' was measured, and a static cylindrical electric field by which <math>p^{2}/(m\gamma)</math> was measured. They confirmed relativity with an upper limit for deviations of ~0.00037.<ref>{{cite journal|author1=Meyer, V. |author2=Reichart, W. |author3=Staub, H.H. |title=Experimentelle Untersuchung der Massen-Impulsrelation des Elektrons|journal=Helvetica Physica Acta|volume=36|year=1963|pages=981–992|doi=10.5169/seals-113412}}</ref>

Also measurements of the charge-to-mass ratio and thus momentum of [[proton]]s have been conducted. Grove and Fox (1953) measured 385-MeV protons moving at ~0.7c. Determination of the angular frequencies and of the magnetic field provided the charge-to-mass ratio. This, together with measuring the magnetic center, allowed to confirm the relativistic expression for the charge-to-mass ratio with a precision of ~0.0006.<ref>{{cite journal|author1=Grove, D. J. |author2=Fox, J. C. |title=e/m for 385-MeV protons (UA7)|journal=Physical Review|volume=90|issue=2 |year=1953|page=378|doi=10.1103/PhysRev.90.333|bibcode = 1953PhRv...90..333. }}</ref>

However, Zrelov ''et al.'' (1958) criticized the scant information given by Grove and Fox, emphasizing the difficulty of such measurements due to the complex motion of the protons. Therefore, they conducted a more extensive measurement, in which protons of 660 MeV with mean velocity of 0.8112c were employed. The proton's momentum was measured using a [[Litz wire]], and the velocity was determined by evaluation of [[Cherenkov radiation]]. They confirmed relativity with an upper limit for deviations of ~0.0041.<ref>{{cite journal|author1=Zrelov, V. P. |author2=Tiapkin, A. A. |author3=Farago, P. S. |title=Measurement of the mass of 600 MeV protons|journal=Soviet Physics JETP|volume=7|issue=3|year=1958|pages=384–387}}</ref>

==Bertozzi experiment==
[[Image:BertozziExp.svg|thumb|300px|Data of the '''Bertozzi experiment''' show close agreement with special relativity. Kinetic energy of five electron runs: 0.5, 1, 1.5, 4.5, 15 [[Electron volt|MeV]] (or 1, 2, 3, 9, 30 in mc²). Speed: 0.752, 0.828, 0.922, 0.974, 1.0 in [[speed of light|c²]] (or 0.867, 0.910, 0.960, 0.987, 1 in c).]]
Since the 1930s, relativity was needed in the construction of [[particle accelerator]]s, and the precision measurements mentioned above clearly confirmed the theory as well. But those tests demonstrate the relativistic expressions in an indirect way, since many other effects have to be considered in order to evaluate the deflection curve, velocity, and momentum. So an experiment specifically aimed at demonstrating the relativistic effects in a very direct way was conducted by [[William Bertozzi]] (1962, 1964).<ref>{{Citation | author=Bertozzi, William | year=1964 | title= Speed and Kinetic Energy of Relativistic Electrons | journal=American Journal of Physics |volume=32| issue=7| pages=551–555 | doi=10.1119/1.1970770|bibcode = 1964AmJPh..32..551B }}</ref><ref>{{Citation | author=Bertozzi, William | year=1962 | title= The Ultimate Speed - An Exploration with High Energy Electrons}} https://www.youtube.com/watch?v=B0BOpiMQXQA</ref>

He employed the [[electron]] accelerator facility at [[MIT]] in order to initiate five electron runs, with electrons of kinetic energies between 0.5 and 15 [[Electron volt|MeV]]. These electrons were produced by a [[Van de Graaff generator]] and traveled a distance of 8.4 m, until they hit an [[aluminium]] disc. First, the [[time of flight]] of the electrons was measured in all five runs – the velocity data obtained were in close agreement with the relativistic expectation. However, at this stage the kinetic energy was only indirectly determined by the accelerating fields. Therefore, the heat produced by some electrons hitting the aluminium disc was measured by [[calorimetry]] in order to directly obtain their kinetic energy - those results agreed with the expected energy within 10% error margin.

==Undergraduate experiments==
Various experiments have been performed which, due to their simplicity, are still used as [[Undergraduate education|undergraduate]] experiments. Mass, velocity, momentum, and energy of electrons have been measured in different ways in those experiments, all of them confirming relativity.<ref name=mar /> They include experiments involving beta particles, [[Compton scattering]] in which electrons exhibit highly relativistic properties and [[positron annihilation]].

{|
|
{| class=wikitable
!colspan=2|Beta particles
|-
|Marvel ''et al.''<ref name=mar>{{Cite arXiv |author1=Marvel, Robert E. |author2=Vineyard, Michael F. | year=2011 | title= Relativistic Electron Experiment for the Undergraduate Laboratory | eprint=1108.5977|class=physics.ed-ph }}</ref>||2011
|-
|Lund ''et al.''<ref>{{Citation |author1=Lund, M. |author2=Uggerhøj, U. I. | year=2009 | title= Experimental special relativity with a meter stick and a clock | journal=American Journal of Physics |volume=77| issue=8| pages=757–761| doi=10.1119/1.3049532|bibcode = 2009AmJPh..77..757L }}</ref>||2009
|-
|Luetzelschwab<ref>{{Citation | author=Luetzelschwab, John W. | year=2003 | title= Apparatus to measure relativistic mass increase | journal=American Journal of Physics |volume=71| issue=8| pages=878–884| doi=10.1119/1.1561457|bibcode = 2003AmJPh..71..878L | doi-access=free }}</ref>||2003
|-
|Couch ''et al.''<ref>{{Citation |author1=Couch, Jack G. |author2=Dorries, Terry K. | year=1982 | title= Measuring relativistic electrons in the undergraduate laboratory | journal=American Journal of Physics |volume=50| issue=10| pages=917–921| doi=10.1119/1.12973|bibcode = 1982AmJPh..50..917C }}</ref>||1982
|-
|Geller ''et al.''<ref>{{Citation |author1=Geller, Kenneth N. |author2=Kollarits, Richard | year=1972 | title= Experiment to Measure the Increase in Electron Mass with Velocity | journal=American Journal of Physics |volume=40| issue=8| pages=1125–1130| doi=10.1119/1.1986771|bibcode = 1972AmJPh..40.1125G }}</ref>||1972
|-
|Parker<ref>{{Citation | author=Parker, Sherwood | year=1972 | title= Relativity in an Undergraduate Laboratory-Measuring the Relativistic Mass Increase | journal=American Journal of Physics |volume=40| issue=2| pages=241–244| doi=10.1119/1.1986498|bibcode = 1972AmJPh..40..241P | s2cid=122167869 }}</ref>||1972
|-
|Bartlett ''et al.''<ref>{{Citation |author1=Bartlett, A. A. |author2=Correll, Malcolm | year=1965 | title= An Undergraduate Laboratory Apparatus for Measuring e/m as a Function of Velocity. I | journal=American Journal of Physics |volume=33| issue=4| pages=327–339| doi=10.1119/1.1971493|bibcode = 1965AmJPh..33..327B }}</ref>||1965
|}
|valign=top |
{| class=wikitable
!colspan=2|Compton recoil electrons
|-
|Jolivette ''et al.''<ref>{{Citation |author1=Jolivette, P. L. |author2=Rouze, N. | year=1994 | title= Compton scattering, the electron mass, and relativity: A laboratory experiment | journal=American Journal of Physics |volume=62| issue=3| pages=266–271| doi=10.1119/1.17611|bibcode = 1994AmJPh..62..266J }}</ref>||1994
|-
|Hoffman<ref>{{Citation | author=Hoffman, Matthiam J. H. | year=1989 | title= The Compton effect as an experimental approach toward relativistic mass | journal=American Journal of Physics |volume=57| issue=9| pages=822–825| doi=10.1119/1.15902|bibcode = 1989AmJPh..57..822H }}</ref>||1989
|-
|Egelstaff ''et al.''<ref>{{Citation |author1=Egelstaff, P. A. |author2=Jackman, J. A. |author3=Schultz, P. J. |author4=Nickel, B. G. |author5=MacKenzie, I. K. | year=1981 | title= Experiments in special relativity using Compton scattering of gamma rays | journal=American Journal of Physics |volume=49| issue=1| pages=43–47| doi=10.1119/1.12659|bibcode = 1981AmJPh..49...43E }}</ref>||1981
|-
|Higbie<ref>{{Citation | author=Higbie, J. | year=1974 | title= Undergraduate Relativity Experiment | journal=American Journal of Physics |volume=42| issue=8| pages=642–644| doi=10.1119/1.1987800|bibcode = 1974AmJPh..42..642H }}</ref>||1974
|}
| valign=top |
{| class=wikitable
!colspan=2|Positron annihilation
|-
|Dryzek ''et al.''<ref>{{Citation |author1=Dryzek, Jerzy |author2=Singleton, Douglas |author3=Suzuki, Takenori |author4=Yu, Runsheng | year=2006 | title= An undergraduate experiment to test relativistic kinematics using in flight positron annihilation | journal=American Journal of Physics |volume=74| issue=1| pages=49–53 | doi=10.1119/1.2142624|bibcode = 2006AmJPh..74...49D }}</ref>||2006
|}
|}

==Particle accelerators==
In modern [[particle accelerator]]s at high energies, the predictions of special relativity are routinely confirmed, and are necessary for the design and theoretical evaluation of collision experiments, especially in the [[ultrarelativistic limit]].<ref name=plett>{{Citation |author1=Plettner, Tomas |author2=Byer, Robert L. |author3=Siemann, Robert H. | year=2005 | title= The impact of Einstein's theory of special relativity on particle accelerators | journal=Journal of Physics B |volume=38| issue=9| pages=S741–S752 | doi=10.1088/0953-4075/38/9/020|bibcode = 2005JPhB...38S.741P |s2cid=53334246 }}</ref>
For instance, [[time dilation]] must be taken into account to understand the dynamics of particle decay, and the [[Velocity-addition formula|relativistic velocity addition theorem]] explains the distribution of [[synchrotron radiation]]. Regarding the relativistic energy-momentum relations, a series of high precision velocity and energy-momentum experiments have been conducted, in which the energies employed were necessarily much higher than the experiments mentioned above.<ref>{{cite book |author=Zhang, Yuan Zhong |year=1997 |title=Special Relativity and Its Experimental Foundations |publisher=World Scientific |isbn=978-981-02-2749-4 |url-access=registration |url=https://archive.org/details/specialrelativit0000chan }}</ref>

===Velocity===
[[Time of flight]] measurements have been conducted to measure differences in the velocities of electrons and light at the [[SLAC National Accelerator Laboratory]]. For instance, Brown ''et al.'' (1973) found no difference in the time of flight of 11-GeV electrons and visible [[light]], setting an upper limit of velocity differences of <math>\Delta v/c=(-1.3\pm2.7)\times10^{-6}</math>.<ref>{{Citation |author1=Brown, B. C. |author2=Masek, G. E. |author3=Maung, T. |author4=Miller, E. S. |author5=Ruderman, H. |author6=Vernon, W. | year=1973 | title= Experimental Comparison of the Velocities of eV (Visible) and GeV Electromagnetic Radiation | journal=Physical Review Letters |volume=30| issue=16| pages=763–766 | doi=10.1103/PhysRevLett.30.763|bibcode = 1973PhRvL..30..763B }}</ref>
Another SLAC experiment conducted by Guiragossián ''et al.'' (1974) accelerated electrons up to energies of 15 to 20.5 GeV. They used a radio frequency separator (RFS) to measure time-of-flight differences and thus velocity differences between those electrons and 15-GeV [[gamma ray]]s on a path length of 1015 m. They found no difference, increasing the upper limit to <math>\Delta v/c=2\times10^{-7}</math>.<ref>{{Citation |author1=Guiragossián, Z. G. T. |author2=Rothbart, G. B. |author3=Yearian, M. R. |author4=Gearhart, R. A. |author5=Murray, J. J. | year=1974 | title= Relative Velocity Measurements of Electrons and Gamma Rays at 15 GeV | journal=Physical Review Letters |volume=34| issue=6| pages=335–338 | doi=10.1103/PhysRevLett.34.335|bibcode = 1975PhRvL..34..335G |osti=1443188 }}</ref>

Already before, Alväger ''et al.'' (1964) at the CERN [[Proton Synchrotron]] executed a time of flight measurement to test the Newtonian momentum relations for light, being valid in the so-called [[Emission theory (relativity)|emission theory]]. In this experiment, gamma rays were produced in the decay of 6-GeV pions traveling at 0.99975c. If Newtonian momentum <math>p=mv</math> were valid, those gamma rays should have traveled at superluminal speeds. However, they found no difference and gave an upper limit of <math>\Delta v/c=10^{-5}</math>.<ref>{{Citation|author1=Alväger, T. |author2=Farley, F. J. M. |author3=Kjellman, J. |author4=Wallin, L. |title=Test of the second postulate of special relativity in the GeV region|journal=Physics Letters|volume=12|issue=3|year=1964|pages=260–262|doi=10.1016/0031-9163(64)91095-9|postscript=.|bibcode=1964PhL....12..260A}}</ref>

=== Energy and Calorimetry ===
The intrusion of particles into [[particle detector]]s is connected with [[electron–positron annihilation]], Compton scattering, [[Cherenkov radiation]] etc., so that a cascade of effects is leading to the production of new particles (photons, electrons, [[neutrino]]s, etc.). The energy of such [[particle shower]]s corresponds to the relativistic kinetic energy and rest energy of the initial particles. This energy can be measured by [[Calorimeter (particle physics)|calorimeters]] in an electrical, optical, thermal, or acoustical way.<ref name=fab>{{Cite journal |author1=Fabjan, Christian W. |author2=Gianotti, Fabiola | year=2003 | title= Calorimetry for particle physics | journal=Reviews of Modern Physics |volume=75| issue=4| pages=1243–1286 | doi=10.1103/RevModPhys.75.1243|bibcode = 2003RvMP...75.1243F |url=https://cds.cern.ch/record/692252/files/RevModPhys.75.1243.pdf}}</ref>

Thermal measurements in order to estimate the relativistic kinetic energy were already carried out by Bertozzi as mentioned above. Additional measurements at SLAC followed, in which the heat produced by 20-GeV electrons was measured in 1982. A [[beam dump]] of water-cooled [[aluminium]] was employed as calorimeter. The results were in agreement with special relativity, even though the accuracy was only 30%.<ref>{{Cite journal |author1=Walz, Dieter R. |author2=Noyes, H. Pierre |author3=Carezani, Ricardo L. | year=1984 | title= Calorimetric test of special relativity | journal=Physical Review A |volume=29| issue=4| pages=2110–2113 | doi=10.1103/PhysRevA.29.2110|bibcode = 1984PhRvA..29.2110W |osti=1446354 }}</ref>
However, the experimentalists alluded to the fact, that calorimetric tests with 10-GeV electrons were executed already in 1969. There, [[copper]] was used as beam dump, and an accuracy of 1% was achieved.<ref>{{Cite journal |author1=Fischer, G. E. |author2=Murata, Y. | year=1970 | title= A beam monitor system for high-intensity photon beams in the multi-GeV range | journal=Nuclear Instruments and Methods |volume=78|issue=1 | pages=25–39 | doi=10.1016/0029-554X(70)90425-8|bibcode = 1970NucIM..78...25F |osti=4752864 }}</ref>

In modern calorimeters called electromagnetic or [[hadron]]ic depending on the interaction, the energy of the particle showers is often measured by the [[ionization]] caused by them. Also excitations can arise in [[scintillator]]s (see [[Scintillation (physics)|scintillation]]), whereby light is emitted and then measured by a [[scintillation counter]]. Cherenkov radiation is measured as well. In all of those methods, the measured energy is proportional to the initial particle energy.<ref name=fab />

=== Annihilation and pair production ===
Relativistic energy and momentum can also be measured by studying processes such as [[annihilation]] and [[pair production]].<ref name=taylor>{{cite book|author1=Edwin F. Taylor |author2=John Archibald Wheeler |title=Spacetime Physics: Introduction to Special Relativity|url=https://archive.org/details/spacetimephysics00edwi_0 |url-access=registration |year=1992|publisher=W. H. Freeman|location=New York|isbn=0-7167-2327-1}}</ref> For instance, the rest energy of electrons and [[positron]]s is 0.51 MeV respectively. When a photon interacts with an [[atomic nucleus]], electron-positron pairs can be generated in case the energy of the photon matches the required [[threshold energy]], which is the combined electron-positron rest energy of 1.02 MeV. However, if the photon energy is even higher, then the exceeding energy is converted into kinetic energy of the particles. The reverse process occurs in [[electron-positron annihilation]] at low energies, in which process photons are created having the same energy as the electron-positron pair. These are direct examples of <math>E_0=mc^2</math> ([[mass–energy equivalence]]).

There are also many examples of conversion of relativistic kinetic energy into rest energy. In 1974, [[SLAC National Accelerator Laboratory]] accelerated electrons and positrons up to relativistic velocities, so that their relativistic energy <math>\gamma mc^{2}</math> (i.e. the sum of their rest energy and kinetic energy) is significantly increased to about 1500 MeV each. When those particles collide, other particles such as the [[J/ψ meson]] of rest energy of about 3000 MeV were produced.<ref>{{Cite web|author=Burton Richter|year=1976|publisher=Nobel lecture 1976|title=From the Psi to Charm – The Experiments of 1975 and 1976|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1976/richter-lecture.html|author-link=Burton Richter}}</ref>
Much higher energies were employed at the [[Large Electron–Positron Collider]] in 1989, where electrons and positrons were accelerated up to 45 GeV each, in order to produce [[W and Z bosons]] of rest energies between 80 and 91 GeV. Later, the energies were considerably increased to 200 GeV to generate pairs of W bosons.<ref>{{Citation | author=LEP collaborations | year=1992 | title= Electroweak parameters of the Z0 resonance and the standard model | journal=Physics Letters B |volume=276| issue=12| pages=247–253 | doi=10.1016/0370-2693(92)90572-L|bibcode = 1992PhLB..276..247. | hdl=2066/124399 | url=https://archive-ouverte.unige.ch/unige:113910 | hdl-access=free }}</ref>
Such bosons were also measured using [[proton]]-[[antiproton]] annihilation. The combined rest energy of those particles amounts to approximately 0.938 GeV each. The [[Super Proton Synchrotron]] accelerated those particle up to relativistic velocities and energies of approximately 270 GeV each, so that the [[center of mass]] energy at the collision reaches 540 GeV. Thereby, [[quark]]s and [[antiquark]]s gained the necessary energy and momentum to annihilate into [[W and Z bosons]].<ref>{{Cite web|author=Carlo Rubbia|year=1984|publisher=Nobel lecture 1984|title=Experimental Observation of the Intermediate Vector Bosons W+, W- and Z0|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1984/rubbia-lecture.html|author-link=Carlo Rubbia}}</ref>

Many other experiments involving the creation of a considerable amount of different particles at relativistic velocities have been (and still are) conducted in [[hadron]] colliders such as [[Tevatron]] (up to 1 TeV), the [[Relativistic Heavy Ion Collider]] (up to 200 GeV), and most recently the [[Large Hadron Collider]] (up to 7 TeV) in the course of searching for the [[Higgs boson]].

==Nuclear reactions==
The relation <math>E_0=mc^2</math> can be tested in [[nuclear reaction]]s, as the percent differences between the masses of the reactants and the products are big enough to measure; the change in total mass should account for the change in total kinetic energy. Einstein proposed such a test in the paper where he first stated the [[equivalence of mass and energy]], mentioning the [[radioactive decay]] of [[radium]] as a possibility.<ref>{{Cite journal|last=Einstein|first=A.|date=1905|title=Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?|journal=Annalen der Physik|language=de|volume=323|issue=13|pages=639–641|doi=10.1002/andp.19053231314|bibcode=1905AnP...323..639E|trans-title=Does the Inertia of a Body Depend Upon its Energy-Content?|issn=1521-3889|doi-access=free|url=http://www.fourmilab.ch/etexts/einstein/E_mc2/www/}}</ref> The first test in a nuclear reaction, however, used the absorption of an incident proton by [[lithium]]-7, which then breaks into two [[alpha particle]]s. The change in mass corresponded to the change in kinetic energy to within 0.5%.<ref>{{cite journal | last1 = Oliphant |first1=M. L. E. | author-link1 = Mark Oliphant | last2 = Kinsey | first2 = B. B. | last3 = Lord Rutherford | author-link3 = Ernest Rutherford | title = The Transformation of Lithium by Protons and by Ions of the Heavy Isotope of Hydrogen | year = 1933 | journal = Proceedings of the Royal Society | volume = 141 | issue = 845 | pages = 722–733 |doi=10.1098/rspa.1935.0071 |bibcode=1935RSPSA.149..406O | url = https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1935.0071}}</ref><ref>{{cite journal | last1 = Oliphant |first1=M. L. E. | author-link1 = Mark Oliphant | last2 = Kempton | first2 = A. R. | last3 = Lord Rutherford | author-link3 = Ernest Rutherford | title = The Accurate Determination of the Energy Released in Certain Nuclear Transformations | year = 1935 | journal = Proceedings of the Royal Society | volume = 149 | issue = 867 | pages = 406–416 |doi=10.1098/rspa.1935.0071 |bibcode=1935RSPSA.149..406O | url = https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1935.0071}}</ref> 

A particularly sensitive test was carried out in 2005 in the [[gamma decay]] of excited sulfur and silicon nuclei, in each case to the non-excited state ([[ground state]]). The masses of the excited and ground states were measured by measuring their revolution frequencies in an electromagnetic trap. The gamma rays' energies were measured by measuring their wavelengths with gamma-ray diffraction, similar to [[X-ray_crystallography#X-ray_diffraction|X-ray diffraction]], and using the well-established relation between [[photon energy]] and wavelength. The results confirmed the predictions of relativity to a precision of 0.0000004.<ref>{{cite web | title = Einstein Was Right (Again): Experiments Confirm that E= mc<sup>2</sup> | year = 2005 | publisher = [[NIST]] | url = https://www.nist.gov/news-events/news/2005/12/einstein-was-right-again-experiments-confirm-e-mc2}}</ref><ref>{{cite journal | last1 = Rainville | first1 = S. | last2 = Thompson | first2 = J.K. | last3= Myers | first3 = E.G.  | last4 = Brown | first4 = J.M. |last5 = Dewey | first5 = M.S. | last6= Kessler | first6 = E.G. Jr. | last7 = Deslattes | first7= R.D. | last8 = Börner | first8= H.G | last9 = Jentschel | first9 = M. | last10 = Mutti | first10 =P. | last11 = Pritchard | first11 = D.E. | date = 2005-12-22 | title = A direct test of E = mc<sup>2</sup> | journal = Nature | volume = 48 | issue = 7071 | pages = 1096–1097 | doi = 10.1038/4381096a | pmid = 16371997 | s2cid = 4426118 | url = https://www.nature.com/articles/4381096a}}</ref>

==References==
{{Reflist}}

==External links==
* Physics FAQ: [http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html List of SR tests]
{{portal|Physics}}

{{Tests of special relativity}}

[[Category:Momentum]]
[[Category:Physics experiments]]
[[Category:Special relativity]]