Muon collider

<h2 id="history">History</h2>
Previous <a href="/facts/Lepton/X4a6MGop">lepton</a> colliders have all used <a href="/facts/Electron/L0KBo5cW">electrons</a> and/or their <a href="/facts/Anti-matter/NvpGDLof">anti-particles</a>, <a href="/facts/Positron/HgV4zBzA">positrons</a>. They offer an advantage over <a href="/facts/Hadron_collider/At9najnt">hadron colliders</a>, such as the <a href="/facts/CERN/y1gwRchm">CERN</a>-based <a href="/facts/Large_Hadron_Collider/XWJCFSqT">Large Hadron Collider</a>, in that lepton collisions are relatively "clean" thanks to leptons being <a href="/facts/Elementary_particle/CTFDM97U">elementary particles</a>, while <a href="/facts/Hadron/C0sd1zty">hadrons</a>, such as <a href="/facts/Protons/clCjepXP">protons</a>, are composite particles. Yet electron-positron colliders cannot efficiently reach the same centre-of-mass energy as hadron colliders in circular accelerators due to their energy loss through <a href="/facts/Synchrotron_radiation/mTsSKmRz">synchrotron radiation</a>.
A muon is about 206 times more <a href="/facts/Mass/HHdc8XmF">massive</a> than the <a href="/facts/Electron/L0KBo5cW">electron</a>, which reduces the amount of <a href="/facts/Synchrotron_radiation/mTsSKmRz">synchrotron radiation</a> from a muon by a factor of about 1 billion. The reduced radiation loss enables the construction of circular colliders with much higher design energies than equivalent electron-positron colliders. This provides the unique combination of high centre-of-mass energy and clean collision environment that is not achievable in any other type of particle collider. It has been shown that a muon collider could achieve energies of several <a href="/facts/Electronvolt/YMT1fqX9">teraelectronvolt</a> (TeV).<a class="footnote-ref" id="fnref:1" href="#fn:1">1</a> In particular, starting from the centre-of-mass energy of 3 TeV, a muon collider is the most energy-efficient type of collider, while at 10 TeV it would have a physics reach comparable to that of the proposed 100 TeV hadron collider, <a href="/facts/Future_Circular_Collider/aqD44oJl">FCC-hh</a>,<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> while fitting in a ring of the size of the LHC (27 kilometres (17 mi)), without the need for a much-more-expensive 100-kilometre-long (62 mi) long tunnel foreseen for the <a href="/facts/Future_Circular_Collider/aqD44oJl">Future Circular Collider</a>. A muon collider also provides a clean and effective way to produce <a href="/facts/Higgs_boson/3LAYXfft">Higgs bosons</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a>
Muons are short-lived particles with a lifetime of 2.2 <a href="/facts/Microsecond/zdW1DEb2">μs</a> in their rest frame. This fact poses a serious challenge for the accelerator complex: muons must be accelerated to a high energy before they decay, and the accelerator needs a continuous source of new muons. It also impacts the experiment design: a high flux of particles induced by the muon decay products eventually reaches the detector, requiring advanced detector technologies and event-reconstruction algorithms to distinguish these particles from collision products. The baseline muon-production method considered today[when?] is based on a high-energy proton beam impinging on a target to produce <a href="/facts/Pion/x5HamzG3">pions</a>, which then decay to muons that have a sizeable spread of direction and energy, which needs to be reduced for further acceleration in the ring. The possibility of performing this so-called 6D cooling of muons has been demonstrated by the <a href="/facts/International_Muon_Ionization_Cooling_Experiment/C2fRGJL3">Muon Ionisation Cooling Experiment</a> (MICE).<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> An alternative production method, Low Emittance Muon Accelerator (LEMMA),<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> uses a positron beam impinging on a fixed target to produce muon pairs from the electron-positron annihilation process at the threshold centre-of-mass energy. The resulting beam does not need the cooling stage, but suffers from a very low muon-production cross section, making it challenging to achieve high <a href="/facts/Luminosity_(scattering_theory)/E6dFeWbW">luminosity</a> with existing positron sources.
Talks were proceeding in 2009.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a><a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> The first dedicated design of the accelerator complex and detector design for the centre-of-mass energies up to 3 TeV was developed within the American Muon Accelerator Program (MAP) during 2010–2015,<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a><a class="footnote-ref" id="fnref:9" href="#fn:9">9</a><a class="footnote-ref" id="fnref:10" href="#fn:10">10</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> after which it was abandoned.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> Interest in the Muon Collider project has increased again in 2020 after the publication of the physics-reach comparison between the 1.5 TeV Muon Collider and the CLIC experiment,<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> followed by the update of the European strategy for particle physics, in which it was recommended to initiate an international design study of a Muon Collider targeting centre-of-mass energies close to 10 TeV.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

<h2 id="muon-acceleration">Muon acceleration</h2>
In 2024, researchers at the <a href="/facts/Japan_Proton_Accelerator_Research_Complex/PpzQDCEw">Japan Proton Accelerator Research Complex</a> (J-PARC) successfully accelerated positive muons for the first time. The process involved creating <a href="/facts/Muonium/dnnS0EbC">muonium</a> atoms by firing a controlled beam of antimuons into a <a href="/facts/Silica_aerogel/cjhmCvSa">silica aerogel</a>. The collision with electrons in the aerogel formed muonium, which was then stripped of electrons using a laser to generate stationary antimuons. These antimuons were then frozen to keep them static. Using an electric field, the researchers accelerated the stationary positive muons to speeds of 4% of the <a href="/facts/Speed_of_light/sKSQwdNx">speed of light</a> (~12 million meters per second). This achievement marked a significant milestone toward the development of muon colliders, with the aim to accelerate muons to 94% of the speed of light by 2028.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a><a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/International_Muon_Ionization_Cooling_Experiment/C2fRGJL3">International Muon Ionization Cooling Experiment</a></li>
<li><a href="/facts/Neutrino_Factory/GEWfwyDn">Neutrino Factory</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="/facts/Elizabeth_Gibney/kbSljqLT">Gibney, Elizabeth</a> (8 August 2022). <a href="https://doi.org/10.1038%2Fd41586-022-02122-y">"Particle physicists want to build the world's first muon collider"</a>. Nature. 608 (7924): 660–661. <a href="/facts/Bibcode_(identifier)/9HtdQSGB">Bibcode</a>:<a href="https://ui.adsabs.harvard.edu/abs/2022Natur.608..660G">2022Natur.608..660G</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1038%2Fd41586-022-02122-y">10.1038/d41586-022-02122-y</a>. <a href="/facts/PMID_(identifier)/JlHAvMHt">PMID</a> <a href="https://pubmed.ncbi.nlm.nih.gov/35941386">35941386</a>.</li></ul>

<h2 id="references">References</h2>

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</ol>

Muon collider open-in-new

Muon collider