Editing Magnetic monopole (section)

== Searches for magnetic monopoles ==
Experimental searches for magnetic monopoles can be placed in one of two categories: those that try to detect preexisting magnetic monopoles and those that try to create and detect new magnetic monopoles.

Passing a magnetic monopole through a coil of wire induces a net current in the coil. This is not the case for a magnetic dipole or higher order magnetic pole, for which the net induced current is zero, and hence the effect can be used as an unambiguous test for the presence of magnetic monopoles. In a wire with finite resistance, the induced current quickly dissipates its energy as heat, but in a [[superconducting]] loop the induced current is long-lived. By using a highly sensitive "superconducting quantum interference device" ([[SQUID]]) one can, in principle, detect even a single magnetic monopole.

According to standard inflationary cosmology, magnetic monopoles produced before inflation would have been diluted to an extremely low density today. Magnetic monopoles may also have been produced thermally after inflation, during the period of reheating. However, the current bounds on the reheating temperature span 18 orders of magnitude and as a consequence the density of magnetic monopoles today is not well constrained by theory.

There have been many searches for preexisting magnetic monopoles. Although there has been one tantalizing event recorded, by [[Blas Cabrera Navarro]] on the night of February 14, 1982 (thus, sometimes referred to as the "[[Valentine's Day]] Monopole"<ref>{{cite journal|title=Physics: The waiting game|first=Geoff|last=Brumfiel|date=May 6, 2004|journal=Nature|volume=429|issue=6987|pages=10–11|doi=10.1038/429010a|pmid=15129249|bibcode=2004Natur.429...10B|s2cid=4425841|doi-access=free}}</ref>), there has never been reproducible evidence for the existence of magnetic monopoles.<ref name="PRL-48-1378" /> The lack of such events places an upper limit on the number of monopoles of about one monopole per 10<sup>29</sup> [[nucleon]]s.

Another experiment in 1975 resulted in the announcement of the detection of a moving magnetic monopole in [[cosmic ray]]s by the team led by [[P. Buford Price]].<ref name="PRL-35-487"/> Price later retracted his claim, and a possible alternative explanation was offered by [[Luis Walter Alvarez]].<ref>{{cite conference|first=Luis W|last=Alvarez|title=Analysis of a Reported Magnetic Monopole|editor=Kirk, W. T.|conference=International symposium on lepton and photon interactions at high energies, Aug 21, 1975|book-title=Proceedings of the 1975 international symposium on lepton and photon interactions at high energies|pages=967|url=http://usparc.ihep.su/spires/find/hep/www?key=93726|access-date=May 25, 2008|archive-url=https://web.archive.org/web/20090204005403/http://usparc.ihep.su/spires/find/hep/www?key=93726|archive-date=February 4, 2009}}</ref> In his paper it was demonstrated that the path of the cosmic ray event that was claimed due to a magnetic monopole could be reproduced by the path followed by a [[platinum]] nucleus [[nuclear decay|decaying]] first to [[osmium]], and then to [[tantalum]].

High-energy particle colliders have been used to try to create magnetic monopoles. Due to the conservation of magnetic charge, magnetic monopoles must be created in pairs, one north and one south. Due to conservation of energy, only magnetic monopoles with masses less than half of the center of mass energy of the colliding particles can be produced. Beyond this, very little is known theoretically about the creation of magnetic monopoles in high-energy particle collisions. This is due to their large magnetic charge, which invalidates all the usual calculational techniques. As a consequence, collider-based searches for magnetic monopoles cannot, as yet, provide lower bounds on the mass of magnetic monopoles. They can however provide upper bounds on the probability (or cross section) of pair production, as a function of energy.

The [[ATLAS experiment]] at the [[Large Hadron Collider]] currently has the most stringent cross section limits for magnetic monopoles of 1 and 2 Dirac charges, produced through [[Drell–Yan process|Drell–Yan]] pair production. A team led by [[Wendy Taylor (physicist)|Wendy Taylor]] searches for these particles based on theories that define them as long lived (they do not quickly decay), as well as being highly ionizing (their interaction with matter is predominantly ionizing). In 2019 the search for magnetic monopoles in the ATLAS detector reported its first results from data collected from the LHC Run 2 collisions at center of mass energy of 13&nbsp;TeV, which at 34.4&nbsp;fb<sup>−1</sup> is the largest dataset analyzed to date.<ref>{{cite journal|url=http://inspirehep.net/record/1736730|title=Search for magnetic monopoles and stable high-electric-charge objects in 13&nbsp;TeV proton-proton collisions with the ATLAS detector|journal=Phys. Rev. Lett.|volume=124|issue=3|pages=031802|first= Georges el al|last=Aad|year=2020|arxiv=1905.10130|doi=10.1103/PhysRevLett.124.031802|pmid=32031842|bibcode=2020PhRvL.124c1802A}}</ref>

The [[MoEDAL experiment]], installed at the Large Hadron Collider, is currently searching for magnetic monopoles and large supersymmetric particles using nuclear track detectors and aluminum bars around [[LHCb]]'s [[VELO]] detector. The particles it is looking for damage the plastic sheets that comprise the nuclear track detectors along their path, with various identifying features. Further, the aluminum bars can trap sufficiently slowly moving magnetic monopoles. The bars can then be analyzed by passing them through a SQUID.