Editing HERA (particle accelerator) (section)

{{Other uses|Hera (disambiguation)}}
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{{Use dmy dates|date=February 2023}}

'''HERA''' ({{langx|de|'''H'''adron-'''E'''lektron-'''R'''ing'''a'''nlage}}, {{langx|en|'''H'''adron–'''E'''lectron '''R'''ing '''A'''ccelerator}}) was a [[particle accelerator]] at [[DESY]] in [[Hamburg]]. It was operated from 1992 to 30 June 2007.<ref>{{cite journal |url= https://www.symmetrymagazine.org/article/september-2007/the-end-of-the-hera-era |title=The end of the HERA era |first=David |last=Harris |journal=Symmetry Magazine |date=September 2007 |volume=04 |issue=7 |accessdate=19 August 2022}}</ref><ref name="CERNcourier_BW">{{cite journal |url=https://cds.cern.ch/record/1734120 |title=End of an era: HERA Switches off |first=Barbara |last=Warmbein |journal=CERN Courier |issue=47 |date=21 August 2007 |accessdate=19 August 2022}}</ref> At HERA, [[electron]]s or [[positron]]s were brought to collision with [[proton]]s at a [[center-of-mass]] [[energy]] of 320&nbsp;[[GeV]].<ref>{{cite journal |url= https://cerncourier.com/a/hera-leaves-a-rich-legacy-of-knowledge/ |title=HERA leaves a rich legacy of knowledge |author1=Heuer, R.-D. |author2=Wagner, A. |journal=CERN Courier |issue=47 |date=21 August 2007 |accessdate=19 August 2022}}</ref> 
HERA was used mainly to study the structure of [[proton]]s and the properties of [[quarks]], laying the foundation for much of the science done at the [[Large Hadron Collider]] (LHC) at the [[CERN]] particle physics laboratory today. HERA is the only [[lepton]]–proton collider in the world to date and was on the energy frontier in certain regions of the kinematic range. 

[[Image:HERA Tunnel.JPG|thumb|A small segment of the HERA tunnel. The proton beam is travelling in the large vacuum tube in the middle to the right, the electron beam tube is below that.]]
[[File:HERA-EWcurrents.webp|thumb|The [[Electroweak interaction|EW interaction]] is mediated to first order therefore when the momentum transfer-squared becomes bigger than the mass of the charged W and the neutral Z boson squared (<{{val|e=4}}) the magnitude of their differential cross sections become comparable so the charged and neutral currents (CC (red) & NC (blue)) appear indistinguishable but it also becomes lower so they look hard to distinguish from the massless photon too, that is EW unification starts to set in.<ref>{{Cite journal |last1=Abramowicz |first1=H. |last2=Abt |first2=I. |last3=Adamczyk |first3=L. |last4=Adamus |first4=M. |last5=Andreev |first5=V. |last6=Antonelli |first6=S. |last7=Antunović |first7=B. |last8=Aushev |first8=V. |last9=Aushev |first9=Y. |last10=Baghdasaryan |first10=A. |last11=Begzsuren |first11=K. |date=2015-12-08 |title=Combination of measurements of inclusive deep inelastic $${e^{\pm }p}$$scattering cross sections and QCD analysis of HERA data |journal=The European Physical Journal C |language=en |volume=75 |issue=12 |pages=580 |doi=10.1140/epjc/s10052-015-3710-4 |s2cid=118069424 |issn=1434-6052|doi-access=free |hdl=2318/1579270 |hdl-access=free }}</ref><ref>{{Cite web |title=DESY News: The most precise picture of the proton |url=https://www.desy.de/news/news_search/index_eng.html?openDirectAnchor=829 |website=desy.de |language=en}}</ref><ref>{{Cite web |title=Douglas Hasell ZEUS |url=http://www.mit.edu/~hasell/DKH_zeus.html |website=mit.edu}}</ref>]]

To collide protons with either electrons or positrons, HERA used mainly [[superconducting magnets]], which was also a world first. At HERA, it was possible to study the structure of protons up to 30 times more accurately than before. The resolution covered structures 1/1000 of the proton in size, facilitating many discoveries concerning the composition of protons from quarks and [[gluon]]s.

The HERA tunnel runs 10 to 25&nbsp;m below ground level and has a [[circumference]] of 6.3&nbsp;km and an inner diameter of 5.2&nbsp;m. For the construction, the same technology was used as for the construction of subway tunnels. Two [[storage ring]]s were located on top of each other inside the tube. One accelerated electrons to energies of 27.5&nbsp;GeV, the other one protons to energies of 920&nbsp;GeV in the opposite direction. Both beams completed their circle nearly at the speed of light, making approximately {{val|47000}} revolutions per second.

There are four [[Interaction point|interaction regions]] around the ring, which were used by the experiments [[H1 (particle detector)|H1]], [[ZEUS (particle detector)|ZEUS]], [[HERMES experiment|HERMES]] and [[HERA-B]]. All these experiments were [[particle detector]]s run by international groups of researchers. These groups developed, constructed and ran the multi-storey, complex measurement devices in many years of cooperative work and evaluated enormous amounts of data.