Editing UA2 experiment (section)

==Results==
[[File:UA2 UA1 press conference, 25 January 1983.jpg|thumb|262px|Press conference on 25 January 1983 when the announcement was made of the discovery of the [[W and Z boson|W boson]] at [[CERN]]. From right to left: [[Carlo Rubbia]], spokesperson of the [[UA1 experiment]]; [[Simon van der Meer]], responsible for developing the [[stochastic cooling]] technique; [[Herwig Schopper]], Director-General of CERN; [[Erwin Gabathuler]], Research Director at CERN, and [[Pierre Darriulat]], spokesperson of the UA2 experiment.]]

===Hadronic jets at high transverse momentum===
The very first result of the UA2 collaboration, published on 2 December 1982, was the first unambiguous observation of hadronic jet production at high transverse momentum from hadronic collisions.<ref>{{cite journal |last1=UA2 Collaboration |date=2 December 1982 |title=Observation of very large transverse momentum jets at the CERN ppbar collider |url=  https://cds.cern.ch/record/904153|journal=Phys. Lett. B |volume=118 |issue=1–3 |pages=203–210 |doi=10.1016/0370-2693(82)90629-3 |bibcode=1982PhLB..118..203B }}</ref> Observations of hadronic jets confirmed that the theory of [[quantum chromodynamics]] could describe the gross features of the strong [[Parton (particle physics)|parton]] [[strong interaction|interaction]].<ref name=Jenni/>

===Discovery of the W and Z bosons===
The UA2 and UA1 collaboration chose to search for the W boson by identifying its [[lepton]]ic decay, because the [[hadron]]ic decays, although more frequent, have a larger background.<ref name=Rubbia/> By the end 1982, the Sp{{overline|p}}S had reached high enough luminosity to permit the observation of <math> W \rightarrow e \nu </math> and <math> W \rightarrow \mu \nu </math> decays. On 22 January 1983, the UA2 collaboration announced that the UA2 detector had recorded four events that were candidates for a W boson. This brought the combined number of candidate events seen by UA1 and UA2 up to 10.  Three days later, CERN made a public announcement that the W boson was found.<ref name=WCERN>{{cite web |last=O'Luanaigh |first=Cian |date=12 March 2015 |title=Carrying the Weak Force: Thirty Years of the W boson |url=https://home.cern/about/updates/2013/01/carrying-weak-force-thirty-years-w-boson |publisher=CERN |access-date=21 June 2017}}</ref>

The next step was to track down the Z boson. However, the theory said that the Z boson would be ten times rarer than the W boson. The experiments therefore needed to collect several times the data collected in the 1982 run that showed the existence of the W boson. With improved techniques and methods, the luminosity was increased substantially.<ref name=Experiments>{{cite web |url=https://cern-discoveries.web.cern.ch/cern-discoveries/Courier/experiments/Experiments.html |title=The experiments |date=1983 |publisher=CERN Courier, CERN Discoveries |access-date=22 June 2017}}</ref> These efforts were successful, and on 1 June 1983, the formal announcement of the discovery of the Z boson was made at CERN.<ref>{{cite web|url=https://home.cern/about/updates/2013/05/thirty-years-z-boson|title=Thirty years of the Z boson {{!}} CERN|website=home.cern|language=en|access-date=2017-06-23}}</ref>

===Search for the top quark===
Throughout the runs with the upgraded detector, the UA2 collaboration was in competition with experiments at [[Fermilab]] in the US in the search for the [[top quark]]. Physicists had anticipated its existence since 1977, when its partner — the [[bottom quark]] — was discovered. It was felt that the discovery of the top quark was imminent.

During the 1987-1990 run UA2 collected 2065 <math> W \rightarrow e \nu </math> decays, and 251 Z decays to electron pairs, from which the ratio of the mass of the W boson and the mass of the Z boson could be measured with a precision of 0.5%.<ref name=Rubbia/> By 1991 a precise measurement for the mass of the Z boson from LEP had become available. Using the ratio of the W mass to Z mass, a first precise measurement of the W mass could be made. These mass values could be used to predict the top quark from its virtual effect on the W mass. The result of this study gave a top quark mass value in the range of 110 GeV to 220 GeV,<ref name=Rubbia/> beyond the reach for direct detection by UA2 at the Sp{{overline|p}}S. The top quark was ultimately discovered in 1995 by physicists at Fermilab with a mass near 175 GeV.<ref name=CDF-1995>{{cite journal |author=F. Abe|display-authors=etal |year=1995 |title=Observation of Top Quark Production in {{SubatomicParticle|Antiproton}}{{SubatomicParticle|Proton}} Collisions with the Collider Detector at Fermilab |journal=[[Physical Review Letters]] |volume=74 |issue=14 |pages=2626–2631 |doi=10.1103/PhysRevLett.74.2626 |pmid=10057978 |bibcode=1995PhRvL..74.2626A|arxiv=hep-ex/9503002 |hdl=2241/103691 |s2cid=119451328 |url=https://zenodo.org/record/1233901 }}</ref><ref name=D0-1995>{{cite journal |author=S. Abachi|display-authors=etal  |year=1995 |title=Search for High Mass Top Quark Production in {{SubatomicParticle|Proton}}{{SubatomicParticle|Antiproton}} Collisions at {{radical|''s''}}&nbsp;=&nbsp;1.8&nbsp;TeV |journal=[[Physical Review Letters]] |volume=74 |issue=13 |pages=2422–2426 |doi=10.1103/PhysRevLett.74.2422 |pmid=10057924  |bibcode=1995PhRvL..74.2422A|arxiv=hep-ex/9411001 |s2cid=119392677 }}</ref>