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A Nobel discovery

Hunting the heavyweights with ua1 and ua2.

UA1 and UA2 were two experiments at CERN’s Super Proton Synchrotron (SPS) accelerator which started taking data in 1981 when the SPS first operated as a proton–antiproton collider. At the time, one of the hottest challenges in particle physics was the hunt for the force-carrier particles predicted by electroweak theory. Named the W and Z bosons, these were heavy particles, so finding them would require an accelerator that could reach an unprecedented level of energy.

Physicists David Cline, Peter McIntyre and Carlo Rubbia suggested modifying CERN’s biggest and newest accelerator at the time, the SPS, from a one-beam accelerator into a two-beam collider. This would collide a beam of protons with a beam of antiprotons, greatly increasing the available energy in comparison with a single beam colliding against a fixed target. Simon Van de Meer at CERN had already invented a way of producing and storing dense beams of protons or antiprotons. The two ideas, combined with the huge effort to develop new technology and engineering at CERN, eventually led to the historic discovery of the W and Z bosons in 1983 by UA1 and UA2.

The discovery was so important that the two key scientists behind the discovery received the Nobel Prize in Physics only a year later. The prize went to Carlo Rubbia, instigator of the accelerator’s conversion and spokesperson of the UA1 experiment, and to Simon van der Meer, whose technology was vital to the collider’s operation.

This was a significant achievement in physics that further validated the electroweak theory. It also helped to secure the decision to build CERN’s next big accelerator, the Large Electron Positron collider, whose job was to mass-produce Z and W bosons for further studies.

Origins of the hunt

In the 1960s three physicists, Steven Weinberg, Abdus Salam and Sheldon Glashow, proposed a theory. They believed that two of the four fundamental forces – the electromagnetic force and the weak force – were in fact different facets of the same force. Under high-energy conditions (such as in a particle accelerator), the two would merge into the electroweak force.

No scientific theory can become established without a solid grounding of experimental proof. The first evidence in support of the theory emerged when the Gargamelle detector at CERN found the neutral current, an essential ingredient to the electroweak theory. Further observations followed to secure the three theorists a Nobel Prize in 1979. However, there were still three hypothetical force-carrier particles described by the theory that no one had managed to find. The W + , W - and the Z 0 bosons remained tantalisingly out of reach until an accelerator could be built with high enough energy to carry out the search – a problem solved by the conversion of the SPS accelerator.

Related links

• Tracking down the weak force
• Nobel prizes
• The W and Z particles: a personal recollection
• When CERN saw the end of the alphabet

CERN Accelerating science

• Archives of the UA1 Collaboration, Underground Area 1 Collaboration

Identity Statement | Context | Content and Structure | Conditions of access and use | Allied materials | Description control | Database

Identity Statement [Top]

Reference code(s).

CERN-ARCH-UA1

From 1978 to 1993

Level of description

Extent of the unit of description.

240 boxes; 27 linear meters; 293 items

Context [Top]

Name of creator.

CERN (Geneva, Switzerland), UA1 Collaboration.

Administrative history

The UA1 project began in 1976; the idea was to detect the communicators of weak interaction (W and Z bosons), which had been postulated but never observed. To achieve this goal, the experiment planned to collide proton beams with antiproton beams in the Super Proton Synchrotron with an energy of 270 GeV. The problem, which Van der Meer solved, was to stock large amounts of antiprotons.

A new type of detector to see the hypothetical bosons. One of the most important and technically advanced items was the large drift chamber, called the central detector. This drift chamber was 6 meters in length and over 2 meters in diameter. The UA1 experiment also had an electromagnetic calorimeter, a hadron calorimeter and a muon detector. The full detector weighed over 2000 tonnes. The results collected by the detector were recorded on magnetic tapes. Carlo Rubbia managed the construction of this large detector.

In summer 1981 the first collision between protons and antiprotons was recorded. The first experiments began in November 1981. At the beginning of 1982 two accidents damaged the UA1 detector, so the experiment was stopped until summer 1982. UA1 and UA2 experiments started again in September 1982 until December 1982, when the accelerators were switched off for two months. During this time data were analysed and physicists were convinced of having discovered the W boson. This was announced in a press conference held on 25 January 1983. The next step was the discovery of Z boson. The experiments on SPS began again on April 1983, and there were soon major results. On 1 June 1983 CERN formally announced the discovery of the Z boson.

The discovery of W and Z bosons ld to a Nobel prize for Carlo Rubbia and Simon Van der Meer: "The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 1984 jointly to Professor Carlo Rubbia, CERN, Geneva, Switzerland and Dr Simon Van der Meer, CERN, Geneva, Switzerland, for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction".

Immediate source of acquisition or transfer

Received from Alan Norton the 30th May 1995. Received from Lutz Naumann the 30th May 1995. Received from Guy Maurin the 30th May 1995. Received from Antoine Lévêque in April 2000.

Content & Structure [Top]

Scope and content.

This collection contains reports, correspondence and official documents related to UA1 Collaboration. It gives an overview of a large, international scientific collaboration.

Appraisal, destruction and scheduling information

All items have been kept in the order in which they were received. Nothing was destroyed.

No further accruals are expected.

System of arrangement

Conditions of access and use [Top]

Conditions governing access.

See file level description and the CERN operational circular No 3 : rules applicable to archival material and archiving at CERN. In general, records on any subject that are over 30 years old, and all records of a purely scientific nature, may be consulted.

Conditions governing reproduction

Copyright is retained by CERN, no reproduction without permission.

Language / scripts of material

Most of the material is written in English.

Finding aids

Listed to file level in the CERN Archives Database.

Allied materials [Top]

Related units of description.

The UA1 Collaboration contains documents concerning similar experiments, but with a different technology.

For a complete (and quite easy to understand) description of the experiments of UA1 and UA2 Collaborations, see : WATKINS, Peter Maitland: Story of the W and Z, 1986.

The central part of the UA1 detector is exposed in the Microcosm since 1999.

Description control [Top]

Archivist's note.

Description prepared by Maryse Moskofian. ISAD(G) description by Marc Reymond.

Date(s) of description

Collection: Geneva, May 2001. ISAD(G) description: Geneva, June 2002. Revised 2007.

• CERN Archives
• Archives guide
• Experimental physics
• Experiments, Detectors and Committees - Super Proton Synchrotron, SPS

The end of the alphabet

In 1983, CERN reached the end of the alphabet when the Laboratory announced the discovery of the long-sought W and Z particles. The announcement was so momentous that, the following year, the two scientists behind the discovery received the Nobel Prize in Physics . In 1984, Carlo Rubbia , the instigator of the conversion of the Super Proton Synchrotron (SPS) into a proton–antiproton collider and spokesman of the UA1 experiment , and Simon van der Meer, who invented the stochastic cooling technology vital to the collider’s operation, received the award from the Nobel Foundation.

To understand the importance of the discovery, one has to go back to three previous Nobel laureates. In the 1960s, Steven Weinberg, Abdus Salam, and Sheldon Glashow had proposed that the electromagnetic force and the weak force – which is responsible, for example, for some types of radioactivity – were both manifestations of a single interaction. According to this theory, three heavy particles, the W + , W – and Z 0 bosons, are responsible for the “electroweak” force between particles.

First evidence of this unified force had already been found at CERN in 1973 by the Gargamelle experiment. But there was still no trace of the famous W and Z bosons, which were too heavy to be produced by the accelerators that existed at that time. The boson hunters were certainly not short of ideas, however. In 1976, David Cline, Peter McIntyre and Carlo Rubbia put forward the idea of converting CERN’s largest accelerator, the SPS, which had just come into operation, into a proton–antiproton collider, which would create sufficiently high energy levels to produce the long-awaited bosons.

It took only three years to transform the accelerator, between 1978 and 1981, during which time two experiments UA1 and UA2 were developed. The two detectors had the same main objective, the hunt for the W and Z bosons, but they differed in many ways. UA1, led by Carlo Rubbia, was the first of the large-scale collaborations, consisting of around 130 physicists. Its detector, which was huge for the time, weighed no less than 2000 tonnes. It had also been set numerous scientific objectives. UA2, which was designed specifically to search for the W and Z particles, was ten times smaller, and brought together a group of some 50 scientists.

The SPS recorded its first proton–antiproton collisions in July 1981. At the end of 1982, around one million events potentially providing evidence for the W and Z bosons had been recorded. On 21 January 1983, the UA1 team announced the discovery of the two W particles, which was confirmed by UA2. Ten times more W bosons were produced during the spring. In May, CERN announced the discovery of the third intermediate boson, the Z 0 .

Beyond its significance as a physics result, the discovery of the W and Z bosons was fundamental in reinforcing the conviction within the scientific community of the need to build the Large Electron Positron (LEP) accelerator, which came into service in 1989. LEP was a veritable Z factory – producing some 20 million Z particles – before becoming a W factory, and so measured the properties of both bosons with extreme precision.

Recollections

The discovery of the W and the Z, promptly recognised by the Nobel Committee, was then so to speak “the tip of the iceberg” of a marvellous and unique adventure in which so many remarkable people from so many different countries […] have proudly contributed. Carlo Rubbia

Carlo Rubbia’s name is closely related to the discovery of the W and Z particles at CERN. In 1984, he was awarded the Nobel Prize in Physics, together with Simon van der Meer, for the work he had done as head of the UA1 collaboration. During his mandate as Director-General of CERN from 1989 to 1993, the Large Electron Positron collider was inaugurated and the four LEP experiments gave their first results.

“I came to CERN for the first time in 1960. Even now, I feel as motivated and enthusiastic for institutionalised international cooperation as I was on the first day, at the time when such an innovative concept, so popular nowadays, was essentially unknown.

CERN was born by a remarkable group of founders, at the threshold of a renewed European prosperity, to promote pure science on a global European scale and to create trust and unity between people of different countries, traditions and mentalities, after the disasters of the Second World War.

CERN has been for us an extraordinary “melting pot”, gathering a large number of remarkable and very young talents from many different countries. Living together – so to say “under the same roof” – and with a satisfactory adequacy of resources, we have been able to operate in a unique climate of absolute scientific freedom with an immense enthusiasm and motivation. We all have enjoyed a “sum-plus”, in which the resultant combination of the team has been far more relevant than the sum of the separate contributions of each of us.

The originality of the CERN accelerator community has been evident from the beginning, with the realisation of the first strong-focusing proton accelerator by John Adams, then in his thirties, and by the remarkable team he had built up. He had the courage of cancelling the already approved 10 GeV weak focusing for a totally innovative 25 GeV Proton Synchrotron. The next adventure was the realisation of the Intersecting Storage Rings, the ISR, which acted as a “reference” for all the subsequent projects, and which was made possible by the vision of the then Director-General, Viki Weisskopf.

However, the physics results, mostly because of non-optimal choices in the instrumentation at those times, were probably, in retrospect, below what they should have been. But the many accelerator innovations, learned with the ISR, allowed features for the SPS that were far more advanced than the ones at Fermilab in the United States, a relatively conventional accelerator, thus making possible a subsequent fast conversion into the SPS collider. An excellent accelerator, the SPS already had all the basic features to become a collider. All that was needed was an “industrial” antiproton source, at a time when even a handful of antiprotons was considered a success. This required overcoming the so-called Liouville theorem, amplifying early studies performed at the ISR by Wolfgang Schnell and Simon van der Meer. Enthusiasm and drive were so high that this jewel, the Antiproton Accumulator was built in less than two years!

The marvellous chain of new accelerators, SPS first and LEP later, have been complemented by the development at CERN of a number of equally revolutionary instrumentation technologies, such as the wire and drift chambers, the calorimeter (Herwig Schopper), and so on, without which all important discoveries in the field world-wide would have been impossible and for which Georges Charpak well deserved his Nobel Prize.

The discovery of the W and the Z, promptly recognised by the Nobel Committee, was then so to speak “the tip of the iceberg” of a marvellous and unique adventure in which so many remarkable people from so many different countries, several of whom unfortunately no longer with us, have proudly contributed.

In order to assess the importance of what has been accomplished by the CERN teams in those days, it is sufficient to point out that until the LHC, the world’s hadronic high-energy frontier was dominated by two proton–antiproton colliders, the first entirely developed at CERN and the second incremented in energy with the Tevatron at Fermilab.

We have tremendously enjoyed this epoch of CERN: we are proud of what we have been able to accomplish. To quote Simon van der Meer: “If they have some idea – however crazy it is – they should check up on it. Once in a hundred times it will turn out to be a good idea.””

This interview is adapted from the 2004 book “Infinitely CERN”, published to celebrate CERN’s 50th anniversary.

UA1 experiment

The UA1 experiment (an abbreviation of Underground Area 1) was a high-energy physics experiment that ran at CERN 's Proton-Antiproton Collider (SppS), a modification of the one-beam Super Proton Synchrotron (SPS). The data was recorded between 1981 and 1990. The joint discovery of the W and Z bosons by this experiment and the UA2 experiment in 1983 led to the Nobel Prize for physics being awarded to Carlo Rubbia and Simon van der Meer in 1984. Peter Kalmus and John Dowell, from the UK groups working on the project, were jointly awarded the 1988 Rutherford Medal and Prize from the Institute of Physics for their outstanding roles in the discovery of the W and Z particles.

It was named as the first experiment in a CERN "Underground Area" (UA), i.e. located underground, outside of the two main CERN sites, at an interaction point on the SPS accelerator, which had been modified to operate as a collider. The UA1 central detector was crucial to understanding the complex topology of proton-antiproton collisions. It played a most important role in identifying a handful of W and Z particles among billions of collisions.[1]

Section of the UA1 detector at Museo nazionale della scienza e della tecnologia Leonardo da Vinci of Milan

After the discovery of the W and Z boson, the UA1 collaboration went on to 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. In June 1984, Carlo Rubbia at the UA1 experiment expressed to the New York Times that evidence of the top quark "looks really good".[2] Over the next months it became clear that UA1 had overlooked a significant source of background.[3] The top quark was ultimately discovered in 1994–1995 by physicists at Fermilab with a mass near 175 GeV.

The UA1 was a huge and complex detector for its day. It was designed as a general-purpose detector.[4] The detector was a 6-chamber cylindrical assembly 5.8 m long and 2.3 m in diameter, the largest imaging drift chamber of its day. It recorded the tracks of charged particles curving in a 0.7 Tesla magnetic field, measuring their momentum, the sign of their electric charge and their rate of energy loss (dE/dx). Atoms in the argon-ethane gas mixture filling the chambers were ionised by the passage of charged particles. The electrons which were released drifted along an electric field shaped by field wires and were collected on sense wires. The geometrical arrangement of the 17000 field wires and 6125 sense wires allowed a spectacular 3-D interactive display of reconstructed physics events to be produced.[5]

The UA1 detector was conceived and designed in 1978/9, with the proposal submitted in mid-1978.[6] See also

UA2 experiment List of Super Proton Synchrotron experiments

http://worldwidescience.org/topicpages/u/ua1+central+detector.html Sullivan, Walter. "Physicists May Have Tracked Last Quark to Lair" (25 June 1984). The New York Times. Retrieved 23 June 2017. Staley, Kent W. (2004). The Evidence for the Top Quark: Objectivity and Bias in Collaborative Experimentation. Cambridge University Press. p. 80. http://cerncourier.com/cws/article/cern/28849/1/cernwz2_5-03 http://worldwidescience.org/topicpages/u/ua1+central+detector.html

"When CERN saw the end of the alphabet". CERN Courier. 1 May 2003.

Further reading "UA1 magnet sets off for a second new life". CERN Courier. 13 March 2008. "The W and Z Particles: A Personal Recollection". CERN Courier. 1 April 2004. "Neutral currents and W and Z: a celebration". CERN Courier. 9 December 2003.

Physics Encyclopedia

Retrieved from "http://en.wikipedia.org/" All text is available under the terms of the GNU Free Documentation License

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First Results of the UA1 Experiment

Cite this chapter.

• M. Pimiä 3  

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The CERN SPS proton-antiproton collider had several short machine development and physics runs during autumn 1981. Figure 1 shows the luminosity achieved during the runs in December 1981. The peak luminosity was 5*10 27 cm −2 s −1 , still far from the design value of 10 30 cm −2 s −1 . For the November and December runs the integrated luminosity amounted to

This talk was presented by M. Pimiä in collaboration with (UA1 Collaboration, CERN): G. Arnison, 10 A. Astburg 10 B. Aubert, 2 C. Bacci 9 R. Bernabei, 9 A. Bézauet, 4 R. Böck, 4 T. J. V. Bowcock, 6 M.Calvetti, 4 P. Catz, 2 S. Centro, 4 F. Ceradini, 9 S. Cittolin, 4 A. M. Cnops, 4 C. Cochet, 11 J. Colas, 2 M. Corden, 3 D. Dallman, 12 S. D’Angelo, 9 M. DeBeer 11 M. Della Negra, 2 M. Demoulin, 4 D. Denegri, 1l D. DiBitonto, 4 Dobrzynski, 7 J. D. Dowell, 3 M. Edwards, 3 K. Eggert, 1 E. Eisenhandler, 6 N. Ellis, 3 P. Erhard, 1 H. Faissner, 1 G. Fontaine, 7 J. P. Fournier, 11 R. Frey, 8 R. Frühwirth, 12 G. Garvey, 3 S. Geer, 7 C. Ghesquiére, 7 P. Ghez, 4 K. L. Giboni, l W. R. Gibson, 6 Y. Giraud-Heraud, 7 A. Givernaud, 11 A. Gonidec, 2 G. Grayer, l0 P. Gutierrez, 8 R. Haidan, 4 T. Hansi-Kozanecka, l W. J. Haynes 10 L. O. Hertzberger,* C. Hodges, 8 D. Hoffmann, 1 H. Hoffmann, 4 D. J . Holthuizen,* R. J. Homer, 3 A. Honma, 6 W. Jank, 4 P. I. P. Kalmus, 6 V. Karimäki, 5 R. Keeler, 6 I. Kenyon, 3 A. Kernan, 8 R. Kinnunen, 5 H. Kowalski, 4 W. Kozanecki, 8 D. Kryn, 7 F. Lacava, 4 J. P. Laugier 11 J. P. Lees, 2 H. Lehmann 1 R. Leuchs 1 A. Leveque l D. Linglin, 2 E. Locci, 11 G. Maurin, 4 T. McMahon, 3 J. P. Mendiburu, 7 M. N. Minard, 2 M. Moricca, 9 F. Muller, 4 A. K. Nandi 10 L. Naumann, 4 A. Norton, 4 A. Orkin-Lecourtois, 7 L. Paoluzi, 7 G. Piano Mortari 4 M. Pimiä, 5 A. Placci, 4 E. Radermacher, l J. Kansdell, 8 H. Reithler, 1 J. P. Revo1, 4 J. Rich, 11 M. Rijssenbeek, 4 C. Roberts, 11 C. Rubbia, 4 B. Sadoulet, 4 G. Sajot, 7 G. Salvi 6 G. Salvini, 9 J. Sass, 11 J. Saudraix 11 A. Savoy Navarro, l1 D. Schinzel, 4 W. Scott, l0 T. P. Shah, 10 M. Spiro, 11 J. Strauss, 12 K. Sumorok 3 F. Szoncso, 12 C. Tao, 4 G. Thompson, 6 E. Tscheslog,j J. Tuominìemi, 5 J. P. Vialle, 4 J. Vrana, 7 V. Vuillemìn, 4 H. Wahl, 12 P. Watkins, 3 J. Wilson, 3 M. Yvert, 2 E. Zurfluh. 4

Aachen l -Annecy (LAPP) 2 -Birmingam 3 -CERN 4 Helsinki 5 -Queen Mary College, London 6 -Paris (Coll. de France) 7 -Riverside 8 - Roma 9 -Rutherford Appleton Lab. 10 -Saclay (CEN) 11 Vienna 12 - Collaboration.

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Pimiä, M. (1983). First Results of the UA1 Experiment. In: Carlson, P., Trower, W.P. (eds) Physics in Collision. Springer, Boston, MA. https://doi.org/10.1007/978-1-4684-8465-6_3

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CERN Accelerating science

W and z particles discovered.

In 1979, CERN decided to convert the Super Proton Synchrotron (SPS) into a proton–antiproton collider. A technique called stochastic cooling was vital to the project's success as it allowed enough antiprotons to be collected to make a beam.

The first proton–antiproton collisions were achieved just two years after the project was approved, and two experiments, UA1 and UA2, started to search the collision debris for signs of W and Z particles, carriers of the weak interaction between particles.

In 1983, CERN announced the discovery of the W and Z particles.The image above shows the the first detection of a Z0 particle, as seen by the UA1 experiment on 30 April 1983. The Z0 itself decays very quickly so cannot be seen, but an electron–positron pair produced in the decay appear in blue. UA1 observed proton-antiproton collisions on the SPS between 1981 and 1993 to look for the Z and W bosons, which mediate the weak fundamental force.

Carlo Rubbia and Simon van der Meer , key scientists behind the work, received the Nobel Prize in physics only a year after the discovery. Rubbia instigated conversion of the SPS accelerator into a proton-antiproton collider and was spokesperson of the UA1 experiment while Van der Meer invented the stochastic cooling technique vital to the collider’s operation.

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UA1 magnet sets off for a second new life

A magnet built originally for the UA1 detector at CERN and later used by the NOMAD experiment has set sail for a new life in Japan. Thirty-five containers carrying 150 pieces departed CERN in the last two weeks of January, with the last components – the large aluminium coils – following in March.

In 2005, at the request of European physicists involved in the international Tokai to Kamioka (T2K) long-baseline neutrino experiment, CERN decided to donate the former UA1 magnet, its coils and other equipment to KEK in Japan. For T2K, which will start in autumn 2009, the Japan Proton Accelerator Research Complex at Tokai will use a 40 GeV proton beam to produce an intense low-energy neutrino beam directed towards the Super-Kamiokande neutrino observatory 300 km away.

Built in 1979, the UA1 magnet was later given a second lease of life with the NOMAD neutrino-oscillation experiment at CERN. Since NOMAD was dismantled in 2000, the magnet has been stored in the open air, exposed to the elements, at CERN’s Prévessin site. All the parts were cleaned, polished and repainted before shipment to Japan, including a general overhaul in readiness for transport. However, many of the parts could not be transported in one piece, especially by sea, so much of the equipment had to be dismantled before being loaded into containers.

The general overhaul, and other work needed to prepare the parts for shipping, took almost a year. On 14 January, one by one, 35 sea-going containers began their long journey to Tokai, 60 km north of Tokyo. They first travelled by train to Antwerp, from where they were bound for the port of Hitachinaka via Pusan, in South Korea. The final, and largest, component – consisting of the four very fragile coils – was scheduled to leave CERN at the end of March. With a height of 4.75 m, the aluminium coils weigh close to 40 tonnes and have been packaged into two 1.70 m wide consignments for transport as an exceptional lorry load to Basel, then by barge to Rotterdam to set sail for Japan.

In focus: detector technology

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CERN Accelerating science

The detector at Underground Area 1 scoured a billion proton-antiproton collisions from the Super Proton Synchrotron for traces of W and Z particles

UA1 (Underground Area 1) was a  particle detector at the Super Proton Synchrotron (SPS). It ran from 1981 until 1990, when the SPS was used as a proton-antiproton collider, searching for traces of W and Z particles in collisions.

Two moveable detectors – UA1 and UA2 – were custom built around the SPS beam pipe for use during proton-antiproton running. They could be rolled back after periods of collision data taking, so that the SPS could revert to fixed-target operation.

The central detector of UA1 was a six-chambered cylinder, 5.8 metres long and 2.3 metres in diameter. It was the largest imaging drift chamber of its day. Charged particles passing through the detector would ionise molecules in the argon-ethane gas mixture inside, releasing electrons. The electrons drifted along an electric field shaped by 170,00 field wires and were collected on 6125 sense wires. The geometric arrangement of these wires allowed UA1 physicists to reconstruct collision events in three dimensions.

UA1 recorded the tracks of charged particles curving in a 0.7 Tesla magnetic field, measuring their momentum, the sign of their electric charge and their rate of energy loss. An 800-tonne conventional electromagnet provided the field using thin aluminium coils enclosing a region of 85 cubic metres. Around the central detector and inside the magnet were 48 electromagnetic subdetectors. Made from layers of lead, their boat-like shape earned them the nickname "gondolas".

Outside the magnet were the calorimeters – detectors that measured the energy particles lost as they passed through. The electromagnetic calorimeter measured the energy of electrons and photons while the hadronic calorimeter sampled the energy of hadrons (particles containing quarks, such as protons and neutrons).

One type of particle, the muon, interacts very little with matter – it can travel through metres of dense material before it is stopped. For this reason, muon chambers – tracking devices specialized for detecting muons – usually make up the outermost layer of a detector. The UA1 detector was no exception: The slab-like arrays of muon chambers that covered the outside of UA1 required some 30 kilometres of extruded aluminium.

The discovery of the W boson in January 1983 was a highlight of the UA1 detector's life. UA1 later informed the design of the multipurpose, “hermetic” detectors developed for the Large Electron Positron Collider and the Large Hadron Collider .

You can see UA1's central detector at the Microcosm exhibit at CERN

CERN Accelerating science

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CERN Accelerating science

The detector at Underground Area 1 scoured a billion proton-antiproton collisions from the Super Proton Synchrotron for traces of W and Z particles.

CERN70: The end of the alphabet

Carlo Rubbia’s name is closely related to the discovery of the W and Z particles at CERN. In 1984, he was awarded the Nobel Prize in Physics, together with Simon van der Meer, for the work he had done as head of the UA1 collaboration

Symposium: Celebrating electroweak milestones | 31 October

CERN Science Gateway will host its first scientific event to celebrate 50 years since Gargamelle discovered neutral currents and 40 years since UA1 and UA2 discovered the W and Z bosons

Symposium: Celebrating electroweak milestones...

W boson turns 40.

Forty years ago today, physicists at CERN announced to the world that they had discovered the electrically charged carrier of the weak force, one of nature’s four fundamental forces

Higgs10: Three-quarters of the way there

The direct discovery of the W and Z bosons at the SppS in 1983 provided solid experimental support for the existence of the Higgs boson

W boson published 30 years ago

On 24 February 1983 the journal <em>Physics Letters B</em> published a paper by the UA1 collaboration describing the discovery of the W boson

CERN Accelerating science

Thirty years of the Z boson

Thirty years ago this week physicists at CERN announced that they had directly observed the Z boson

31 May, 2013

By Kelly Izlar

This image taken by the UA1 experiment at CERN on 30 April 1983 was later confirmed to be the first detection of a Z particle (Image: UA1/CERN)

On 1 June 1983 physicists at CERN announced that they had directly observed the  Z boson . This discovery was greeted with jubilation as it confirmed the electroweak theory, a cornerstone of the Standard Model of particle physics developed during the 1970s.

Although physicists working with the Gargamelle bubble chamber at CERN had presented the first indirect evidence of Z bosons a decade earlier, the first definitive observation arose out of research done at the Super Proton Synchrotron (SPS) accelerator at CERN.

In the late 1970s, physicists Carlo Rubbia, Peter McIntyre and David Cline suggested upgrading the SPS from a one-beam particle accelerator to a two-beam particle collider. Smashing protons and antiprotons head-on would create enough energy to produce Z particles, as well as the related W bosons .

The new face of the SPS incorporated stochastic cooling , a technique used to collect and cool antiprotons that had been invented by Simon van de Meer at CERN in 1968.

Two detectors, UA1 and UA2, were positioned at different points around the collider to collect particle debris from the high-energy collisions. The physicists began sifting through collision data in 1981, and just two years later they found the first unambiguous signals of the Z boson. The discovery of Z bosons was an extraordinary technical triumph, confirming a critical aspect of the Standard Model. Carlo Rubbia and Simon van der Meer received the 1984 Nobel prize in physics for the discovery.

Their work was expounded upon by research at the Large Electron-Positron collider – approved by the CERN Council in 1981 and commissioned eight years later – which produced millions of Z bosons for precise measurements of electroweak interactions.

During 11 years of research, LEP's experiments provided a detailed study of the electroweak interaction. LEP was closed down on 2 November 2000 to make way for the construction of the  Large Hadron Collider  in the same tunnel.

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