UA1 detector

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The UA1 detector was a particle detector at the Super Proton Synchrotron at CERN .

View into the central drift chamber of the UA1 detector
Central drift chamber of the UA1 detector

history

In the search for a quick and inexpensive way to generate the previously undiscovered W and Z bosons , a proposal was submitted to CERN in 1977 to convert the Super Proton Synchrotron (SPS), which had just been put into operation a year earlier, into a proton - antiproton -Collider to be rebuilt in order to have enough energy to generate the new particles. Two detectors were planned to detect the particles, UA1 and UA2. In 1978 the plans to rebuild the SPS and to build the UA1 detector were decided. The development was led by Carlo Rubbia .

The converted PLC and the new detectors went into operation in July 1981.

In 1983 the observation of the W and Z bosons was published, for which the Nobel Prize in Physics was awarded to Carlo Rubbia and Simon van der Meer the following year .

In 1987 the "Antiproton Collector" was put into operation to increase the luminosity of the SPS by a factor of about 10.

With the UA1 detector, they participated in the search for the previously undiscovered top quark . The energy range covered corresponded to a quark mass of 60 GeV / c².

Operation continued until 1989. After the UA1 detector at the SPS had ended, the magnet was used in the NOMAD neutrino oscillation experiment at CERN from 1991 to 1999 . In 2005 it was decided to donate the magnet, which has meanwhile been stored outdoors, to the J-PARC near Tokai for the T2K experiment to investigate the neutrino oscillation . The magnet has since been rebuilt in Japan.

technology

The UA1 detector had the dimensions of about 6x6x10 m, weighed about 2000 t and consisted of several systems arranged concentrically around the collision center.

Micro vertex detector

UA1 detector, Museo nazionale della scienza e della tecnologia Leonardo da Vinci , Milan.

From 1985, the UA1 detector had a drift chamber within the central detector, the Micro Vertex Detector (MVD). With the MVD, particle tracks could be reconstructed with an accuracy of up to 65 µm.

The MVD had an outside diameter of 18 cm, the beryllium beam pipe with a diameter of 5 cm and a wall thickness of 1 mm ran through it centrally . The chamber had a length of 8 m and was filled with a mixture of 53% argon and 47% ethane at 3 bar. The wires each ran parallel to the beam pipe, with a fast comparator for evaluating the difference signal being connected between the two ends of the 256 signal wires for longitudinal spatial resolution.

Later, the detector's metal tubes were replaced with carbon fiber ones to reduce scattered radiation .

Central drift chamber

The central drift chamber was used to reconstruct particle tracks and enabled a spatial resolution of the trajectories of 100–300 µm. The functionality of the drift chamber was based heavily on the bubble chambers that had been common up to that point .

The central chamber was 6 m long, had an outer diameter of 2.2 m and was filled with 60% ethane and 40% argon at ambient pressure. The outer shell had a thickness of 5 cm and was built in a plastic sandwich construction. The pulling of the wires caused the shell to be deformed by 8 cm. The correct tension of each individual wire was adjusted like tuning a piano by mechanically vibrating the wire and tuning it to the correct frequency.

6000 signal recording wires ran parallel to the magnetic field, arranged in planes and evenly distributed in 25 m 3 chamber volume. The distance between the wire planes was based on the drift speed of the ions and the frequency with which particle packets are collided with the SPS. The repetition time of the SPS was 3.8 µs, the maximum drift time 3.6 µs and the distance between the wire levels was 18 cm.

The chamber has been open to the public in the CERN Microcosm Museum since 1999.

calorimeter

Calorimeters are used to determine particle energies; the particles to be measured must be absorbed in the detector.

At the start of operation in 1981, the UA1 detector was equipped with an internal electronic and an external hadronic calorimeter. The calorimeters were made up of scintillators and lead absorbers and connected to photomultipliers above the magnetic core via fiber optics .

Since considerable radiation damage was already evident in the scintillators in 1984, a replacement by radiation-resistant calorimeters was planned, especially since further increases in luminosity were planned. From 1987 to 1989 the detector was operated without the electromagnetic calorimeter; the conversion to the new calorimeter lasted until 1989. The new calorimeters worked on the principle of an ionization chamber and consisted of layers 3.3 mm thick with tetramethyl Pentane-filled cells, alternating with layers of 2 mm depleted uranium , an outer calorimeter layer used 5 mm thick uranium absorber plates.

Almost the entire space around the collision center was closed with the calorimeters, only an opening angle of 0.2 ° on the jet pipe remained unobserved.

magnet

A magnetic field of 0.7 T perpendicular to the beam direction was generated in the UA1 detector in a volume of 80 m 3 . The winding of the magnet was made of aluminum. Large-area muon detectors were later built into the iron core.

Muon detector

Muons can penetrate the calorimeter and are detected by another layer of detectors. The entire magnet was surrounded by multilayer muon drift chambers that were crossed for two-dimensional location determination.

From the end of 1984 to August 1985, the muon detection system was expanded to include additional drift chambers with a total area of ​​800 m 2 and 50,000 channels. The new chambers were built into the iron core of the magnet. The walls of the iron core consist of three iron blocks, each 20 cm thick, riveted to one another, the drift chambers were placed between these blocks and also on the inside of the magnet. The new chambers made it possible, among other things, to track the curved trajectory of the muons in the iron core. The resolution of the system was between 300 µm and 1.2 mm. The chambers were operated with a filling gas of 75% isobutane and 25% argon at 5 mbar overpressure.

Web links

Commons : UA1-detector  - collection of images, videos and audio files

Individual evidence

  1. ↑ Pierre Darriulat: The W and Z particles: a personal recollection ( English ) CERN Courier. Oct. 4, 2004. Retrieved Jan. 9, 2010.
  2. ↑ a b CERN: CERN Scientific Information Service: The UA1 Collaboration collection, Underground Area 1 Collaboration ( English ) CERN. 2007. Retrieved May 14, 2010.
  3. ↑ A Nobel discovery Hunting the heavyweights with UA1 and UA2 ( English ) CERN. Retrieved Jan. 9, 2010.
  4. ↑ a b c K. Touminiemi: Search for the Top Quark in UA1 and in the other Hadron Collider Experiments . In: Acta Physica Polonica B . 21, No. 4-5, Nov. 15, 1990, pp. 327-343.
  5. ↑ a b D. Denegri: Top search in the UA1 ( English , PDF; 449 kB) CERN UA1 Collaboration. Jan 16, 1989. Retrieved May 14, 2010.
  6. ↑ Experiments at CERN: A 4 $ \ pi $ Solid Angle Detector for the SPS used as a Proton-Antiproton Collider at a Center of Mass Energy of 540 GeV ( English ) CERN. Retrieved Jan. 9, 2010.
  7. ↑ a b UA1 magnet sets off for a second new life ( English ) CERN Courier. March 13, 2008. Retrieved January 9, 2010.
  8. ↑ Koichiro Nishikawa, T2K spokesperson, KEK .: T2K: Tokai to Kamioka ( English ) CERN Courier. July 8, 2008. Retrieved January 9, 2010.
  9. ↑ a b c d Daniel Denegri: When CERN saw the end of the alphabet ( English ) CERN Courier. Retrieved May 1, 2003.
  10. ↑ Cennini et al .: A micro vertex detector for experiment UA1 at the CERN Sp $ \ overline {p} $ S collider ( English , PDF; 203 kB) CERN. Nov. 26, 1985. Retrieved May 6, 2010.
  11. ↑ a b J.D. Dowell: The UA1 experiment with ACOL ( English , PDF; 586 kB) 6th Topical Workshop on Proton-Antiproton Collider Physics. Nov 20, 1986. Retrieved Jan 9, 2010.
  12. ↑ UA1 Collaboration: The UA1 central detector ( English , PDF; 1.2 MB) CERN. Jan 27, 1990. Retrieved May 6, 2010.
  13. ↑ M. Krammer: Results from a full scale UA1 uranium-TMP calorimeter module ( English , PDF; 236 kB) 5th Int. Wire Chamber Conference. Apr 25, 1989. Retrieved Jan 9, 2010.
  14. ↑ G. Bauer et al: Upgraded muon detection system for UA1 based on limited-streamer tubes ( English , PDF; 987 kB) CERN UA1 Collaboration. Oct 13, 1986. Retrieved Jan 14, 2010.