WA70 experiment

The WA70 experiment was a collaboration between the Universities of Geneva, Glasgow, Liverpool, Milan and Neuchatel using the facilities of the OMEGA spectrometer at CERN.[1]

The WA70 calorimeter viewed from downstream of the beam line. Photo by R.W. Poultney 1986

The purpose of the experiment was to study direct photons produced in proton-proton and proton-pion collisions within a fixed target of liquid hydrogen at the CERN SPS.[2] The experiment was proposed on 6 August 1980 [2] and formally approved on 22 October 1981.[3] Preliminary data was taken in 1983 with physics runs in 1984, 1985 and 1986.[4]

A novel feature of the experiment was a liquid scintillator calorimeter,[5] which was built in quadrants and designed to measure the energy of direct photons and other particles produced by the collisions. This was situated downstream of the liquid hydrogen target.

Results were presented at scientific conferences and published in scientific journals.[6] The measured cross section for direct photon production was in agreement with predictions from perturbative QCD.[7]

The spokesperson for the experiment was Professor Michel Martin,[2] and participants included Dr. Fabiola Gianotti[8] (who went on to become CERN's first woman Director General).

References
  1. Bonvin, E.; Bopp, R.; Carroll, L. J.; Cass, A. J.; Chung, S. U.; Donnat, M.; Dorsaz, P. A.; Feliks, M. E.; Fluri, L.; Jackson, J. N.; Kienzle-Focacci, M. N.; Lynch, J. G.; Martin, M.; Mathys, L.; Negus, P. J.; Perini, L.; Poultney, R.; Range, W. H.; Rosselet, L.; Snow, S. W.; Thompson, A. S.; Turnbull, R. M.; Werlen, M. (1989). "Double prompt photon production at high transverse momentum byπ − on protons at 280 GeV/c". Zeitschrift für Physik C Particles and Fields. 41 (4): 591–598. doi:10.1007/BF01564702. ISSN 0170-9739. S2CID 119370172.
  2. Bachmann, L. (6 August 1980). Proposal to the SPSC : study of direct photon events in hadronic collisions (PDF) (Report). CERN. CERN-SPSC-80-61 ; SPSC-P-147. Retrieved 28 January 2020.
  3. Decision of the 54th Meeting of the Research Board held on 22 October 1981 (PDF) (Report). CERN. 23 October 1981. CERN-DG-RB-81-21. Retrieved 28 January 2020.
  4. "WA70/OMEGA/DIRPHOTON : Study of Direct Photon Events in Hadronic Collisions". The CERN Experimental Programme. CERN. Retrieved 28 January 2020.
  5. Bonesini, M.; et al. (1987). "A Lead-Liquid Scintillator Electromagnetic Calorimeter for Direct Photon Physics". Nuclear Instruments and Methods. A261 (3): 471–480. Bibcode:1987NIMPA.261..471B. doi:10.1016/0168-9002(87)90356-1.
  6. "List of WA70 publications recorded by CERN". CERN Document Server (CDS). CERN. Retrieved 28 January 2020.
  7. Martin, Michel (1988). "Direct Photon Production by π-p, π+p and pp Interaction at 280 GeV/c: Results from the WA70 Experiment at CERN". QCD Hard Hadronic Processes. NATO ASI Series. 197. pp. 113–124. doi:10.1007/978-1-4684-8842-5_9. ISBN 978-1-4684-8844-9. ISSN 0258-1221.
  8. "Recorded WA70 publications with Fabiola Gianotti as author". INSPIRE-HEP. Retrieved 28 January 2020.
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