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The Experiments The experiments 1.6 x 1029. By the time the run never has a new energy range given U A1 and U A2 represent the accumu­ closed on 3 July the integrated lumi­ so many important new results so lation of many years of knowledge nosity had reached 1.5 x 1035. The quickly. A fitting tribute to the inven­ and experience in the design, con­ threshold of machine performance tiveness, skill and ingenuity of the struction and operation of particle had been crossed for observation of machine physicists who made it all physics experiments. the Z particles. happen. The CERN Intersecting Storage Rings (ISR), a masterpiece of a ma­ chine, was built ahead of its time in Future plans the sense that only towards the end of its lifetime has it been equipped At the PS the present ten bunches with detectors that do justice to thW from the booster will be 'box car' available physics. stacked in the transfer line so as to The designers of the UA1 and give five bunches in the PS. This pro­ UA2 detectors had no reason to be cess can then be repeated to feed in caught in the same trap. For the SPS another five bunches and the pro­ proton-antiproton collider, the aim cess of combination in the PS ring was to have maximum detector ca­ will result in putting more protons pability right from the start, with ade­ (some 2x 1013) on the antiproton quate tracking and calorimetry (ener­ production target at the AA. gy deposition measurements); maxi­ In the AA new ferrite pick-ups will mum solid angle coverage and pow­ On 1 July, Herwig Schopper toasts CERN's improve precooling at higher antipro­ achievements at a crowded party to erful data handling systems. ton fluxes and a series of improve­ celebrate the end of the epic 1983 Despite their immense size, the ments to the cooling electronics are antiproton run in the SPS. two experiments which discovered under way. A new injection damper (Photo CERN39.7.83) the W and Z particles are not readily should improve injection of the anti­ visible to a visitor to the CERN site. protons into the PS. In the SPS, the The proton-antiproton collisions number of colliding bunches will be which the experiments study take increased from the present three per place underground in the ring of the beam, the low beta insertion could SPS machine, and the detectors ar|| be made stronger and it might be housed in deep caverns. possible to increase the peak energy The 7-kilometre underground SPS of the collider to 310 GeV to increase ring was designed and built for the W and Z production rates. 'fixed-target' experiments. For this Longer term, the possibility of ad­ research, high energy proton beams ding a separate ring, an Antiproton are made to fly off tangentially from Collector, ACOL, has been studied the ring. These beams provide the with the aim of accumulating antipro­ particles which feed the experi­ tons at ten times the present rate. ments, installed in large, relatively This is similar to the scheme at Fer­ easily accessible experimental halls. milab where a proton-antiproton col­ Viewed from the elevated gang­ lider of up to 1000 GeV energy per ways, these CERN experimental halls beam has become feasible with the resemble aircraft hangars, but with operation of their superconducting beamlines and detectors replacing synchrotron (see page 380). aircraft. The UA1 and UA2 under­ Although the collider, scheduled to ground halls look very different, but run for physics again in autumn are of the portent of things to come 1984, has yet to reach its somewhat at LEP and other giant new machines ambitious design performance, this to supply colliding particle beams. has hardly detracted from the rich­ Detectors studying colliding ness of the physics results. Perhaps beams have to surround the region 370 CERN Courier, November 1983 A view of the UA 1 detector during installation. The two halves of the main magnet/hadron calorimeter are drawn apart, showing inside the elements of the electromagnetic calorimeter surrounding the cylindrical space to be occupied by the inner tracking chamber. When assembled, most of the UA 1 detector is covered by its large outer slabs of muon detectors. (Photo CERN 229.2.81) vating teams began work, a vast mm mm wm Imm physics effort was being mobilized across Europe. Responsibility for the various components of the UA1 and UA2 detectors was delegated to the different research centres in the collaborations, including of course CERN. Literally hundreds of man-years of heroic effort went into the design, assembly and testing of the thou­ sands of units for the various sub­ assemblies of the detectors. Wire by wire, and crate by crate, the elec­ tronics grew, and piece by piece the equipment for the detectors came together. The high efficiency at­ tained during the 1983 run (80 per cent) bears witness to the thorough­ ness of this preparation and ground­ work. The logistics of this work were far- reaching, and sometimes had to overrule physics requirements. The size of some components, for exam­ ple, was found to be limited by the where the beams are brought to­ down the machine. The detectors transport and handling services gether. Simply to get the envisaged could be rolled back when a period of available. ^etectors into the SPS ring would data-taking was completed and the In both detectors, different types pave demanded a mammoth effort of SPS reverted to fixed-target opera­ of particles are identified and studied construction and engineering. As if tion. In these underground garages by looking at their behaviour as they the task of installing a 2000-ton de­ and shielded by movable walls, the pass through successive layers of tector with fraction of a millimetre experimenters could assemble ap­ the apparatus, each of which has a precision in a confined underground paratus or tinker with their detector, specific function. space was not enough, there were only several feet away from the in­ Another problem is posed by the other restrictions. At the SPS, collid­ tense high energy proton beams in rarity of the phenomena being er physics would not replace fixed the SPS. sought. To be sure of catching a few target operation. While the collider The countryside around CERN is Z particles over a period of about experiments were assembled, the far from flat. Although the two ex­ two months, the detectors would machine would continue to operate, periments are only about one kilo­ have to be exposed to a few thou­ and even once the detectors were metre distant in the SPS ring, the sand proton-antiproton collisions commissioned, the machine would beampipe for UA1's collisions is per second. To examine all this data run alternate periods of fixed target about 20 metres below the surface, in detail at once was out of the ques­ and collider physics according to a while that for UA2 is some tion, and both experiments use 'trig­ prearranged schedule. 50 metres underground. The civil en­ gers' — pre-programmed selection Thus the underground caverns had gineering for the UA1 premises criteria which ensure that potentially to be made large enough to provide which began in 1979 used the 'cut valuable physics is recorded on spe­ room for the completed detectors to and cover' method, while the aptly cial magnetic tapes for subsequent be positioned in the ring, plus enough named 'cathedral' for UA2 was ex­ analysis. Thanks to skilful triggering 'garage' space so that they could be cavated from within. and subsequent data handling, the assembled without having to shut While the earthmoving and exca­ captured information can be filtered CERN Courier, November 1983 371 Cross-section of the UA 1 detector. The collision region is surrounded in turn by the central tracking detector, the electromagnetic calorimeter, the magnet/hadron calorimeter and the muon detectors. On either side are the forward and 'very forward' detectors covering particles emerging close to the beam pipe. Not shown are the 'very very forward' detectors ('Roman pots'), some 20 metres from the central detector. Portrait of UA1 Aachen Technische Hochschule muon chambers Annecy (LAPP) 'bouchons' (electromagnetic calorimeter end-caps) Birmingham hadron calorimeter, trigger processor CERN magnet, compensators, central de­ tector, experimental area, comput­ ing, overall coordination Queen Mary College, London hadron calorimeter, trigger processor Paris, College de France forward detectors and analysed even while the experi­ over a maximum solid angle. Particle Riverside, ments are still running. energies are measured both by their University of California Most interest lies in the triggers curvatures in the internal magnetic 'very very forward' detectors which select out those events pro­ field, and by energy deposition (calo- ducing particles flying out at large rimetry). Both electrons and muons Rome angles to the direction of the colliding are sought. 'very forward' detectors beams, as these particles character­ The 7000 gauss magnetic field is ize the violent frontal collisions which supplied by an 800-ton conventional Rutherford Appleton Laboratory shake the constituents of the pro­ electromagnet using thin aluminium hadron calorimeter, tons and antiprotons. coils and enclosing a region of trigger processor 85 cubic metres. Inside the magnet The UA 1 experiment and surrounding the beam pipe Saclay carrying the particles are six shells of 'gondolas' (eletromagnetic Carlo Rubbia, leader of the UA1 drift chambers containing 6000 calorimeter) team, describes his immense detec­ sense wires with image readout, pro­ tor as 'a series of boxes, each one viding a reconstruction of the emerg­ Vienna doing what the previous one couldn't ing particle tracks in a cylindrical electromagnetic calorimeter do' — a modest description of some volume 6 m long and 2.6 m in dia­ electronics and phototubes 2000 tons of sophisticated precision meter around the beam crossing apparatus packed with advanced point.
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