To hit a resonance spot-on, the Detection of a J/psi (decaying into an -positron pair) in the experiment at Well behaved antiproton beam can either be accel­ the CERN Intersecting Storage Rings (ISR) erated using the r.f. phase displace­ using a stored antiproton beam incident on ment method, or can be adjusted a hydrogen gas jet target. For this In her review talk on weak decays at experiment only one of the ISR rings is used. smoothly (but more slowly) using the the Brighton Conference, Cecilia momentum cooling system. With Jarlskog paid tribute to the excellent 3 m A of circulating antiprotons and a posed spins (like the eta-c) work of the Bristol/Geneva/Heidel­ design figure target density of which can decay into pairs of gamma berg / Orsay / Rutherford / Stras­ 6x1013 atoms/cm2, proton-anti- rays. bourg collaboration's experiment at proton collision luminosity was In the initial data samples, the pro­ CERN (WA2). This thorough high 1.5 x 1030 cm"2 s1. duction of chis appears to be a bit statistics study of the weak semi- After initial success with the J/psi, lower than expected, but it is too ear­ leptonic decays of heavy attention turned to other particles. ly to draw firm conclusions. Addi­ (hyperons) has produced decisive re­ The J/psi and heavier counterparts tional data from runs next year will sults. consist of a charmed quark and anti- shed further light on these states. Each type corresponds to quark bound together with their The high 'tunability' of the machine a different mixture of and spins parallel, but carrying no relative might enable other narrow states to within the accepted SU3 classifica­ angular momentum. Other particles be encountered. There has been talk tion of particles, their semi-leptonic (chis) have a similar quark spin confi­ recently of candidate Higgs particles decays can be described according guration, but carry one unit of orbital lying in the region. The systematic to an elegant model proposed by angular momentum. They are recog­ energy sweeps available from the Nicola Cabibbo in 1963 with only nized by their decays into electron- ISR should enable a thorough search three parameters: the Cabibbo angle positron pairs (from J/psis) plus a to be made, providing a fitting con­ 0C and two 'transition elements' F gamma ray. Also possible are the clusion to the physics career of this and D. At the time only three quark 'singlet' charmonium states with op- wonderful machine. flavours were known, but the ideas

418 CERN Courier, December 1983 Hyperon semi-leptonic decays in good shape. Apart from the case of free neutron decay (n p) all the data come from the WA2 experiment at CERN. According to the Cabibbo theory, the lines should intersect at one point. The centre of the small black ellipse is the best estimate of the common point of intersection of the lines, and the size of the ellipse indicates the experimental uncertainties. This is the best evidence so far for the correctness of the Cabibbo model, applied to so many different particle systems. The shaded bands represent experimental errors.

pious non-leptonic hyperon decays. The WA2 experiment has looked at an extensive list of semi-leptonic decays of ksi, sigma and lambda hy­ perons. For several of the decays considered, precision reached the level at which radiative effects due to emission and absorption of photons had to be taken into account. For each semi-leptonic decay the rate and the decay distributions give independent relations between the

three parameters F, D and sin 6C. Powerful additional constraints on the parameters of the model come from experiments on free neutron decay. The results from the WA2 experiment, whether considered alone or with the addition of the neutron decay constraints, are in complete accord with the Cabibbo model. Accelerator School successfully launched have been extended to cover the charged particles produced in the The first course of the newly created conventional six-quark picture of to­ forward direction by the interaction CERN Accelerator School under the day. of the 210 GeV SPS proton beam on leadership of Kjell Johnsen was held A major problem in previous tests a target. A 'DISC Cherenkov counter at CERN from 11-21 October. Its of the Cabibbo model had been the identified different kinds of hyperons subject, 'Antiprotons for Colliding necessity to combine data from (sigmas and ksis), about four per Beam Facilities', was selected ob­ many different experiments ana­ thousand charged beam particles. viously in the light of the recent spec­ lysed under a variety of assumptions Wire chambers on either side of the tacular achievements in this field. which were liable to produce incon­ DISC particle identifier accurately The School will be back-tracking in sistent results. The objective of the measured the directions of the parti­ its next planned course in September WA2 experiment was to make a co­ cles enabling their momenta to be 1984 with a basic course on acceler­ herent, comprehensive and precise measured to within one per cent. ator physics accessible to post-uni­ Study of the various hyperon semi- Downstream of the DISC was a versity science and engineering stu­ leptonic decays measured in a single 10-metre long helium-filled decay re­ dents. apparatus, and to see how the re­ gion, followed by a magnetic spec­ The School has several aims in the sults compared with the Cabibbo trometer which measured the general context of broadening the model. charged particles emitted in the hy­ base of accelerator physics knowl­ One of the unique features of the peron decays. An impressive arsenal edge in Europe. There is need to initial experimental programme at of detectors, including a lead-glass attract young people into this field, the CERN SPS super proton synchro­ array, a gas Cherenkov counter, particularly with the tremendous tron when it began operations in transition radiation detectors and a challenge of mastering new acceler­ 1976 was its high energy charged lead scintillator shower counter iden­ ation techniques so as to be able to hyperon beam. A magnetic channel, tified . Together these de­ continue the advance of high energy short so as to minimize the hyperon tectors provided excellent discrimi­ physics into the next century. In addi­ decay losses, selected 100 GeV nation against the much more co­ tion, accelerator physics has increas-

CERN Courier, December 1983 419