sions produces two mutually oppo­ not be reconciled by a simple 'phase ance behaviour is in good agreement site jets, giving typical cigar-shaped space' model which assumes a with a simple quark-antiquark mod­ events. purely statistical decay pattern. el, the resonance decays show a As the energy is increased, one of Both theoreticians and experi­ totally different behaviour. these jets is seen to grow wider, but mentalists have shown vivid imagi­ Collinear back-to-back jets are in a very special way. Rather than nation in inventing procedures and ruled out as the dominant effect, but simply getting fatter with a cylindri­ names to describe this jet analysis, the data is in good agreement with a cal profile, it becomes planar, and at but the underlying structure is clear three-gluon decay model in which higher energies the jet clearly splits by simple visual inspection. Quanti­ the gluon fragmentation is assumed into two, giving an overall event with tative analysis is less clear-cut, but to be similar to that of a quark. Thi^ three coplanar jet components. the results of all the PETRA groups three-gluon process is the lowest The observed frequency of these are in line with QCD. order QCD contribution to the decay events agrees with quantum chro- Another scene of QCD predictions of upsilons into hadrons, and is now modynamics (QCD) calculations on is still the decay of the upsilon into clearly distinguishable from a simple the emission of hard gluons. The hadrons, as measured by PLUTO at statistical phase space description. events are incompatible with pure DORIS before its move to PETRA. quark-antiquark formation and can­ While the neighbouring off-reson­ Lepton/Photon highlights The Lepton/Photon Symposium at CERN (see September issue, been scanty. Also from SPEAR held at Fermilab at the end of August page 249) qualified for inclusion in came news of a candidate pseudo- was dominated by the results of jet the Symposium because the experi­ scalar (spin zero, negative parity) analysis in PETRA electron-positron ment triggers on lepton pairs, and charmonium state at 2980 MeV. A annihilations (see above). However although no new information was previous pseudoscalar charmonium many other important results available, it was still a feature. candidate at 2820 MeV from DES\ emerged which were highlighted New results on neutrino-electron had not been confirmed at SPEAR by Leon Lederman in his summary scattering came from the fine­ and a new level is therefore welcome talk. grained calorimeter of a Virginia / (see September issue, page 246). PETRA, as well as giving the new Maryland / Oxford / Pekin collabo­ An unexpected contribution was evidence for gluon production, has ration. This is the first time that data the new signal seen by the CHARM also shown that quantum electro­ on this reaction has been available detector in a neutrino beam dump dynamics is as good as ever, even at from a large counter experiment, and experiment at CERN (see page 31 3). high energies. the results underline yet again the While others preferred to adopt a The continued non-appearance of success of the Weinberg-Salam cautious wait and see attitude, the sixth quark flavour at PETRA is model. Preliminary results on anti- Lederman was in more optimistic not yet a problem, but it is unfor­ neutrino-electron scattering were mood, pointing out that here might tunate that no firm indications of this also presented from the fine­ be the first signs of the tau quark mass are available from theo­ grained calorimeter of the CERN / neutrino. ry, unlike the intermediate bosons of Hamburg / Amsterdam / Rome / These Lepton/Photon Symposia weak interactions where confident Moscow ('CHARM') collaboration. started in a modest way at MIT in predictions can be made. Other new Charmed baryons have been re­ 1 963 to cover a specialized area of data from PETRA comes from two ported before, but now they have particle physics research, but have photon exchange mechanisms, been pinpointed in electron-positron now grown to cover the most excit­ while at SPEAR, the two photon collisions at SPEAR. These precision ing developments, as was demon­ process has been used to measure measurements could open up the strated by the Fermilab meeting. the eta prime lifetime. field of charmed baryon spectro­ The candidate beauty signal seen scopy, where information so far has 308 CERN Courier, October 1979 .