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CORNELL CLEO's F Top, the spectrum of the phi meson plus pion combination seen in the CLEO detector at the Cornell CESR electron-positron ring, showing the clear F meson signal at 1970 MeV. The phi mesons are picked up from their decay into two kaons. Bottom, using kaon pairs away from the phi mass makes the signal disappear. Getting under way is an extensive programme of testing and calibra­ tion of production shower counters, hadron calorimeters and tracking chambers, using Tevatron beams. If all goes well, there will be a prelimi­ nary test run of the partially com­ pleted detector with colliding beams of low luminosity in 1985. Most of the central and forward calorimetry should be in place, but it is unlikely that the complete tracking, trigger, and data acquisition systems will be available until the full physics runs begin in 1986. CORNELL CLEO's F The CLEO (Cornell / Harvard / Ithaca College / Ohio State / Rochester / Rutgers / Syracuse / Vanderbilt) col­ laboration working at the CESR elec­ tron-positron ring at Cornell has found an F meson candidate in a new decay mode and at a lower mass than previously observed. The charmed F meson is the strange­ ness-carrying partner of the D me­ sons, and consists of a charmed quark bound with a strange anti- quark. Although observations of D me­ sons are routine, the F meson has remained elusive. A DASP (DESY) electron-positron annihilation experi­ ment and a more recently CERN pho­ ton experiments utilizing the Omega spectrometer provided the stron­ gest F evidence. The Omega experi­ the weak decay of the charmed kaons. A clear phi signal above a ments gave the F mass as quark. The previous experiments substantial background was ob­ 2020 ± 15MeV. have relied on detection of one or served in the two-kaon mass spec­ The F meson can be observed more pions along with an eta, ob­ trum. Charged kaon pairs, consistent through the weak decay of its served through its decay into two with the phi mass, were selected for charmed quark into a strange quark. photons. In the CLEO detector, the further analysis. They were com­ The decay modes most accessible to phi-pi mode was observed by recon­ bined with other charged particles, experimental detection are those in structing the phi from two charged assumed to be pions, to give a phi which the new strange quark and the kaons. plus pion mass spectrum, and the original strange antiquark combine Phi-meson candidates were iden­ mass peak at 1970 ± 5 MeV has a to form either an eta or a phi meson, tified from combinations of oppo­ width consistent with the exper­ with a few pions being produced by sitely charged tracks interpreted as imental resolution. No mass peak is CERN Courier, January/February 1984 15 At the DESY Theory Workshop — Gerhard Mack and Harry Lehmann (right). (Photo DESY) observed if two-kaon masses above or below the phi are used to create the phi-pi mass spectrum. This un­ derlines that the observed peak is due to phi mesons and not back­ ground combinations. Further evidence that this en­ hancement is the F meson comes from examining its production and decay. In background electron-posi­ tron annihilation, charmed quark pro­ duction accounts for 40 per cent of the event rate. The momentum frac­ tion (momentum/beam energy) dis­ PETRA improvement programme in the DESY calendar. The sixth such tribution of F events agrees with which began back in 1982. From workshop, held a few months ago, those of D events measured earlier 37.2 GeV, the energy was nudged to explored the new jet information by CLEO. Also, the product of the F 40.2 towards the end of 1982, and culled from the summer conference production rate and the relative oc­ reached 43.19 last July (see October season. However the number of out­ currence of the phi-pi decay is one- 1983 issue, page 311). To achieve standing questions in this area still third of the product for D° production 45 GeV, the PETRA r.f. power and appears to exceed that of clear an­ followed by decay to kaon plus pion, the number of accelerating cavities swers. in good agreement with a simple were eventually doubled. The organizing committee, L. Sto- quark counting argument. To run at 45 GeV, all the available dolsky (chairman), K. Schilling (depu­ Angular distributions of the two space is filled by accelerating cavi­ ty chairman), H. Joos and T. Walsh kaons and the pion further support ties. There are now 112 of them had in the back of their minds a the proposition. The phi meson has working at 500 MHz, with a total of comparison of simple models with spin 1, the pion has spin zero, and 672 cells. In addition, 24 cavities standard quark-gluon gauge theory the F meson should have spin zero. running at 1 GHz with a total of 152 (QCD). However, it became clear that These assignments lead to two cells are used to improve the accel­ the qualitative successes of QCD characteristic angular distributions, eration process. This 1 GHz system have so shaped our thinking that sim­ which are in good agreement with is used at lower energies to increase ple models don't generate much en­ the data in the peak, after subtracting the bunch length. thusiasm any more. On the other background. The energy required to run this hand quantitative tests of QCD are This observation of an F signal at system amounts to about 17 MW only at an accuracy of about 20 per 1970MeV in the phi-pi spectrum (from the mains) of which 9.6 reach cent, which leaves much theoretical was announced last summer and has the cavities. Since they are not su­ and experimental work to be done. been confirmed by the ARGUS ex­ perconducting, the cavities' losses Discussion of observed jet struc­ periment at DORIS (see December are high — only about 1 MW is finally ture was fuelled by comparison of 1983 issue, page 423). used by the beam to compensate results from proton-antiproton colli­ for emitted synchrotron radiation. sions and electron-positron annihila­ These energy losses underline the tion. Although mainly gluon jets are DESY potential usefulness of supercon­ studied in proton-antiproton colli­ 45 GeV - and still ducting cavities for handling high en­ sions at the CERN Collider and quark- ergy electron beams. antiquark jets in electron-positron in­ topless! teractions, the jet similarities are Late in the evening of 9 December, Theory workshop nevertheless striking. However K. the champagne was broken out at Fialkowski mentioned that multiplici­ DESY. The PETRA electron-positron Concentrating on the common ty of different types of jets at me­ storage ring passed from 44.98 GeV ground between current theory and dium energies could differ. total energy to 45.01, thus surpas­ experiment, the annual Theory For a quantitative explanation of sing the 45 GeV design value for the Workshop is now a traditional event jet structure, the theoretical input to 16 CERN Courier, January/February 1984 .
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