Observation of direct processes in photoproduction at HERA

Jets in photoproduction events have been studied with the ZEUS detector for gammap centre-of-mass energies ranging from 130 to 2 50 GeV. The inclusive jet distributions give evidence for the dominance of resolved photon interactions. In the di-jet sample the direct processes are for the first time clearly isolated. Di-jet cross sections for the resolved and direct processes are given in a restricted kinematic range

Silicon strip detectors with capacitative charge division

Measurements of the behaviour of various high-resolution silicon strip detectors with capacitive charge division have been made in a high-energy particle beam. The results are compared with an electrostatic model which calculates the charges deposited on the strips after the passage of a minimum ionizing particle. Good agreement is found and the model is used to propose a method of improving the charge-division properties of such detectors

A measurement of muon pair production in e+e- annihilation at centre of mass energies {Mathematical expression} GeV

The reaction e+e-→μ+μ- has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction of Rμμ=σμμ/σo=0.932±0.018±0.044 and Aμμ=(-10.6-2.3+2.2±0.5)%. At 38.3 GeV we find Rμμ=0.951±0.072-0.057+0.063 and Aμμ=(+1.7-8.6+8.5±0.5)%. At 43.6 GeV we measure Rμμ=0.921±0.037±0.055 and Aμμ=(-17.6-4.3+4.4±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions. © 1988 Springer-Verlag

BOSE-EINSTEIN CORRELATIONS OBSERVED IN e+ e- ANNIHILATION AT A CENTER-OF-MASS ENERGY OF 34-GeV

Bose-Einstein correlations between pairs of charged particles produced in e+e- annihilation into hadronic final states have been studied as a function of Q2, the relative momentum squared of the two particles in their centre of mass, and as functions of various pairs of kinematic variables. The observed Bose-Einstein enhancement reveals correlation between the position and time of particle emission, and the space-time structure of the source is shown to differ from that of a pion fireball. While most features of the data are well accounted for in terms of the space-time structure of a simple string model, the correlations are better described by the simple function 1+αe-βQ2. The implications of this result are discussed. The principal features of three particle correlations are explained in terms of the structure of the source inferred from the observed two particle correlations. © 1986 Springer-Verlag

A STUDY OF JETS FROM b QUARKS PRODUCED IN e+ e- ANNIHILATIONS AT S**(1/2) = 35-GeV TO 46-GeV.

Ab enrichment technique using the longB lifetime has been developed, by which ∼600 hadronic events with >65%b purity are obtained. The properties of the associated jets are studied, with comparisons made between them and those in hadronic data in whichb quarks make up only 10% of the total, and jets in Monte Carlo events. The distributions in rapidity and multiplicity yield two new determinations of the fragmentation variablez forb hadrons and confirm that theb fragmentation function is hard. We also present the first measurement of the relative strength of the strong interaction coupling of theb quark compared with the average of all flavour

EVIDENCE FOR LOCAL COMPENSATION OF BARYON NUMBER IN e+ e- ANNIHILATION

We have studied at CM energies of 14, 22 and 30-36.7 GeV e+e- annihilation events in which the hadronic final state contains both a proton and an antiproton in the momentum range 1.0 < p < GeV/c. We find that such pairs are produced predominantly in the same jet and conclude that baryon-antibaryon production is dominated by a mechanism involving local compensation of baryon number. © 1984

MEASUREMENT OF THE RADIATIVE WIDTH OF THE eta-prime (958) IN TWO PHOTON INTERACTIONS

The reaction e+e-→e+e-η′(9 58) has been observed by detecting the final state π+π-γ. The two-photon width of the η′ has been measured to be Γ(η′→γγ) = 5.1±0.4±0.7 keV. A search for the ι(1440) has been made in the ρ{variant}0γ final state. An upper limit has been obtained for the product Γ(ι(1440) → γ)gg), B (ι→ρ{variant}0γ) < 1.5 keV (95%CL). © 1984