Results on e + e − annihilation into hadrons at c.m. energies between 22 and 31.6 GeV are presented. The data were accumulated with the PLUTO detector at PETRA. The events are dominantly of the two-jet type. The value of the relative hadronic cross section R =3.88 ± 0.22 along with the details of the sphericity and thrust distribution rule out an open (tt̄) channel (Q t = 2 3 ) below 30 GeV. The inclusive muon results support the above conclusion.
CROSS SECTIONS CORRECTED FOR BEAM-GAS SCATTERING BACKGROUND, INITIAL STATE RADIATION, TAU HEAVY LEPTON CONTRIBUTION AND TWO-PHOTON EVENTS.
We present evidence for a narrow Y ∗ with a mass of 3.17 GeV and a width ⩽ 20 MeV decaying to ΣKK̄ + pions, ΛKK̄ + pions and ΞK + pions. The data come from two high statistics K − p bubble chamber experiments with a sensitivity of ≈100 eV/ μb at 8.25 GeV/ c and ≈ 45 eV/ μb at 6.5 GeV/ c .
OBSERVATION OF R(3170) ONLY DECAYING INTO 5 OR 6 PARTICLES (CROSS SECTION NOT CORRECTED FOR DECAYS WITH MORE THAN ONE UNSEEN FINAL STATE PARTICLE).
A peak in the pK−π+ and p¯K+π− invariant-mass spectra at 2.285±0.006 GeV/c2 is observed, which is associated with the lowest-lying charmed baryon (Λc). A cross section times branching ratio of 0.037±0.012 nb at Ec.m.=5.2 GeV is measured with a substantial fraction of the events produced with an equal recoiling mass. New measurements of inclusive p and Λ cross sections are also presented, allowing an estimate of the branching ratio B(Λc→pK−π+)=0.022±0.010.
THE TOTAL INCLUSIVE CHARMED LAMBDA CROSS SECTION IS DERIVED FROM THE OBSERVED PRODUCTION RATE VIA THE <P K- PI+> CHANNEL USING THE STEP IN INCLUSIVE PROTON PRODUCTION AT THE CHARMED-BARYON THRESHOLD AND REASONABLE ASSUMPTIONS. THE BRANCHING RATIO (LAMBDA/C+ --> P K- PI+) IS THEN 2.2 +- 1.0 PCT.
ACTUALLY TWICE THE INCLUSIVE ANTI-PROTON CROSS SECTION (EACH BARYON PAIR IS COUNTED TWICE).
EACH BARYON PAIR PRODUCED IS OF COURSE COUNTED TWICE IN THIS CROSS SECTION.
We have measured the production of massive muon pairs in hadronic collisions at the CERN Super Proton Synchrotron (SPS). A clear signal of production of the ϒ resonance by π + of 200 GeV/ c and π − of 200 and 280 GeV/ c on a platinum target is observed.
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Hadron jets produced in e + e − annihilation between 13 GeV and 31.6 GeV in c.m. at PETRA are analyzed. The transverse momentum of the jets is found to increase strongly with c.m. energy. The broadening of the jets is not uniform in azimuthal angle around the quark direction but tends to yield planar events with large and growing transverse momenta in the plane and smaller transverse momenta normal to the plane. The simple q q collinear jet picture is ruled out. The observation of planar events shows that there are three basic particles in the final state. Indeed, several events with three well-separated jets of hadrons are observed at the highest energies. This occurs naturally when the outgoing quark radiates a hard noncollinear gluon, i.e., e + e − → q q g with the quarks and the gluons fragmenting into hadrons with limited transverse momenta.
NORMALIZED TRANSVERSE MOMENTUM DISTRIBUTION WITH RESPECT TO THE SPHERICITY AXIS AT 13, 17, AND 27.4 TO 31.6 GEV.
A search has been made for direct photon production in pBe interactions at 200 and 300 GeV/ c over the kinematic region 1.5 < P ⊥ < 4.0 GeV/ c and −0.7 < X F < 0 (90° < θ cms < 160°). An excess of single photons above that which is predicted from the measured π 0 and η 0 production is observed. Theratio of γ / π 0 production is calculated assuming that the excess arises from direct photon production. We find that this ratio averages 0.070 ± 0.025 (including systematic errors) in this region of X F and P ⊥ for our 200 and 300 GeV/ c data. We have used our measured value of the η / π 0 ratio of 0.47 ± 0.10 in the determination of the γ / π 0 ratio. The variation of γ / π 0 with X F , P ⊥ , X R and θ cms presented.
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Measurements of the reactions e++e−→e++e−, μ++μ−, and τ++τ− at PETRA energies (s12=13,17,27.4,30 and 31.6 GeV) are reported. The results show that these reactions agree well with the predictions of quantum electrodynamics thus determining that all the known charged leptons are pointlike particles to a distance < × 10−16 cm.
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We report the analysis of the spatial energy distribution of data for e+e−→hadrons obtained with the MARK-J detector at PETRA. We define the quantity "oblateness" to describe the flat shape of the energy configuration and the three-jet structure which is unambiguously observed for the first time. Our data can be explained by quantum chromodynamic predictions for the production of quark-antiquark pairs accompanied by hard noncollinear gluons.
AVERAGE OBLATENESS AS A FUNCTION OF SQRT(S) AND OF THRUST AND OBLATENESS DISTRIBUTION (1/N)*DN/DOBLATENESS AT 17 AND 27.4 TO 31.6 GEV. THESE DATA ARE RATHER DETECTOR DEPENDENT.
This paper presents production and decay characteristics of 500 high-mass, high-resolution μ+μ− pairs produced in π− Be collisions at 150 and 175 GeV/c. The data do not agree with a simple Drell-Yan production mechanism, but indicate that higher-order quantum-chromodynamic corrections must be included.
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Results on the hadronic final state in e/sup +/e/sup -/ annihilation at 13, 17 and 27.4 GeV are presented. There is no compelling evidence for the existence of the t quark in these data, which are in general agreement with a simple quark parton model. Some tentative indications of QCD effects are observed in the p/sub T//sup 2/ distributions.
TAU HEAVY LEPTON CONTRIBUTION SUBTRACTED.
INCLUSIVE HADRON SPECTRUM. THESE DATA AT 13, 17 AND 27.4 GEV ON S*D(SIG)/DX ARE INCLUDED IN THE RECORD OF R. BRANDELIK ET AL., PL 89B, 418 (1980).
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