Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant α s is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C -parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Y cut , before these variables are computed. The combined result from all shape variables of pre-clustered events is α s ( M Z 2 = 0.117±0.005 for a renormalization scale μ= 1 2 M Z . For μ values between M Z and the b-quark mass, the result changes by −0.009 +0.006 .
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Error contains both experimental and theoretical errors.
An experimental study was made of a ωπ 0 system produced in the charge exchange reaction π − p→ ωπ 0 n at 8.95 GeV/ c . The moment analysis was performed to study the spin-parity of the system in the mass region between 1.04 and 1.88 GeV. A clear peak of b 1 (1235) was observed in the J PC = 1 +− wave. No significant structure was seen in the 1 −− wave. An upper limit is obtained to be at most 1.9 μb for σ ( π − p→X 0 n)Br(X 0 → ωπ 0 ) for X 0 with a width of 130 MeV at 1480 MeV, where C(1480) meson with J PC = 1 −− has been reported in a φπ 0 decay mode.
Upper limit for pi- p --> X0 n (X0 --> omega pi0) with width 130 MeV at 1480 MeV where the C(1480) has been reported with JPC = 1-- in the phi pi0 decay mode.
The cross section for K + meson production in collisions of 36 Ar ions on a 48 Ti target has been measured at an incident energy of 92 MeV per nucleon. A description of the experimental set-up is given. Twelve events attributed to monoenergetic muons following the decay of stopped kaons have been identified. From these events, one infers a production cross section of 240 pb. Data are briefly discussed.
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NUCLEUS IS P, C, AL.
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T - MOMENTUM TRANSFER FROM BEAM PROTON TO LEADING PROTON.
We report a measurement of the electroweak parameters sin2θw and ϱ based on the ratios of neutral current to charged current events measured in the Fermilab narrow-band neutrino beam at energies of 30–240 GeV. The data are fully corrected for radiative effects, heavy-quark production, and other effects. The best value for sin2θw obtained, sin2θw=0.239±0.011, is consistent with the most recent values fromW andZ production, as well as from other neutrino experiments.
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The production of the neutralK− (892) resonances by 200 GeVK− andπ− has been studied over the kinematic range 0.0<xf<1.0 andpt2<5.0 GeV2. Longitudinal and transverse momentum distributions are presented. In addition the decay angular distributions inK− fragmentation to\(\bar K^{0*} \) have been investigated.
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We present a new high-statistics measurement of the cross section for the process e+e−→e+e−π+π− at a center-of-mass energy of 29 GeV for invariant pion-pair masses M(π+π−) between 350 MeV/c2 and 1.6 GeV/c2. We observe the f2(1270) and measure its radiative width to be 3.15±0.04±0.39 keV. We also observe an enhancement in the π+π− spectrum near 1 GeV. General agreement is found with unitarized models of the γγ→π+π− reaction that include final-state interactions.
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Statistical errors only.
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