We present the first measurement of the left-right cross section asymmetry (ALR) for Z boson production by e+e− collisions. The measurement was performed at a center-of-mass energy of 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure ALR to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be sin2θWeff=0.2378 ±0.0056(stat)±0.0005(syst).
R and L refer to Right and Left handed beam polarization.
Effective weak mixing angle.
We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon Si28 ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.
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The subthreshold production of neutral pions was studied in the reactions 24 Mg(α,π 0 )X at 43 MeV·. A and 24 Mg( 16 O,π 0 )X at 24 and 33 MeV·. A . The energies and emission angles of the two coincident photons from the π 0 -decay were measured with a lead glass shower detector. The cross sections of 3.5 and 6.6 nb from the 16 O-induced reactions are compatible with other experiments in this energy region. For the α-induced reaction a production cross section of 1.3 nb was found. Here, only 22 MeV above the absolute threshold, the pion emission from an excited Δ -nucleon hole state is strongly suppressed. The differential cross sections at very backward angles are by an order of magnitude bigger than the yields at 90° pointing to a strong absorption of the produced pions by the larger target nucleus.
No description provided.
We report on a study of the differential cross section d σ /d y for the processes of elastic ν μ - and ν μ - electron scattering. The data on which this analysis is based were recorded between 1987 and 1990 with the CHARM II detector in the wide band neutrino beam at the CERN-SPS. For the first time the shapes of these y -distributions have been determined in a model-independent way. A fit to the data yields for the squares of the neutral coupling constants the ratio g R 2 / g L 2 =0.60 ± 0.19 (stat.) ± 0.09 (syst.).
Cross sections in arbitrary units.
Cross sections in arbitrary units.
Value of SIN2TW obtained from data.
The pp→ppη reaction is studied at energies near the η production threshold. The total cross sections at nominal machine energies of 1260, 1265, and 1300 MeV are 90±15, 790±120, and 3460±690 nb, respectively. None of the existing perturbative model calculations reproduces the energy dependence, which deviates strongly from phase space. This suggests that the cross section is enhanced in the near vicinity of the production threshold by a large η−pp scattering length.
No description provided.
Total cross-section measurements of the π+p→π+π+n reaction at pion kinetic energies of 180, 184, 190, and 200 MeV are reported. The threshold value for the amplitude a(π+π+) as well as the s-wave, isospin 2, ππ scattering length a20 were determined. The results were found to be in agreement with chiral perturbation theory and inconsistent with the calculations of Jacob and Scadron and the model of dominance by quark loop anomalies.
No description provided.
We present results from the initial run of Fermilab experiment E706. The data include incident π− and p beams at 500 GeV/c on Be and Cu targets, and span the kinematic ranges of transverse momentum and rapidity of 3.5≤pT≤10 GeV/c and −0.7≤yc.m.≤0.7, respectively. We have measured cross sections for π0 and direct-photon production, as well as the ηπ0 production ratio. From the data on Be and Cu, we have extracted the nuclear dependence of π0 production, parametrized as Aα. The cross sections are compared with next-to-leading-log QCD predictions for different choices of the QCD momentum scales and several sets of parton distribution functions.
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The analyzing power AN of proton-proton elastic scattering in the Coulomb-nuclear interference region has been measured using the 200-GeV/c Fermilab polarized proton beam. A theoretically predicted interference between the hadronic non-spin-flip amplitude and the electromagnetic spin-flip amplitude is shown for the first time to be present at high energies in the region of 1.5 × 10−3 to 5.0 × 10−2 (GeV/c)2 four-momentum transfer squared, and our results are analyzed in connection with theoretical calculations. In addition, the role of possible contributions of the hadronic spin-flip amplitude is discussed.
No description provided.
The yields and average transverse momenta of pions, kaons, and antiprotons produced at the Fermilab p¯p collider at s=300, 540, 1000, and 1800 GeV are presented and compared with data from the energies reached at the CERN collider. We also present data on the dependence of average transverse momentum 〈pt〉 and particle ratios as a function of charged particle density dNcdη; data for particle densities as high as six times the average value, corresponding to a Bjorken energy density 6 GeV/fm3, are reported. These data are relevant to the search for quark-gluon phase of QCD.
PT RANGE FROM 0 TO INFINITY.
PT RANGE FROM 0 TO INFINITY.
No description provided.
Using the CLEO-II detector at CESR, we have observed the D s 1 (2536) + in the decay modes D s1 + →D ∗0 K + and D ∗+ K S + , and measured its fragmentation and production ratios. Using the helicity angle distribution of the daugter D ∗0 , we obtain new evidence for the assignment of 1 + for the spin and parity of the D s 1 + . We also set upper limits on the decays D s1 + →D s ∗+ λ, D 0 K + and D + K s 0 .
No description provided.
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