Antiproton-proton and proton-proton small-angle elastic scattering was measured for centre-of-mass energies s =30.6, 52.8 and 62.3 GeV at the CERN Intersectung Storage Rings. In addition, proton-proton elastic scattering was measured at s =23.5 GeV . Using the optical theorem, total cross sections are obtained with an accuracy of about 0.5% for proton-proton scattering and about 1% for antiproton-proton scattering. The measurement of the interference of the Coulomb scattering and the hadronic scattering permits a determination of the ratio of the real-to-imaginary part of the forward hadronic scattering amplitude. Also presented are measurements of the hadronic slope parameter.
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The process e + e − → π 0 + anything has been measured at c.m. energies of 14 and 34 GeV for π 0 energies between 0.5 and 4 GeV. The ratio of π 0 to π ± production for π momenta between 0.5 and 1.5 GeV/ c is measured to be 2 σ ( π 0 )/ [ σ ( π + ) + σ ( π − )] = 1.3 ± 0.4 (1.2 ± 0.4) at 14 (34) GeV. The scaled cross section ( s / μ )d σ /d x when compared with lower energy (4.9–7.4 GeV) π 0 data indicates a substantial scaling violation.
COMPARISON OF PI0 WITH CHARGED PION CROSS SECTIONS (SCALED BI 1/S TO SAME ENERGIES).
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We have measured the reactions e + e − → e + e − → μ + μ − and e + e − → γγ at c.m. energies between 12 and 31.6 GeV. Excellent agreement with the predictions of QED has been found, resulting in cut off parameters Λ + > 112 GeV and Λ − > 139 GeV for the first process and Λ + > 34 GeV and Λ − > 42 GeV (95% c.1.) for the last one. A limit on the Weinberg angle of sin 2 θ W < 0.55 (95% c.1.) has been obtained.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
Using data from the TPC/Two-Gamma experiment at the SLAC e+e− storage ring PEP, a C=+1 resonance has been observed in the π+π−π0γ final state resulting from the fusion of one nearly real and one quite virtual photon. The actual decay channel is probably π+π−π0π0, where one final-state photon is not detected, and the mass of the fully reconstructed state would be approximately 1525 MeV. A four-pion decay mode in turn implies that the resonance has even isospin. The nonobservation of this R(1525) when both initial-state photons are nearly real suggests a spin-1 assignment. Since the large measured value of the product of the branching ratio into π+π−π0π0 and the γγ coupling makes it unlikely that this state is the mostly s¯s f1(1510), its interpretation may lie outside of conventional meson spectroscopy. There is a second, less-significant enhancement observed in the same reaction at a four-pion mass centered around 2020 MeV.
No description provided.
Coupling parameter times the effective form factor.
We report a measurement of the e+e−→e+e−pp¯π+π− process with the TPC/Two-Gamma facility at the PEP e+e− storage ring at SLAC. Forty-five pp¯π+π− events were identified in data corresponding to an integrated e+e− luminosity of 142 pb−1. The cross section for γγ→pp¯π+π− is given both as a function of the γγ center-of-mass energy Wγγ, with Wγγ between 2.5 and 5.5 GeV, and as a function of the in variant mass squared q2 of one of the photons, with −q2<7 GeV2. This cross section falls much less rapidly with Wγγ than does the cross section for a similar process, γγ→pp¯. No Δ0Δ¯0 production is observed, and only a small fraction of the events at low Wγγ is consistent with γγ→Δ++Δ¯−−, Δ++p¯π−, or Δ¯−−pπ+. In an expanded search through the same data, four events compatible with either ΛΛ¯(Λ→pπ−) or Σ0Λ¯(Σ0→Λγ) production were found.
Statistical errors only.
Data read from graph.
The inclusive production cross sections and mean multiplicities of π±, K±, p, and p¯ in e+e− annihilation at a c.m. energy of 29 GeV have been measured with the time-projection chamber at PEP, using ionization energy loss to separate particle types. On average, 10.7±0.6 π±, 1.35±0.13 K±, and 0.60±0.08 p,p¯ are contained in an annihilation event. The fraction of pions among final-state particles decreases from over 95% at 0.3 GeV/c momentum to about 60% at high momentum; the kaon and proton fractions rise correspondingly.
PARTICLE FRACTIONS.
PARTICLE FRACTIONS.
PARTICLE FRACTIONS.
Hadron production by e + e − annihilation has been studied for c.m. energies W between 13 and 31.6 GeV. As a function of 1n W the charged particle multiplicity grows faster at high energy than at lower energies. This is correlated with a rise in the plateau of the rapidity distribution. The cross section s d σ /d x is found to scale within ±30% for x > 0.2 and 5 ⩽ W ⩽ 31.6 GeV.
CHARGED PARTICLE MULTIPLICITIES.
RAPIDITY DISTRIBUTION.
RAPIDITY DISTRIBUTION.
Measurements ofR, sphericity and thrust are presented for c.m. energies between 12 and 31.6 GeV. A possible contribution of at\(\bar t\) continuum can be ruled out for c.m. energies between 16 and 31 GeV.
No description provided.
We report measurements of π±K±, and p, p¯ inclusive cross sections and fractions in e+e− annihilation at s=29 GeV, for the momentum interval 0.01<z=ppbeam<0.90. The analysis is based on approximately 70 pb−1 of data collected with the TPC2γ detector facility at the SLAC storage ring PEP. Detector upgrades result in significantly improved momentum coverage and precision of the data, compared to previous measurements.
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The production of charmed D* mesons in e+e− annihilations at a center-of-mass energy of 29 GeV has been studied using the time-projection-chamber (TPC) detector at the SLAC storage ring PEP. The production cross section, fragmentation function, and forward-backward asymmetry due to electroweak effects are measured, and a limit on D0-D¯0 mixing is determined.
No description provided.
No description provided.