C. R. Sun

New channeling effects in the radiative emission of 150 GeV electrons in a thin germanium crystal

Abstract The orientation dependence of the radiative emission of 150 GeV electrons and positrons incident at small angles with respect to the 〈110〉 axial direction of a thin (0.185 mm) Ge crystal has been observed. The processes are well understood, except for channeled electrons, which radiate unexpected high energy photons.

Study of the decay B¯(0)→D+l¯ν¯

Using a sample of 484 000 {ital B} mesons collected with the CLEO detector at the Cornell Electron Storage Ring, we have measured {ital B}({ital {bar B}}{sup 0}{r arrow}D{sup *+}l{sup {minus}}{nu}) and found that the polarization of the {ital D}{sup *+} is small. These results are compared with models of semileptonic {ital B} decay.

Extraction from TeV-range accelerators using bent crystal channeling

Abstract Plans and first results from Fermilab Experiment 853 are presented. E853 is an experiment to test the feasibility and efficiency of extracting a low-intensity beam from the halo of the Tevatron using channeling in a bent silicon crystal. The motivation of the experiment is to apply crystal extraction to trans-TeV accelerators like the LHC. Channeling developments related to crystal extraction and some early results from accelerator studies at the Tevatron are presented.

Measurement of the isospin mass splitting Ξ+cΞ0c

Abstract Using the CLEO detector, we present a measurement of the mass of the charged charmed strange baryon Ξ + c and its neutral counterpart the Ξ 0 c . The Ξ + c is observed through its decay to Ξ - π + π + , and its mass is measured to be (2467±3±4) MeV. The isospin mass splitting of the Ξ c system is found to be M ( Ξ + c )- M ( Ξ 0 c )=(−5±4±1)MeV.

A measurement of the tau lifetime

The tau lepton lifetime is measured using four different methods with the DELPHI detector. Three measurements using one prong decays are combined, accounting for correlations, resulting in ττ=298 ±7 (stat.)±4 (syst.) fs while the decay length distribution of three prong decays gives ππ=298±13 (stat)±(syst.) fs. The combined result is ττ=298±7 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay is found to be 0.985±0.013, compatible with lepton universality.

Measurement of axial effects on the pair creation by 30–150 GeV photons and on the radiation emitted by 150 GeV electrons and positrons in Ge crystals

Abstract Crystal-assisted processes around the 〈110〉 axis of a Ge crystal cooled to 100 K have been investigated at CERN with 150 GeV e− and e+ incident beams and 30–150 GeV incident photons. A large enhancement of the radiation emitted by incident e+ and e− is observed. Electrons are found to radiate more than positrons. When the crystal is tilted around 〈110〉 clear channeling effects are still observed. However the radiation enhancement persists at angles much larger than the channeling critical angle. The total pair creation rate by photons aligned along 〈110〉 has also been measured: in contrast with what is observed for a random orientation, the rate increases sharply with the photon energy. A scan through 〈110〉 shows that the pair production does not reach a maximum for axial incidence but at a tilt angle which decreases when the photon energy increases. These measurements indicate that crystal assisted pair production is not governed by the channeling of the created electrons.

DEFLECTION OF HIGH ENERGY CHANNELED CHARGED PARTICLES BY ELASTICALLY BENT SILICON SINGLE CRYSTALS

An experiment has been carried out to observe the deflection of charged particles by planar channeling in bent single crystals of silicon for protons with energy up to 180 GeV. Anomolous loss of particles from the center point of a three point bending apparatus was observed at high incident particle energy. This effect has been exploited to fashion a “dechanneling spectrometer” to study dechanneling effects due to centripital displacement of channeled particle trajectories in a bent crystal. The bending losses generally conform to the predictions of calculations based on a classical model.

Deflection of charged particles in the hundred GeV regime using channeling in bent single crystals

Abstract An experiment has been carried out to observe the deflection of charged particles by planer channeling in bent single crystals with momenta between 12 and 180 GeV and with angular deflections up to 27 milliradians. Anomalous losses of particles from the center point of a three point bending apparatus have been observed at high incident particle energy. This effect has been employed as a “dechanneling spectrometer” to study dechanneling effects caused by bending. The bending losses generally conform to theories of bending dechanneling based on the classical channeling model.

Measurement of γγ widths of charmonium states

Abstract Using the CLEO detector at the Cornell Electron Storage Ring, we have searched for two-photon production of charmonium in four-track final states. We have measured Γ γγ ( η c )=5.9 +2.1 −1.8 ±1.9 keV, and we have obtained 95% CL upper limits of Γ γγ ( X c 0 ) Γ γγ ( X c 2 )

Strong field interactions of high energy electrons and photons in Ge crystals

Abstract The experimental results obtained in a high energy experiment (30–200 GeV), with γ, e + , e − , incident around Ge crystallographic directions are presented. The pair creation process is well reproduced by QED in strong field. The radiation process in very strong field is much less understood especially in channeling conditions.