H. Anderhub

Test of a high resolution drift chamber prototype

Abstract The performance of a drift chamber prototype for a colliding beam vertex detector in a test beam at DESY is described. At one (two) atmosphere gas pressure a spatial resolution of 40 μm (30 μm) per wire for one cm drift length was achieved with a 100 MHz Flash-ADC system. An excellent double track resolution of better than 300 μm over the full drift length of 5 cm can be estimated.

Measurement of the Shadowing of High-Energy Cosmic Rays by the Moon: A Search for TeV-Energy Antiprotons

The shadowing of high-energy cosmic rays by the Moon has been observed with a significance of 9.4 standard deviations with the L3 + C muon spectrometer at CERN. A significant effect of the Earth magnetic field is observed. Since no event deficit on the east side of the Moon has been observed, an upper limit at 90% confidence level on the antiproton to proton ratio of 0.11 is obtained for primary energies around 1 TeV.

A time expansion chamber as a vertex detector for the experiment mark j at desy

Abstract The design and results from a beam test for a small vertex detector, now installed in the DESY MARK J experiment, are presented. The concept of this drift chamber is based on the time expansion principle with readout planes inclined to solve the left-right ambiguity. A spatial resolution of 35 μm, varying weakly as a function of drift length and azimuthal angle, has been achieved.

A TIME EXPANSION CHAMBER AS A VERTEX DETECTOR

Abstract A high-resolution drift chamber based on the time expansion principle has been built as a vertex detector for the Mark J experiment at DESY. The chamber design and the associated control and readout system are described. Results on chamber performance obtained from test beam measurements and first results from running at PETRA are reported.

Formation of the lightest muonic atoms in low density gases

Abstract A novel technique devised to produce light muonic atoms efficiently in low pressure gases (10 to 600 torr at 300 K) has been successfully implemented in helium. Muons produced by in-flight decay of 40 MeV/ c pions are trapped in a magnetic bottle filled with the low density gas. The high-yield formation of muonic atoms is demonstrated by detecting the characteristic X-rays as well as the μ-decay electrons.

A measurement of the strong coupling constant αs to complete second order

The strong interaction coupling constant αs has been measured with a new method, the planar triple energy correlation in the reaction e+e- → hadrons at center-of-mass energies ranging from 14 GeV to 46.78 GeV. A complete second-order perturbative QCD calculation was used. ΛMS = 110 ± 30 −55+70 MeV is found.

Search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model in e+e−interactions at s= 189 GeV

A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed using 176.4 pb -1 of integrated luminosity collected by L3 at a center-of-mass energy of 189 GeV. No signal is observed, and the data are consistent with the expected Standard Model background. Lower limits on the masses of the lightest neutral scalar and pseudoscalar Higgs bosons are given as a function of tanβ. Lower mass limits for tanβ>1 are set at the 95% confidence level to be m h > 77.1 GeV and m A >77.1 GeV.A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed using 176.4 pb−1 of integrated luminosity collected by L3 at a center-of-mass energy of 189 GeV. No signal is observed, and the data are consistent with the expected Standard Model background. Lower limits on the masses of the lightest neutral scalar and pseudoscalar Higgs bosons are given as a function of tanβ. Lower mass limits for tanβ > 1 are set at the 95% confidence level to be mh > 77.1 GeV and mA > 77.1 GeV. Submitted to Phys. Lett. B