J. Alcaraz

The L3 silicon microvertex detector

Abstract The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

A high resolution muon detector

Abstract The design and operation of precision drift chambers with multisampling as well as the concepts and methods for reaching an extraordinary degree of precision in mechanics and calibration are described. Specific instruments were developed for this purpose. The concept of reproducible positioning and the implementation to 30 μm accuracy, showing stability over three years, is given. Calibration and analysis with UV-laser and cosmic test measurements are outlined with the critical results. The experience of calibration and reliability of the large system in an actual L3 running experiment is analyzed. The resolution under “battle conditions” at LEP resulted in Δp p = (2.50±0.04)% at 45.6 GeV and will be presented in detail. The concept is well suited for future TeV energies.

Indirect dark matter search with diffuse gamma rays from the Galactic Center with the Alpha Magnetic Spectrometer

The detection of non-baryonic dark matter through its gamma-ray annihilation in the centre of our galaxy has been studied. The gamma fluxes according to different models have been simulated and compared to those expected to be observed with the Alpha Magnetic Spectrometer (AMS), during a long-term mission on board of the International Space Station. Under the assumption that the dark matter halo is composed of the lightest, stable supersymmetric particle, the neutralino, the results of the simulations in the framework of mSUGRA models, show that with a cuspy dark matter halo or a clumpy halo, the annihilation gamma-ray signal would be detected by AMS. More optimistic perspectives are obtained with the Anomaly Mediated Supersymmetry Breaking (AMSB) model. The latter leads also to a cosmologically important 6Li abundance. Finally, the discovery potential for the massive Kaluza-Klein dark matter candidates has been evaluated and their detection looks feasible.

A study of the dimensional stability of the AMS silicon tracker

The Alpha Magnetic Spectrometer (AMS) is designed as an independent module for installation on the International Space Station (ISS) for an operational period of 3 years. The AMS is the first cosmic ray spectrometer equipped with a large area silicon tracker . A preliminary version of the detector was flown on the NASA space shuttle Discovery during June 2–12, 1998. Results for the dimensional stability of the silicon tracker planes based on the flight data, and the metrology data recorded before and after the flight, are presented.

Track fitting in slightly inhomogeneous magnetic fields

A fitting method to reconstruct the momentum and direction of charged particles in slightly inhomogeneous magnetic fields is presented in detail. For magnetic fields of the order of 1 T and inhomogeneity gradients as large as 1 T/m the typical momentum bias due to the proposed approximations is of the order of few MeV, to be compared with scattering components of the order of 20 MeV or even larger. This method is currently being employed in the reconstruction programs of the AMS experiment.

Tau lepton leptonic branching fractions from L3

We have measured the branching fractions of the τ lepton into electrons and muons with the L3 detector at LEP. The sample used in analysis has been collected during 1991, 1992 and 1993 around the Z peak, with an integrated luminosity of 61 pb −1 . A preliminary result yields: BR ( τ − → e − ν ¯ e ν τ ) = ( 17.69 ± 0.17 ± 0.08 ) % ( 1 ) BR ( τ − → μ − ν ¯ μ ν τ ) = ( 17.36 ± 0.17 ± 0.07 ) % ( 2 ) where the first error is statistical and the second one is systematic.

A method to use CCDs as tracking devices with reduced dead time at room temperature

Abstract We discuss in this paper a method for track reconstruction using CCD arrays in high event rate experiments. The method is based on the correlation of the information obtained from the continuous readout in opposite directions of two CCDs placed close together and the time at which a minimum ionizing particle crosses the CCDs. This time is obtained by a trigger device and is measured in units of the CCD line clock. The technique is described in detail and the results of experimental tests, performed at the CERN SPS on a prototype using commercial arrays TH7882 are discussed. Efficiencies larger than 95% have been obtained in the reconstruction of space points of beam tracks. The reconstruction algorithm is able to filter out noisy pixels up to ∼ 0.1% of the total number, thus allowing reliable operation at room temperature. These results show that both the effective readout dead time and the generation of ghost tracks can be significantly reduced.