Abstract
A scintillating fibre tracker is proposed to measure elastic proton scattering at very small angles in the ATLAS experiment at CERN. The tracker will be located in so-called Roman Pot units at a distance of 240 m on each side of the ATLAS interaction point. An initial validation of the design choices was achieved in a beam test at DESY in a relatively low energy electron beam and using slow off-the-shelf electronics.Here we report on the results from a second beam test experiment carried out at CERN, where new detector prototypes were tested in a high energy hadron beam, using the first version of the custom designed front-end electronics. With a spatial resolution of 25 μm an adequate tracking performance was obtained, under conditions which are similar to the situation at the LHC.In addition, the alignment method using so-called overlap detectors was studied and shown to have the expected precision.
Highlights
Reason, dedicated FE electronics have been designed for ALFA
The results from the DESY test together with GEANT4 simulations made it possible to predict that the obtained spatial resolution of 36 μm would decrease to about 20 25 μm if ALFA was operated in a high energy hadron beam
The ATLAS experiment is planning to measure the absolute luminosity from elastic scattering at very small angles using a scintillating fiber tracker called ALFA
Summary
The beam test was carried out at the CERN SPS H8 beam which is a secondary beam in the CERN North Area. The primary target consists of a 30 cm long Beryllium plate. We have used for most of the period a secondary beam at 230 GeV=c (70% p and 30% π+ ) and for a few days a 20 GeV=c secondary beam (mainly π+ beam with a small p contamination). The ALFA detector was mounted on a table which allowed the detector to be translated in the direction of the axes of the plane transverse to the beam, as well as being rotated around these axes. The trigger was based on a 30 30 mm plastic scintillator and its signal was put in coincidence with the signal from a second scintillator that had dimensions similar to the active area of the particular ALFA prototype used
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