Optimisation of a silicon microstrip telescope for UA9 crystal channeling studies

G Hall,T James,M Pesaresi

doi:10.1088/1748-0221/15/05/c05014

Abstract

A charged particle telescope based on silicon microstrip sensors has been used for several years for data taking at high rates in the CERN H8 beam line using a range of different incident particles. The electronic readout and data acquisition system is based on that developed for the CMS Tracker, and provides almost deadtime-free operation at trigger rates of up to about 10 kHz. The telescope was designed to characterise crystals in channeling studies by the UA9 experiment with the primary objective to validate them for use in a future LHC beam collimation system, hence is optimised for measurement of a single particle in the outgoing arm. The telescope has also been used for other studies of fundamental phenomena associated with the channeling process and further LHC applications. Some of these require a different layout of the telescope, for example to achieve a larger angular acceptance to study longer channeling crystals, or modifications to sensor operating conditions because of the very large electric charge and consequent ionisation energy loss associated with heavy ions. The telescope and its performance are described. Possible improvements are discussed.

Highlights

Telescope layout and operationThe “standard” layout of the apparatus is shown in figure 1; each arm has a length of approximately 10 m
An obvious target for modifications would be to improve the angular resolution, which for a telescope with long arms requires reduction in the material budget which can only be achieved by thinner sensors
Based on about ten years of operations, considerable experience has been gained using a silicon microstrip telescope whose performance is mostly well understood, calculations seem presently to underestimate slightly the achievable performance compared to measurements

Summary

Telescope layout and operation

The “standard” layout of the apparatus is shown in figure 1; each arm has a length of approximately 10 m. The original objective was to measure performance of crystals to be used for LHC beam collimation This requires excellent angular resolution, sufficient to select particles within the critical channeling angle θc [5], the long lever arms. Automated scans from incident direction to the channeling angular region, with (mostly) a single particle in the telescope, were required to achieve high statistics, and rapid location of the channeling angle In practice this was speeded up by precise laser alignment of the crystal on the goniometer which simplified the identification of the channeling peak. The main changes since have been to the DAQ and track reconstruction software to increase as much as possible the data taking rates, and to handle different beam conditions, as well as improve the user-friendliness of the system

Track reconstruction and telescope performance

Possible future developments

Findings

Summary