Some results from the Thin Gap Gas Chamber detector prototype for the DELPHI end-caps

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Abstract

Thin Gap Gas Chambers were proposed for a possible upgrade of the end-caps of the DELPHI detector at LEP. Two full prototypes were built and tested at the CERN 20 GeV/c SPS pion beam. The main construction parameters of the detector and the on-board front-end electronics characteristics are reviewed. Test beam results from the full prototypes, showing the general feasibility of the detector, will be presented.

Introduction

A detector based on Thin Gap Gas Chambers (TGGC) was proposed to improve the trigger and tracking performances in the DELPHI 1, 2end-cap regions at LEP200.

A large number of constraints had to be taken into account in the design of the detector, due to the necessity to fit within the actual structure of the DELPHI detector.

The TGGCs have one of their cathode planes etched with a high granularity pattern of triangular pads, to meet the trigger geometry requirement, while the other cathode plane is etched with strips either radial or transverse to the beam direction.

The chamber is made of multilayer printed-circuit boards (PCB) providing a compact and reliable structure.

The same requirements also constrained the design of the front-end electronics, placed on two independent multilayer PCBs on top of the chamber, which perform a full on-board signal processing.

The tests carried out on the complete prototypes, at the 20 GeV/c SPS pion beam at CERN, have shown the general feasibility of the detector. The chamber and the front-end electronics were tested and found to meet the design specifications.

With respect to previous applications, this work proved the practicability of this kind of detector when a high granularity is required on a large size detector, and therefore, many readout channels and a VLSI electronics are involved.

As the behavior of the DELPHI forward trigger and tracking at LEP200 turned out to be fully satisfactory, the Collaboration decided not to proceed with the detector upgrade. The working group was encouraged to proceed with the construction and full tests of the prototypes, as foreseen in the original project.

Some of the properties of TGGCs, a very thin and robust multiwire chamber providing big and fast signals, make this kind of detector an interesting solution for various applications in future experiments.

Section snippets

Overview and design considerations

The detector was designed to improve the redundancy and the hermeticity of the forward trigger and tracking at LEP200 and help to solve the left–right ambiguity of the forward tracking chambers. The location of the detector just after the Forward Chamber A would provide a polar angle coverage between 10° and 30° and a full coverage in azimuth.

Many constraints had to be taken into account in the design of a detector which had to be fully integrated into the actual structure of the DELPHI

Test beam results

To study the behavior of the chamber a series of tests were carried out using a 20 GeV/c pion beam at the CERN SPS. The trigger came from the coincidence between two scintillation counters. The data were readout and written to disk by the Fast-bus data acquisition system, allowing immediate analysis of the data set.

A display of a few events is shown in Fig. 4. The hit pads are hatched and the lines show the position of the hit strips. The signal rise-time was measured to be ≈20 ns.

A comparison of

Summary

A detector based on Thin Gap Gas Chambers was designed to improve the trigger and tracking capabilities in the DELPHI end-caps at LEP200. Two full prototypes were built and tested. Technical problems due to the many constraints have been faced and solutions have been described. The chamber multilayer PCBs and on-board VLSI electronics allowed to satisfy the design requirements. The test beam results have shown stable operating conditions. The front-end electronics has been tested on the chamber

Acknowledgements

We would like to thank G. Mikenberg for his advise and the Weizmann Institute of Science for the help given with the chamber graphite layer; G. Leder of the HEPHY Institut für Hochenergiephysik for many useful discussions and suggestions, I. van Vulpen of NIKHEF for the help given with the tests. We express our gratitude to L. Gatignon and collaborators for their help in the setup of the beam line. We wish also to thank J.E. Augustin, H. Foeth and D. Treille for initiating this work.

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