A RICH Multiplicity Veto for the HERA-B Experiment

TL;DR

The paper describes the development and successful implementation of a high-efficiency multiplicity veto system for the HERA-B experiment, which reduces high-multiplicity events before triggering, enhancing data quality.

Contribution

It introduces a modular RICH multiplicity veto system with a programmable threshold, improving event selection in the HERA-B detector.

Findings

Veto efficiency of 99.9991% achieved

System successfully integrated into routine data-taking

Modular design allows flexible event rejection

Abstract

We present the design and commissioning of a new multiplicity veto for the HERA-B detector, a fixed-target spectrometer originally designed to study the physics of B mesons in proton-nucleus interactions. The HERA-B trigger is a message-driven multi-level track trigger. The first level trigger (FLT) consists of custom-made electronics, and the higher trigger levels are implemented as PC farms. The multiplicity veto has been designed to reject high-multiplicity events before they enter the trigger chain. A veto signal is generated based on the comparison of the number of photons in part of the HERA-B ring-imaging Cherenkov counter (RICH) with a programmable threshold. The RICH Multiplicity Veto is a modular system. First the hits in 256 detector channels are summed by Base Sum Cards (BSC), then FED Sum Cards (FSC) sum the subtotals of up to eight BSCs. Finally the Veto Board (VB) takes the veto decision based on the sum of up to 14 FSCs. The RICH Multiplicity Veto has been successfully installed and commissioned in HERA-B. The measured veto efficiency is (99.9991+/-0.0001)%, and the system is used in the routine data-taking of the HERA-B experiment.