Synchronization methods for the PAC RPC trigger system in the CMS experiment

Abstract

The PAC (pattern comparator) is a dedicated muon trigger for the CMS (Compact Muon Solenoid) experiment at the LHC (Large Hadron Collider). The PAC trigger processes signals provided by RPC (resistive plate chambers), a part of the CMS muon system. The goal of the PAC RPC trigger is to identify muons, measure their transverse momenta and select the best muon candidates for each proton bunch collision occurring every 25 ns. To perform this task it is necessary to deliver the information concerning each bunch crossing from many RPC chambers to the trigger logic at the same moment. Since the CMS detector is large (the muon hits are spread over 40 ns), and the data are transmitted through thousands of channels, special techniques are needed to assure proper synchronization of the data. In this paper methods developed for the RPC signal synchronization and synchronous transmission are presented. The methods were tested during the MTCC (magnet test and cosmic challenge). The performance of the synchronization methods is illustrated by the results of the tests.

Modeling of Synchronous Data Streams Processing in the RPC Muon Trigger System of the CMS Experiment

“…2). Finding of four the most energetic muons by means of a cascade sorting from over 5 thousand candidates is realized properly only when the input data are synchronized [5] (processes (5-7) in fig 2). The results of muon measurements are forwarded to the GMT of CMS and are referenced to a particular physical event.…”

“…The distribution model (12) was used to prepare a universal, parameterized transmission and synchronization module of packet streams [5]. Its general structure was presented in Fig.…”

“…The implementation of real content identifiers in the stream transmission is a foundation of a complex monitoring algorithm and automated calibration of the synchronization for the whole RPC MT. This solution considerably increases the system reliability and provides fast localization of irregularities [5].…”

“…The core of the testing environment are Global Runs of the CMS experiment with participation of most of the subsystems. The RPC MT system participated in 2006 in the Magnet Test and Cosmic Challenge (MTCC) [5]. The field obtained in the CMS magnet was 3.8 T.…”

“…For example, the node (7) is, in physical realization, a cascade of nondependent sorting circuits distributed on several PCBs and positioned one next to the other in a single VME crate; • The node may bridge a number of sub-networks or separate networks. The above systemization of the characteristics was a foundation to prepare a coherent hardware and software 1 solutions 1 The synchronization software for the RPC MT is not presented here as it was described in details elsewhere [5], [6].…”