Global Muon Trigger emulator TWiki

Global Muon Trigger

Description

CMS has a sophisticated muon system with special dedicated trigger chambers in addition to the normal tracking chambers. The RPC trigger chambers produce a pattern of hits, the drift tube and cathode strip tracking chambers deliver track vectors at each muon station. Regional triggers of the three subsystems, the PAC trigger of the RPCs and the DT and CSC track finders, all deliver muon tracks. In general, a muon will be found by both by the RPC and the DT or CSC track finders. The task of the Global Muon Trigger (GMT) is to combine the results of all these subsystems by finding the four best muons of every bunch crossing and transmitting them to the Global Trigger (GT). In addition to finding the four best muons the GMT appends two bits set by the Calorimeter Regional Trigger, a MIP bit and an isolation bit, also called quiet bit, to each of the muon data words. The MIP bit is set if the calorimeter energy is consistent with the passage of a minimum ionizing particle, the isolation or quiet bit is set if a certain energy threshold in the trigger towers surrounding the muon is not exceeded. Both bits are used in the GT to suppress background and to improve selectivity.

Interface

The Global Muon Trigger receives 4 muon candidates from the DTBX based barrel Muon Trigger Track Finder, 4 muon candidates from the CSC based endcap Muon Trigger Track Finder and 8 muon candidates (4 barrel + 4 endcap) from the RPC Trigger (at the moment all implemented as std::vector<L1MuRegionalCand>). In addition it receives 252 isolation and 252 MIP bits from the calorimeter trigger (interface to be defined). The main class L1MuGlobalMuonTrigger is an EDProducer. It produces a vector of GMT muon candidates for the Global Trigger std::vector<L1MuGMTCand> and a collection of readout records L1MuGMTReadoutCollection. All interface classes reside in DataFormats/L1GlobalMuonTrigger.

Quality code

Quality codes are sent with each muon from the L1 Global Muon Trigger to the L1 Global Trigger. They are used in the Global Trigger in order to include only certain qualities of candidates in certain trigger algorithms. The current definition of the quality codes is given in the table below. The definition may change in the future. It is therefore safer not to rely on the quality codes in the analysis code but to use the provided interpretation Methods in class L1MuGMTCand

bool useInSingleMuonTrigger();
bool useInDiMuonTrigger();
bool isMatchedCand();
bool isHaloCand();

Configuration

A set of default parameters can be found in the L1MuGMTParameters.cfi file in the data directory of the package (L1TriggerConfig/GMTConfigProducers).

New parameter has been added (>21X) in order to accommodate different versions of low quality assignment LUT. VersionSortRankEtaQLUT=1 is adapted for full CMS geometry and VersionSortRankEtaQLUT=2 for startup geometry (staged RPC).

Cancel-decision logic configuration

There are four cancel-out units in the GMT. In the hardware, two of them are located in the Barrel Logic FPGA and two of them in the Forward Logic FPGA (as indicated in the thirs row of the table, below).Each unit has two groups of muons as an input (first/second). If a muon in the first group and a muon in the second group match in eta an phi, then either of them (or both) may be cancelled, depending on the configuration of the cancel-decision logic. The table below lists the possible cancel-options and the default settings. The options correspond to one bit each in the cancel decsision configuration word and may be freely combined. 'is matched' in the table refers to the muon being matched with a complementary muon in its main matiching unit. For example the default configuration of the DT/CSC cancel-out unit means: if a DT and a CSC muon are matched in space and if the CSC muon is matched with an RPC muon in its main matching unit but the DT muon is not matched with an RPC muon in its main matching unit, then the DT muon will be cancelled.

Tests and examples

The test directory of the package contains a steering file runGMT.cfg which uses a built-in external input source to feed GMT emulator with pre-generated data stored in an ascii format as it is used for hardware tests (an exapmle is provided). The file runGMTTest.cfg adds a small EDAnalyzer which dumps the GMT data. The file runGMTTree.cfg shows how to create a simple root tree with all GMT related information needed to validate the GMT. writeLUTsAndRegs.cfg generates LUTs and register configuration which can be loaded into the HW.

Links

The main Global Muon Trigger page

-- Main.imikulec - 31 May 2006