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Claudia-Elisabeth WulzInstitute for High Energy PhysicsVienna
Level-1 Trigger Menu Working GroupCERN, 9 November 2000
Global Trigger Overview
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
CMS Level-1 Trigger
GLOBAL TRIGGER
CalorimeterLocal Trigger
DTLocal Trigger
CSCLocal Trigger
Regional CalorimeterTrigger
Regional CSCTrigger
RPCTrigger
CSCHits
RPCHits
DTHits
Calorimeterenergy
Global CalorimeterTrigger
Global Muon Trigger
Regional DTTrigger
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Global Trigger
For physics running the Global Trigger uses only input from the calorimeters and the muon system. Trigger specific sub-detector data are used. The high resolution data are used by the Higher Level Triggers. Apart from the trigger data, special signals from all sub-systems may be used for calibration, synchronization and testing purposes (technical triggers). The TTC System is an optical distribution tree that is used for the transfer of the Level-1 Accept signal and timing information (LHC clock etc.) between the trigger and the detector front-ends. The Trigger Control System controls the delivery of L1A signals and issues bunch crossing zero and bunch counter reset commands. There is a facility to throttle the trigger rate in case of buffers approaching overflow conditions. The Event Manager controls the Higher Level Triggers and the Data Acquisition.
Global Trigger Environment
L1 calorimetertrigger
L1 muontrigger
GLOBAL
TRIGGER
PROCESSOR
TriggerControlSystem
TTCsystem
DetectorFront-Ends
DAQ Event
ManagerTechnicaltriggers
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Trigger Examples of explorable physics channels
1 HSM, H, A, H±, W, W’, t, B-physics channels2 HSM, h, H, A, Z, Z’, V, , LQ, Bs
0 ->2, , ’, ’’+e/HSM, H, A, t, WW, WZ, W, , V+jet(s)HSM, h, H, A, , LQ, t+ET
m t, , LQ, WW, WZ, W1 e/HSM, h, H, A, W, W’, t, B-physics channels2 e/HSM, h, H, A, Z, Z’, WW, WZ, W, , LQ2 jets QCDe/+jet(s) HSM, h, H, A, , LQ, QCD ( +jets, W+jets)+ HSM, H, A, e/+HSM, H, A, +jets H± jets+ET
m , H±
˜ g , ˜ q
˜ g , ˜ q ˜ g , ˜ q
˜ g , ˜ q
˜ g , ˜ q , ˜ l
˜ l , ˜ χ0 , ˜χ±
˜ l , ˜ χ0 , ˜χ±
˜ g , ˜ q
˜ l , ˜ χ0 , ˜χ±
Examples of Trigger Conditions
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Basic Principles of the Global Trigger
For most other comparable experiments the trigger is based on counting objects exceeding thresholds. Only summary information is available. This implies applying thresholds at local or regional levels. In CMS, only the Global Trigger takes decisions, i.e. no cuts (except inherent thresholds for defining a jet, isolation criteria etc.) are applied by lower level trigger systems. The trigger decision is based on detailed information about a trigger object, which includes not only pT or ET, but also location. For muons, quality information and charge are also available. This enables selecting specific event topologies. The objects are ordered by rank.An algorithm is a combination of trigger objects satisfying defined threshold, topology and quality conditions. There are 128 trigger algorithms running in parallel. The resulting bits are available in the trigger data record. The Global Trigger runs dead-time free by principle, i.e. a L1 Accept/Reject decision is issued with every bunch crossing. The Trigger Throttle System may, however, inhibit a L1A in case of e.g. buffer overflow warning. For each algorithm a rate counter and a programmable prescale factor (up to 16 bits) are available. The L1 decision is taken by a Final OR of which up to 8 are available for physics.
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Input to Global Trigger
Best 4 isolated electrons/photons ET, ,
Best 4 non-isolated electrons/photons ET, ,
Best 4 central jets ET, ,
Best 4 forward jets ET, ,
Best 4 - jets ET, ,
Total ET ET
Missing ET ETmiss, (ET
miss)6 jet counts (central jets)2 jet counts (forward jets)Best 4 muons pT, sign, , , quality, MIP, ISO
4 inputs (approximately 100 bits) are still free.
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Board Layout of the Global Trigger
PSB (Pipeline Synchronizing Buffer) Input synchronizationGTL (Global Trigger Logic) Logic calculationFDL (Final Decision Logic) L1A decisionTIM TimingGTFE (Global Trigger Frontend) Readout
L1Ato TTC, DAQ
FromTTC
FromDetector
L1Ato TTC, DAQ
ToDAQ
FromTTC
Backplane with point-to-point and readout links
PSB GTL FDL TIM GTFE
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Algorithm Logic
The Algorithm Logic is performed in the GTL boards located in the Global Trigger crate.
The first step consists of applying conditions to groups of trigger objects: Particle Conditions and Delta Conditions. This step is sufficient for many algorithms already.
Algorithm calculations requiring more complex correlations between different particles are performed in a second step, the so called Algorithm AND-OR.
Object configurations can not only be selected, but also vetoed.
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Particle Conditions
Particle Condition for 2 back-to-back isolated electrons
Particle Condition for 2 back-to-back isolated opposite-sign muonswith MIP bits set
Particle Conditions are applied to a group of objects of the same type. The conditions are: ET or pT thresholds, /-windows, bit patterns for isolation, quality, charge, and spatial correlations (, ) between objects of the same type.
eis.(1)
eis.(2)
ET(1) > ET(1)threshold
ET(2) > ET(2)threshold
0o ≤ φ(1)<360o
0o≤φ(2)<360o
170o≤|φ(1)-φ(2)|<190o
+(1)
μ-(2)
pT(1) > pT(1)threshold
pT(2) > pT(2)threshold
0o ≤ φ(1) < 360o
0o ≤ φ(2) < 360o
170o ≤ |φ(1) - φ(2)| < 190o
ISO(1) = 1, ISO(2) = 1MIP(1) = 1, MIP(2) = 1SGN (1) = 1, SGN(2) = -1
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Delta Conditions
Delta Conditions refer to the calculation of spatial correlations (, ) between objects of different types. The correlations are restricted to “close” and “opposite/far”. This is actually also the case for same type objects. More detailed angular relations can be calculated by the Higher Level Triggers.
170o ≤ |φ(Jet) - φ(ETmissing)| < 190o
Jet
ETmissing
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Algorithm AND-OR
Next step: Actual algorithm calculations.Logical combinations (AND-OR) of objects are determined.
eis.
ETmissing
ET(eis.) > ET(eis.)threshold
ETmissing > ET
threshold
Pa rticle Condition forisola te d e le ctron
Pa rticle Condition formiss ing ET
ALGORITHM AND
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Algorithm AND-OR
ETmissing
OR
Particle Condition formissing ET
Particle Conditions for muons
Particle Conditions for isolated electrons
ET(eis.) > ET(eis.)threshold pT(μ) > pT(μ)thresholdET
missing > ETthreshold
OR
ALGORITHM AND-OR
ANDAND
eis .
ETmiss ing
eis . μ
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Basic Trigger Setup
In the stable phase of the experiment the trigger is set up via Run Control using predefined menus which include reasonable thresholds for different luminosities. These thresholds may be changed by the physicist, without reconfiguring the logic chips. Most of the 128 algorithms are available for physics running. The basic rule is to keep the trigger menus as simple as possible. If not all interesting physics processes can be caught with these, more sophisticated logic may be used, but careful studies of trigger efficiencies have to be made. If a new algorithm (i.e. one not already present on the chips) becomes necessary, the chips can be reprogrammed by experts. The timescale for this is a few hours, but it should not happen too often.
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Setup- and Placement Program
Event Generator
Example for Expert Setup Procedure
Claudia-Elisabeth Wulz Nov. 2000 L1 Trigger Menu Working Group
Overview of Features and Flexibility
The trigger logic is largely programmable.
Particle energy or momentum thresholds and (or windows can be set separately for each object. Different thresholds for central and forward regions are therefore possible.
Templates for muon quality, including MIP, isolation and charge information can be selected.
Space correlations are possible between all objects, but restricted to “close” and “opposite/far”.
Jets are actually separated into central and forward jets. There are also 8 jet multiplicities, 2 of which are reserved for the forward jets.
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