Claudia-Elisabeth Wulz Institute for High Energy Physics Vienna Level-1 Trigger Menu Working Group CERN, 9 November 2000 Global Trigger Overview

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


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


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


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.


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.


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


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.


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


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


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


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


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.


Setup- and Placement Program

Event Generator

Example for Expert Setup Procedure


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.

Documents

Claudia-Elisabeth Wulz Institute for High Energy Physics Vienna Level-1 Trigger Menu Working Group CERN, 9 November 2000 Global Trigger Overview