Level-1 Trigger Menus

CMS WeekMumbai, Dec. 2000

Claudia-Elisabeth WulzInstitute for High Energy Physics

Vienna

Level-1 Trigger Menus

Claudia-Elisabeth Wulz Mumbai, Dec. 20002

Introduction

Definition of Trigger Menu:

Set of algorithms running concurrently in the Global Trigger.Set of algorithms running concurrently in the Global Trigger.

There may be different sets for different run conditions (B-physics at low luminosity, heavy ion runs, discovery physics at high luminosity, calibration etc.). Run control must record the used menu.

Remember: If an event does not pass Level-1, it is gone forever If an event does not pass Level-1, it is gone forever and will never make it to a physics publication!and will never make it to a physics publication!


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


L1 Menu Working Group

Established during TriDas Week 9 Nov. 2000. Every interested Every interested person is invited to join and to provide his or her ideas!person is invited to join and to provide his or her ideas!

Presentations at initial meeting:

• Introduction

• Global Trigger overview

• Calorimeter Trigger overview

• Muon Trigger overview

• Trigger menu requirements from physics point of view

• Trigger menu requirements from HLT point of view

• Trigger menu requirements from DAQ point of view

W. Smith

C.-E. Wulz

S. Dasu

G. Wrochna

M. Dittmar

P. Sphicas

S. Cittolin


TasksTasks

Provide initial trigger menus to capture the interesting physics. Menus for calibration etc. should also be established. Menus should not be considered fixed once and for all, but will evolve with experience gained. The flexibility and special features of the CMS L1 trigger should be optimally used. Check that trigger design is capable of handling all physics and technical requirements. Provide corresponding suitable trigger parameters (at level of global trigger and at regional and perhaps local levels). Allocate suitable bandwidths for categories of algorithms.

L1 Menu Working Group


CMS Level-1 Trigger

GLOBAL TRIGGER

CalorimeterLocal Trigger

DTLocal Trigger

CSCLocal Trigger

Regional CSCTrigger

RPCTrigger

CSCHits

RPCHits

DTHits

Calorimeterenergy

Global CalorimeterTrigger

Global Muon Trigger

Regional CalorimeterTrigger

Regional DTTrigger


Basic Principles of the L1 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.


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


Input to Global Trigger

Best 4 isolated electrons/photons ET, ,

Best 4 non-isolated electrons/photons ET, , Best 4 central jets (|| 3) ET, , Best 4 forward jets (3 || 5) 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.


Features and Flexibility of Global Trigger

The Global 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.


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.


Predefined Algorithms


2 Forward Jets in opposite -hemispheres


4 muons with template conditions


2 muons with space and charge correlations


Features and Flexibility of Calorimeter Trigger

Trigger PrimitivesTrigger PrimitivesFine grain veto: max ET in -strip pair vs total trigger tower ET

Trigger TowersTrigger TowersSeparate ET cutoffs for e/ and /jet/ET triggersH/E veto: ECAL vs HCAL ET ratio, can be non-linearActive tower definition: programmable ET cut to adjust for pileup4x4 trigger tower region level for jets: ET cut for pileup suppression, cut on active tower count for veto /jet candidate level: -dependent center region threshold and ET lookupPossible additional Global Calorimeter Trigger algorithms: ET of jets, missing ET of jets


Features and Flexibility of Muon Trigger

DT, CSC, RPCDT, CSC, RPCpT scale of all 3 systems (DT, CSC, RPC) programmable, can in principle be different for all 3, but Global Muon Trigger must convert to a common scale.Global Muon TriggerGlobal Muon TriggerImplementation of the matching scheme, many tunable parametersDT, CSCDT, CSCTRACO: LUTS for correlation of BTIs, filters for ghost suppressionTrack Finder: Extrapolation windows, assignment LUTs, filters for ghosts (also in Global Muon Sorter)RPCRPCpatterns, gate (noise suppression)


HLT, DAQ and L1 interplay

Check decision-making and filtering of Level-1Check decision-making and filtering of Level-1Disentangle detector and trigger malfunctions, monitor rejected eventsCheck seed-generator function of Level-1Check seed-generator function of Level-1Regional reconstruction of HLT depends on what L1 sends! Need to reconstruct also objects that did not fire the L1 trigger.Storage of L1 Trigger parametersStorage of L1 Trigger parametersNeed database, pointer to it is major element of “run number”. Event is not simply identified by run and event number, but by data structure containing run conditions. Run = time between fill start and end.Minimum Bias eventsMinimum Bias eventsNeed full reconstruction. Example of use: check events that systematically fail e/ trigger, but fire the jet trigger.


HLT, DAQ and L1 interplay

Importance of prescalingImportance of prescalingAutomatic or fixed. For automatic prescaling need good and traceable luminosity measurement! Check trigger efficiencies at lower thresholds than in main trigger menu, flag events for calibration.

Dynamic changes of trigger menuDynamic changes of trigger menuRelax thresholds and optionally change algorithms as luminosity drops.

Trigger typeTrigger typeOption in the Global Trigger, no strong demand yet ...

Trigger menu recordingTrigger menu recordingShould be in database accessible both by the Global Trigger Processor and the HLT farm.

DAQ issuesDAQ issuesLocal event filter rate 1000 Gbit/s, event storage 5 Gbit/s. Recording rate can be greater than 100 Hz.


Physics considerations

Hardware Trigger(< 100 kHz) HLT (< 100 Hz) Analysis (10 6-7 events?)raw calibration almost final calibration best calibration

subdetectors with coarse almost full detector fine segmentation and full detector available

detector segmentation combination of tracks calo and systemsingle (isolated) objects verify trigger object(s) signal optimization

with p T cuts object matching with tracks accurate track matchingmultiple object triggers mass of clusters + tracks precision mass calculations

- correlations complicated , and pT selection criteriasatisfy physics needs with hardware satisfy physics requirements with software be "undisturbed" by trigger conditions

Trigger cuts should be softer than physics selection criteria, but some rates will be too high! Need compromise.Need compromise.

High Q2: Exciting, possibly exotic physicsMedium Q2 and low x physics: New domain of strong interactionsLow Q2: b and c physics with unprecedented statistics


Physics considerations

Physicists have many different points of view. Examples: can(not) be measuredRapidity gap events are interesting/boring

Physicists want redundancy.Example: high mass Drell-Yan lepton pairs

After discovery physicists want to explore. Need to study more difficult signatures.

q q→ W(→ lv)bb

Can(not) trigger on invisible particles (e.g. νν νν X events)


Statistics considerations

107 events/day at rate of 100 HzAccuracy for cross-section measurements: ± 1%-> 105 accepted signal events -> ± 0.3% statistical error

Cross section (σxBR) Events/day Comment1mb1b

1011

108Canre doeveryhourCanre do daily

100nb10nb1nb

107

106

105

D oinearlyrunningD oinearlyrunningD oinearlyrunning

1pb1fb

1000.1

If not triggered… gone foreve !r


Large and low cross section measurements

Low cross section• Important not to lose any event

Example: Bso -> + - (BR 3.5 x 10-9)

• After discovery can accept worse S/B ratio for BR measurements

Large cross section (σ x BR > 100 nb)• Prescaling• Accept 1 Hz rate for a few days and make analysis• Use luminosity lifetime: use free rate near end of fill• Combination of all three above


Simulation studies

Physics goals• Observation, evidence, exclusion• Cross section measurement • BR measurement• Measurement of trigger effiency

(control channels, lower thresholds, etc.), background

Simulation studies to be done• SM Higgs, SUSY, higher dimensions, exotica, …• b and t physics• QCD and other SM physics• New signatures as we go along


Conclusions

Baseline trigger design suitable and flexible enough for most Baseline trigger design suitable and flexible enough for most imagined signaturesimagined signatures

Reasonable thresholds can be setReasonable thresholds can be set Redundancy for high Q2 processes

Rates for most triggers okRates for most triggers okRates for many single object triggers relatively high, multi-object triggers should be made use of

Topology and quality options availableTopology and quality options availableNeed scenarios for use

Please join L1 Menu Working Group!Please join L1 Menu Working Group!

Level-1 Trigger Menus

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