Level-1 Trigger Menus

1. Level-1 Trigger Menus

2. Introduction Definition of Trigger Menu: 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 and will never make it to a physics publication! Therefore: F

3. Examples of Trigger Conditions Trigger Examples of explorable physics channels 1 m HSM, H, A, H±, W, W’, t, B-physics channels 2 m HSM, h, H, A, Z, Z’, V, , LQ, Bs0 ->2m, , ’, ’’ m+e/g HSM, H, A, t, WW, WZ, Wg, , V m+jet(s)HSM, h, H, A, , LQ, t m+ETm t, , LQ, WW, WZ, Wg 1 e/g HSM, h, H, A, W, W’, t, B-physics channels 2 e/g HSM, h, H, A, Z, Z’, WW, WZ, Wg, , LQ 2 jets QCD e/g+jet(s) HSM, h, H, A, , LQ, QCD (g +jets, W+jets) m+t HSM, H, A, e/g+t HSM, H, A, t+jets H± jets+ETm , H±

4. 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 L1 Menu Working Group Established during TriDas Week 9 Nov. 2000. Every interested person is invited to join and to provide his or her ideas! Presentations at initial meeting:

5. L1 Menu Working Group • Tasks • 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.

6. CMS Level-1 Trigger

7. 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.

8. 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

9. Input to Global Trigger Best 4 isolated electrons/photons ET, h, f Best 4 non-isolated electrons/photonsET, h, f Best 4 central jets (|h| £3) ET, h, f Best 4 forward jets (3 < |h| <5) ET, h, f Best 4 t- jets ET, h, f Total ETSET Missing ETETmiss, f(ETmiss) 6 jet counts (central jets) 2 jet counts (forward jets) Best 4 muons pT, sign, f, h, quality, MIP, ISO 4 inputs (approximately 100 bits) are still free.

10. Features and Flexibility of Global Trigger The Global Trigger logic is largely programmable. Particle energy or momentum thresholds and h (or f) 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.

11. 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.

12. Predefined Algorithms

13. 2 Forward Jets in opposite h-hemispheres

14. 4 muons with template conditions

15. 2 muons with space and charge correlations

16. Features and Flexibility of Calorimeter Trigger Trigger Primitives Fine grain veto: max ET in h-strip pair vs total trigger tower ET Trigger Towers Separate ET cutoffs for e/g and t/jet/ET triggers H/E veto: ECAL vs HCAL ET ratio, can be non-linear Active tower definition: programmable ET cut to adjust for pileup 4x4 trigger tower region level for jets: ET cut for pileup suppression, cut on active tower count for t veto t /jet candidate level:h-dependent center region threshold and ET lookup Possible additional Global Calorimeter Trigger algorithms: SET of jets, missing ET of jets

17. e/g and jet/t Algorithms

18. Features and Flexibility of Muon Trigger DT, CSC, RPC pT 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 Trigger Implementation of the matching scheme, many tunable parameters DT, CSC TRACO: LUTS for correlation of BTIs, filters for ghost suppression Track Finder: Extrapolation windows, assignment LUTs, filters for ghosts (also in Global Muon Sorter) RPC patterns, gate (noise suppression)

19. HLT, DAQ and L1 interplay Check decision-making and filtering of Level-1 Disentangle detector and trigger malfunctions, monitor rejected events Check seed-generator function of Level-1 Regional reconstruction of HLT depends on what L1 sends! Need to reconstruct also objects that did not fire the L1 trigger. Storage of L1 Trigger parameters Need 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 events Need full reconstruction. Example of use: check events that systematically fail e/g trigger, but fire the jet trigger.

20. HLT, DAQ and L1 interplay Importance of prescaling Automatic 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 menu Relax thresholds and optionally change algorithms as luminosity drops. Trigger type Option in the Global Trigger, no strong demand yet ... Trigger menu recording Should be in database accessible both by the Global Trigger Processor and the HLT farm. DAQ issues Local event filter rate 1000 Gbit/s, event storage 5 Gbit/s. Recording rate can be greater than 100 Hz.

21. 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 combination of tracks calo and m system detector segmentation single (isolated) objects verify trigger object(s) signal optimization with p cuts object matching with tracks accurate track matching T multiple object triggers mass of clusters + tracks precision mass calculations h-f correlations complicated h, f and pT selection criteria satisfy 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. High Q2: Exciting, possibly exotic physics Medium Q2and low x physics: new domain of strong interactions Low Q2: b and c physics with unprecedented statistics

22. Physics considerations Physicists have many different points of view. Examples: can(not) be measured Rapidity 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.

23. Statistics considerations 107 events/day at rate of 100 Hz Accuracy for cross-section measurements: ± 1% -> 105 accepted signal events -> ± 0.3% statistical error

24. Large and low cross section measurements • Low cross section • Important not to lose any event • Example: Bso -> m+ m- (BR @ 3.5 x 10-9) • After discovery can accept worse S/B ratio for • BR measurements • Large cross section (s 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

25. 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

26. Conclusions Baseline trigger design suitable and flexible enough for most imagined singatures Reasonable thresholds can be set Redundancy for high Q2 processes Rates for most triggers ok Rates for many single object triggers relatively high, multi-object triggers should be made use of Topology and quality options available Need scenarios for use Please join L1 Menu Working Group!

27. Board Layout of the Global Trigger PSB (Pipeline Synchronizing Buffer) Input synchronization GTL (Global Trigger Logic) Logic calculation FDL (Final Decision Logic) L1A decision TIM Timing GTFE (Global Trigger Frontend) Readout

28. 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.

29. Particle Conditions Particle Conditions are applied to a group of objects of the same type. The conditions are: ET or pT thresholds, h/f-windows, bit patterns for isolation, quality, charge, and spatial correlations (Dh, Df) between objects of the same type. Particle Condition for 2 back-to-back isolated electrons Particle Condition for 2 back-to-back isolated opposite-sign muons with MIP bits set

30. Delta Conditions Delta Conditions refer to the calculation of spatial correlations (Dh, Df) 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.

31. Algorithm AND-OR Next step: Actual algorithm calculations. Logical combinations (AND-OR) of objects are determined.

32. Algorithm AND-OR