the trigger system of the cms experiment

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The Trigger System of the CMS experiment

10-th INTERNATIONAL CONFERENCEON INSTRUMENTATION FOR COLLIDING BEAM PHYSICS

Budker Institute of Nuclear Physics,Siberian Branch of Russian Academy of Science,

Novosibirsk, RussiaFebruary 28 - March 5, 2008

Marta FelciniUniversity College Dublin

on behalf ofthe CMS Collaboration

Triggerconditionsdeterminesthe picture

we see

The CMS Trigger System

INSTR08 – Novosibirsk Febr. 28th-Mar.5th, 2008

Marta Felcini, UCDCMS Collaboration

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Outline

- The LHC design parameter and status- The CMS detector and status- The CMS trigger system-- The Level-1 trigger system-- The High Level Trigger system-- Trigger tables for initial luminosities-- Trigger performance-- Summary and conclusion



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LHC Design Luminosity

≤

See V. Papadimitriou talk for comparisonwith Tevatron luminosities and parameters

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LHC Startup Luminosity Approx 30 days of beam time to establish first collisions 1 to 43 to 156 bunches per beam N bunches displaced in one beam for LHCb Pushing gradually one or all of:

Bunches per beam Squeeze Bunch intensity Each step lasts ~week Interaction points

P 1 (ATLAS) & 5 (CMS)

Bunches Nb

* Protons/bunch

nb

Luminosity

L

Pileup Minbias rate

1 x 1 18 1010 1027 Low 55 Hz

43 x 43 18 3 x 1010 3.8 x 1029 0.06 20 kHz

43 x 43 4 3 x 1010 1.7 x 1030 0.28 60 kHz

43 x 43 2 4 x 1010 6.1 x 1030 0.99 200 kHz

156 x 156 4 4 x 1010 1.1 x 1031 0.50 400 kHz

156 x 156 4 9 x 1010 5.6 x1031 2.3 2 MHz

156 x 156 2 9 x 1010 1.1 x1032 5.0 4 MHz

(see also W. Witzeling’s talk)



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Exploded View of CMS



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The CMS Detector

HCAL

Magnet

Tracker

Muon chambers

ECAL

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CMS Detector Status Construction of the CMS experiment is almost completed and the

installation is very advanced.

See talks from H.-J- Simonis, M. Ryan, M. Sobron, A. Staiano Commissioning work already carried out gives confidence that CMS will

operate with the expected performance. Commissioning using cosmics with more and more complete setups

(complexity and functionality) going apace. Computing, Software & Analysis: 24/7 Challenges @ 50% of 2008

conducted. Preparations for the rapid extraction of physics being made.

Around May’08 CMS will be in the closed configuration; Field ON, taking cosmics, in anticipation of beam.



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CMS Taking Data (Cosmic Challenge)Run 2605 / Event 3981/ B 3.8 T

Reconstructed global muon

Barrel MuonChambers

Every aspect of final CMSfrom detector to trigger to offline software has to work to produce these plots



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CMS Trigger and DAQ Architecture

Emphasis on modularity high-speed networking CPU computing power

The unique CMS trigger architecture only employs two trigger levels: Level-1 trigger, implemented using custom electronics High Level Trigger, implemented on a large cluster of commercial CPUs

40 MHz

100 kHz

100 Hz

CMS Online: Trigger and DAQ

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Detector Frontend

Computing Services

Readout Systems

Filter Systems

Event ManagerBuilder NetworksRun

Control

Level 1 Trigger

LHCL1 accept RAW Data 100 GB/s

Underground Control Room

(USC)

ReadoutL1 Electronics

Surface Control Room

(SCX)

HLT Filter FarmsReadout Builders

Data to Surface(D2S)



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CMS Level-1 Trigger. The Level-1 trigger, implemented using custom electronics, inspects events at the full bunch-crossing rate, while selecting hundred kHz for further processing

Example:ECAL L1 trigger electronics

Trigger primitives computed on the detectorModularity: Trigger Tower (25 channels in Barrel) 5 VFE Boards (5 channels each) / 1 FE Board1 Fibre sends trig primitives (every bunch Xing) 1 Fibre sends data (on Level1 accept)

Front/Rear view Front/Rear view with 20 with 20

supercrystals supercrystals mountedmounted

Supercrystals:

25 PbWO4 crystals

L1 ElectronIdentification L1 Electron

Isolation Card

See also M: Ryan’s talk



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CMS High Level Trigger

The HLT accesses full event information (full granularity) seeded by L1 objects using “off-line quality” algorithms

L1 Input rate <~40 MHzL1 latency: 3.2 μsL1 Output rate: 100kHz-50kHz (startup)

L2 and L3 merged into High Level Trigger (HLT)

HLT ~ startup: 50kHz input rate ~2000 CPUs ~40 ms average per event

Further online selection is performed in the high-level trigger (HLT) which reduces the hundred kHz input stream to hundred Hz of events written to permanent storage.

The HLT system consists of a large cluster of commercial CPUs : the HLT Filter Farm

The Plan: from start-up to discovery



The CMS Trigger System 14

Luminosity range

1029s-1cm-2-1031s-1cm-2

1031s-1cm-2-1033s-1cm-2

1033s-1cm-2-1034s-1cm-2

Goals

Calibrate and align all the sub-detectors

Measure the Standard Model processes: b-phys. , W/Z ,top Use them for more refined detector calibration

Detector well calibrated andresponse well understoodEnter the “Discovery Mode¨

Definition ofSignal

Definition ofBackground

QCD events Machine, detector noise

Standard Model processes:b-phys., W/Z ,top

As above and QCD events

New “expected” Physics: Higgs Supersymmetry New unknown: ???

As above and Standard Model processes

The trigger criteria at each luminosity must be adapted to the plan and goals of the experiment

Define trigger criteria to optimize trigger performance in serving the above plan

@ 1032s-1cm-2 collect O(100/pb)/mo, O(1/fb)/ y (Tevatron now: ~4/fb/expt)

In the next slide I will show examples for 1032s-1cm-2 luminosity (intermediate luminosity range)

Trigger Criteria and Performance




Trigger criteria (thresholds) must be chosen to optimize the trigger performance depending on luminosity, machine and detector conditions.

The trigger performance is measured by three quantities: Background rejection – determine total rate to storage – must be kept lowSignal efficiency – determine signal rate to storage – must be kept highCPU time consumption – must be kept low - avoid dead-time and inefficiencies.

The flexibility of the trigger system allows to introduce modifications in an efficient manner for optimal performance adapted to the actual running conditions while taking data

The robustness of the algorithms which determine the trigger primitives (quantities on which the trigger decision is taken) also ensure that the system will not be too sensitive to detailed changes with respect to the expected conditions.

The actual experimental (machine and detector) conditions will only be known when collisions and data come .The actual trigger performance will be measured with real data

In preparation for data taking, we can use our present best knowledge of the detector response and possible machine condition scenarios to define trigger criteria before data taking,and adjust them when real collisions and data will be available.

Design of Trigger Tables for Early Data Taking




In preparation for data taking, to optimize trigger performance at a given luminositywe prepare trigger tables depending on the expected luminosity and expected pile-up conditions as well as the expected detailed response of all sub-detectors

The set of kinematic requirements (trigger criteria) on physics objects at each trigger level is called trigger table.

Procedure to design a trigger table:

start with fully simulated events of all known physics processes (QCD, W/Z, top) including pile-up (overlapping) events depending on luminosity; reconstruct physics objects (electron, muon, jet, etc) coarsely at Level-1 and precisely at the HLT; calculate trigger rates for all (single object, double object, cross-object) triggers; choose trigger criteria in order to

minimize background rate maximize signal rate keep the CPU time consumption within the capability of the system

define a trigger table for the given luminosity and pile-up conditions.

Level-1 Trigger Rates and Tables




Trigger rates for QCD EventsL=1032s-1cm-2

Design tables for 17kHz L1 output rate1/3 actual initial capability of 50 kHz

How do we allocate bandwidth between the different triggers?

General guidelines:

Keep muons down to tow pT at modest bandwidth cost

Give higher bandwidth to electron/photons for further processing in the HLT

Give even higher bandwidth to energy and jet triggers (energy calibration)

1 kHz

10kHz

Trigger class Allowed Rate

Muon (single or double) 2 kHz

Electron/photon (single or double) 3 kHz

Jets or Total Transverse Energy 6 kHz

Tau jets 3 kHz

Combination of triggering objects 3 kHz

Total Level-1 output rate 17 kHz

For single object triggers:- Muon rates are low- Electron rates are high at low Et- Jet rates are high also at high Et

For double object triggers (not shown here) rates are one to more orders of magnitude lower than for single object triggers: allow to keep low thresholds at small bandwidth cost.

HLT Rates and Tables



Single muon HLT rates L=1032s-1cm-2

Dimuon HLT rates L=1032s-1cm-2

Design HLT tables for 150 Hz HLT output rate 50% of actual initial capability of 300 Hz

Share bandwidth according to detector and physics priorities at the given luminosity

Trigger Threshold (GeV) Note

1μ 16

1μ 11 isolation

2μ 3

At this luminosity set muon trigger thresholds as low as possible (detector and physics studies)

Allow 1/3 of total bandwidth for muon triggers

Examples of muon and electron (next page) triggers rates and tables at L=1032s-1cm-2:

Muon HLT table -Total rate: 30 Hz

Muon HLT – Signal efficiencies

HLT Rates and Tables


Trigger Threshold(GeV)

Notes

1e 17

1e 15 isolation

2e 12

2e 10 isolation

1γ 40

1γ 30 isolation

2γ 20

2γ 20 isolation

High-ET EM 80 looser cuts

Very high-ET EM 200 looser cuts

Electron HLT rates L=1032s-1cm-2

Trigger class AllowedRate

Muon (single or double) 50 Hz

Electron/photon (single or double) 30 Hz

Single jet or multi-jet orMissing Transverse Energy (MET)

30 Hz

Tau and b-jets 20 Hz

Combination of triggering objects 20 Hz

Total HLT output rate 150 Hz

Overview of bandwidth sharing among the different trigger classes a L=1032s-1cm-2

Given the relatively low trigger thresholdsaffordable at this luminosity

Signal (W/Z, top, Higgs, etc) efficiencies arehigh: 70 to 100% depending on topology

Electrons/Photons HLT tableTotal rate: 30 Hz

CPU Time Performance



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Key issue for the HLT selection is the CPU power required for the execution of the algorithms

Measured average processing times (Core 2 5160 Xeon 3.0 GHz) for running the complete HLT Table including the data unpacking time on L1-accepted QCD (pT= 0 - 300 GeV/c), EWK (W /Z) and pp->μX samples.

Weighted sum of contributions from all processes: 43 ± 6 ms

For start-up scenario with DAQ processing capability of 50kHz of L1 accepted events the average of 40 ms per event translates into ~2000 commercial CPUs for the HLT filter farm This was the projected size of the farm from extrapolations back in 2002 at the time of the DAQ and HLT TDR



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The CMS Trigger System: SummaryThe CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy of 14 TeV, starting this year, Summer 2008

The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz. The unique CMS trigger architecture only employs two trigger levels:

The Level-1 trigger, implemented using custom electronics, inspects events at the full bunch-crossing rate, while selecting up to hundred kHz for further processing.

The high-level trigger (HLT) reduces the hundred kHz input stream to hundred Hz of events written to permanent storage. The HLT system consists of a large cluster of commercial CPUs (the “HLT Filter Farm"), running off-lne quality reconstruction algorithms on fully assembled event information.

L1 and HLT tables have been developed for early luminosities. A total DAQ bandwidth of 50 kHz is assumed. Fast selection and high efficiency is obtained for the physics objects and processes of interest using inclusive selection criteria.The overall CPU requirement is within the system capabilities

Conclusion: CMS is ready to take data efficiently when collisions come …

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The Trigger System of the CMS experiment

10-th INTERNATIONAL CONFERENCEON INSTRUMENTATION FOR COLLIDING BEAM PHYSICS

Budker Institute of Nuclear Physics,Siberian Branch of Russian Academy of Science,

Novosibirsk, RussiaFebruary 28 - March 5, 2008

Marta FelciniUniversity College Dublin

on behalf ofthe CMS Collaboration

Thank youto the Organizing Committee for your kind invitationand to my CMS friends and colleaguesfor the opportunity to represent CMSin this prestigious and inspiring Conference



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Reserve

Data Flow

CERN ColloqDec07 tsv 24

Raw Data:2000 Gbit/s

High Level Trigger10 TeraFlops

Controls:1 Gbit/s

Controls:1 Gbit/s

To regional centersTo regional centers10 Gbit/s

Remote control rooms

Remote control rooms

Controls:1 Gbit/s

Detector Frontend

Computing Services

Readout Systems

Filter Systems

Event ManagerBuilder NetworksRun

Control

Level 1 Trigger

Events Data:10 Gbit/s

Tier 050 TeraFlops

CMS data flow and on(off)-line computingCMS data flow and on(off)-line computing




Data Acquisition

CERN ColloqDec07 tsv 26

Expectations of Luminosity Buildup




Early Physics Programme Prior to beam: early detector commissioning

Readout & trigger tests, runs with all detectors (cosmics, test beams) Early beam, up to 10pb-1:

Detector synchronization, alignment with beam-halo events, minimum-bias events. Earliest in-situ alignment and calibration

Commission trigger, start “physics commissioning”: Physics objects; measure jet and lepton rates; observe W, Z, top And, first look at possible extraordinary signatures…

Physics collisions, 100pb-1: measure Standard Model, start search 106 W l (l = e,); 2x105 Zll (l =e, ); 104 ttbar+X

Improved understanding of physics objects; jet energy scale from W j j’; extensive use (and understanding) of b-tagging

Measure/understand backgrounds to SUSY and Higgs searches Initial MSSM (and some SM) Higgs sensitivity Early look for excesses from SUSY& Z/jj resonances. SUSY hints (?)

Physics collisions, 1000pb-1: entering Higgs discovery era Also: explore large part of SUSY and resonances at ~ few TeV

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LHC-vs-Tevatron rates

Huge stats for Standard Model signals. Rates@1033

~108 events/1fb-1 W (200 Hz)~107 events/1fb-1 Z (50 Hz)~106 events/1fb-1 tt (1 Hz)

These will be used as control/ calibration samples for searches beyond the Standard Model

They can also be used to scrutinize the Standard Model further.

e.g. top sample is excellent for understanding lepton id. (incl. taus), jet corrections, jet energy scale, b tagging, ….



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Experimental ChallengeLHC Detectors (especially ATLAS, CMS) are radically different from the ones from

the previous generations

High Interaction Rate

pp interaction rate 1 billion interactions/sData can be recorded for only ~102 out of 40 million crossings/secLevel-1 trigger decision takes ~2-3 s electronics need to store data locally (pipelining)

Large Particle Multiplicity

~ <20> superposed events in each crossing~ 1000 tracks stream into the detector every 25 nsneed highly granular detectors with good time resolution for low occupancy

large number of channels (~ 100 M ch)

High Radiation Levels

radiation hard (tolerant) detectors and electronics

LHC Luminosity

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number of protons perbunch

number of bunches

revolution frequency

relativistic factor

normalized transverse emittance

betatronic function at the Interaction Point (IP)

depends on the beam energy and on the focusing strength of theinsertion

Geometric factor F by which the luminosity is reduced,

transverse and longitudinalrms beam size at the IP.

full crossing angle



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The CMS Trigger SystemAbstract

The CMS experiment will collect data from the proton-proton collisions delivered by the Large Hadron Collider (LHC) at a centre-of-mass energy of 14 TeV.

The CMS trigger system is designed to cope with unprecedented luminosities and LHC bunch-crossing rates up to 40 MHz. The unique CMS trigger architecture only employs two trigger levels. The Level-1 trigger is implemented using custom electronics and inspects events at the full bunch-crossing rate, while selecting hundred kHz for further processing. The Level-1 electronics has many tunable parameters and look-up-tables, whose configuration we have optimized for early data taking. Further online selection is performed in the high-level trigger (HLT) which reduces the hundred kHz input stream to hundred Hz of events written to permanent storage.

The HLT system consists of a large cluster of commercial CPUs (the "Filter Farm"), running sophisticated reconstruction algorithms on fully assembled event information. The HLT software includes all major features of the offline reconstruction code. The flexibility provided by a fully programmable environment implies that algorithms can be easily changed to improve the events selection in multiple physics channels, as well as deal with diverse experimental conditions.

The coherent tuning of the HLT algorithms to accommodate multiple physics channels is a key issue that defines the physics reach of the experiment. In this presentation we will discuss the strategies and trigger configuration developed for the start-up physics program of the CMS experiment. We will also discuss the expected CPU performance of the HLT algorithms.

the trigger system of the cms experiment

Documents

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khz43 x

mhz156 x

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ucdcms collaboration

trigger levels

anticipation of beam

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