Triggering. Example: Suppose you d like to take an exceptional photograph of the CN-tower.

Transcription

1 Triggering Example: Suppose you d like to take an exceptional photograph of the CN-tower. Poor strategy: Take pictures continuously until your film is used up or camera memory is full Better strategy: Watch and wait until something interesting happens (human trigger)...but this could take a long time Best strategy: Build a trigger! (e.g. light sensor, camera records only the most interesting event) Trigger PHY2405 Experimental HEP Richard Teuscher 1

2 Lecture Outline Part 1: Introduction General characteristics of triggers Physics Motivation LHC Triggers ATLAS Level 1 Trigger Part 2: Advanced Technology for triggers Higher Level Triggers ZEUS HLT ATLAS HLT Commissioning ATLAS Triggers Today Cosmic ray muon trigger Problem set PHY2405 Experimental HEP Richard Teuscher 2

3 Basic Trigger: Photographer Trigger Rate R: speed at which you can record images / event Event size: S Bandwidth: B = S * R Deadtime: time during which trigger is busy Can t take two photos at the same time Data acquisition is dead while one photo is being recorded. Ideally deadtime << % Efficiency: ε = N recorded N Total _ events Events recorded / total interesting events Purity: p = N good N recorded Ratio of good events / total events Example: digital camera Max trigger rate ~ 3 Hz Event size ~ 3 MB Data acquisition rate ~ 3 MB * 3Hz ~ 9 MB/s Deadtime depends on camera Efficiency/purity depend on photographer PHY2405 Experimental HEP Richard Teuscher 3

4 Simple Trigger in High Energy Physics: Scintillator Paddles Testbeams (e.g. CERN, Fermilab, DESY, ) Cosmic ray setups, detector commissioning Photomultiplier (PMT) + Amp Photomultiplier (PMT) + Amp Threshold Discriminator Threshold Discriminator Gate PHY2405 Experimental HEP Richard Teuscher 4

5 Testing a subdetector for the ATLAS experiment at CERN Pair of scintillators for cosmic ray trigger. Test setup in surface building Dec 03. Physicist Hadronic calorimeter modules equipped with final electronics and cables (trigger, fibre optic readout, control) to counting room 75 m distant PHY2405 Experimental HEP Richard Teuscher 5

6 Basics of Triggers and Data Acquisition (DAQ) Systems Triggers divided into levels Each level a successive approximation First Level Trigger (Level-1) Fast decision times ~ s Typically specialized hardware Data from detectors stored in pipeline until decision of accept/reject Decision must be made before end of pipeline (latency time) Higher level(s) (HLT / L2 / L3) Longer decision times ~ ms Typically Farm of Linux PC s, highspeed network Partial or full event data now in memory DAQ: Data flow from detector through buffers to storage on tape/disk PHY2405 Experimental HEP Richard Teuscher 6

7 40 MHz 75 khz ~2 khz ~ 200 Hz RoI Builder L2 Supervisor L2 N/work L2 Proc Unit Complicated Example: Trigger / DAQ for the ATLAS Experiment at CERN Event Filter Processors Trigger LV L1 H L T LVL2 L2P RoI ROIB Event Filter EFP EFP EFP EFP 2.5 μs ~ 10 ms L2SV L2N 40 MHz Calo MuTrCh ROS Other detectors Lvl1 acc = 75 khz RoI data = 1-2% ROD ROD ROD 120 GB/s ~ sec RoI requests Lvl2 acc = ~2 khz ~4 GB/s EFacc = ~0.2 khz ROB ROB ROB DFM EB SFI EFN SFO EBN D E T RO D A T A F L O W DAQ FE Pipelines Read-Out Drivers 120 GB/s Read-Out Links Read-Out Buffers Read-Out Sub-systems ~2+4 GB/s Dataflow Manager Event Building N/work Sub-Farm Input Event Builder Event Filter N/work Sub-Farm Output ~ 300 MB/s PHY2405 Experimental HEP Richard Teuscher 7 Note: Don t memorize details understand basics, analyze

8 LEP Triggers much simpler Low rate Hz in e + e - collider at LEP from Every event a good event Example: OPAL trigger coincidence matrix of subdetectors in bins of ( PHY2405 Experimental HEP Richard Teuscher 8

9 Trigger driven by Physics PHY2405 Experimental HEP Richard Teuscher 9

10 Physics: What Gives Particles Mass? The Higgs Mechanism To understand the Higgs mechanism, imagine that a room full of physicists chattering quietly is like space filled with the Higgs field a well-known scientist walks in, creating a disturbance as he moves across the room and attracting a cluster of admirers with each step... Professor Higgs... this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field... PHY2405 Experimental HEP Richard Teuscher 10

11 Higgs: What Gives Particles Mass? The missing piece of the Standard Model is the Higgs (H) Spin-0 particle forming a scalar field everywhere in the universe Example of a scalar field (temperature) Coupling of the Higgs field to a particle generates its mass n.b. p/n mass from gluon fields, quark motion Breaks electroweak symmetry: W,Z massive Higgs properties predicted except its own exact mass We know it must lie in the range 114 GeV < M H < 1.2 TeV Previous direct searches at CERN Precision electroweak data (CERN, Fermilab) Higgs PHY2405 Experimental HEP Richard Teuscher 11

12 Search Channel Depends on M H bb W W ZZ PHY2405 Experimental HEP Richard Teuscher 12

13 Intermediate Mass Higgs 130 < M H < 500 GeV + H ZZ l l l l ( l = e, μ) 4 high p T leptons golden channel Narrow mass peak, small background + Entries/ 0.25GeV Corrections: BREM+eISO+Presampler mzz Entries χ / ndf / 14 Prob Constant ± Mean 130 ± Sigma ± H->ZZ->4e Entries/0.5 GeV 600 H->ZZ->μμμμ 400 σ = 1.4 GeV σ=1.4 GeV ZZ Invariant Mass (GeV) m PHY2405 Experimental HEP Richard Teuscher μμμμ (GeV) m ZZ (GeV) 13 m ZZ (GeV)

14 Low mass Higgs m H <140 GeV : H γγ 100 fb -1 H γγ: decay is rare (BR ~ 10-3 ) Hardest region: small signal on large background With good calorimeter resolution can observe a mass peak Estimate background from sidebands PHY2405 Experimental HEP Richard Teuscher 14

15 The Large Hadron Collider (LHC) Questions about the Higgs, unification, and dark matter should be answered by probing physics at the TeV scale To probe physics at ~ 1 TeV in p-p collisions, need: E(quark) > 1 TeV E(proton) > 6 TeV LHC p-p collider: 7 TeV x 7 TeV High luminosity: Design luminosity of L=10 34 cm -2 s -1 Physics Rate = L x nb. σ ~ 1/s -> 2*s requires factor 10 in L Design 100 fb -1 / year per experiment PHY2405 Experimental HEP Richard Teuscher 15 Luminosity cm -2 s -1 Luminosity [cm -2.s -1 ] 1.E+35 1.E+34 1.E+33 1.E+32 1.E+31 1.E+30 ISR LEP2 LEP1 HERA SppS 7 x TeVatron LHC 100 x Center-of-mass energy [GeV] s Energy (GeV)

16 LHC First collisions 2007 pp collider 14 TeV 100 fb -1 / y / experiment 25 ns bunch spacing ~ billion collisions / s 9T Supercond. magnets 26.7 km ring PHY2405 Experimental HEP Richard Teuscher 16 Energy (2 LHC beams) = 11 GJ = 7% of energy stored in an aircraft carrier at 30 knots

17 LHC Bunch Structure The LHC will have ~ 3600 bunches It is being built in the existing LEP tunnel (27 km) Distance between bunches = 27 km / 3600 = 7.5 m Time between bunches = 7.5 m / c = 25 ns PHY2405 Experimental HEP Richard Teuscher 17

18 Collisions at the LHC Collisions at the LHC Proton proton collisions: protons / bunch Crossing rate of p-bunches: 40 Million / s Luminosity: L = cm -2 s -1 ~ 1 billion pp collisions / s (superposition of 25 pp-interactions per bunch crossing: pile-up) ~1600 charged particles in the detector high particle densities demanding requirements for the detectors and trigger PHY2405 Experimental HEP Richard Teuscher 18

19 The Price of High Luminosity: Pileup Total event rate: R = L x σ inelastic (pp) cm 2 s 1 x 70 mb 700 MHz ~ 25 inelastic minimum bias low-p T events produced on average in each bunch crossing of 25 ns pile-up e.g. Golden Higgs channel: H ZZ 4μ Reconstructed tracks p T >25 GeV Trigger PHY2405 challenge: Experimental billions HEP and billions Richard of Teuscher min-bias events for every Higgs event 19!

20 Production Rates for LHC at L = cm -2 s -1 (10% design Luminosity) Process Events/s Events / year (10 fb 1 ) W eν Z ee SM Higgs SUSY Exotics tt bb QCD jets (p T > 200 GeV) H (m =130 GeV) g ~ g ~ (m = 1 TeV) Black holes m > 3 TeV (M D =3 TeV, n=4) Wealth of physics: LHC is a b-factory, top factory, W/Z factory, Higgs factory, SUSY factory, PHY2405 Experimental HEP Richard Teuscher 20

21 Alice Heavy-ion programme Atlas General-purpose detector 4LHC Experiments CMS General-purpose detector LHCb Dedicated b-physics PHY2405 Experimental HEP Richard Teuscher 21

22 ATLAS (A Toroidal LHC ApparatuS) 2 T Solenoid Hadronic Tile calorimeter Muon spectrometer Toroid magnets p 7 TeV p 7 TeV 22 m Inner Detectors Total mass ~ 7000 tonnes Electromagnetic barrel calorimeter 46 m Forward calorimeter Endcap calorimeter PHY2405 Experimental HEP Richard Teuscher 22

23 Scale of ATLAS PHY2405 Experimental HEP Richard Teuscher 23

24 LHC Trigger Overview PHY2405 Experimental HEP Richard Teuscher 24

25 Comparison of Triggers PHY2405 Experimental HEP Richard Teuscher 25

26 40 MHz Trigger / DAQ of the ATLAS Experiment at CERN Trigger DAQ ~2.5 μs Three logical levels LVL1 - Fastest: Only Calo and Mu Hardwired Hierarchical data-flow On-detector electronics: Pipelines 10 s PB/s (equivalent) 23 overlap ev/25ns 1400 particles/25ns ~ ms ~ sec. LVL2 - Local: LVL1 refinement + track association LVL3 - Full event: Offline analysis Event fragments buffered in parallel Full event in processor farm ~ 200 Hz Physics ~ 300 MB/s -> 1 CD / 2 sec PHY2405 Experimental HEP Richard Teuscher 26

27 ATLAS Level 1 PHY2405 Experimental HEP Richard Teuscher 27

28 We want to extract this PHY2405 Experimental HEP Richard Teuscher 28 Higgs Z Z 2electrons+2muons

29 from this PHY2405 Experimental HEP Richard Teuscher 29 Higgs Z Z 2electrons+2muons +23 MinBias

30 Level-1 Trigger Physics motivation: pp collisions produce mainly hadrons with low transverse momenta p T ~ 1 GeV Most interesting physics includes particles (hadrons and leptons) with high p T H(120 GeV) : p T ( ) ~ GeV W e M(W) = 80 GeV, p T (e) ~ GeV Strategy: Select signal with high thresholds Electrons, muons, jets Typical thresholds: Single muons with p T > 20 GeV Dimuons p T > 6 GeV Single e/g with p T > 30 GeV Di-electrons with p T > 20 GeV Single jet with p T > 300 GeV PHY2405 Experimental HEP Richard Teuscher 30 p p z p T

31 Particle identification Muon detector HAD calorimeter e EM calorimeter Inner tracker ν γ n p µ PHY2405 Experimental HEP Richard Teuscher 31

32 ATLAS L1: Calorimeter + Muon systems Calorimeter Muon system Simple algorithms Small amount of data Localized decisions Complex algorithms Large amount of data Need to link data from sub-detectors PHY2405 Experimental HEP Richard Teuscher 32

33 Overview of ATLAS LVL1 trigger Radiation tolerance, cooling, grounding, magnetic field, no access ~7000 calorimeter trigger towers O(1M) muon trigger channels Calorimeter trigger Jet / Energy-sum Processor Pre-Processor (analogue E T ) Cluster Processor (e/γ, τ/h) Muon Barrel Trigger Muon central trigger processor Muon trigger Muon End-cap Trigger Design all digital, except input stage of calorimeter trigger Pre-Processor Central Trigger Processor (CTP) Local Trigger Processors (LTP) Timing, Trigger, Control (TTC) PHY2405 Experimental HEP Richard Teuscher 33 Latency limit 2.5 μs

34 ATLAS Isolated Electron Algorithm = - log (tan( /2)) Pseudorapidity PHY2405 Experimental HEP Richard Teuscher 34

35 Level-1 Muon Trigger 1) Extrapolate tracks along windows defined by p T threshold 2) Form coincidences between layers RPC = resistive plate chambers TGC = thin gap chambers MDT = monitored drift tubes PHY2405 Experimental HEP Richard Teuscher 35

36 L1 Muon Trigger Efficiency L= Efficiencies have been computed for startup luminosity (10 33 ) and a nominal safety factor (x1): track χ 2 > 3 Single muon efficiency curves have been obtained for two different p T thresholds: p T = 6 GeV/c p T = 20 GeV/c Set trigger thresholds well below range you want to analyze From CERN Trigger Meeting Jan PHY2405 Experimental HEP Richard Teuscher 36

37 Efficiency & fakes vs. track χ 2 cut Single muons with p T = 100 GeV Single muons with p T = 11 GeV PHY2405 Experimental HEP Richard Teuscher 37

38 Selection (Trigger Menu) MU20 (muon p T >20 GeV) 2MU6 EM25I (isolated electron p T > 25 GeV) 2EM15I J200 (jet p T > 200 GeV) 3J90 2*10 33 cm -2 s -1 (20% design Lumi) cm -2 s -1 (full Lumi) ATLAS L1 Trigger Rates (khz) 4J J60 + xe TAU25I + xe MU10 + EM15I Others (pre-scales, calib, ) Total ~ 25 ~ 40 LVL1 trigger rate (high lum) = 40 khz Total event size = 1.5 MB Total # Readout Links (ROL) = 1600 Design system for 75 khz --> 120 GB/s (upgradeable to 100 khz, 150 GB/s) Uncertainty ~ factor 2 Design system for 100 khz PHY2405 Experimental HEP Richard Teuscher 38

39 Level-1 latency Interactions every 25 ns Cable length ~100 meters In 25 ns particles travel 7.5 m In 25 ns signals travel 5 m 22 m Weight: 7000 t Total Level-1 latency = (TOF+cables+processing+distribution) PHY2405 Experimental HEP 44 m For 2.5 μsec, all signals must be stored in electronics pipelines = 2.5 μsec Richard Teuscher 39

40 Digitisation options (ATLAS c.f. CMS) ATLAS scheme Calorimeter signals Analogue Σ for trigger Digitisation Trigger BC clock (every 25 ns) (Digitizer) Pipeline (analogue) Register Digitisation Readout Calorimeter signals CMS scheme BC clock (every 25 ns) Readout & trigger Digitisation (40 MHz) (Digitizer) Pipeline Register (digital) Digital Σ for trigger Readout Trigger PHY2405 Experimental HEP Richard Teuscher 40

41 Example of Chain: From Front End Electronics to Trigger Process PMT signals from ATLAS Hadronic Tile Calorimeter (TileCal) Electronics located in 256 drawers Up to 45 PMT s/drawer 16 bit dynamic range Up to 2 TeV in a single cell Down to 30 MeV per cell Must see 350 MeV/cell for Calibration, monitoring, e - ID Readout should not degrade calorimeter energy resolution Electronics noise low when merging cells into jets Radiation tolerant LVL1 Trigger tower sums ATLAS TileCal Drawer Electronics 6m PHY2405 Experimental HEP Richard Teuscher 41

42 Operation of TileCal: Measure light produced by charged particles in plastic scintillator. PMT WLS fiber Front End Electronics 7λ Plastic scintillator inside steel absorber structure Φ Particles 2 fibres / scintillator. Bundle fibres to form cells of 0.1 x 0.1 (η,φ) 2 PMT sper cell PHY2405 Experimental HEP Richard Teuscher 42

43 TileCal Electronics Drawers Readout electronics Drawer mechanics. PMT blocks HV distributor 2 sections, each l=1.5 m m=50 kg Drawer Cross section 10 cm PHY2405 Experimental HEP Richard Teuscher 43

44 TileCal Front End Electronics 45 channels (PMT s) Digitizers with 2.5 ms pipeline Optical G-LINK Interface card detector Counting room Readout System (ROS) and Readout Buffer (ROB) ROD (readout driver) Level 1 Accept Drawer 256 in total Analogue Trigger Level 1 Tower sums Calorimeter Trigger PHY2405 Experimental HEP Richard Teuscher 44

45 Summary: The Trigger Architecture for the ATLAS Experiment at CERN 40 MHz 75 khz 2.5 μs Level 1 trigger Region of Interest RoI ~1 khz ~100 Hz ~10 ms ~1 sec High Level Trigger Rate Latency = decision time Level 2 trigger Event Filter PHY2405 Experimental HEP Richard Teuscher 45

46 ATLAS Event PHY2405 Experimental HEP Richard Teuscher 46