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DasuCMSTriggerUCSD

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Information about DasuCMSTriggerUCSD
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Published on October 7, 2007

Author: Barbara

Source: authorstream.com

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CMS Trigger Strategy:  CMS Trigger Strategy Sridhara Dasu, University of Wisconsin, CMS Collaboration The Large Hadron Collider:  The Large Hadron Collider Physics in LHC Era:  Physics in LHC Era Electroweak Symmetry Breaking Scale Higgs discovery and higgs sector characterization Quark, lepton Yukawa couplings to higgs New physics at TeV scale to stabilize higgs sector Spectroscopy of new resonances (SUSY or otherwise) Find dark matter candidate Multi-TeV scale physics (loop effects) Indirect effects on flavor physics (mixing, FCNC, etc.) Bs mixing and rare B decays Lepton flavor violation Rare Z and higgs decays Planck scale physics Large extra dimensions to bring it closer to experiment New heavy bosons Blackhole production Trigger Challenge Low  40 GeV The LHC Trigger Challenge:  The LHC Trigger Challenge Physics at EWSB scale 115 < Mhiggs < 250 GeV Decays to gg, WW*, ZZ* 2-g PT~20 GeV, Lepton PT ~ 40 GeV TeV scale supersymmetry Multiple leptons, jets and LSPs (missing PT), HT ~ 300 GeV QCD Background Jet ET ~ 250 GeV, rate = 1 kHz Jet fluctuations  electron BG Decays of p, k, B  muon BG Technical challenges 40 MHz input  fast processing 100 Hz output  physics selection 109 events per year  ≤102 higgs events Multi Level Trigger Strategy:  Multi Level Trigger Strategy Level 1 Coarse object identification Limited isolation L1T Algorithms:  tracking:  L1T Algorithms:  tracking Link local track segments (in CSC) into distinct 3D tracks (FPGA logic) Reconstruction in  suppresses accelerator muons Measure pT, , and  of the muon candidates in the non-uniform fringe field in the endcap iron (SRAM LUTs) Require 25% pT resolution for sufficient rate reduction Send highest quality candidates for combination with other  detectors (similar algorithm for DT in barrel) and make final L1 trigger decision with pT cut Calorimeter Trigger Geometry:  Calorimeter Trigger Geometry EB, EE, HB, HE map to 18 RCT crates Provide e/g and jet, t, ET triggers Trigger towers:  =  = 0.087 HCAL ECAL HF L1T Algorithms: e/:  L1T Algorithms: e/ Triggers are mostly due to energetic 0s in em-rich jets L1T: t / Jet Algorithm:  L1T: t / Jet Algorithm Jets are real - however, difficult to get low pT jets -jets are mostly fake Missing / Total ET Algorithm:  Missing / Total ET Algorithm 20o 0o 40o 360o …… -5 5 0 h f ET MET Strip ET sum over all h LUT For sums ET scale LSB (quantization) ~ 1 GeV is used Df = 20o used instead of HCAL tower size: Df = 5o L1 MET is easily spoiled by instrumental problems L1 Trigger System Production:  L1 Trigger System Production RCT Receiver card RCT Jet/Summary card RCT Electron isolation card Custom ASICs Large FPGAs SRAM Gbit/s Optical links Dense boards Optical links SRAM FPGA CSC Track-Finder Example Level-1 Trigger Table (L=2 x 1033):  Example Level-1 Trigger Table (L=2 x 1033)  3 safety factor  50 kHz (expected start-up DAQ bandwidth) Only muon trigger has low enough threshold for B-physics (aka Bsmm) Level-1 Trigger Rates:  Level-1 Trigger Rates 30-40 GeV for m or e 20 GeV each for gg 250 GeV jets 80 GeV tt Trigger cuts determine physics reach! Efficiency for Hgg and H4 leptons = >90% (in fiducial volume of detector) Efficiency for WH and ttH production with Wln = ~85% Efficiency for qqH with Htt (t1/3 prong hadronic) = ~75% Efficiency for qqH with Hinvisible or Hbb = ~40-50% Ground Reality at L1 Trigger:  Ground Reality at L1 Trigger No tracker in level-1 trigger Electron, photon and p0 looks the same Trigger level muon PT is poorly measured Jet trigger limitations Limited capability to get low PT jets Limited calorimeter resolution: Calibration to take out h,f variation in response Poor measurement of missing ET At best the resolution can be: Calibration not possible Underlying event and pileup contribution Additional limitations due to trigger calculations Most of L1 output are mistags - Another factor of 1000 rejection at HLT The High-Level Triggers:  The High-Level Triggers In CMS all trigger decisions beyond Level-1 are performed in a Filter Farm running ~normal CMS reconstruction software on “PCs” The filter algorithms are setup in several steps HLT does partial event reconstruction “on demand” seeded by the L1 objects found, using full detector resolution Algorithms are essentially offline quality but optimized for fast performance HLT Executable Structure:  HLT Executable Structure 1 0 1 1 0 0 1 1 0 0 1 0 0 1 1 0 0 1 0 0 1 0 0 Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 1 Step 2 Step 3 Step 4 Step 1 Step 2 Step 3 Step 4 Step 5 Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 0 1 0 0 128-bit L1 Word HLT Bits … HLT Algorithm Steps Path stops when a selection step fails  e/ 2 e/    MET 1-Jet 2-Jet e+Jet HT HLT e/ Selection:  HLT e/ Selection Initial steps using calorimeter (“Level-2 e/”): Search for matching Level-1 e/ object Use 1-tower margin around 4x4-tower trigger region Bremsstrahlung recovery “super-clustering” Select highest ET cluster Bremsstrahlung recovery: Road along f — in narrow -window around seed Collect all sub-clusters in road  “super-cluster” HLT t-jet tagging:  HLT t-jet tagging Final steps in HLT paths involve tracking which is more time consuming Reconstruct tracks only in the region of interest around “Level-2” tagged objects Example HLT Trigger Menu (L=2x1033):  Example HLT Trigger Menu (L=2x1033) Standard Model Higgs Decay:  Standard Model Higgs Decay 115 < MH < 130 GeV Hbb dominates - however, to avoid backgrounds, use Hgg MH > 130 GeV HWW*, HZZ*, HWW, HZZ (at least one lepton to avoid backgrounds) HWW(*)ln ln HZZ(*)4 leptons qqHWWln jj qqHZZll nn qqHZZll jj Hgg qqHtt ttHWb Wb bb WHln bb MSSM Higgs:  MSSM Higgs Higgs sector: h0, H0, A0, H± Light higgs h0 - standard model like At high tanb, Hbb, Htt and Hcc dominate qqbbH large and well understood Measure decay to bb and tt Challenges Trigger, b and t tagging qqH - Low mass H challenges:  qqH - Low mass H challenges D. Zeppenfeld et al. Higgs production in weak boson fusion Accompanied by jets in the forward direction Forward jet characteristics Lower jet ET (underlying event + pileup problem) Challenge for trigger (level-1 and higher levels) Trigger on higgs decay products Decays to Z (ee, mm) or photons (OK) Low threshold electron/photon algorithm Decays to t Narrow jet tag - dedicated t algorithm (~OK) Tag jets with location information (Can do this at Level-1) Additional reduction in background Require two forward tag jets Require Dh between the jets Decays to b jets (dominant but dirty mode) Four jet trigger including forward tag jets Require Dh between jets Require two jets to be central (b tagging) Diffractive Higgs Trigger:  Diffractive Higgs Trigger Rewarding if there is sufficient production Tagged protons give good MH measurement Since expected s is small, need all H decays Central detector Two Low PT jets from low mass Higgs decay Must tag as b-jets at HLT |h|<2.5 Essentially nothing else in the detector Require small HT - ETjet1 - ETjet2 Pileup persists Proton taggers Too far to be part of trigger Trying to get around speed of light problem SUSY Efficiencies:  SUSY Efficiencies MSUGRA provides a benchmark Summary:  Summary LHC Trigger is Challenging The choice of physics studied is already made at level-1 trigger Choices made with calorimeter and muon systems only Complete object reconstruction at higher level trigger Optimum resolution online with calibration and alignment Includes b/t tagging in high level trigger farms Both CMS and ATLAS have designed trigger systems for golden discovery modes (lepton, diphoton, muti-jets…) Exploit qqH, WH, ttH production to cover difficult regions Definitive exploration of higgs sector is assured Pickup searches for new particles where left off by Tevatron Innovative designs may allow more measurements Topological selection starting from level-1 Low mass higgs & some MSSM higgs decays to tt Measurement of Yukawa couplings Invisible higgs decays

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