Presentation on theme: "1 The ATLAS Missing E T trigger Pierre-Hugues Beauchemin University of Oxford On behalf of the ATLAS Collaboration Pierre-Hugues Beauchemin University."— Presentation transcript:
1 The ATLAS Missing E T trigger Pierre-Hugues Beauchemin University of Oxford On behalf of the ATLAS Collaboration Pierre-Hugues Beauchemin University of Oxford On behalf of the ATLAS Collaboration The XIV International Conference on Calorimetry in High Energy Physics Beijing, China, May 10 th -14 th 2010
2 Outline Motivation of a Missing E T trigger Overview of the ATLAS Missing E T at Level 1 Overview of the ATLAS HLT Missing E T algorithms Results from 7 TeV ATLAS data Online to offline comparison Data to MC comparison Missing E T trigger and ATLAS commissioning Summary and future plans
3 Motivation for a Missing E T trigger Can be used in combination with some other trigger signatures Ex: Allow to study non-boosted W Estimate efficiency of other uncorrelated triggers First data-driven estimate of electron efficiency for W e events Discover new physics processes involving undetectable particles. Ex: Dark matter candidates An Missing E T trigger plays an important role in the ATLAS physics program
4 Missing E T at Level 1: an overview Trigger Towers (TT) are built: sum of calo cells in an - range of ~0.1x0.1, over full depth of each calo Calorimeter Pre-processor (PPr) Jet/Energy processor Jet Elements (JE) are formed Digitalize TT E T signal Apply noise subtraction Sum 4 TT, HAD and EM Missing E T is computed Ex and Ey are computed from JEs A Look Up Table tells, from E X and E Y, which Missing E T thresholds passed Communicate results to the CTP
5 HLT Missing E T algorithms L2 Feature Extraction (FEX) algorithm: only corrects the L1 Missing E T for muon contribution Bandwidth limitation EF FEX algorithms: full granularity and resolution of calorimeter to refine L1/L2 Apply 1-sided, 3-sigma cut noise suppression on each cells Take muon corrections from EF muon measurement Apply calibrations to improve resolution Hypotheses testing algorithms: use different elements from FEX for chains specific purpose Possibility of many different trigger chains with no extra cost in timing
6 7 TeV data: L1 to offline correlation L1 Missing E T smaller than offline due to hard noise suppression After offline clean-up XE10 Before offline clean-up XE10 Lowest L1 Missing threshold (10 GeV) don’t pick up events with Missing E T due to bads jets No efficiency problem ATLAS standard jet clean-up cuts remove noisy and badly timed jets Noise averaged out in Jet Elements (JEs)
7 7 TeV data: EF to offline correlation Strong correlation between EF and offline measurements. Both for Missing E T and Sum E T Standard ATLAS jet clean-up cuts applied Offset between EF and offline is an expected feature: Artefact of our 1-sided 3-sigma noise suppression cut Sum E T Missing E T
8 7 TeV data: data to MC comparison The data EF Missing E T distribution agrees well to MC distribution for collision events Standard ATLAS Jet clean-up cut applied EF Missing ET measurement is well understood!
9 Data to MC: EF Missing E T turn-on curves Missing E T turn-on curve: efficiency of a trigger Missing E T selection as a function of an offline Missing E T reference. Sharp turn-on curves minimal distortion of the offline Missing E T Excellent agreement between data and MC EF Missing E T > 20 GeV = 95% EF Missing E T > 5 GeV The EF Missing ET trigger perform as expected on physics events
10 Data to MC: EF Sum E T turn-on curves Sum E T turn-on curve: computed similarly as Missing E T turn-on minimal distortion of the offline Sum E T measurement by trigger The EF Sum E T trigger perform as expected on physics events Plateau reached before the 30 GeV due to EF offset (shown above) EF Sum E T > 100 GeV = 95% EF Sum E T > 30 GeV
11 Missing E T and detector commissioning Missing E T trigger rate is the most sensitive to detector problems: It is a global quantity not limited to a narrow - region. Rates are dominated by steeply falling QCD Missing E T distribution Many problems have already been found thank to Missing E T trigger: LAr cabling (HEC and barrel) LAr FEB headers (bugs in DSP code) Tile: bug in collecting data and noise description Muon EF time-out and different muon FEXes have been debugged Missing ET trigger is a precious tool to debug overall detector
12 Summary The Missing E T trigger performed well on first LHC 7 TeV collision data Strong correlation with offline quantities Good agreement with Monte Carlo simulations Steep turn-on curves directly measured in data Missing ET trigger can be safely used to: Study the performance of different object Combined with other signature for a wider kinematic reach Hopefully find new physics! Help bringing ATLAS to a normal mode of running Demonstrate the feasibility of a trigger based on global object
15 Setup for Missing E T trigger commissioning Run a simplified version of L1/HLT algorithms: No calibration is applied at any level EM scale Missing E T measurement Only trigger chains with no muon corrections are activated ▬ Muon corrections are computed by the FEX can be studied offline Special Missing E T trigger chains for commissioning: Force FEX to run over all L1 accept events, without accepting events For debugging purpose: we run 3 EF FEX algorithms in parallel: Standard cell-based noise suppression Cell base, no noise suppression FEB-based ▬ use the collective info of the up to 128 cells attached to Front-End Boards to gain speed Extra algorithms will disappear after commissioning, but will be enabled in cosmic menu (run in empty bunch crossing)
Your consent to our cookies if you continue to use this website.