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Digital Filtering Performance in the ATLAS Level-1 Calorimeter Trigger David Hadley on behalf of the ATLAS Collaboration

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ATLAS Trigger and L1Calo Architecture Digital Filter Implementation Digital Filter Performance Outline

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ATLAS Trigger and L1Calo Architecture

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ATLAS Trigger ATLAS three level trigger: Level 1 : hardware-based, pipelined with a fixed latency

Noise Rejection Noise PDF for a single tower (left). The total probability of noise output > 0.5GeV for all towers in the LAr EM Barrel (right). Improved noise rejection with a matched/common filter but little difference between them. 26/05/2010Digital Filter Performance - David Hadley - RT201016

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Energy Resolution from Detector Noise Energy residual (measured-simulated) for a 25GeV pulse (left). Gaussian width of energy residual is plotted for all towers in the LAr EM barrel (right). Again, little difference between Matched and Common. Clear improvement over Pass-through. 26/05/2010Digital Filter Performance - David Hadley - RT201017

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Optimising Usage of the Look-up Table Range Using a peak coefficient of 15 gives the best precision for matching the filter to the pulse shape. Precisely matching to individual towers pulse shape does not significantly improve performance. We can change the peak coefficient to optimise the usage of the look-up table (LUT) range. 26/05/2010Digital Filter Performance - David Hadley - RT201018

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Choice of Filter Coefficients for Early LHC Running Based on these studies the strategy decided for 2009- 2010 running: Common filter applied across entire calorimeter layer, matched to the average pulse shape in that layer. Coefficients scaled to optimise usage of the LUT range. 26/05/2010Digital Filter Performance - David Hadley - RT201019 RegionFilter EM Layer(1,8,13,10,7) Hadronic Layer(1,9,15,11,5) FCal(0,2,13,5,0)

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Look-up Table E T Calibration Analogue gains are applied to scale the input pulses to 4 ADC per GeV. LUT table applies pedestal subtraction, noise cuts and final E T calibration. At present, only scale filter output back to the input scale. Initial calibration of the LUT slopes were based on calibration pulses. Preliminary checks of correlation show calibration is working well for collisions. Nominal 4 ADC input to 1 LUT output, expect a gradient . 26/05/2010Digital Filter Performance - David Hadley - RT201020

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Summary L1Calo Pre-processor digital filter shows good performance in selecting the correct bunch-crossing, rejecting noise, and improving energy resolution. The Common digital filter configuration was implemented for 2009-2010 running. Initial cross checks of LUT calibration with collision data are encouraging. The process of understanding and optimising the trigger with collisions is continuing. We are looking forward to new physics events identified with L1Calo! 26/05/2010Digital Filter Performance - David Hadley - RT201021

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Backup Slides 26/05/2010Digital Filter Performance - David Hadley - RT201022

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Performance with Different Peak Coefficients BCID efficiency: Energy resolution: Noise probability:

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L1Calo Trigger (in full) Sliding-window algorithms search for high-E T objects. In reality windows are processed in parallel. Central cluster > threshold. Hadronic and e.m. isolation requirements in surrounding towers. e/gamma and /hadronJet and energy-sum ECAL+HCAL Operates on jet elements 2x2 towers. Energy in window (EM+Had) > threshold. Variable window size. Same module does total-E T and missing-E T triggers. Double counting is avoided by requiring a local E T maximum. 26/05/201024Digital Filter Performance - David Hadley - RT2010