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Noise Cuts and Thresholds

Noise Cuts and Thresholds. a zero event analysis. Noise cut tests. Investigation of background rates As a function of noise cuts Lowest threshold values Results also available in elog https://atlasop.cern.ch/elog/ATLAS/ATLAS/64717 Based on short investigation on 7 th December

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Noise Cuts and Thresholds

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  1. Noise Cuts and Thresholds a zero event analysis L1Calo Joint Meeting 11th-13th January 2010

  2. Noise cut tests • Investigation of background rates • As a function of noise cuts • Lowest threshold values • Results also available in elog • https://atlasop.cern.ch/elog/ATLAS/ATLAS/64717 • Based on short investigation on 7th December • Stable and quiet calorimeter conditions • This talk addresses only non-beam backgrounds • No comment on physics rates and backgrounds L1Calo Joint Meeting 11th-13th January 2010

  3. Introduction to noise cuts • Reduce number of 1 GeV pulses • Both real and due to noise • Keep background rates under better control • Especially for Jet triggers • Soften and shift threshold turn-on • Especially for Jet triggers • Caused much trigger menu debate last year • Debate is likely to continue! • Current default noise cut is ‘4’ L1Calo Joint Meeting 11th-13th January 2010

  4. What does noise cut 4 mean? • Noise cut is applied after Finite Impulse Filter (FIR) sum • FIR sum is an integer value • Zero level dependent on pedestal • Resolution varies, but typically 0.25-0.3 MeV • Taking a typical value of 0.28 MeV and effective pedestal 40 L1Calo Joint Meeting 11th-13th January 2010

  5. Tower Occupancy with no noise cut Remember: 1 % = 400 kHz • The 1 GeV occupancy of towers is very sensitive • Tower RMS (typically 250-400 MeV) • Effective pedestal: 40, 40.1, 40.2, etc • Very approximate example from toy MC: • RMS: 300 MeV • Ped 39.5: 0 % • Ped 40: 0.01 % • Ped 40.5: 0.1 % • RMS 400 MeV • Ped 39.5: 0.01% • Ped 40: 0.1 % • Ped 40.5: 2 % L1Calo Joint Meeting 11th-13th January 2010

  6. Also we do have cosmics • Cosmics rates for lowest thresholds well established • Some bad tower noise contribution, but mostly real • With standard noise cut 4: • J5: 5.0 Hz J10: 2.0 Hz • TAU5: 4.0 Hz TAU6: 3.0 Hz • EM3: 0.3 Hz • FJ3: 0.0 Hz L1Calo Joint Meeting 11th-13th January 2010

  7. Variation of noise cuts J10_win6 rate 200 Hz NB currently overestimating energy here • Essentially only 2 extra settings to try • 2 and 3 • However, 3 had noise contribution from one tower • Alternative 3* configuration • ‘Bad’ tower at 4, others at 3 L1Calo Joint Meeting 11th-13th January 2010

  8. Thoughts on noise cuts • Jet rate is the one that needs most care • But J5 is certainly not intended as a standalone trigger! • J10 also tipping over the edge (win6 is ‘better’) • Noise cut 3 looks feasible on a short timescale • When? (Requires coordination with menu group) • EM and Tau items are very insensitive • This is expected, but reassuring • For example, to generate extra false EM3 triggers, need • A tower which hits 3 GeV, but not 4 GeV, regularly • A nearby tower with noise hit of 1 GeV • EM towers are on the lower end of RMS spectrum L1Calo Joint Meeting 11th-13th January 2010

  9. Bonus for five • Noise investigation was very quick • So decided to look at thresholds • But note kept noise cut at 4 for these tests • EM2, TAU4 and maybe even J4 look feasible • But be careful of Jet triggers and noise cuts • FJ behaviour is amazing L1Calo Joint Meeting 11th-13th January 2010

  10. Here’s one I prepared earlier... • One of Alan’s first comments was ‘what about Missing Et’ • I can’t answer that, but on SumEt • eloghttps://atlasop.cern.ch/elog/ATLAS/ATLAS/53404 • Noise/cosmic rate test performed 23rd October • Before significant progress on energy calibration • TE thresholds: • 50 GeV: 0.2 Hz • 25 GeV: 0.5 Hz • 15 GeV: 1.0 Hz • 10 GeV: 2.0 Hz • 8 GeV: 8.0 Hz • Current lowest TE threshold is 150 GeV • Beam rate of this item is essentially 0 • We believe there’s some scope to reduce this • To put it mildly... L1Calo Joint Meeting 11th-13th January 2010

  11. Conclusions • Noise cuts will continue to be an issue • Some change sooner may be better than later • I’m still sceptical of going to 2 in the near future • Does it actually require a Level-1 threshold change? • Scope to reduce thresholds • From a pure noise/cosmics perspective • Not clear there’s a physics case for TAU, J or FJ • In fact FJ3 is possibly already too low for physics purpose • However there is a clear physics case for EM2 • Also the TE, JE thresholds seem to high to be useful L1Calo Joint Meeting 11th-13th January 2010

  12. Backup (thanks to Andrew) 2EM3 2EM2 L1Calo Joint Meeting 11th-13th January 2010

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