Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 1 Calibration of L1Calo L1Calo Calibration Overview L1Calo Calibration Overview Calibration Status & Refinements Calibration Status & Refinements Hardware Problems Hardware Problems Longer-term Questions Longer-term Questions

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 2 Overview of L1Calo Signals

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 3 Main Elements of L1Calo Calibration Timing  Optimum calibration requires ADC timing to < 2-3 ns.  Measure tower-by-tower in beam data. Receiver gains  Set ADCs to uniform 250 MeV EM scale  Based on pulsers, check with beam Filter & LUT Slope  Filter improve S/N, ET calibration, Bunch Crossing ID performance  LUT “slope” is the final calibration adjustment

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 4 Main Elements of L1Calo Calibration Timing  Optimum calibration requires ADC timing to < 2-3 ns.  Measure tower-by-tower in beam data. Receiver gains  Set ADCs to uniform 250 MeV EM scale  Based on pulsers, check with beam Filter & LUT Slope  Filter improve S/N, ET calibration, Bunch Crossing ID performance  LUT “slope” is the final calibration adjustment Output: tower  Uniform tower calibration  ~1 GeV deposited ET per count, EM scale

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 5 Also Affecting Trigger Calibration Tower calibration ≠ trigger calibration Noise cuts  One-sided – towers below threshold are zeroed.  Triggers combining many low-E T towers can be sensitive. BCID efficiency turn-on  Only use “in-time” towers. Full efficiency reached between 2- 3 GeV.  Performance not critically sensitive to filter coefficients Trigger Thresholds  Set to produce desired turn-on What you compare against  Offline algorithm & calibration

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 6 Calibration History TWiki: L1CaloCommissioningChanges

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 7 Calibration History TWiki: L1CaloCommissioningChanges Last significant calibration change

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 8 Calibration History TWiki: L1CaloCommissioningChanges Last significant calibration change Stable throughout > 98% of 2010 data- taking

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 9 Originally reliant on pulsers  Provide signals with controllable E T, good statistics for all channels  But expected to have systematic differences in pulse shape & timing Calibration using collision data Calibration using Physics Events  Timing by fitting pulse shapes  Needs events with E T >> noise in all channels  Tower E T by comparison with corresponding cell sums  Requires wide range of E T in each tower  Only recently had necessary statistics for these studies

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 10 Trigger Tower Timing Quite stable:  Luminosity now sufficient to gather data for timing fit quickly  One good run will do most channels  Some low-activity channels need longer  Most channels within ±3ns  Further improvement desirable, but effects on calibration will be small  Will need ongoing checks  Two global timing changes this summer EM, run  Global 2ns clock phase change made in RF2TTC module 1 day after these data were collected!

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 11 Receiver gains & ADC Calibration Generally good correlation with cell readout  Most detector partitions  Across full E T range Exception: EMEC 1.5<  <1.8  Incorrect PS weight in tower sum affects pulser calibration  Effect understood, can be corrected.

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 12 Corrections to ADC scales FCAL 2/3 gains:  FCAL 2/3 “towers” are added in pairs before digitization.  Believe gain variations between pair likely cause of deviation Physics signal scales:  Pulser and physics signals not identical.  Observe differences of the order of 2%  Corrections being calculated

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 13 Corrections to Final ET Scale LUT slopes:  LUT slopes are sensitive to the physics pulse shape, which differs from the calibration pulses.  Shifts scale relative to ADC calibration  Can now measure effect and apply corrections LUT filling:  LUT filling scheme causes slight tendency towards underestimation of some pulse ET values  A small bias, visible mainly at low ET.  Can correct with online software change

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 14 EM Transition Region One Trigger Tower spans transition  Need to combine signals in receivers in USA15  Analogue summation before L1Calo electronics.  Timings need to be measured and cables cut to length  O(45ns) difference between EMB and EMEC timings  Measurement with data – pulser timing different  Hence different partial towers in this region in some periods  Cutting cables is a one-shot operationStatus  Data collected and timings estimated  A few problematic towers identified  Spread within one cable (4 TT) a bit large  Should be able to reduce using Tower Builder Board settings

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 15 Applying Corrections Optimisation vs Stability  Priority was to keep calibration stable for 2010 pp run  Rather than apply quick fixes as each effect understood  Most can be applied for HI run  FCAL 2/3 gains most difficult on that timescale  EM scale calibration will not be complete until after transition towers connected  Expect this to be 2011  Will require some further work to understand signals once connected.

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 16 HV Trips Effects vary  PS trips: small loss of signal  Tile: drawer off, towers dead  Accordion: 50% signal loss Flagging status  Performed by detector groups Difficult area: accordion trips  Reduced gain can be corrected offline  Hence data usable for physics  But L1Calo and HLT both affected  Trying to correct at L1 would be “messy”

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 17 Calibration Strategy for 2011 Run Priority: Establish an understood EM scale  Corrections to ADC, LUT scales to to match calibration to readout  Mostly few % effects  Corrections for long-term reduced HV, endcap PS weights  Larger, but localised  Finalise timings  Connect up and calibrate transition towers Will bad towers be fixed in shutdown?  Dead OTX or Tile drawers, for example  If so, will need to establish calibration for these towers Conclusion: start 2011 with EM scale calibration

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 18 Calibration Strategy for 2011 Run Are there other changes which might improve performance?  Reduce trigger tower noise cuts?  Rather promising in MC. In reality…?  Eta-dependent corrections?  e.g. for material effects?  Trigger threshold tuning?  Will be needed if we do either of the above

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 19 Trigger Refinements Effects of any changes must be studied using real data (Old MC plots used to illustrate points in following slides)

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 20 Noise Cut Tuning MC: lower cuts improve performance  Sharper turn-on for jet, MET  Reduced ET-dependence of L1 jet response Tests with data-taking in early 2009 less positive  Very modest effects seen  Data had other imperfections, e.g. timing, not present in MC. Did these mask effects?  Would larger reductions help more? Study effects with recorded data  ESD contains ADC data, so can simulate effect of reduced cuts

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 21 Material Corrections Trigger response varies with   Material effects a major factor Can tower calibration compensate?  In principle, to some extent, but with caveats:  Corrections should depend on object and E T. Tower-based corrections cannot take this into account.  Over-correction results in hot spots, increased rate.  Region where corrections largest still partially-connected, not understood. “EM scale” “LUT Calib” MC electrons, p T > 25 GeV

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 22 Investigating Material Corrections Possible approach  Study LUT-based corrections  Keep ADC data on EM scale for reference, monitoring  Digital correction, can be studied reliably in data analysis  Base on electron response ( GeV p T ?)  Simpler to define & understand than jets  Less sensitive to other parameters which may change  Don’t change overall E T scale  Mid-barrel response as referenceConstraints  Need fully understood EM scale first  Can start investigation sooner, but not conclude  Transition region incomplete  Currently would have to exclude  Noise cut changes would affect results  Mostly for jets, low-ET e/ . Reason not to tune for these  Need to understand effects on all triggers, E T ranges

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 23 An Alternative Approach A purely personal suggestion: I don’t suppose that the next slide will make me popular, but wanted all options to be on the table…

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 24 Modulating Trigger Thresholds with  Modules span fixed  ranges  Can load different threshold values into different modules  Modulate threshold value with   Could use to make turn-on more uniform, improve overall sharpness  Corrections depend on object E TQuestions/Drawbacks  Complicates threshold setting  Does not help MET  Is module eta granularity enough?

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 25 Modulating Trigger Thresholds with  Modules span fixed  ranges  Can load different threshold values into different modules  Modulate threshold value with   Could use to make turn-on more uniform, improve overall sharpness  Corrections depend on object E TQuestions/Drawbacks  Complicates threshold setting  Does not help MET  Is module eta granularity enough?

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 26 Changing Conditions: Pileup  Place-holder – not much to say: main thing is what’s observed about different effects in first crossing of train and subsequent  Note that we have jet element thresholds that can be applied to JEM triggers – may be useful to stabilise TE if luminosity variation within a fill becomes an issue.  Don’t so far see a need to raise tower thresholds etc, but keep under review. Currently out-of-time pileup actually reduces signal levels, which would favour opposite

Alan Watson Atlas Trigger Workshop, Amsterdam, 18-22/10/10 27 Summary Another place-holder, but points to cover  Status not at all bad: timing within couple of ns, most scales good to few %  Work to do to finish EM scale, but we know what the steps are. Could have done most of them sooner, can do most quickly  Still a few odd channels, such as transition, where we will need a bit longer to get the calibration finalised and understood  Accordion HV trips problematic for us. May be a small effect on physics so far, but it’s a potential complication  Are some ideas to investigate for improving trigger performance. We have the tools to do the studies, but at least any calibration adjustments should start from good EM scale (noise cuts less so)