e/gamma Trigger Overview

1. e/gamma Trigger Overview • Overview on what the e/g trigger does • Main e/g triggers for L=1031 • Commissioning strategy • Summary Monika Wielers (RAL)

2. L1 EM Calorimeter selection • EM/Tau Trigger • Input ET per trigger tower (digitised signal, ET given in 1 GeV steps) • For seed finding use sliding 44 window of TTs (size: 0.10.1) • Requirements to build RoIs • 2x2 core (EM+Had) is local ET maximum • Most energetic of the 4 EM 21 combinations > ET(thr) • In case isolation is required • ET in ring around 22 core  EM ring isolation threshold • ET in 22 had. core behind EM core  Had core isol. thr. • ET in ring around 22 had core  Had ring isol. threshold Monika Wielers (RAL)

3. HLT Structure L1 2EM3 Chain 2e5; input =“L1_2EM3” Chain 2e5; input =“L2_2e5” Signature (2e5) Signature (2e5) Sequence (e): [EM3  ’e5-FEX, e5-Hypo, …’e5] Sequence (e): [e5  ’e5-FEX, e5-Hypo, …’e5] y/n y/n y/n y/n HLT 2e5 chain Signature (2e5) Signature (2e5) L2 EF • Algorithms for feature extraction (FEX) and applying requirements (hypothesis). • Configurable by parameters • Results cached by HLT steering • Sequences: FEX and hypo algos producing TriggerElements (TE) • Chains: Ordered lists of defined numbers of TriggerElements • Steering aborts chains as soon as a given step fails (early reject) • Menu: Collection of chains (and passthroughs + prescales) • In python or xml, recorded in database Monika Wielers (RAL)

4. Electron Sequence Sequence Data EF_e20 L2_e20 EM18 RoI EMTauRoI T2CaloEgamma TrigCaloRec SiTrack IdScan TrigEMCluster TrigL2CaloHypo TrigInDetTrack Collection TrigElectron TrigL2IDCaloHypo L2Result CaloClusterC. TrigEgammaRec (electron set-up) egammaCont. TrigEFEgammaHypo EFResult Calorimeter reconstruction • Look for cell with maximal energy in 2nd EM layer within =0.20.2 (RoI size: 0.40.4) • Build 3x7 cluster around this seed • Apply cluster correction (leakage outside the cluster, s-shape etc.) • Calculate shower shape variables • ET in 1st layer of hadronic calorimeter behind EM shower • Shower shape in 2nd EM sampling R= E(37)/E(77) • Shower shape in 1st EM sampling Eratio=(E(1st max)-E(2nd max)) / (E(1st max)+E(2nd max)) • TrigL2CaloHypo selects good e-candidates based on above criteria Monika Wielers (RAL)

5. L2 electron reconstruction • Track reconstruction • Both SiTrack and IdScan are executed • Both algos are based on tracking in Pixel/SCT • IdScan main feature: determination of z-position of primary vtx • SiTrack main feature: track seeds start from combinatorial pairing of space points from first 2 layers • In the future also TRTSegFinder (TRT track reco) will be run • Once we have collected first data we will select ‘best’ tracking option for all slices (e/g, tau, muon) and continue with one algo (at most 2) • L2 ID-Calo hypothesis • Require track is found in front of calo • Calculate E/p, (track-cluster), (track-cluster) • Select good electron candidates on above selections and pT(track) Monika Wielers (RAL)

6. EF electron reconstruction • Re-use offline reconstruction • Cluster reconstruction • Use sliding window algorithm for seed finding • Input to slw: artificially cut towers of size =0.0250.025 • Use 37 cluster around cluster seed • Apply cluster corrections (leakage outside cluster, s-shape, etc.) • egammaRec reconstruction • Build shower shapes • Tracking reconstruction • Runs default inside-out tracking • Attempt Bremsstrahlung recovery • Build track-cluster matching quantities • Hypothesis algorithm • Apply selections based on IsEM bits • Note: EF selections should be looser than offline ones, we are working on this right now Monika Wielers (RAL)

7. Photon selection Algorithm Data EF_g20 L2_g20 EM18 RoI EMTauRoI T2CaloEgamma TrigCaloRec TrigEMCluster TrigL2PhotonHypo TrigPhoton L2Result CaloClusterC. TrigEgammaRec (photon set-up) egammaCont. TrigEFPhotonHypo EFResult • Photon sequence similar to electron sequence • Photon sequence only uses calorimeter based reconstruction and hypothesis algos • Cluster reconstruction at L2 and EF done in same way • Possibility to do photon conversion at EF • Implemented for testing, but this option won’t be run at start-up • Initially the photon slice will run as electron no-track slice • The same calo based selections will be applied Monika Wielers (RAL)

8. Primary egamma Triggers • These are the triggers which should be used by any physics analyses • Note: w.r.t. previous rate numbers g20 rate has gone up by a factor of 2-3, eff increased by ~20% due to bug fixes • em105_passHLT is very high pT trigger put in mainly for you • Only applies L1 threshold cut, can’t get looser for e/g … • Gustaaf advocates 2g10 trigger which is not in 1031 menu, but in MC one • Photon identification becomes difficult below ET=20GeV, so if this is an issue it would be good to see some feasibility study • In addition we have other triggers for monitoring, eff. extraction, back-up, calibration and test triggers, see • https://twiki.cern.ch/twiki/bin/view/Atlas/L31TriggerMenu Monika Wielers (RAL)

9. What do we do if rate is too high (1031 menu) • depends on why it’s too high, generally • tighten identification cuts • raise ET threshold • prescale (obviously a ‘last resort’ for primary triggers) • Priority list • 1st need to know the rates  then priority list! • e20_loose: priority trigger, with high threshold rates under control • as currently work ongoing on offline start-up selection cuts and as some trigger cuts are tighter than offline one, might rethink that ? • 2e5_medium: priority, un-prescaled while allowed by L1 rate (+ e5) • e10_medium: low threshold, a lot of electrons (though no ‘clean’ source), might need changing • move up threshold/tightened depending on e20, 2e5 • g20_loose: can go up in threshold plus pre-scaling g20_loose • Be careful as g20 == e20_no_track • em105_passHLT: should be ~1Hz, if not add HLT ET threshold Monika Wielers (RAL)

10. Egamma back-up triggers • Note: some primary trigger would be prescaled, need to under- stand better what we ‘loose’ and what prescales are acceptable • g105_veryloose means only ET cut is applied at EF • There are more backups for particular channels, e.g. e20_loose_xe15 Monika Wielers (RAL)

11. Commissioning of e/g triggers • Commissioning/understanding of e/ triggers long iterative procedure • Once we have the first signal events trigger/offline loop will start and little by little we’ll learn • Initially simple menu with limited number of triggers defined • runs initially with L1 only then enable HLT in pass-through • Run more complete commissioning menu offline • In first iteration concentrate on electrons as photons are harder to understand as there is not yet a clean source of photons available • Use MC to go from electrons to photons • Electron identification implies good understanding of calo and tracker • In beginning rely on cut based optimisations ‘carefully set by hand’ (offline has same approach) • Selections based on many different criteria • ET, had. leakage, shower shapes in 1st and 2nd EM sampling • Track match • Cluster-track matching variables • Criteria eta dependent, quite some diff. in barrel / end-cap • Some criteria easier to extract than others. Monika Wielers (RAL)

12. Evolution towards higher luminosities • Not useful to spend too much time on this • analysing early data will help us understanding the trigger, detector and offline combined performance • Above depends on stability of detector, how much data we have already collected, how much time we have to analyse the data, … • Will only give some ideas here, the rest we’ll sort out when we face the 2nd physics run • Data from 1st physics run will allow to • optimising selection cuts, thus reducing the rate • This should result in adequate rejection for high pT triggers • New optimisations will also take into account possible losses due to pileup (remember: diff no pile / 1033 pileup for tight selection of 1033 triggers ~1%, not dramatic) • After review of L2 tracking from 1st data we’ll hopefully only run one L2 tracking algorithm for all slices • Photons will evolve using tighter calo cuts than electrons • In the moment use out main triggers with tighter cuts to get an idea what we might have at that time Monika Wielers (RAL)

13. Summary of what we need as input from physics groups • If you use any of the primary triggers in your analysis we would like to understand better • Which analysis uses which e/g trigger? • What is the best thing to do in case the rate is too high? • Is it better to raise thresholds, tighter selections, pre-scale? • Would be good to have some plots with effect of increase of trigger threshold, tighter cuts • If rate is too high that’s the input we need to decide what best to do for optimal physics reach • Is your favourite trigger already in our list of back-up triggers? • If none of the primary triggers is ok for your analysis come and talk to us • We will post info in our wiki with info on all analyses using electrons and photon triggers (will be created in next few days) • https://twiki.cern.ch/twiki/bin/view/Atlas/TrigEgamma • We’ll also post some example how to raise ET cuts of a given trigger in simple way in your analysis • Menu and justifications to be found in • https://twiki.cern.ch/twiki/bin/view/Atlas/TriggerPhysicsMenu Monika Wielers (RAL)