On Calorimeter Thresholds for Jet Reconstruction Marek Zieliński ( Rochester) Jet MET, 12 February 2008

Marek Zieliński 2 Introduction l Hierarchy of thresholds: è Online Zero Suppression à Driven by channel occupancy requirements à “Typical” ZS: 1-3 ADC; in HB 3ADC ~500 MeV avg, range è Offline thresholds for cells (RecHits) and towers à Thresholds for jet and MET reco could be different; should they? l Current scheme for offline thresholds è Energy cell thresholds to cut out majority of noise è ET tower thresholds to cut out majority of pileup & UE è Default in CMSSW: Scheme B for cells + tower ET>0.5 GeV

Jet MET, 12 February 2008 Marek Zieliński 3 Goals and Tools l Revise the value of cell thresholds è Cell thresholds can have a significant impact on the observed response to low energy particles è Optimization of tower ET threshold best done as part of pileup studies è Scheme B was derived based on ORCA 871 MC à CMS Note-2006/020 è Many changes in HCAL simulation since then l Information to consider (per subdetector) è Amount of noise within jet cone vs threshold è Amount of real jet energy removed vs threshold è Jet resolution vs threshold è Jet rapidity distribution at low pT è … no clear single measure for optimization…

Jet MET, 12 February 2008 Marek Zieliński 4 “A Brief History of Noise…” l Measurements and simulation of noise are performed by members of HCAL DPG using a variety of data l Description of noise changed significantly in CMSSW 152 è From ORCA times till 14x, noise patterns had a discrete pattern per HCAL subdetector è From 152 onward, realistic HCAL calibrations (based on DB values)  ADC/GeV,  noise and other constants improved l Corrections for ZS/threshold effects will be done by JEC group HB ORCA 871 CMSSW 140 RecHits Salavat CMSSW 152 RecHits Salavat

Jet MET, 12 February 2008 Marek Zieliński 5 The Real Data: GREN l Analysis of GREN RecHit data from Daniel Miner è GR run l New results and MC much closer (need to separate HB & HE) l While the dust settles, I’ll continue with MC… Mean: 0.36 Sigma: 0.78 “Old” gains and pedestals“New” gains and pedestals Mean: Sigma: 0.297

Jet MET, 12 February 2008 Marek Zieliński 6 “Cell Thresholds” and Noise (152) l A “first look” using the HCAL constants in 152 è effects of cell thresholds on noise in jets for five different regions of the calorimeter: HB, HO, HE, EB, and EE (HF not considered here) è No simulation of online ZS l A pure noise file generated in CMSSW 152 was used è All tower-level thresholds were removed including those on crystals è Checked against a CMSSW 152 single muon plus noise RelVal sample with no thresholds and compared to Salavat’s plots à Single muon plus noise files are dominated by noise in HCAL and ECAL l To estimate noise contributing to a jet, energy was summed from cells within a cone R=0.5 è Two methods used è Thresholds applied to emEnergy, hadEnergy, outerEnergy

Jet MET, 12 February 2008 Marek Zieliński 7 HAD Noise per HB Tower in 152 l Noise level in the “pure noise” file agrees with noise seen in RelVal single-muon file and shown in HCAL DPG meetings Noise energy in HB cells The 152 noise file (private production) The 152 single-  file (RelVal sample) The 152 RecHits (HCAL DPG study) Salavat

Jet MET, 12 February 2008 Marek Zieliński 8 Noise in Cone in HB (Threshold = 0) One cone per event moved randomly in HB (illustrates expected spread of jet noise values) l Two methods è to sum the noise contributions within cone R = 0.5 Average of all HB towers, normalized to cone area (better accuracy for mean value) Used for Noise vs Threshold plots

Jet MET, 12 February 2008 Marek Zieliński 9 Noise in Cone in HE & HO (Threshold = 0) l Sum of hadEnergy contributions from all HE/HO towers, normalized to cone area è In HE, different from applying thresholds per cell The 152 noise file HE HO

Jet MET, 12 February 2008 Marek Zieliński 10 “HAD Thresholds” and Noise in Cone l Average noise in R=0.5 cone vs threshold è Compare to Scheme B Thresholds: HB 0.9, HE 1.4, HO 1.1 GeV è Scheme B thresholds seem larger than necessary for all regions Scheme B Pat Buchinski

Jet MET, 12 February 2008 Marek Zieliński 11 “Cell Thresholds” and Energy Loss in Jets l Question: How much real jet energy is lost by imposing calorimeter cell energy thresholds? l Analysis: è QCD ptHat > 90 GeV in CMSSW 152 (1000 events), jet pT > 40 GeV è No noise è No thresholds except optional Tower ET>0.5 GeV è Apply thresholds on emEnergy, hadEnergy, outerEnergy “by hand” è Recalculate jet energy components l Results change when tower ET>0.5 GeV is applied (default in jet reco) Zhen Qi

Jet MET, 12 February 2008 Marek Zieliński 12 Thresholds and Jet Energy Loss in Barrel l Energy loss = Subtract energy with thresholds from energy with threshold=0 l Jet energy loss could be reduced by lowering thresholds, esp in HB è Tower ET>0.5 GeV threshold has big impact è Energy loss due to crystal cuts not studied (in EB or EE) Zhen Qi

Jet MET, 12 February 2008 Marek Zieliński 13 Jet Resolution vs Thresholds l Methodology: è Used 50 < pThat< 80 GeV dijet sample è Defined “MC truth” response and resolution:  mean response  = mean(p T corr /p T gen )  scaled resolution:  (p T corr /p T gen )/   Derived  and  for 5 threshold schemes 1. T0: HB:0. HO:0. HES:0. HED:0. 2. T1: HB:0.3 HO:0.3 HES:0.3 HED: T2: HB:0.5 HO:0.5 HES:0.6 HED: T3: HB:0.7 HO:0.8 HES:1.0 HED: T4: HB:0.9 HO:1.1 HES:1.4 HED:1.4 = Scheme B à Kept EM cuts and tower ET cut at default values à 100k events each à MCJet corrections applied (same à Two p T gen bins: and GeV à Separately for jets in Barrel and Endcap

Jet MET, 12 February 2008 Marek Zieliński 14 HB: Jet Response & Resolution vs T 20<p T gen <40 GeV 50<p T gen <80 GeV Zhen Qi   Reprocessing without the Tower ET cut

Jet MET, 12 February 2008 Marek Zieliński 15 HE: Jet Response & Resolution vs T 20<p T gen <40 GeV 50<p T gen <80 GeV  Zhen Qi Reprocessing without the Tower ET cut

Jet MET, 12 February 2008 Marek Zieliński 16 Jet  Distributions l The impact of low cell thresholds of 0.5 GeV was HUGE in ORCA è default cell energy threshold E>0.5 GeV (black) è Higher threshold 0.8 GeV (red) was similar to Scheme B in Barrel è nominal tower threshold ET>0.5 GeV for both cases l Not observed in è consistent with significantly lower noise è tower ET>0.5 GeV cut seems to suppress the noise by itself è tuning noise thresholds coupled with the choice of tower cut for PU ORCA CMSSW Zhen Qi

Jet MET, 12 February 2008 Marek Zieliński 17 Jet Matching Efficiency & “Fakes”  reco is the standard jet matching efficiency è No significant effect of lowering the thresholds from Scheme B (black) to flat 0.5 GeV cut (red)  fake is the standard jet mismatch rate (aka “fake rate”)  a small effect near  = 0 for lower thresholds – a few real fake jets?! Cosmin Dragoiu

Jet MET, 12 February 2008 Marek Zieliński 18 Conclusions & Outlook l A first look at Noise-in-Cone and Jet-Energy-Loss vs calorimeter “cell” thresholds a la ORCA study è Scheme B thresholds seem to be higher than necessary è Value of JEL strongly affected by tower ET cut è Jet resolutions improve for lower thresholds l Things to investigate: è Effects of online ZS è Correlation of tower ET and cell thresholds è Re-optimization of ECAL cuts è Impact of thresholds on jet “efficiencies” and “fake rates” l Crucial to coordinate threshold studies with è HCAL improvements of pedestals/noise (HCAL DPG) è GR noise studies (Daniel Miner, Efe,…) è JEC offset studies (Daniel, Ia Iashvili…) è Pileup suppression (Ia, Olga,…) l Looking for help/volunteers

Jet MET, 12 February 2008 Marek Zieliński 19 Some Questions… l What HCAL ZS settings are expected for real data? è when will be known? l Are ECAL thresholds & noise finalized in simulation? l What CMSSW version to use? è Salavat: may want to wait for 2xx l What MC samples are required? l What additional info/studies are needed to achieve consensus about thresholds? l What is current thinking about “safety factors” when facing the unknowns of real data taking?

Backups

Jet MET, 12 February 2008 Marek Zieliński 21 Considering Zero-Suppression From Davide, 27 Aug 2007

Jet MET, 12 February 2008 Marek Zieliński 22 HAD Noise per Tower in HE & HO l Difference in HE due to multiple cells per tower in HE The 152 RecHits Salavat The 152 noise file HE HO HE HO

Jet MET, 12 February 2008 Marek Zieliński 23 “HAD Thresholds” and Noise in Cone l Average noise in R=0.5 cone vs threshold è Compare to Scheme B Thresholds: HB 0.9, HE 1.4, HO 1.1 GeV è Scheme B thresholds seem larger than necessary for all regions Scheme B

Jet MET, 12 February 2008 Marek Zieliński 24 “EM Thresholds” and Noise in Cone l Average noise in R=0.5 cone vs threshold on SumEB/SumEE è Compare to Scheme B Thresholds: Sum EB 0.2, SumEE 0.45 GeV è “SumEM” thresholds depend on crystal thresholds; are these final? No crystal thresholds applied when making CaloTowers. “Standard” crystal thresholds applied in CaloTowers: EB 0.9 / EE 0.45 GeV EB EE EB EE Results slightly different than in ORCA: 1.9 (EB) and 0.2 (EE) GeV for SumEM threshold = 0. Is this consistent with changes in EM noise and/or thresholds since ORCA??

Jet MET, 12 February 2008 Marek Zieliński 25 Avg Jet Energies in Endcap vs Thresholds l Jet energy loss could be reduced by lowering thresholds Zhen Qi

Jet MET, 12 February 2008 Marek Zieliński 26 “Cell Thresholds” and Energy Loss in Jets l Jet energy loss could be reduced by lowering thresholds è But not much gain in Endcap after tower ET>0.5 GeV threshold Zhen Qi