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On Calorimeter Thresholdsfor Jet Reconstruction
Marek Zieliński (Rochester)
Jet MET, 12 February 2008
Jet MET, 12 February 2008 Marek
Zieliński 2
Introduction
Hierarchy of thresholds: Online Zero Suppression
Driven by channel occupancy requirements “Typical” ZS: 1-3 ADC; in HB 3ADC ~500 MeV avg, 300-900 range
Offline thresholds for cells (RecHits) and towers Thresholds for jet and MET reco could be different; should they?
Current scheme for offline thresholds Energy cell thresholds to cut out majority of noise ET tower thresholds to cut out majority of pileup & UE Default in CMSSW: Scheme B for cells + tower ET>0.5 GeV
Jet MET, 12 February 2008 Marek
Zieliński 3
Goals and Tools Revise the value of cell thresholds
Cell thresholds can have a significant impact on the observed response to low energy particles
Optimization of tower ET threshold best done as part of pileup studies Scheme B was derived based on ORCA 871 MC
CMS Note-2006/020 Many changes in HCAL simulation since then
Information to consider (per subdetector) Amount of noise within jet cone vs threshold Amount of real jet energy removed vs threshold Jet resolution vs threshold Jet rapidity distribution at low pT … no clear single measure for optimization…
Jet MET, 12 February 2008 Marek
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“A Brief History of Noise…”
Measurements and simulation of noise are performed by members of HCAL DPG using a variety of data
Description of noise changed significantly in CMSSW 152 From ORCA times till 14x, noise patterns had a discrete pattern per
HCAL subdetector From 152 onward, realistic HCAL calibrations (based on DB values)
ADC/GeV, noise and other constants improved
Corrections for ZS/threshold effects will be done by JEC group
HB
ORCA 871CMSSW
140 RecHits
Salavat
CMSSW
152 RecHits
Salavat
Jet MET, 12 February 2008 Marek
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The Real Data: GREN
Analysis of GREN RecHit data from Daniel Miner GR run 30333
New results and MC much closer (need to separate HB & HE) While the dust settles, I’ll continue with 1.5.2 MC…
Mean: 0.36Sigma: 0.78
“Old” gains and pedestals “New” gains and pedestals
Mean: 0.003Sigma: 0.297
Jet MET, 12 February 2008 Marek
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“Cell Thresholds” and Noise (152)
A “first look” using the HCAL constants in 152 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) No simulation of online ZS
A pure noise file generated in CMSSW 152 was used All tower-level thresholds were removed including those on crystals Checked against a CMSSW 152 single muon plus noise RelVal sample
with no thresholds and compared to Salavat’s plots Single muon plus noise files are dominated by noise in HCAL and ECAL
To estimate noise contributing to a jet, energy was summed from cells within a cone R=0.5 Two methods used Thresholds applied to emEnergy, hadEnergy, outerEnergy
Jet MET, 12 February 2008 Marek
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HAD Noise per HB Tower in 152 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)
Two methods 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
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Noise in Cone in HE & HO (Threshold = 0)
Sum of hadEnergy contributions from all HE/HO towers, normalized to cone area In HE, different from applying thresholds per cell
The 152 noise fileHEHO
Jet MET, 12 February 2008 Marek
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“HAD Thresholds” and Noise in Cone
Average noise in R=0.5 cone vs threshold Compare to Scheme B Thresholds: HB 0.9, HE 1.4, HO 1.1 GeV Scheme B thresholds seem larger than necessary for all regions
Scheme B
Pat Buchinski
Jet MET, 12 February 2008 Marek
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“Cell Thresholds” and Energy Loss in Jets
Question: How much real jet energy is lost by imposing calorimeter cell energy thresholds?
Analysis: QCD ptHat > 90 GeV in CMSSW
152 (1000 events), jet pT > 40 GeV No noise No thresholds except optional
Tower ET>0.5 GeV Apply thresholds on emEnergy,
hadEnergy, outerEnergy “by hand” Recalculate jet energy components
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
Energy loss = Subtract energy with thresholds from energy with threshold=0 Jet energy loss could be reduced by lowering thresholds, esp in HB
Tower ET>0.5 GeV threshold has big impact 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 Methodology:
Used 50 < pThat< 80 GeV dijet sample Defined “MC truth” response and resolution:
mean response = mean(pTcorr/pT
gen)
scaled resolution: (pTcorr/pT
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:0.3 3. T2: HB:0.5 HO:0.5 HES:0.6 HED:0.6 4. T3: HB:0.7 HO:0.8 HES:1.0 HED:1.0 5. T4: HB:0.9 HO:1.1 HES:1.4 HED:1.4 = Scheme B Kept EM cuts and tower ET cut at default values 100k events each MCJet corrections applied (same Two pT
gen bins: 20-40 and 50-80 GeV Separately for jets in Barrel and Endcap
Jet MET, 12 February 2008 Marek
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HB: Jet Response & Resolution vs T
20<pTgen<40 GeV
50<pTgen<80 GeV
Zhen Qi
Reprocessing
without the
Tower ET cut
Jet MET, 12 February 2008 Marek
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HE: Jet Response & Resolution vs T
20<pTgen<40 GeV
50<pTgen<80 GeV
Zhen Qi
Reprocessing
without the
Tower ET cut
Jet MET, 12 February 2008 Marek
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Jet Distributions The impact of low cell thresholds
of 0.5 GeV was HUGE in ORCA default cell energy threshold E>0.5
GeV (black) Higher threshold 0.8 GeV (red) was
similar to Scheme B in Barrel nominal tower threshold ET>0.5
GeV for both cases
Not observed in 1.5.2 consistent with significantly lower
noise tower ET>0.5 GeV cut seems to
suppress the noise by itself tuning noise thresholds coupled
with the choice of tower cut for PU
ORCA
CMSSW 1.5.2
Zhen Qi
Jet MET, 12 February 2008 Marek
Zieliński 17
Jet Matching Efficiency & “Fakes”
reco is the standard jet matching efficiency 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
A first look at Noise-in-Cone and Jet-Energy-Loss vs calorimeter “cell” thresholds a la ORCA study Scheme B thresholds seem to be higher than necessary Value of JEL strongly affected by tower ET cut Jet resolutions improve for lower thresholds
Things to investigate: Effects of online ZS Correlation of tower ET and cell thresholds Re-optimization of ECAL cuts Impact of thresholds on jet “efficiencies” and “fake rates”
Crucial to coordinate threshold studies with HCAL improvements of pedestals/noise (HCAL DPG) GR noise studies (Daniel Miner, Efe,…) JEC offset studies (Daniel, Ia Iashvili…) Pileup suppression (Ia, Olga,…)
Looking for help/volunteers
Jet MET, 12 February 2008 Marek
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Some Questions…
What HCAL ZS settings are expected for real data? when will be known?
Are ECAL thresholds & noise finalized in simulation? What CMSSW version to use?
Salavat: may want to wait for 2xx
What MC samples are required?
What additional info/studies are needed to achieve consensus about thresholds?
What is current thinking about “safety factors” when facing the unknowns of real data taking?
Jet MET, 12 February 2008 Marek
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HAD Noise per Tower in HE & HO
Difference in HE due to multiple cells per tower in HE
The 152 RecHits
Salavat
The 152 noise file
HEHO
HE HO
Jet MET, 12 February 2008 Marek
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“HAD Thresholds” and Noise in Cone
Average noise in R=0.5 cone vs threshold Compare to Scheme B Thresholds: HB 0.9, HE 1.4, HO 1.1 GeV Scheme B thresholds seem larger than necessary for all regions
Scheme B
Jet MET, 12 February 2008 Marek
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“EM Thresholds” and Noise in Cone Average noise in R=0.5 cone vs threshold on SumEB/SumEE
Compare to Scheme B Thresholds: Sum EB 0.2, SumEE 0.45 GeV “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 EEResults 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
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Avg Jet Energies in Endcap vs Thresholds
Jet energy loss could be reduced by lowering thresholds
Zhen Qi