on calorimeter thresholds for jet reconstruction marek zieliński ( rochester) jet met, 12 february...

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


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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…


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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


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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


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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


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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


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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


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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


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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


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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


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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


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


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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


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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


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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


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


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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


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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?

Backups


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Considering Zero-Suppression

From Davide,

27 Aug 2007


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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


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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


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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??


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Avg Jet Energies in Endcap vs Thresholds

Jet energy loss could be reduced by lowering thresholds

Zhen Qi


Zieliński 26

“Cell Thresholds” and Energy Loss in Jets

Jet energy loss could be reduced by lowering thresholds But not much gain in Endcap after tower ET>0.5 GeV threshold

Zhen Qi

on calorimeter thresholds for jet reconstruction marek zieliński ( rochester) jet met, 12 february...

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