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Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

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Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting , IPPP January 2008
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Page 1: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Jet Calibration in ATLAS

Mark Hodgkinson

ATLAS UK Meeting , IPPP

January 2008

Page 2: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Contents

• Introduction to detectors used in Jet reconstruction

• Hadronic calibrations for jets• Validation of hadronic energy scale• In Situ Calibrations• Other contributions from UK• Conclusions

Far more work goes on than I am showing in this talk - as far as I know all UK jet performance work is in this talk…So this talk is biased to topics the UK is involved in…

Page 3: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Introduction

• Calorimeters used by default forjet finding• Trackers also being used for widervariety of tasks in jet group nowadays

• Charged componentseen in tracker

Charged and neutral components seen in calorimeter

Jet Finders

• ATLAS uses Cone 0.4 and 0.7• Also use Kt D = 0.4 and D = 0.6

Jets

• We measure jets kinematics via a spray of hadrons after the hadronisation process• Ideally associate all hadrons to the correctparton uniquely

Page 4: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Calorimeter input to Jet FindingCaloTowers:• Towers are fixed grid of 0.1 x 0.1 in eta and phiCaloTopoClusters:• Define any CaloCells with |E| > as seed cells• Add any neighbouring cells (3D) with |E| > to seed• Repeat with new neighbours, until no neighbours pass• Noise suppression built in• Search for local maxima to decide if cluster needs

splitting€

4σ noise

2σ noise

Page 5: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Why We Need a Calibration

• Hadronic Showers complex:

- Visible electromagnetic energy (electrons, photons, 0

decays) ~50%

- Visible energy from ionisation ~25%

- Invisible energy from nuclear interactions (excitation, break up) ~25%

- Escaped energy (e.g. neutrinos) ~2%• Also account for visible energy in dead material

• Jet response varies over the detector - e.g. in crack regions many particles cannot be detected• Charged particles with low pT bent out of cone in calorimeter

A Gupta(Chicago)

M Hodgkinson(Sheffield)

Hadronic Scale

Particle Jet Scale

Parton Scale

• Energy not included in reconstructed jet, that doescome from the hadronisation• Energy from underlying event included in reconstructed jet

Page 6: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Jet Calibrations

2 minimisation :

• Where

• Truth reference is generator level truth jet

2 =E e − E truth

e

E truthe

⎝ ⎜

⎠ ⎟

e

∑2

E e = wiE ie

Vi

⎝ ⎜

⎠ ⎟

i= cells

∑ E ie

H1 Style (BNL)

Local Hadron Calibration(Oxford,Stockholm,MPI Munich)

• Reference energy is true single pion energy (weights alsotested on test beam data!)• Takes us to hadronic scale, not particle jet scale• Need additional corrections (magnetic field etc) on top - not done yet• Classify clusters as EM or Hadronic• Hadronic clusters get weights applied (12.0.6), dead material corrections (12.0.6) and out of cluster (not in 12.0.6) corrections

0.4 < < 0.5

0.4 < < 0.5

Plots by C Issever, K Lohwasser (Oxford)and E Bergeaas (Stockholm)

Page 7: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Energy Flow with eflowRec = 0 single ± TDR:Tracking: p

T/p

T 0.036%p

T1.3%

Calo: E/E 50%/E

• Charged particle response from single pion Monte Carlo• In eflowRec remove energy due to charged pion showers on cell by cell basis via ordering principle• Remaining clusters undergo local hadron calibration

Local Hadron TopoClusterEnergy Flow H1 TopoCluster

M Hodgkinson, R Duxfield, D Tovey (Sheffield)

Pt = 17-140 GeV

• Cone 0.4, J1-J3 dijets, || < 1.8• Improves linearity, comparable width• Improved width of jet energy resolution by discarding tracks matched to showers split into multiple clusters• At 6 GeV 60% of pions have < 80% energy in leadingcluster - work in progress to deal with this• Also plan to derive H1 style weights

• Hadronic W mass resolution improved dueto better linearity and angular resolution• Used sample 5200 (semileptonic top)• 4 Highest pt jets (H1 topocluster) pT > 50 GeV• Refined missing ET > 40 GeV/E = 3.54 ± 0.49

EFlow LocalHadronCalo Only

/E = 5.02 ± 0.61

Page 8: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Check of Hadronic Scale• Use tracking to check if hadronic scale is correct in calorimeter• Minimum Bias events cover 400 MeV -> 10 GeV• Tau decays (W,Z) cover 10 GeV -> 140 GeV• Overlapping showers a problem just like in energy flow for

jets• Have to suppress backgrounds (QCD di-jets and tau

decays to neutral particles)• Need isolated charged hadrons - isolation criteria means

taus cannot be used -> Try for QCD

M HodgkinsonQCD Di-jets

• Can select 7000 tracks from QCD jets in first year (i.e.use shower shape cuts, but not QCD rejection)• Not enough CSC (full sim) data to investigate…• Cannot use Atlfast due to calorimeter cuts used to selectisolated charged hadrons

J. Lu, D. Gingrich (Alberta):

QCD J1

QCD

Minimum Bias

• Use loose cuts and subtract background• Background E/P measured from control sample

E

P

⎝ ⎜

⎠ ⎟i

measured

=E

P( i− j )

⎝ ⎜ ⎜

⎠ ⎟ ⎟

background

×E

P

⎝ ⎜

⎠ ⎟j

isolated

j

∑N DavidsonE Barberio(Melbourne)

pT=10 GeV

Page 9: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

In Situ Calibration

• Jet energy scale is not uniform in h

• Di-jet (Sheffield, Heidelberg and Argonne) samples are used

Paul Hodgson (Sheffield)QCD di-jets

Di-Jet Balancing

• Cut on to ensure jets back to back(suppress ISR/FSR effects)• pt balance = pt_probe/pt_ref• Relative Jet Energy Scale can be determined to < 1% with3 pb-1 data (assuming nominal jet prescales, J70 prescale is 5, do not change)

0.4 < < 0.6 is reference region

Paul Hodgson

• Plan to try technique in FDR

P Hodgson

• + Jet, Z + Jet (M Hurwitz - Chicago)• W mass template method - J Schwindling (Saclay)

Other Methods

Page 10: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

In Situ Calibration at High Pt

• Di-jet, + jet cross-sections are high pt is low• Balance high pt jet with a number of calibrated low pt jets• Glasgow, Tokyo, Heidelberg, Alberta• 1% error on JES, if low pt jets well calibrated• Systematic bias found by D.Clements, C. Buttar• Partly due to unclustered soft activity - mitigated with

larger cone sizes, lower jet seed pT

Jet Balancing

F Ruehr (Heidelberg)

Cone 0.7280->1120 GeV Pt

D Clements, C ButtarPythia standalone

TruthReco

Page 11: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

UK Software

• K Lohwasser (Oxford), V Giangiobbe (INFN Pisa)

• Should be used to make standard jet performance plots

JetPerformance

Y-Splitter

• J Butterworth, A Davison, P Sherwood (UCL)• Y scale is splitting scale into subjets• Useful for finding e.g. hjgh pT W->qq

Mid-Point Jet Algorithm

• S Thompson and C Cheplakov (Glasgow)• Provides infrared safety• Performance as good as standard algorithms• Implemented in ATLAS software

Page 12: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Conclusions• ATLAS pursuing a range of approaches to

calibrating jet energy: - Initial calibration (H1 style , Local Hadron style

+ jet corrections, energy flow) - Validation of hadronic calibrations with E/P

methods - Jet balancing (di-jet) to get uniform response - + jet (Z + jet), W->qq also useful - Then we can bootstrap calibration up to the

very high pt jets - jet balancing favoured• UK is providing useful software for use in Jets

work (JetPerformance, Y Splitter, Mid Point algorithm , eflowRec)

Page 13: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Documents• Local Hadron Calibration Performance - E Bergeaas, C Issever, K Jon-And, K Lohwasser,

B King, D Milstead: ATL-COM-LARG-2007-010

• Energy Flow for Jets - M Hodgkinson, D Tovey, R Duxfield: ATL-COM-PHYS-2007-082

• Jet Fragmentation and E/P work - M Hodgkinson, J Lu, D Gingrich, N Davidson, E Barberio: https://twiki.cern.ch/bin/view/Atlas/JetEoPCSCNote

• DiJets - various talks in JetRec phone meetings

• Gamma + Jet - https://twiki.cern.ch/bin/view/Sandbox/MartinaHurwitzSandbox

• High Pt JES - again see talks in JetRec phone meetings

• JetPerformance - talk in 28th Nov JetRec phone conference

• Ysplitter - J Butterworth, A Davison, E Ozcan, P Sherwood: ATL-PHYS-INT-2007-015

• Mid Point Algorithm in ATLAS - A Cheplakov,S Thompson: ATL-PHYS-PUB-2007-007

• General very detailed introduction to all these issues by P Loch and M Lefevre at:

https://twiki.cern.ch/twiki/bin/view/Atlas/IntroductionToHadronicCalibration

Page 14: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

BACKUPExtra Information

Page 15: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

Minimum BiasN.Davidson, E.Barberio (Melbourne)

• Apply loose cuts and subtract background • Use control sample of late showering charged hadrons (MinBias)• Can define EMoutercone which only contains energy frombackground• Solve set of linear equations

E

P

⎝ ⎜

⎠ ⎟i

measured

=E

P( i− j )

⎝ ⎜ ⎜

⎠ ⎟ ⎟

background

×E

P

⎝ ⎜

⎠ ⎟j

isolated

j

pT=10 GeV

• Recover signal distribution• Also check mean is consistent within errors - yes, butneed more statistics to get to 1% precision• Still needs more work to reduce signal contaminationin control region (3%->1%)• However this idea looks promising - if it works can be usedpotentially for higher energy tracks in QCD jets

EM Had

±

Outer

Outer

Page 16: Jet Calibration in ATLAS Mark Hodgkinson ATLAS UK Meeting, IPPP January 2008.

In Situ Calibration Methods

• Photon is well measured (EM scale) - - use balance of + Jet to get to jet energy scale

Hadronic W Decays Template Method

• Generate template histograms of mjj using differentsigma and mean for jet resolution • Find which one fits best to data• Read of Jet Energy Scale from template• Stable wrt event selection, combinatoric background shiftsscale 1%

J Schwindling (Saclay)


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