Jet Calibration at CDF Sandro De Cecco Sandro De Cecco 18 mars 2008 - Paris Sandro De Cecco

Jet Production Measurements Hadronic showers EM showers Unfold measurements to hadron level  Correct for efficiency, smearing Correct theory (pQCD) for non-perturbative effects  Underlying Event, Fragmentation Q ~ QCD Q >> QCD Well defined jet algorithm required  At calorimeter, hadron and parton levels 18 mars 2008 - Paris Sandro De Cecco

CDF calorimeter Wall Had Plug Central Central and Wall (||<1.2): Scintillating tile with lead (iron) as absorber material in EM (HAD) section Coarse granularity: ~800 towers Non-compensating non-linear response to hadrons Rather thin: 4 interaction lengths Nearly no noise Resolutions: EM energies: /E=13.5% / √E  1.5% HAD energies: /E=50% / √E  3% Plug (1.2<||<3.6): Similar technology to central Resolution: EM energies: /E=16 % / √E  1% HAD energies: /E=80 % / √E  5% Thicker: 7 interaction lengths Plug Central 18 mars 2008 - Paris Sandro De Cecco

Cone Jet Algorithms and pQCD Iterative cone algorithms Staring from seeds, iteratively cluster particles in cones of radius RCONE and look for stable cones (pT-weighted centroid) Infrared and Collinear Safety Fixed order pQCD contains not fully cancelled infrared divergences Inclusive jet cross section affected at NNLO Tevatron Run II Cone Algorithm: Midpoint Uses midpoints between pairs of proto-jets as additional seeds  Infrared and collinear safety restored Merging/Splitting Emulated in NLO pQCD calculation by merging 2 partons only if they are within R’ = RCONE  RSEP of each other Arbitrary parameter RSEP: prescription RSEP = 1.3 (based on parton level approximate arguments) below threshold (no jets) above threshold (1 jet) 18 mars 2008 - Paris Sandro De Cecco

kT Algorithm Inclusive kT algorithm Merging pairs of nearby particles in order of increasing relative pT D parameter controls merging termination and characterizes size of resulting jets pT classification inspired by pQCD gluon emissions Infrared and Collinear safe to all orders in pQCD No merging/splitting No RSEP issue comparing to pQCD jet 18 mars 2008 - Paris Sandro De Cecco

CDF Jet calibration overview Calibrate EM and HAD calorimeters in situ Reconstruct jets (JetClu cone algorithm):PTraw Correct jets in plug calorimeter w.r.t. central “relative corrections”: frel use di-jet data (versus ) Correct for Multiple pp Interactions : UEM Correct measured jets back to particle level jets: tune MC simulation: fabs Response of calorimeter to single particles Fragmentation: Pt spectra in data Correct for Underlying Event: UE Correct particle jet back to parton: OC and … Splash-out systematics Systematic error associated with each step 18 mars 2008 - Paris Sandro De Cecco

Two different approaches CDF and DØ use very different approaches Documented in CDF Run 2: hep-ex/0510047 (accepted by NIM) DØ Run 1: NIM A424: 352-394 (1999) DØ Run 2: http://www-d0.fnal.gov/phys_id/jes/public/plots_v7.1/index.html Main difference: CDF uses test beam and single particles measured in-situ to understand absolute response of single particles deduce jet response using simulation Cross check with calibration processes like photon-jet data DØ uses photon-jet data to measure absolute response Extra correction for “showering” necessary Other differences: CDF corrects separately for underlying event, multiple interactions, out-of-cone energy DØ includes all these effects into one correction factor 18 mars 2008 - Paris Sandro De Cecco

Overview: CDF and DØ CDF calibrates PT DØ calibrates Energy PTcorr: calibrated jet PT PTraw: raw jet PT F: eta-dependent correction R: absolute response MI: multiple interactions DØ calibrates Energy Ecorr: calibrated jet E Eraw: raw jet E F: eta-dependent correction R: absolute response O: offset energy includes MI, noise, UE S: showering corrections Systematic error associated with each step additional corrections to get to parton energy 18 mars 2008 - Paris Sandro De Cecco

In Situ Calorimeter Calibration I Minimum Ionising Particle (MIP): J/Ψ and W muons peak in HAD calo: ≈2 GeV Peak in EM calo: ≈300 MeV Check time stability and run1 versus run2 Applicable where muon coverage: <1.4 E/p of electrons: p calibrated on J/Ψ mass Time dependence of E/p checked 18 mars 2008 - Paris Sandro De Cecco

In Situ Calorimeter Calibration II Z→ ee peak: Set absolute EM scale in central and plug Compare data and MC: mean and resolution Applied in Central and Plug MinBias events: Occupancy above some threshold: e.g. 500 MeV Time stability Phi dependent calibrations: resolution 18 mars 2008 - Paris Sandro De Cecco

Relative Corrections - dijets 18 mars 2008 - Paris Sandro De Cecco

Relative Corrections Mapping out cracks and response of calorimeter Central at ~1 by definition D0: Response similar in central and forward Two rather large cracks CDF: Response of forward better than of central Three smaller cracks Difficulties: depends on ET Can be (most often is initially) different for data and MC 18 mars 2008 - Paris Sandro De Cecco

Detector to Particle Level Do not use data since no high statistics calibration processes at high Et>100 GeV Extracted from MC  MC needs to Simulate accurately the response of detector to single particles (pions, protons, neutrons, etc.): CALORIMETER SIMULATION Describe particle spectra and densities at all jet Et: FRAGMENTATION Measure fragmentation and single particle response in data and tune MC to describe it Use MC to determine correction function to go from observed to “true”/most likely Et: Etrue=f ( Eobs, , conesize) 18 mars 2008 - Paris Sandro De Cecco

Single Particle Response Low Pt (1-10 GeV) in situ calibration: Select “isolated” tracks and measure energy in tower behind them Dedicated trigger Perform average BG subtraction Tune GFlash to describe E/p distributions at eack p (use π/p/K average mixture in MC) High Pt (>8 GeV) uses test beam: Could try τ-leptons Non-linearity: response drops by 30% between 10 and 1 GeV 18 mars 2008 - Paris Sandro De Cecco

Fragmentation Due to non-linearity of CDF calorimeter big difference between e.g. 1 10 GeV pion 10 1 GeV pions Measure number of and Pt spectra of particles in jets at different Et values as function of track Pt: Requires understanding track efficiency inside jets Ideally done for each particle type (π, p, K) E.g. difference in fragmentation between Herwig and Pythia may result in different response 18 mars 2008 - Paris Sandro De Cecco

Absolute Correction from MC Wanted: Most likely true Et value for given measured Et value BUT cannot be obtained universally for all analyses since it depends on Et spectrum: E.g. most likely value in falling spectrum dominated by smearing from lower Et bins Different for flat Et spectrum (e.g. top or new resonance) CDF: Provide standard “generic” jet corrections using flat Pt spectrum Individual analyses determine their “specific” residual corrections themselves from their MC 18 mars 2008 - Paris Sandro De Cecco

Flat vs. QCD Spectra For both spectra With a Flat spectrum. Avg For both spectra There is an average PT shift of hadron jets to calorimeter jets. With a Flat spectrum. After accounting for the average shift there are roughly as many low PT as high PT jets “smearing” into the calorimeter PT bin. With a QCD spectrum After accounting for the average shift, there are significantly more low PT jets than high PT jets “smearing” into the calorimeter PT bins. The QCD spectrum correction is therefore significantly lower. Hadron Jet PT Calorimeter Jet PT Avg Hadron Jet PT Calorimeter Jet PT 18 mars 2008 - Paris Sandro De Cecco

Absolute Corrections Use MC with “flat” Et distribution Separately for each cone size: 0.4, 0.7 and 1.0 Correction factor decreases with Et due to non-linearity of calorimeter, e.g. cone 0.4: 50 GeV: ≈25% 500 GeV: ≈15% Systematic errors due to Test beam precision γ-Jet and Z-jet balancing agreement between data and simulation after correction  18 mars 2008 - Paris Sandro De Cecco

Photon-Jet PT balance CDF pTjet/pT-1 Agreement within 3% but differences in distributions Data, Pythia and Herwig all a little different These are physics effects! 18 mars 2008 - Paris Sandro De Cecco

Z-jet PT balance CDF pTjet/pTZ-1 pTjet/pTZ-1 Better agreement of data and MC than in photon-jet data In progress of understanding this better together with Herwig and Pythia authors – different L scale 18 mars 2008 - Paris Sandro De Cecco

Multiple pp Interactions Extra pp interactions will increase the jet Et values of primary hard interaction subtract off average energy in cone per interaction: Number of interactions = Number of observed vertices Random cone in MinBias data: Et versus Nvtx E.g. ≈0.8 GeV per vertex for cone 0.7 18 mars 2008 - Paris Sandro De Cecco

Corrections from Particle Jet to Parton Underlying event (UE) and Out-of-cone (OOC) energy Only used if parton energy is wanted Requires MC modeling of UE and OOC Differences are taken as systematic uncertainty 18 mars 2008 - Paris Sandro De Cecco

Underlying Event Underlying event definition: “beam-beam remnants”: energy from interaction of spectator partons “Initial state radiation”: energy radiated off hard process before main interaction Not wanted when e.g. measuring the top quark mass Can be estimated using Monte Carlo Measurements led to tuning of MC generators: PYTHIA, Herwig+Jimmy 18 mars 2008 - Paris Sandro De Cecco

Measuring the Underlying Event Leading Jet Direction “Transverse” region very sensitive to the “underlying event”! Many studies exist about underlying event: Checkout talks by Rick Field/U. of Florida At LHC we will need to measure it: Expect it to be much harder than at Tevatron 18 mars 2008 - Paris Sandro De Cecco

Out of Cone Energy (OOC) Original parton energy that escapes the cone E.g. due to gluon radiation Jet shape in MC must describe data: measure energy flow in annuli around jet Differences between data and MC Lead to rather large systematic uncertainty Herwig Pythia 0.06 0.04 Data 0.02 (OOCData-OOCMC)/pT 0.0 0.02 0.04 Herwig Pythia 0.06 40 80 120 PT (GeV) 18 mars 2008 - Paris Sandro De Cecco

Energy Flow Inside Jets Jet shapes governed by multi-gluon emission from primary parton Test of parton shower models Sensitive to underlying event structure Sensitive to quark and gluon mixture in the final state Phys. Rev. D 71, 112002 (2005) (1-) 37 < pT < 380 GeV/c 18 mars 2008 - Paris Sandro De Cecco

Underlying Event & Hadronization correction jet Calorimeter level 1.2 Hadron level Parton level 18 mars 2008 - Paris Sandro De Cecco

Jet Energy Scale Uncertainties CDF and DØ achieve similar uncertainties after following very different paths before 18 mars 2008 - Paris Sandro De Cecco

Other calibration samples 18 mars 2008 - Paris Sandro De Cecco

In-situ Measurement of JES Additionally, use Wjj mass resonance (Mjj) to measure the jet energy scale (JES) uncertainty 2D fit of the invariant mass of the non-b-jets and the top mass: JES M(jj)- 80.4 GeV/c2 Mjj Measurement of JES scales directly with data statistics 18 mars 2008 - Paris Sandro De Cecco

Wjj Calibration in Top Events CDF (1 fb-1): JES = 0.99 ± 0.02 DØ (0.3 fb-1): JES = 0.99 ± 0.03 Fit for ratio of JES in data to JES in MC Constrain JES to 2% using 166 events At LHC will have 45,000 top events/month! 18 mars 2008 - Paris Sandro De Cecco (jet)

Z->bb Zbb decay mode: Suppresses QCD background more than signal Difficult to trigger CDF uses secondary vertex trigger D0 uses semi-leptonic decays collected by muon trigger Use this to measure difference between data and MC JES, e.g. DØ: Data: =81.0 +/- 2.2 =10.7 +/- 2.1 MC: =83.3 =13.0 18 mars 2008 - Paris Sandro De Cecco

Using jets in analysis 18 mars 2008 - Paris Sandro De Cecco

W/Z bosons + Jets (HF) production The study of W / Z / g + Jets production is very relevant: to QCD: High q2 ( ~Mboson) interactions, perturbative theory Less leading diagrams ( wrt pure Jets production) Test Monte Carlo generators (ALPGEN…) Probe for protons PDF (in particular W/Z + H.F. ) for many high pT analysis where W/Z+HF is a main background: Top quark cross section and mass Single Top cross section Search for low mass Higgs boson several SUSY searches 18 mars 2008 - Paris Sandro De Cecco

W+jet(s) Production ..+ PS Background top, Higgs, SUSY… Stringent test of pQCD predictions Test Ground for ME+PS techniques (Special matching  MLM, CKKW to avoid double counting on ME+PS interface) ..+ PS 18 mars 2008 - Paris Sandro De Cecco Affected by cutoff and soft radiation

Soft radiation in Z+jet(s) Implementation of proper modeling of UE still needed in W/Z+Jet(s) Monte Carlo….very important LHC will use "extra jets" veto in Higgs analyses to reduce QCD bckg. 18 mars 2008 - Paris Sandro De Cecco

Diphoton Production g g g g g g q q q g q g g LO (Pythia) off Phys. Rev. Lett. 95, 022003 (2005) Diphoton Production relevant for future H-> gg searches at the LHC (K-factors applied to LO pQCD MCs ) LO (Pythia) off g q q g g g q g q g g NLO (DIPHOX) g g 18 mars 2008 - Paris Sandro De Cecco

Electrons and Jets Hadronic Calorimeter Energy Electromagnetic Calorimeter Energy Jets can look like electrons, e.g.: photon conversions from 0’s: ~13% of photons convert (in CDF) early showering charged pions And there are lots of jets!!! 18 mars 2008 - Paris Sandro De Cecco

The Isolation Cut  candidates Non-isolated isolated Isolation cut: Draw cone of size 0.4 around object Sum up PT of objects inside cone Use calorimeter or tracks Typical cuts: <10% x ET <2-4 GeV Isolation is very powerful for isolated leptons E.g. from W’s, Z’s Rejects background from leptons inside jets due to: b-decays photon conversions pions/kaons that punch through or decay in flight pions that shower only in EM calorimeter This is a physics cut! Efficiency depends on physics process The more jet activity the less efficient Depends on luminosity Extra interactions due to pileup  candidates Non-isolated isolated 18 mars 2008 - Paris Sandro De Cecco

Jets faking Electrons Jets faking “loose” electrons Fake Rate (%) Jets can pass electron ID cuts, Mostly due to early showering charged pions Conversions:0ee+X Semileptonic b-decays Difficult to model in MC Hard fragmentation Detailed simulation of calorimeter and tracking volume Measured in inclusive jet data at various ET thresholds Prompt electron content negligible: Njet~10 billion at 50 GeV! Fake rate per jet: Loose cuts: 5/10000 Tight cuts: 1/10000 Typical uncertainties 50% Jets faking “loose” electrons Fake Rate (%) 18 mars 2008 - Paris Sandro De Cecco

Feynman Talk at Coral Gables (December 1976) 1st transparency Last transparency “Feynman-Field Jet Model” 18 mars 2008 - Paris Sandro De Cecco

Backup 18 mars 2008 - Paris Sandro De Cecco

Underlying Event Everything but the hard scattering process Initial state soft radiations Beam-beam remnants Multiple Parton Interactions (MPI) Studied in the transverse region Leading jet sample Back-to-back sample 18 mars 2008 - Paris Sandro De Cecco

New Underlying Event Studies MB ET(jet#2)/ET(jet#1) > 0.8 Back-to-Back Df12 > 150o Suppresses contribution from additional hard radiation Pythia Tune A describes the data Herwig underestimates UE activity Extended to 250 GeV jets 18 mars 2008 - Paris Sandro De Cecco

New Underlying Event Studies MAX (MIN) for the largest (smallest) charged particle density in transverse region MAX-MIN sensitive to remaining hard contribution MIN specially sensitive to the remnant-remnant contribution 18 mars 2008 - Paris Sandro De Cecco

Studies on Jet Fragmentation Jet shape dictated by multi-gluon emission form primary parton Test of parton shower models and their implementations Sensitive to quark/gluon final state mixture and run of strong coupling Sensitive to underlying event structure in the final state 18 mars 2008 - Paris Sandro De Cecco

Jet shapes PYTHIA Tune A describes the data PRD. 71, 112002 (2005) (enhanced ISR + MPI tuning) PYTHIA default too narrow MPI are important at low Pt HERWIG too narrow at low Pt We know how to model the UE at 2 TeV for QCD jet processes 18 mars 2008 - Paris Sandro De Cecco

Studies on Δf between jets PRL 94, 221801 (2005)  Studies on Δf between jets LO in Df NLO in Df LO limited at hard (Mercedes Star) and soft limits for third emission NLO closer to data…however soft gluon contributions are needed PYTHIA (enhanced ISR) & Herwig provide best description across the different regions… 18 mars 2008 - Paris Sandro De Cecco