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The CMS commissioning for physicsand first results D. Contardo (IPN Lyon)

On behalf of the CMS collaboration

Outline

Tracking and b-tagging Jet and Missing ET Electrons and Photons Muons Particle Flow Cosmic muons Charged Hadrons Underlying Events Bose Einstein Correlation J/ψ measurement W, Z measurement

IPRD10, Siena 07 June 2010

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2010 data taking conditions

CMS operation (see A. Ryd) > 98% of channels in operation > 90% data taking efficiency (overall data taking) > 99% computing efficiency Integrated luminosity ~ 20 nb-1

Trigger conditions Minium Bias trigger for low luminosity based on scintillating counters and Hadron Forward calorimeter gated by beam pick-up counters, efficiency ~ 90% Full physics trigger menu deployed with squeezed beams, rates compatible with MC expectations, commissioning on going at 2x1029cm-2s-1, HLT rate ~ 200-400 Hz

Analyzed data Data qualification, Noise and Background cleaning and filtering are implemented → continuous improvements Not yet all statistics analyzed → frequent reprocessing synchronized with improved detector calibrations and CMSSW software

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Track Reconstruction

See : J. Bernardini

Ξ-→Λπ-

Λ→ pπ-

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Reconstructed track parameters

η, Φ, dxy, dz, #hits, χ2… distributions are well reproduced by Monte Carlo track multiplicity is slightly underestimated for low Pt tracks

→ Tuning of MC is ongoing

Track selectiondz <10sσ(pt)/pt < 5%

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Primary Vertex study from track splitting method → Asymptotic resolution not reached at 900 GeV (low track multiplicity and Pt)

Primary Vertex

Discrimination of two vertices within few mm without fakes → tuning on going

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Reconstruction of Resonances

D0

Good Tracker calibration and track reconstruction performance dE/dx identification of π, K, p, d at low Pt (see L. Quertenmont) → Φ… Efficient reconstruction of detached vertices → K0s, Lambdas…

Ξ-

Mass of resonances within 0.1% of PDG → Study of mass w.r.t. (η,Pt) for momentum scale corrections Width of resonances well reproduced by MC : Material Budget description at ~ % level → MB studies : photon conversions, nuclear interactions, multiple scattering, energy loss Track reconstruction efficiency → Ratios of rates D0→Kπ / D0→Kπππ (+ other methods) Yields of strange resonances underestimated in MC

PDG Mass: 1321.71 ± 0.07

PDG Mass:1864.84 ± 0.17

MC Mass :1.863 + 0.002 GeVMC resolution :0.014 + 0.002 GeV

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b-tagging

Double b-jets candidate

L=6.2 mmL/S=43M=2.9 GeVPt=25.7 GeV/c

L=8.6 mmL/S=55M=3.1 GeVPt=17.2 GeV/c

Pt=43.7 GeV/c

Pt=40.3 GeV/c

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b-tagging : IP significancePFlow Jets anti-kT, Pt > 40 GeV, ⎮η⎮< 1.5Tracks in Jets Pt > 1 GeV

Track counting : IP significance of 2nd - 3rd track Jet probability : Combined info of all tracks

Good impact parameter resolution and tracker alignment performance Good modeling of Alignment Parameter Errors (see E. Chivite)

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b-tagging : Secondary Vertices

Other variables :Vertex Mass, Fraction of Charged Particles, flight distance, number of SV per Jet

Kalman vertex finderJet Pt > 10 GeV, ⎮η⎮< 2.4

Flight Significance Likelihood ratio combination of variables

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b-tagging : soft muons

Relative momentum of lepton w.r.t. Jet axis Soft lepton IP significance

Studies of mis-tagging and efficiency on going (all b-tagging methods) → currently limited by statistics and performance dominated by low Pt

Jet Pt > 10 GeV, ⎮η⎮< 2.4

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Electrons and Photons

Energy, rapidity, and azimuth distributionsof the channel with highest ET in ECAL forminimum bias events→ Good modeling of ECAL response in MC

(see T. Orimoto)

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π0 and η Resonances

π0 → γγPT(γ) > 0.4 GeV, PT(pair) > 1 GeV

MC based correction applied according to cluster η and energy

0.43 nb-1 1.46M π0

0.43 nb-1 25.5k η

η → γγPT(γ) > 0.5 GeV, PT(pair) > 2.5 GeV

Width and S/B reproduced by MC Masses within 2% of PDG

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Electron reconstructionGaussian Sum Filter for electron tracks reconstruction to account for Bremsstrahlung losses ECAL driven : Et cut ~ 4 GeV + fraction of HCAL energy + track matching Tracker driven : looser cuts + matching + recovery of brems. + multivariate estimator → lower Pt, improvement for e in jets

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CMS Experiment at LHC, CERNRun 133450 Event 16358963Lumi section: 285Sat Apr 17 2010, 12:25:05 CEST

Dijet Mass : 764 GeV

Jet and Missing ET

Jet 2 pT : 244 GeV

Jet 1 pT : 253 GeV

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Dijet distributions

Jets reconstructed with the anti-kT R=0.5 Jet energy correction in Pt and η Dijet selection : Jet Pt > 25 GeV, ΔΦ > 2.1, |η| < 3 3 Jet energy reconstruction methods → Loose ID cuts on number of components and neutral/charged energy fraction

Calorimeter jets Calorimeter + Track jets Particle Flow jets

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Missing Transverse EnergyInclusive Jet selection

Calo jets JPT jets PF jets

Monte-Carlo reproduce data on 5 orders of magnitudes Resolution as a function of ΣET also in good agreement with MC High MET tails due to noise and background → on going progress in cleaning and filtering

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Muons

J/ψ → µµ candidate

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“Global Muons” combined fit of Muon and matched Tracker tracks“Tracker Muons” tracker tracks matched to one Muon station segment

Muons

“Global Muons”17500 tracks

“Tracker Muons”89500 tracks

(lower Pt cutoff)

Distributions dominated by low Pt light hadron decay muons (red),good agreement with MC prediction including heavy flavor decays (blue),

Punch-through (black) and fakes (green)

24%73%3%1%

9%84%4.5%3%

19Particle Flow

Particle Flow

Particles in jets

Photon

Neutral hadron

Charged hadron

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Particle Flow track and calorimeter cluster link

Track Pt > 1 GeV/c and N hits ≥ 15 Cell size link 0.02 in ECAL 0.1 in HCAL

Calorimeter response as expected in MC → response within 2% and 5% for ECAL and HCAL

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Particle Flow Jet composition

Jet energy composition

65% charged hadrons 20% photons 10% neutral hadrons

Fraction of component energy in data and MC in good agreement → Overall uncertainty in energy ~ 1%

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Particle Flow Electron Identification

MV estimator cut improves purity and distribution centered around 1

Gaussian Sum Filter tracks matched to ECAL clusters plus Multivariate estimator based on : Track-ECAL matching (Δη, Eseed/Pout, Etot/Pin, ΣEγ/Pin-Pout) ECAL shower width and HCAL-ECAL energy fraction Track parameters : Pin-Pout/Pin and track quality parameters (chi2, #hits…)

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Particle Flow Isolation Isolation defined by ΣPT in a defined cone around particle (Pt > 500MeV/c below) Study from random cone method on charged hadrons from underlying events → lepton and photon isolation study on going

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Cosmic Muon Charge Asymmetry High energy cosmic muon measured during 2008 and 2009

R = Nµ+/Nµ- → High precision measurement

→ Good understanding of alignment and momentum scale up to TeV/c (Global Muon : Muon Stations + Tracker)

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Three methods : Tracks, Pixel tracklets and clusters Pt measurement down to 100MeV/c Results corrected to non single diffractive cross section Diffraction controlled from forward activity measurement

Charged Hadrons measurement

→ Rise of the particle density at 7 TeV steeper than in model predictions

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Underlying events

Minimum Bias event selection with leading track Jet Pt > 3 GeV Particle density and Pt scalar sum in transverse region Pt > 0.5 and ⎮η⎮< 2.4

Study at 7 TeV on going→ Generator tuning

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Bose Einstein Correlation Enhancement of same sign boson emission versus reference sample (same sign… 7 ref samples combined) at small relative momentum →(dN/dQ)/ (dN/dQ)ref / (dN/dQ) MC/ (dN/dQ)MC

ref

→ Size of correlated particle emission increase with particle density

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J/ψ measurement

On going studies Mass w.r.t. η and Pt → track momentum scale Prob and Tag rates → tracking efficiency

Signal events: 1230 ± 47Sigma: (42.7 ± 1.9) MeVM0: 3.092 ± 0.001 GeVS/B = 5.4 (M0 ± 2.5σ)χ2/ndof = 1.1

datatotalfitbackgroundfit

µ+µ−invariant mass [GeV/c2]

Lint=15nb‐1

J/ψ → µµ Mass within 0.2% of PDG Resolution of 1.5% S/N ~ 5.4 (2.5 σ)

J/ψ → ee Mass within 2% of PDG Resolution of 4% S/N ~ 2.5 (2.5 σ)

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Event selection : Muon id cuts (global and tracker, IP, Nhits, χ2 …), Pt > 25 GeV, |η|<2.1 Isolation ΣPT (tracks) + Σ (calo) < 0.15*pµ

T in a R < 0.3 cone Muon-MET acoplanarity < 2

Monte Carlo : Signal : MC normalized to NLO cross section and 16nb‐1integrated luminosity Background : QCD, Z → µµ, W → τν, Z → ττ, ttbar

W →µν measurement

70 candidates observed, 57 with MT > 50 GeV

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W →eν measurement Monte Carlo :

Signal : MC normalized to NLO cross section and 12nb‐1integrated luminosity Background : QCD, γ + Jet, W → τν, Z → ττ, Z → ee, ttbar

Two event selections :Electron ET >20 GeV, id and iso 80 %,no MET cut

Electron ET >18 GeV, CiC Electron id and iso, MET and ΣET cut

37 candidates with MT > 50 GeV 40 with MT > 50 GeV - 2 BG expected

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Z → µµ measurementEvent selection :

Muon id selection (global and tracker, IP, Nhits, χ2 …), Pt > 20 GeV, |η|<2.1 Loose Isolation ΣPT (tracks) + ΣET (calo) in a R < 0.3 cone

Monte Carlo : Signal : MC normalized to NLO cross section and 16nb‐1integrated luminosity Background : QCD, W → µν, ttbar

5 Z →µµ candidates

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Z → ee measurementEvent selection :

Both electrons with an EM Cluster with Et > 10 GeVLoose electron iD and isolation criteria

Monte Carlo : MC normalized to NLO cross section and 17nb‐1integrated luminosity Background : QCD, W +Jet, Z → ττ, γ + Jet, ttbar

5 Z →ee candidates

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The CMS detector commissioning and calibration are well advanced with performance in good agreement with expectations

The physics object reconstruction software are commissioned for physics analyses.

The CMS detector is properly modeled in the Monte Carlo Re-tuning of the generation is on going (Minimum Bias - QCD) good agreement is observed for first W and Z candidates

CMS is ready for higher luminosity operation Studies of efficiencies and systematic errors are on going Early physics measurements will be presented at ICHEP

Summary