the cms commissioning for physics and first results · the cms commissioning for physics and first...
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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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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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“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%
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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