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Pasquale Noli XXII Cycle

Determination of the pp  ZX  μ + μ − X inclusive cross section with a simultaneous fit of Z yield, muon reconstruction, Isolation cut and High Level Trigger efficiencies. Pasquale Noli XXII Cycle. Tutors : Chiar. mo Prof. C.Sciacca Dr L. Lista – Dr F. Fabozzi. Outline.

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Pasquale Noli XXII Cycle

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  1. Determination of the pp ZX  μ+μ−Xinclusive cross section with a simultaneous fit ofZ yield, muon reconstruction, Isolation cut and High Level Trigger efficiencies. Pasquale Noli XXII Cycle Tutors: Chiar.mo Prof. C.Sciacca Dr L. Lista – Dr F. Fabozzi

  2. Outline • LHC and CMS description • Eventselection • Fiducial and kinematicalcuts • Di-muonscategories • Fitstrategy • Analysisresults • Fitstability • Comparisonofresults at differentLuminosityscenarios • Toy Monte Carlo study • Systematicsofcross-sectionmeasurement • Conclusions

  3. The Large Hadron Collider • Energy: √s = 14 TeV • 7 times larger than TEVATRON • Search for new massive particles up to 5 TeV/c2 • L = 1034 cm-2 s-1 • Biggest cryogenic system in the word: • 1232 superconducting dipoles working at 1.9 K to provide a magnetic field B= 8.3 Tesla • Cost: ≈ 4 biliion€ (accelerator + experiments) • Human resources: > 5000 peoples invloved

  4. Event rates production @ √s =14 TeV and L= 1034 cm-2 s-1

  5. LHC Physics Goals • Precise Standard Modelmeasurements: • QCD jet cross section and αs • Top quark (factory !): mass, couplings and decayproperties • Searchof Standard ModelHiggsboson in the range 115 GeV/c2 < mH < 1 TeV/c2 • Searchforphysicsbeyond the Standard Model: • SUSY • Extradimentions • Technicolor • B-physics • Mainly at LHCb: CP-violation in the B-channel • Heavyions • Mainly at ALICE: phasetransitionfromhadronictoquark-gluon plasma

  6. The Compact Muon Solenoid The Compact Muon Solenoid is a high granularity detector built around and inside a superconducting solenoid that provides a strong magnetic field of 4 T. • Inner Tracker • Silicon Pixel and Microstrips • Electromagnetic Calorimeter ECAL • Scintillating lead tungstate crystals • Hadronic Calorimeter HCAL • Scintillator brass sandwich • Muon system • Drift tube (BARREL) • Cathode Strip Chambers (ENDCAP) • Resistive Plate Chambers (BARRL-ENDCAP) • Trigger system: • L1 (custom electronic) 40MHz  100 kHz • HLT (processors farm) 100kHz  100 Hz

  7. The Inner Tracker • Pixel Tracker: • Made by 100  150 μm cells • Resolution of 10 μm in the r-𝜙 plane and 20 μm in the r-z plane • Microstrip Tracker: • Divided in 4 different parts TIB,TOB, TID, and TEC • Resolution: 25 μm in the r-𝜙 plane and 230 μm in the r-z plane TIB • Resolution: 32-52 μm in the r-𝜙 plane and 530 μm in the r-z plane TID, TOB, and TEC

  8. Calorimetric system ECAL : HCAL : HB HE HO

  9. The Muon system • Muon Trigger • Muon identification • BX identification • Pt measuraments • Standalone resolution: 9% (up to 200 GeV/c) , 15-40 % (1 TeV/c) depending on η • with Tracker resolution improve: 5% at 1 TeV/c • Correct charge assignment 99% DT RPC CSC

  10. Z candidates: Recovs Monte Carlo • Good agreement w.r.t MC sample • Low longitudinal momentum • Low transverse momentum • Flat distribution in 𝜙 Generator cut

  11. Z candidates: no MC matched Combinatorial background ispeaked at low valuesofinvariant mass Itdecreasesrapidly(log scale) forinvariant mass increasing M μμ∈[60, 120] GeV/c2 S/B ≈ 0.1 % 86 % only 1 Z 0.4 % no Z 13.6% >1 Z

  12. Z events selection Two muon candidates (or 1 muon + 1 track) with: • || < 2, pt > 20 GeV/c • 60 < m < 120 GeV/c2 • Track Isolation : pt < 3 GeV/c • HLT single not-isolated muon :HLT_Mu15 5 statisticaly indipendent event categories allow to fit 5 parameters. • 1) Z->µ µ : two global muons, 2 HLT matches • 2)Z->µ µ : two global muons, 1 HLT match • 3)Z->µ s : global + stand-alone, global µ HLT matched • 4)Z->µ t : global + track, global µ HLT matched, • 5)Z->µ µ : two global muons, at least 1 HLT match Both muons isolated at least one muon not isolated • Z->µ s contributes to track efficiency estimate • Z->µ t contributes to muon system efficiency estimate • Z-> µ µ not iso contributes to isolation cut efficiency estimate

  13. Di-muon categories μμ, 2HLT μμ, 1HLT μt Signalpeak Negligiblebkg Signalpeak Negligiblebkg Signalpeak pol. background μs μμ, no-iso Five independent categories (golden, stand-alone, tracks, ...) Signalpeak Negligiblebkg Signalpeak pol. background ∫Ldt = 45 pb-1 CMS AN -2009/005

  14. Efficiencies from data μμ, 2HLT μμ, 1HLT μt μs μμ, no-iso • Data driven simultaneous estimate of • Z yield • eff. of tracking reconstruction • eff. of muon reconstruction • eff. trigger • eff. Isolation cut

  15. Fit model Differential event yields Background shapes fitted as exponential  polynomial Data driven signal shapes Signal yield expressions • fpeak(m) : Z➝μ+μ-= Z➝μ+μ-2HLT +Z➝μ+μ-1HLT • mass spectra • f speak(m): taken from Z➝μ+μ-removing the track component to one of the two muons to mimic a standalone muon

  16. Signal shapes fpeak(m) In good agreement f speak(m)

  17. Chi-squared definition • Five observables • Five unknown signalparameters • plus background shapes and yields Other estimators, for example Poissonian Likelihood Ratio, lead to very similar results

  18. Fit Results @ 10 TeV, 45 pb-1 μt μs μμ, no-iso CMS AN -2009/005

  19. Fit stability: 133 to 5 pb-1 Fit stable down to ~ 5 pb-1 Z yield (normalized) εiso εtrk CMS PAS -2009/001 εHLT εs.a.

  20. Toy Monte Carlo study • 1000 Toy experiments generated for 45 pb-1 • True parameter taken from our full Monte Carlo fit Z yield εs.a. Mean 0.12±0.03 σ =0.99 ±0.02 Mean 0.36±0.04 σ = 1.14±0.03 Small biasfor Zs (low stat.) εtrk Mean 0.08±0.03 σ = 1.01±0.03 Mean -0.04±0.04 σ = 1.03±0.03 Mean: 0.0680.034 σ: 1.021  0.028 εiso εHLT CMS AN -2009/005

  21. Toy Monte Carlo @ 133 pb-1 Mean 0.26 ± 0.24 σ = 1.03 ± 0.02 Mean 0.0955± 0.023 σ = 0.99± 0.02 Z yield No biaswhen Zs has larger stat. εs.a. εtrk Mean 0.085 ±0.024 σ = 1.04 ± 0.02 Mean 0.007±0.024 σ = 1.03±0.02 Bias decreasing w.r.t @ 45pb-1 Mean: 0.010.02 σ: 0.98  0.02 εHLT εiso CMS AN -2009/005

  22. Systematics • Main systematic uncertainties addressed • Background estimation • Efficiency correlation • Acceptance: • Choise of generator type • PDF uncertainties • Muon scale and resolution • Luminosity

  23. Conclusions… • Analysisstrategyisabletodeterminefrom data: • Z yield • eff. of tracking reconstruction • eff. of muon system reconstruction • eff. Trigger • eff. Isolation cut • Allows to measure cross section with the very early data (few pb-1) • Needs a smaller amount of statistics w.r.t. the Tag & Probe • Complementary to Tag &Probe with high statistics • Accurate and fast method • Run a single analysis step + a single fast fit • Suitable for prompt applications: • DQM • ‘Z counting’ for luminosity monitoring • Analysis is approved by CMS and an “early paper ” is done • Waiting for the real data

  24. LHC started on the 23thOctober 2009 Global machine checkout 2009 450 GeV Collisions CMS Control room Trial rump up Rump up commissioning to 1.2 TeV Xmas Rump up commissioning to 3.5 TeV 2010 Collisions at √s = 7 TeV Pilot physics First data are taken and analyzed

  25. CMS first data CMS Event display: J/Ψcandidate in ppcollision at √s =2.36 TeV J/Ψcandidate withinvariant mass 3.032 GeV/c2 Twomuons in forward part of CMS The analysischainisabletoreconstruct the particle in the event !!!

  26. Grazie dell’attenzione

  27. Backup

  28. Transverseslicethrough CMS

  29. Signal-Background Number of candidates in each category after the selection with an invariant mass in the range [60-120] GeV=c2. Here Z = Z1HLT+ Z2HLT . The separate contributions from signal and background processes are shown. An integrated luminosity of 45 pb-1 is assumed.

  30. Isolation variable ∆Rveto = 0.015

  31. FitResults @ 10 TeV, 10 pb-1

  32. Misure di Efficienza dai dati • Tag & probe • Campione di eventi Z e e (μμ ) • TAG : elettrone(muone) selezionato con • criteri molto stringenti • PROBE : elettrone(muone) selezionato • con dei criteri più larghi dipendenti dalle selezioni richieste nelle varie analisi • Massa invariante Tag-Probein una finestra di massa intorno alla massa della Z • Mappa delle efficienze in funzione di pt, η, Φ TAG PROBE # probe passanti la selzione ε = # tutti i probe corrisp. a un tag • Problemi • Alta statistica necessaria per evitare un binning rozzo • Contaminazione residua dei fondi

  33. T&P – Fit Comparison • WereweighZmumuinvariant mass • distributionsusing : • Fitrecontructionefficiencyvalues(black) • T&Precontructionefficiencyvalues(red) YieldwithT&P Nzµµ =8962 ± 97 Consistentwithfitresult Nzµµ =8827 ± 98 The twodistributions are in good agreement toeachother

  34. Accettanza geometrica

  35. Sistematiche Accettanza geometrica PDF and Generator Pt Scale

  36. Correlations (I) N0 = total numberofproducedevents p1 p2 muons 3-momenta f0probability density function (1) (2) (3) (4)

  37. Correlations (II) (5) (6) (7)

  38. Standalone-HLT Efficiency Correlation Track-IsolationEfficiencyCorrelation

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