1. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 1 The Discovery Potential of the Higgs Boson at CMS in the Four Lepton Final State David Futyan UC Riverside

2. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 2 Overview Introduction: LHC and CMS Motivation for Higgs boson searches Decay channels observable at the LHC Signal and background processes: Cross-sections and branching ratios Event generation and simulation Online selection Offline reconstruction of electrons and muons Offline event selection Evaluation of background from data Significance with background systematics Potential for measurement of Higgs boson properties: Mass, width, cross-section Experimental systematic uncertainties

3. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 3 The LHC (Large Hadron Collider) CERN CMS Switzerland France ALTAS LHCb ALICE Geneva Proton-proton collider: √s = 14 TeV Luminosity = 10 34 cm -2 s -1 17 miles in circumference Due to begin operation summer 2007

4. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 4 The CMS Detector (Compact Muon Solenoid) Muon Chambers 4 Tesla Superconducting Solenoid Silicon Tracker Silicon Pixel Detector HCAL Crystal ECAL Magnet Return Yoke General purpose detector Over 2000 people from 160 institutes 12500 tonnes General purpose detector Over 2000 people from 160 institutes 12500 tonnes

5. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 5 CMS Detector Slice

6. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 6 CMS Under Construction

7. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 7 The Higgs Boson A key objective of the LHC is to elucidate the origin of mass. Higgs mechanism: Provides an explanation for electroweak symmetry breaking in the Standard Model: Gives rise to the massive Z and W vector bosons and the massless photon. =>Lies at the core of the Standard Model - without the Higgs mechanism the SM is neither consistent nor complete. Provides mechanism through which gauge bosons and fermions acquire mass. Predicts the existence of one physical scalar, neutral Higgs boson.

8. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 8 Higgs Boson Mass Constraints Higgs boson mass not predicted by the theory - free parameter of the standard Model: Must be determined experimentally. Current limits: Combined lower limit from direct searches at LEP: m H > 114.4 GeV/c 2 (95% CL). Higgs boson contributes to radiative corrections to electroweak observables. Consistency fits to electroweak precision measurements from LEP, SLC, Tevatron yield an indirect upper limit: m H < 207 GeV/c 2 (95% CL).

9. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 9 The Higgs Boson Production at the LHC Dominant production mechanisms: Gluon-gluon fusion contributes around 80% of the total Decay channels:

10. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 10 Decay channels of SM Higgs boson which yield highest sensitivity for discovery at the LHC: H  W + W -  2 l 2 H  ZZ ( * )  4 l H   LHC Search Channels for the Higgs Boson l = electron or muon LEP Limit = 114.4 GeV/c 2 EXCLUDED

11. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 11 The H  ZZ  4l Channel Most sensitive channel for the discovery of the Higgs boson at the LHC for a wide range of masses. Exceptionally clean signature of 4 isolated high p T leptons, with relatively small backgrounds. For m H >2m Z : “Golden channel”, with 2 real Z bosons Mass of Higgs boson can be directly reconstructed from the invariant mass of the 4 leptons Direct measurement of mass Direct measurement of width for large m H (>200 GeV)

12. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 12 General Strategy Detailed analyses have been developed largely independently for each of the three final states: 4e: LLR (France), Split (Croatia), Rome/INFN 4  Florida, FNAL, Cambridge, 2e2  : UC Riverside, Bari/INFN (Italy) Common to all channels (allows coherent combination of results): Event generation, detector simulation. Signal and background production and decay processes considered and their NLO cross-sections and branching ratios. Straight forward counting experiment approach - Cut based analyses: Look for local event excess over expected background. Details of event selections developed differently in each of the 3 channels. Analyses are designed as if real data were being analyzed: Full detailed simulation of CMS detector geometry and response. Simulation of LHC conditions in first years of running at L = 2×10 33 cm -2 s -1. Full treatment of systematic errors included in significance evaluation. Techniques developed to measure the size of the residual background from LHC data.

13. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 13 Production Cross-Section and Branching Ratio BR(H  ZZ ( * )  4l) is the branching ratio to a final state containing only e and  including  decay products. Sum of gg fusion, WW fusion, ZZ fusion BR(H  ZZ(*)  4l), including BR(  e  )

14. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 14 Enhancement for 4e and 4  Final States For 4e and 4  final states, enhancement of signal cross-section due to constructive final state interference between like-sign electrons or muons originating from different Z ( * ) bosons: Calculated using CompHEP

15. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 15 Signal Monte Carlo Event Generation Signal samples generated with PYTHIA for 18 mass points between 115 and 600 GeV. Higgs production mechanisms simulated: gg fusion, WW fusion, ZZ fusion. Z bosons forced to decay to e,  with  forced to decay to e  10000 events generated per mass point, for each final state (4e, 4 , 2e2  ) Events re-weighted to correspond to: where

16. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 16 Background Processes Reducible backgrounds: qq/gg  tt  W + W - bb  4l + X (PYTHIA) qq/gg  (Z ( * ) /  *) bb  4l + X (CompHEP interfaced with PYTHIA) Irreducible non-resonant continuum background: qq  Z ( * ) /  *)(Z ( * ) /  *)  4l (PYTHIA) Process  LO (pb) NLO K-factor  NLO (pb) tt  W + W - bb --840 e + e - bb115 2.4  0.3 276     bb 116 2.4  0.3 279  Z ( * ) /  *)(Z ( * ) /  *) 18.7 K NLO (m 4l ) +0.2 28.9 (Z ( * ) /  *) bb {

17. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 17 t-channel dominates: 90% m 4l 2m Z s-channel simulated for 4  final state only MCFM generator used to calculate an K-factor to account for all NLO processes: Function of 4 lepton invariant mass:  Z ( * ) /  *)(Z ( * ) /  *) Background Z(*)/*Z(*)/* Z(*)/*Z(*)/* l+l+ l-l- l+l+ l-l- q q Z(*)/*Z(*)/* Z(*)/*Z(*)/* q q l-l- l-l- l+l+ l+l+ q = u,d,s,c or b LO cross-section 18.07pb (from MCFM generator):

18. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 18 Significant NNLO box diagram process not included in the simulation: TOPREX generator used to obtain ratio  (gg  ZZ  4l)/  (qq  ZZ  4l): ~20% Total NLO cross-section =  LO (K(m 4l ) + 0.2) = 29pb (for average K(m 4l )=1.35) All events re-weighted at analysis level using this m 4l dependent K-factor.  Z ( * ) /  *)(Z ( * ) /  *) Background Z(*)/*Z(*)/* Z(*)/*Z(*)/* g g l+l+ l-l- l+l+ l-l- q

19. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 19 Other Potential Backgrounds Zcc can also give 4 leptons in the final state: Investigated with full detector simulation - found to be negligible Other potential sources of background investigated at generator level: Wbb Wcc Single top bbbb bbcc cccc All found to be negligible } All leptons non-isolated } One or more fake leptons

20. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 20 Detector Simulation Generated Monte Carlo events for all generated samples are passed through a highly detailed simulation of the CMS detector, including: Precise simulation of the complete detector geometry: all material in the detector including cables, services etc. Detailed simulation of the 4T magnetic field. Full simulation of detector response for all detector components: information used as input to the analysis fully simulates real LHC data. Generated events are mixed with pile-up events to simulate the LHC conditions at “low luminosity” (2×10 33 cm -2 s -1 ) Several inelastic pp collisions per bunch crossing Corresponds to conditions during the initial phase of data taking.

21. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 21 Cross-Section Times Branching Ratio Generator level kinematic preselection includes the final state lepton flavor requirement (4e, 2  or 2e2  ), plus generator level cuts: Electrons: p T >5GeV, |  |<2.5 Muons: p T >3GeV, |  |<2.4 For 2e2  case: ttZbbZZ  fb  840x10 3 555x10 3 28.9x10 3 .BR.  fb  744 39037.0

22. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 22 4-lepton Invariant Mass After Generator Pre-selection Same on linear scale s-channel ZZ production m H =140 GeV signal

23. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 23 Online Selection LHC bunch crossing rate is 40MHz. Multiple events per bunch crossing CMS Trigger consists of a Level-1 trigger followed by a High Level Trigger. HLT is a software trigger involving full reconstruction of physics objects. Triggers chosen for H  ZZ  4l channels: Single triggers were also considered for the 2e2  channel but were found not to benefit the final significance. ChannelTrigger  single electron || double electron  Single muon || double muon   double electron || double muon

24. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 24 HLT Selection Efficiencies tt: 0.399 ± 0.001 Zbb: 0.661 ± 0.001 ZZ: 0.896 ± 0.004 tt: 0.399 ± 0.001 Zbb: 0.661 ± 0.001 ZZ: 0.896 ± 0.004 For 4  channel, HLT efficiency is close to 100% for all samples 4e 2e2 

25. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 25 Muon Reconstruction and Selection Muons are reconstructed with high efficiency with CMS: Require  + and  - reconstructed with p T >7 in the barrel and p T >13 in the endcaps. Require M(μ + μ - )>12GeV for all permutations (excludes low mass resonances). These cuts have little effect on signal efficiency.

26. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 26 Electron Reconstruction Lowest p T electron in H  ZZ  4e events around 10GeV: Electrons radiate on average half their energy before reaching the ECAL due to: Strong magnetic field (4 Tesla) 1 X 0 of material in the inner tracker Energy is radiated as photons which may in turn convert to e+e- before reaching the ECAL - significant spread of energy in .

27. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 27 Electron Reconstruction Sophisticated algorithms developed, motivated by the H  ZZ  4e analysis, in order to achieve good reconstruction efficiency for low p T electrons: Use of Gaussian Sum Filter tracking - electron track is reconstructed right out to ECAL surface. Measure bremsstrahlung energy loss: Categorization of electrons according to amount of radiated energy, ECAL cluster shape, cluster-track matching. Combine ECAL energy and tracker momentum measurements based on measurement uncertainties:

28. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 28 Electron Selection Electron reconstruction has a significant background from fakes (e.g.  + /  0 overlap from underlying event). Selection important to exclude potential backgrounds which can fake one or more electrons. 4e analysis: Cut based selection: E calo /p Track < 3. Track cluster matching: |  | <0.02 and |  |<0.1 E HCAL /E ECAL <0.2 p T > 5 GeV Loose isolation:  pT/pT < 0.5 (cone R=0.2) 2e2  analysis: Likelihood developed based on similar variables. Require likelihood>0.2. Select electron and positron with highest likelihoods.

29. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 29 Electron Reconstruction Efficiency (4e channel)

30. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 30 For the signal, and for the irreducible ZZ background, all 4 leptons are isolated and originate from the primary vertex. For the reducible tt and Zbb backgrounds, 2 of the leptons are associated with b-jets → non-isolated and with displaced vertices. For all three channels, offline selection consists of two set do cuts: Vertex/Impact parameter and Isolation cuts - reduce Zbb and tt only. Kinematic cuts :lepton p T and lepton invariant mass cuts - reduce all backgrounds. The offline selection for the 2e2  channel is described on the following slides. Offline Event Selection

31. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 31 Vertex and Impact Parameter Cuts (2e2  ) 3 variables chosen: High background rejection for 95% signal efficiency. Largely uncorrelated: (1) Transverse distance from  +  - vertex to beam line < 0.011 cm (2) 3D Distance between  +  - and e + e - vertices < 0.06 cm (3) Transverse impact parameter significance of lepton with highest IP significance < 7 Combined Efficiency (%) Signal89-91 tt14.5 ± 0.2 Zbb13.0 ± 0.1

32. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 32 Tracker Isolation (2e2  ) Cut on  p T of all reconstructed tracks in the event which satisfy: p T >0.9 GeV At least 5 hits Within region defined as the sum of cones of size  R 0.015 around each lepton. Consistent with originating from the reconstructed primary vertex to within  z<0.2cm Cut

33. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 33 Kinematic Distributions for Reconstructed Leptons Shown for events passing HLT and with e + e -  +  - reconstructed

34. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 34 Kinematic Cuts (2e2  ) Lepton pT cuts: p T 1 > thr1 p T 2 > thr2 p T 3 > thr3 p T 4 > thr4  +  - and e + e - invariant mass cuts: m Z1 < thr5 m Z2 > thr6 Four lepton invariant mass cuts: thr7 < m H < thr8 leptons sorted in decreasing order of p T m Z1 = max(m  +  -,m e+e- ), m Z2 = min(m  +  -,m e+e- )

35. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 35 Kinematic cuts are optimized simultaneously together with the isolation  p T threshold. Cut optimization performed using MINUIT by maximizing significance, defined by the Log-Likelihood ratio: Cuts optimized independently for each Higgs mass. To exclude effects of limited MC statistics: For each cut obtained from the automatic optimization: Plot S cL vs cut value with all other cuts fixed. Assign final cut value by inspection, such that S cL is as close as possible to the maximum whilst retaining smooth variation of cut value as a function of m H. where Optimization of Selection Cuts (2e2  ) 

36. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 36 Optimised Kinematic Cuts (2e2  )

37. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 37 .BR.  After Each Cut x-axis categories: Preselection, L1, HLT, 4 leptons, Vertex, Isolation, Lepton p T, Z mass, Higgs mass 2e2 

38. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 38 4 Lepton Invariant Mass Before/After Offline Selection Before offline selection After offline selection m H =130 GeV m H =200 GeV 2e2 

39. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 39 Final Selected Events per fb -1 and N S /N B m H (GeV)120140160180200250300400500 N signal for 10fb -1 1.911.77.88.736.429.119.418.09.6 N background for 10fb -1 1.52.0 4.016.213.64.13.72.6 2e2 

40. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 40 Summary of Offline Selection for 4e Channel Longitudinal impact parameter significance for all electrons < 13 Transverse impact parameter significance of reconstructed Z ( * ) bosons: < 30 for highest m e+e- < 15 for lowest m e+e- Isolation, required separately for each electron, cone size  R<0.2: Tracker isolation: (  p T tracks )/p T e < 0.1 Hadronic isolation: (  E T HCAL )/p T e < 0.2 Electron quality requirements Further cuts on track-cluster matching, cluster shape, HCAL/ECAL Kinematic cuts on lepton p T, m Z1, m Z2, m 4e

41. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 41 Summary of Offline Selection for 4  Channel Find that only the following cuts are critical: Isolation: Tracker and calorimeter: threshold applied to the least isolated muon Single p T threshold for each mass applied to all but the lowest p T muon Lowest pT muon already required to have p T >7(13) in the barrel (endcaps) Four lepton invariant mass cuts Additional cuts (impact parameter,  +  - inv. mass) do not significantly improve results. Cut optimization procedure similar to 2e2  analysis, but uses a minimization program named GARCON recently developed by the H  ZZ  4  group. Calorimeter Isolation for least isolated muon

42. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 42 Evaluation of the  Z ( * ) /  *)(Z ( * ) /  *) Background Systematic error on the no. on background events in the signal region enters into the significance calculation. Direct simulation of  Z ( * ) /  *)(Z ( * ) /  *)  4l subject to the following uncertainties: Theoretical uncertainties: PDFs and QCD scale variations NLO and NNLO production cross-section uncertainties Relies entirely on existing SM constraints and theoretical knowledge Experimental uncertainties: LHC luminosity MC modeling of detector response, material budget etc Energy scales (ECAL calibration) and resolution electron and muon reconstruction and kinematic selection efficiencies Electron and muon islolation efficiencies Such uncertainties are difficult to evaluate from first principles. More robust approach is to evaluate the size of the background directly using the LHC data.

43. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 43 Evaluation of the  Z ( * ) /  *)(Z ( * ) /  *) Background from Data 2 Approaches: 1) Use single Z boson production: Single Z bosons will be produced with a high rate at the LHC. Production cross-section will rapidly be measured directly to a high precision Can use ratio of production cross-sections for  Z ( * ) /  *)(Z ( * ) /  *) and single Z production to evaluate the  Z ( * ) /  *)(Z ( * ) /  *) background.  Cancellation of luminosity uncertainties.  Reduction of PDF and QCD scale uncertainties for low m H.  Partial cancellation of experimental uncertainties. 2) Direct measurement through counting the number of events in the sidebands (i.e. excluding the signal peak) of the 4-lepton invariant mass distribution: Full cancellation of all uncertainties except PDF and QCD scale uncertainties (not fully cancelled because may affect the shape of the m(4l) distribution). Disadvantage: Limited by statistics of the background rate in the sidebands. Approach 2 is used here as the most robust solution.

44. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 44 Evaluation of  Z ( * ) /  *)(Z ( * ) /  *) Background from Sidebands Points represent a simulation of LHC data for the relevant integrated luminosities: Total no. of events generated randomly from a Poisson distribution with mean = total expected events from all processes (signal and background). For each event, 4 lepton invariant mass generated randomly according to the histogram formed from the sum of the MC distributions for signal and background. ∫L = 9.2 fb -1 ∫L = 5.8 fb -1 2e2 

45. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 45 Background Systematic Errors Theoretical uncertainty on the ratio  Statistical error on background measurement from data: High statistical error at high m H due to low statistics in sidebands due to hard lepton p T cuts and large signal width. 2e2 

46. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 46 Background Systematic Errors: Theory Systematic uncertainty from PDFs and QCD scale estimated using the MCFM event generator. 20 eigenvectors of the CTEQ6M PDFs varied by  1 . QCD normalization and factorization scales varied independently up and down by factor 2 from nominal values  R =  F = 2m Z.

47. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 47 Significance Calculation Counting experiment significance, ScP: Defined as no. of sigmas of a Gaussian distribution equivalent to Poisson probability of observing equal to or greater than N Obs events, given  B expected events: An extended form of the ScP estimator is used which takes into account the systematic uncertainty on  B.

48. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 48 Significance for 2e2  Channel m H (GeV)120140160180200250300400500 N signal at ∫ L for 5  28.010.713.419.621.221.713.114.617.8 N back at ∫ L for 5  21.41.83.59.19.410.12.83.05.3

49. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 49 Combined Significance for 30 fb -1 Without systematic Uncertainties: where

50. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 50 Combined Significance for 30 fb -1 Systematic uncertainties included:

51. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 51 Higgs Mass Measurement from Gaussian Fit Statistical error on measurement of m H : Measured Higgs mass from Gaussian fit for high statistics mH=140 GeVmH=200 GeV mH=500 GeV Shown as fraction of true mass 2e2 

52. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 52 Higgs Width Measurement from Gaussian Fit Direct measurement of width possible with  stat<30% for m H  200 GeV Shown as fraction of true width 2e2 

53. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 53 Higgs Cross Section Measurement Uncertainty 1% 2% 3% Shown as fraction of expected no. of signal events 2e2 

54. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 54 Summary Standard Model Higgs boson with mass in range 130≤m H ≤500 GeV observable in the channel H  ZZ ( * )  4l with > 5  significance with 10fb -1 of integrated luminosity, excluding a 15 GeV gap close to m H =170 GeV (40fb -1 ). If mass lies in the range 190≤m H ≤400 GeV, 5  significance can be attained with 4fb -1. Size of ZZ*/  * background determined from data in sidebands with systematic uncertainty included in ScP significance calculation.

55. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 55 Aknowledgements H  ZZ  4e: S. Baffioni, C. Charlot, F. Ferri, R. Salerno, Y. Sirois (LLR, France) N. Godinovic, I. Puljak (Split, Croatia) P. Meridiani (Rome and INFN, Italy) H  ZZ  4  : S. Abdullin (FNAL) D. Acosta, P. Bartalini, R. Cavanaugh, A. Drozdetskiy, A. Korytov, G. Mitselmakher, Y. Pakhotin, B. Scurlock (Florida) A. Sherstnev (Cambridge) H  ZZ  2e2  : D. Futyan, D.Fortin (UC Riverside) D. Giordano (Bari and INFN, Italy)

56. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 56 Backup Slides

57. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 57 Electron Experimental Systematic Uncertainties Material budget: Change in amount of material traversed by electron before reaching the ECAL affects: electron identification and selection efficiencies energy scale and resolution Material budget can be measured using single electron events, using the observed fraction of energy lost through bremsstrahlung, since energy radiated is proportional to material thickness traversed: where p in and p out are the measured momenta at the innermost and outermost point on the GSF electron track. where

58. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 58 Electron Experimental Systematic Uncertainties 2% uncertainty shown to have almost no effect on electron reconstruction efficiency: With electron statistics from single Z production corresponding to ~10fb -1, can measure tracker material thickness to a precision better than 2%:

59. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 59 Electron Experimental Systematic Uncertainties Electron reconstruction efficiency and energy scale can be controlled using tagged electrons from Z  ee events: Select Z  ee events for which at least one leg is a “golden” electron (no bremsstrahlung), plus kinematic constraint on Z boson mass for second leg. Use second leg to estimate uncertainties on reconstruction efficiencies and on the energy scale. Systematic uncertainty on electron reconstruction efficiency and energy scale taken to be <1%

60. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 60 Muon Experimental Systematic Uncertainties Measure muon reconstruction efficiency from data to better than 1% precision: Use sample of muon HLT triggers with p T >19 GeV. Count no. of Z  2  events in the resonance of the inv. mass distributions built from: HLT muon + reconstructed muons HLT muon + all tracks Ratio gives the efficiency. Can measure to better than 1%. Efficiency of isolation cut measured by evaluating energy flow in isolation cones around random directions in Z  2  events. Can measure to better than 2%. Uncertainty on p T resolution and p T scale evaluated using resonance peaks from Z  2  and J/  2  events to high precision.

61. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 61 Monte Carlo Event Generation Details In all samples, Z and W bosons forced to decay to e,  with  forced to decay to e  No forcing of b decays in Zbb and tt background events. In  Z ( * ) /  *)(Z ( * ) /  *) and  Z ( * ) /  *)bb backgrounds, require m  Z ( * ) /  *) > 5 GeV Non-perturbative PDFs in the proton taken from CTEQ6 distributions Global QCD analysis combining all existing relevant deep inelastic and jet cross-section measurement results. QED final state radiation (“internal bremsstrahlung”) simulated by interfacing the event generators with dedicated software package PHOTOS.

62. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 62 True Significance of Local Event Excess Search for new phenomena in a wide range of parameter space - in this case narrow resonance in very broad range of invariant masses: Problem of overestimating significance of a “local discovery” Need to reduce the significance according to the number of chances of getting it:

63. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 63 Reconstructed Invariant Masses of e + e - and  +  - Electron pair Muon pair m H = 130 GeV

64. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 64 CP Nature of Higgs: Shape of M Z* Distribution Shape of M Z * distribution depends on CP nature of Higgs Compare theoretical M Z * distributions with result of convolution of reconstructed M Z * distribution with efficiency of selection for M Z *. Similar approach possible using cos  distribution of the angle between the planes containing the lepton pairs - important for M H >2M Z

65. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 65 Choice of Trigger Natural choice from physics viewpoint is to trigger on Z: (i) Take OR of 2e and 2  triggers Another possible choice is: (ii) Take OR of 1e, 2e, 1  and 2  Consider fraction of events passing (ii) which fail (i). i.e. pass single triggers only: For background, corresponds to close to half of events  using 1e||2e||1  ||2  trigger results in almost twice as much background as 2e||2  trigger For signal, using 1e||2e||1  ||2  rather than 2e||2  increases final no. of events after all offline cuts by 160 and <5% for m H <160. But this gain is offset by the fact that the no. of ZZ background events after offline cuts increases by a similar fraction. Conclusion: use OR of double electron and double muon triggers Before offline cuts After offline cuts

66. Higgs to Four Leptons at CMS 18th May 2006 David Futyan UC Riverside 66 Recovery of QCD Internal Bremsstrahlung At least one IB photon present in 40-45% of H  ZZ ( * )  2e2  events At least one IB photon with p T >5 GeV present for 10-30% of events (increasing with m H ) 2/3 emitted by electrons, 1/3 by muons Distinguish from other photons from the underlying event using tendency to be collinear with parent lepton. Z e e  RR If >=1 reconstructed photons found within cone of size  R<0.3 around any of the 4 reconstructed leptons, photon with smallest  R is considered as an IB photon 4-momentum added to Z boson invariant mass prior to Z mass window cuts.