Constraints on the Higgs Width

Transcription

1 Constraints on the Higgs Width Andrew Whitbeck (Fermilab) On behalf of the CMS collaboratsion!! Americas Workshop on Linear Colliders May 14, 2014 Results shown are from: CMS-PAS-HIG

2 Higgs Properties Discovery of a Higgs boson in bosonic decay channel (confidence of fermionic decays growing) Couplings & spin/parity constraints are thus far consistent with SM Higgs expectations Direct searches for invisible decays Model dependent constraint on decay width: ΓBSM <.6 We can now constrain the width to high precision in a nearly model independent way new handle for new physics!2

3 Main Principle Zero-width approximation is inadequate for off-shell ZZ production Significant fraction of Higgs events produced off-shell (~7%) yeilds after experimental cuts Kauer & Passarino, JHEP 08 (2012) 116!3

4 Width Constraints Comparing on-peak & off-peak ZZ yields constrains total width (assuming couplings constant w/ m4l) Interference with gg->zz conitinuum effects yeilds and kinematics Caola, Melnikov (Phys Rev D 88 (2013) )!! Can exploit this with matrix element tools!4

5 MC simulation gluon-gluon fusion modelled with gg2vv and MCFM NNLO/LO k-factors derive for signal as a function of m4l same k-factors used for contin. ZZ events (demonstrated to be true for WW 1 ) 10% uncertainty additional systematic unc. Vector boson fusion modelled with PHANTOM Contribute 7-10% of the yeild VH and tth don t contribute to high mass region Passarino (arxiv: ) 1 Bonvini et. al. (Phys Rev D88 (2013) )!5

6 On-peak measurements Derived from 4l Run I legacy measurements arxiv: Resonance signal strength measured: μggh,tth = μvbf,vh = μ = Resonance mass: mh = /- 0.4 (stat) 0.2 (syst) GeV!6

7 Off-peak measurements Combining information from 4l and 2l2ν channels 4l: clean channel 2l2ν: large branching fraction (mt/et miss ) Gen level w/ analysis-level cuts Width and signal strength parametrized in likelihood:!! Fit for r using events distributions in off-peak region Same procedures apply to all ZZ and WW decays Kauer & Passarino, JHEP 08 (2012) 116!7

8 4l analysis: selection 4 well isolated leptons: pt > 7 (5) GeV for electrons (muons) At least one lepton w/ pt > 20 GeV and another w/ pt > 10 GeV OSSF lepton pair with mll closest to mz: 40 < mll < 120 GeV Other pair: 12 < mll < 120 GeV All opposite sign dilepton pairings: mll > 4 GeV Background estimations are derived from MC for qqzz (POWHEG) and ggzz (gg2vv) ; data control regions are used for Z+X backgrounds!8

9 4l Analysis 2D ( m4l, Dgg ) shape analysis Dgg designed, within the Matrix Element Likelihood Approach, to isolate ggzz! exploit all information from ZZ decay kinematics Dgg, a requires choice of signal strength, studies show Γ/ΓSM 10 in analysis of Run1 data, use a=10 results are insensitive to the value of a used!9 P(Dgg mzz)

10 4l Shapes Yield and projected shapes (signal width 25x expectation)!10

11 4l Shapes Yield and projected shapes in signal-enhanced region Dgg>0.65 ; m4l>330 (signal width 25x expectation)!11

12 4l Results!12

13 4l Results ΓH = MeV ΓH/ΓSM< % CL observed (expected)!13

14 2l2ν Analysis Reconstruction and selections are the same as Run I legacy analysis: CMS collab., PAS-HIG Well isolated leptons (p T >20 GeV) ; m ll - m Z < 15 GeV ; missing E T > 80 GeV Vetoing 3rd lepton and b-tagged jets (for Z + heavy-flavor jets) Event categorized based on number of jets VBF-like: two jets with m jj > 500 GeV && Δη > 4.0 >=1 jet: excludes VBF-like events 0 jets Background estimation: data driven for reducible background (top, WW, W + jets, and Z + jets) MC simulation for ZZ and WZ continuum Fit distributions of m T (0, 1-jet) and missing E T (VBF-like)!14

15 2l2ν Shapes Expected/Observed distributions for each category: (signal width 10x expectation) 0-jet >=1-jet VBF-like!15

16 2l2ν Results ΓH = MeV ΓH/ΓSM< % CL observed (expected)! assuming μ = 0.93!16

17 Combined Results ΓH = MeV ΓH< 17.4 (35.3) 95% CL observed (expected)!17

18 Conclusions First measurement constraining total width of the Higgs boson using high mass diboson events combining two ZZ channels (4l, 2l2ν) optimized sensitivity to 4l kinematics using matrix element information (including interference effects) Γ H = MeV 95% C.L. limits: Γ H < 17.4 MeV Γ/Γ SM < 4.2 dramatic improvement compared to previous model independent measurements: Γ H < 3.4 GeV (on-peak data)!18

19 Backup!19

20 4l on-shell analysis Use 3D probability distribution, built on m4l, Dbkg, pt4l, Djet Dbkg - discriminant built with the matrix element likelihood approach (MELA) to suppress qq->4l background Djet - discriminant to separate VBF from ggf signals for events with at least 2 jets ; pt4l used otherwise!20

21 MELA Discriminant Build discriminant from Matrix Element (via MCFM) :! Input variables:!21

22 Syst. Unc. on yields!22