ATLAS Standard Model Higgs Results Andrew Mehta For the ATLAS Collaboration LHCP, Barcelona, 13 May 2013 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Introduction 10 Months since observation of a new particle Since then: More data taken More channels analysed Final state observables used to measure properties Focus now on understanding particle’s properties In this talk: Mass and signal strength Couplings Spin/Parity Rare Decays Note: This talk is overview only. Many more details in parallel session talks and: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Mass and Signal Strength 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Evidence for a new Particle γγ, ZZ and WW channels updated with full data Clear evidence for a new particle seen in these channels 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Combined significance Combined significance almost at 10 σ. No doubt about discovery of a new particle But is it the SM Higgs Boson? 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Mass Measurement Accurate mass from ZZ and γγ channels. mH=125.5± 0.2 (stat) ± 0.6 (sys) GeV mγγ-mZZ=2.3 ±0.7 (stat) ±0.6 (sys) GeV Mass difference compatibility 1.5% (2.4σ). With alternative conservative systematic treatment compatibility rises to 8% 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Signal Strengths Signal strength μ = σ/σSM measured assuming mH =125.5 GeV No large deviation from SM prediction Compatibility of combined μ value and SM μ=1 is 9% Global compatibility between 5 measured μ values and μ=1 is 8% 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Couplings 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Production Modes gluon-gluon fusion (ggF) dominant Several measurements of vector-boson fusion (VBF) Data not yet very sensitive to VH and ttH Combine VBF and VH (both scale with V-H coupling) Combine ggF and ttH (both scale with t-H coupling) μVBF+VH/μggF+ttH = 1.2-+0.7-0.5 3.1 σ significance of non-vanishing VBF 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Fermion and Vector Couplings Vector coupling (κV) measured indirectly and directly in many channels Fermion coupling (κF) measured: - directly in H→bb and H→ττ – not well measured yet - indirectly via loop gg→H Combined –no assumption on Higgs Width Measure ratio of fermion to vector couplings: λFV=0.85+0.23-0.13 Fermion and vector couplings non-zero and consistent with SM. Still have a sign ambiguity 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Spin 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Measurement of Spin SM prediction for Higgs is JP =0+ J=1 unlikely after H→γγ observation but possible in some models Decay angles e.g. cosθ* (polar angle of daughters in H rest frame) reconstructed in H→γγ and H→ZZ H→WW also sensitive but decay angles not directly reconstructed – use other final state variables Results analysed in a graviton inspired model which has an unknown production mechanism – fraction of qq to gg Spin 2+ hypothesis tested in all channels H→ZZ used to test 0- and 1+ scenarios 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Spin from H→γγ Reconstruct decay angle from photons Sensitive to spin but not parity Fit background and signal in bins of cosθ* Spin 0 favoured. 14/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Spin from H→WW Combine several variables in a multivariate discriminant (boosted decision tree) Variables used: mll, PTll, Δφll, mT 0+ 2+ Spin 0 favoured. 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Spin from H→ZZ Combine several variables using a boosted decision tree Variables used: Φ, θ1, θ2, m12, m34, θ*, Φ1 Sensitive to parity and spin. Spin 0+ favoured. 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Spin Summary Test statistic is ratio of likelihoods of 2 spin hypotheses Compatibility with spin 0 Compatibility with spin 2 3 channels combined exclude 2+ at 99.9% CL independent of production mode H→ZZ excludes 0-, 1+ and (1-) and >95% (94%) CL. 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Rare Decays 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Search for H→Zγ Reconstruct Z→ll and photon Take mass difference between H and Z Observed limit at MH=125 GeV is 18.2 × SM cross section (95% CL) 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Search for H→μμ Look for a peak in μμ mass spectrum Observed limit at MH=125 GeV is 9.8 × SM cross section (95% CL) 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Search for H→invisible 100 % H→invisible BF Assuming SM ZH production rate (MH=125 GeV) H→invisible BF <65% observed (84% expected) at 95% CL. 13/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta HSG5 Meeting Summary 2012 data confirm beyond doubt the existence of a new particle. Signal strengths compatible with SM Mass is measured to mH=125.5± 0.2(stat) ± 0.6 (sys) GeV >3σ observation of VBF production mode Non-zero fermion and vector couplings Couplings consistent with SM Non-SM spin/parity disfavoured Particle looks very much like the SM Higgs 13/05/2013 Andrew Mehta HSG5 Meeting

Andrew Mehta HSG5 Meeting References Higgs couplings: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-034 Higgs mass: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-014 Higgs spin: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-040 γγ: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-012 γγ spin : https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-029 ZZ: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-013 WW: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-030 WW spin: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-031 ττ: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-160 bb: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2012-161 μμ: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-010 Zγ: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-009 ZH→invisible: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-009 13/15/2013 Andrew Mehta HSG5 Meeting

Andrew Mehta HSG5 Meeting Backup 17/04/2019 Andrew Mehta HSG5 Meeting

Andrew Mehta, ATLAS SM Higgs LHCP2013 Couplings Summary 14/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Couplings Summary 14/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013

Andrew Mehta, ATLAS SM Higgs LHCP2013 Mass Measurement 14/05/2013 Andrew Mehta, ATLAS SM Higgs LHCP2013