Higgs Physics and SUSY Searches with ATLAS Max Goblirsch, on behalf of the MPP ATLAS group MPP Project Review 2014, 15.12.2014
Searching for Physics Beyond the Standard Model with ATLAS One main objective of the LHC: Search for physics beyond the standard model . Two approaches: Indirect - precision measurements Direct - production of new particles g ˜ H t g Probe the standard model (SM) at New particles can also be directly high precision. produced . Look for signs of deviations from the Profit from growing collision energies. SM. Look for excesses over SM in The classic LHC probe: top quarks - predicted decay topologies. See talk this morning! Prominent example: Supersymmetry A brand-new probe: The Higgs searches . boson ! The MPP ATLAS group plays an important role in both fields . Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 2 / 17
Measurement of the Higgs boson mass and decay width in the H → ZZ → 4 ℓ channel H.Kroha, S.Kortner, O.Kortner, R.Röhrig, K.Ecker, F.Sforza, S.Stern Phys. Rev. D. 90, 052004 Knowledge of the Higgs boson mass is essential for predicting all other Higgs boson properties New: Highly reduced systematic uncertainty due to improved energy calibration procedures. Now much lower than CMS analysis. → Muon momentum calibration with Z → µµ and J / Ψ → µµ data. → Development of an analytic description of the mass resolution. Events / 2.5 GeV Channel Measured Mass [GeV] ATLAS 35 Data → → µ l Signal (m = 125 GeV = 1.51) H ZZ* 4 H H → ZZ → 4 ℓ 124 . 51 ± 0 . 52(stat) ± 0 . 06(sys) ∫ 30 Background ZZ* -1 s = 7 TeV Ldt = 4.5 fb H → γγ 125 . 98 ± 0 . 42(stat) ± 0 . 28(sys) ∫ Background Z+jets, t t -1 s = 8 TeV Ldt = 20.3 fb 25 Systematic uncertainty Combined 125 . 36 ± 0 . 37(stat) ± 0 . 18(sys) 20 Compatibility of results from the two channels: 2.0 σ 15 10 First limits on Higgs boson natural width: 5 Γ H < 2 . 6 GeV (95 % CL) 0 80 90 100 110 120 130 140 150 160 170 Made possible by analytical description developed at MPP! m [GeV] 4 l Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 3 / 17
Probing the tensor structure of the H → ZZ coupling H.Kroha, S.Kortner, O.Kortner, K.Ecker ATL-PHYS-PUB-2013-013 The H → ZZ → 4 ℓ channel allows for a full reconstruction of the final state kinematics - ideal for spin/CP measurements! SM Higgs: Spin 0, CP even ATLAS & CMS results point towards Spin 0 + with high probability Beyond the standard model contributions could affect HZZ coupling (loops) µν f ∗ ( 2 ) µν + . . . A ( X J = 0 → ZZ ) = v − 1 [ g 1 m 2 + g 2 f ∗ ( 1 ) + g 4 f ∗ ( 1 ) µν ˜ f ∗ ( 2 ) µν V ǫ ∗ 1 ǫ ∗ ] 2 � �� � � �� � � �� � Tree-level SM CP-even CP-odd → Probe for admixtures in decay amplitudes by measuring final state angular distribution (sensitive to CP) Sensitivity study for integrated luminosities 300 fb − 1 and (3000 fb − 1 ): | g 2 | / g 1 < 1 . 39 (0.81) at 95% CL | g 4 | / g 1 < 1 . 03 (0.49) at 95% CL Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 4 / 17
Measurement of the Higgs coupling to Vector bosons S.Kortner, H.Kroha, J.Bronner ATLAS-CONF-2014-060, CERN-THESIS-2014-031 The H → WW channel allows a study of the Higgs coupling to vector bosons. New: Observation of Higgs boson decays to WW (6.1 σ ) Evidence for the Vector Boson Fusion (VBF) production mechanism(3.2 σ ) → Measurement of Higgs production via vector boson fusion with WW decay as a direct probe of the Higgs boson coupling to vector bosons Transverse mass distribution in the VBF channels Events / 20 GeV H → WW* H → WW → e ν µ ν ATLAS Prelim. ∫ -1 s = 8 TeV, L d t = 20.3 fb 20 Obs stat ± 10 Exp ± syst H 0 0 VBF Events / 20 GeV H → WW → e ν e ν / μνμν H 30 ggF Top 20 DY WW Measured VBF Signal strength: 10 Misid 0 0 50 100 150 VV µ = 1 . 28 ± 0 . 4(stat) ± 0 . 25(sys) m [GeV] T Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 5 / 17
Measurement of the Higgs coupling to fermions S.Kortner, H.Kroha, D.Zanzi ATLAS-CONF-2014-061, CERN-THESIS-2014-085 The Higgs boson’s direct coupling to fermions can be measured in the H → ττ and H → b ¯ b decays first evidence for the H → ττ coupling (4 . 6 σ ) New: Multivariate analysis approaches, reduction of systematic uncertainties. Major contribution from fully hadronic final state. ln(1+S/B) w. Events / 10 GeV ATLAS Preliminary Data 80 → τ τ H µ H VBF+Boosted (125) ( =1.4) Z → τ τ s -1 = 7 TeV , 4.5 fb Others s -1 60 , 20.3 fb = 8 TeV Fakes Uncert. 40 20 0 weighted (Data-Bkg.) 20 H µ (125) ( =1.4) H µ (110) ( =1.6) 10 H µ (150) ( =6.2) 0 50 100 150 200 m MMC [GeV] τ τ Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 6 / 17
Measurement of the Higgs coupling to fermions H.Kroha, S.Kortner, F .Müller, F .Sforza arXiv:1409.6212 The Higgs boson’s direct coupling to fermions can be measured in the H → ττ and H → b ¯ b decays Improved search for VH → Vb ¯ b , but no evidence yet (1 . 5 σ ). Ongoing optimisation for run 2 based on the substructure of boosted b-jets Run 2: Measure coupling to the top quark in the t ¯ tH production channel ATLAS Preliminary Total uncertainty Weighted events after subtraction / 20.0 GeV ATLAS Data 2012 10 ± σ µ 1 on m = 125.36 GeV VH(bb) ( µ =1.0) H ∫ -1 s = 8 TeV Ldt = 20.3 fb Diboson arXiv:1408.7084 → γ γ Uncertainty H 0+1+2 lep., 2+3 jets, 2 tags Weighted by Higgs S/B 8 µ + 0.27 = 1.17 0.27 - arXiv:1408.5191 → → H ZZ* 4l 6 µ + 0.40 = 1.44 0.33 - arXiv:1412.2641 → → ν ν H WW* l l 4 µ 0.23 = 1.09 + 0.21 - JHEP11(2014)056 → W,Z H b b 2 µ 0.4 = 0.5 + 0.4 - ATLAS-CONF-2014-061 → τ τ H 0 µ 0.4 = 1.4 + - 0.4 50 100 150 200 250 0 0.5 1 1.5 2 ∫ s = 7 TeV Ldt = 4.5-4.7 fb -1 µ Signal strength ( ) m [GeV] ∫ -1 s = 8 TeV Ldt = 20.3 fb bb released 09.12.2014 Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 7 / 17
Combined coupling fits ATL-PHYS-PUB-2014-016, ATLAS-CONF-2014-009 Combine the results into a study of the Higgs boson couplings Common fit of couplings to fermions and vector bosons from individual measurements Currently still limited accuracy - expect major improvements in run 2 MPP to contribute to individual measurements and global fit → Important future ingredients: ttH and VH → Vb ¯ b - no significant observation yet F κ LHC Run 1 SM ∫ −1 Best fit s = 7 T eV Ldt = 4.6−4.8 fb 3 68% CL ∫ −1 s = 8 T eV Ldt = 20.7 fb 95% CL → γ γ Combined H , ZZ*, WW* 2 private comparison 1 0 Prospects −1 300 fb −1 −1 3000 fb (68% CL) 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 κ V Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 8 / 17
Interpreting the couplings measurement - Dark Matter at the LHC ATL-PHYS-PUB-2014-017 Major goal for run 2: use Higgs couplings results to constrain dark matter (DM) Higgs portal scenario : Competitive with direct searches at low DM masses χ q χ H Z Z ℓ − q ℓ + Further sensitivity to DM at the LHC: Direct search for invisible Higgs decays 1 Direct search for recoils off invisible particles (Monojets) 2 Direct SUSY searches (R-Parity conservation) assume presence of DM 3 Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 9 / 17
Search for neutral MSSM Higgs bosons S.Kortner, H.Kroha, A.Manfredini ATLAS-CONF-2014-049, CERN-THESIS-2014-080 Higgs searches can also directly target new physics models Recently published ATLAS searches for MSSM higgs bosons based on 2012 data Exclusion limits on MSSM paramters (tan β, m A ) for various models Strong implications on viability of SUSY models Large range of tan β values excluded Heavier H/A bosons with m A / H > 200 GeV preferred ( m max ) h if discovered boson is the h ATLAS-MPP: fully leptonic final state ( H → ττ → ℓννℓνν ) → Important for excluding A/H masses below 200 GeV Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 10 / 17
Direct searches for Supersymmetry - Top Squarks JHEP 06 (2014) 124 H.Kroha, O.Kortner, M.Flowerdew, N.Köhler A light top squark is a key ingredient to natural supersymmetry Challenging phase-space region for existing searches: t m (˜ t ) ≈ m ( t ) p ˜ χ 0 t ˜ New analysis approach exploiting spin correlations in the 1 dileptonic t ¯ t decay greatly enhances sensitivity χ 0 ˜ ˜ t 1 p → Strong MPP effort - to be extended to general stop searches in run 2 t ~ ~ ~ ∼ 0 → χ t t production, BR( t t) = 1 Fraction of decays 1 1 1 1 ) [GeV] 300 0.13 Qualitative Illustration ATLAS s SM t t p i n 0.12 c o ~ ~ 0 ∫ ∼ r SUSY t t t t + 2 -1 r → χ 250 L dt = 20.3 fb , s =8 TeV e 0 1 l 1 a t ∼ χ i 0.11 o n m( σ SUSY Observed limit ( ± 1 ) s th Expected limit ( 1 σ ) ± exp 200 0.1 All limits at 95% CL no spin correlations 0.09 150 +m ∼ 0 χ 1 >m t 0.08 m ~ t 1 y 100 b 0.07 s d i s e SM/SUSY 0 0.5 1 1.5 2 2.5 3 y 1.5 t e l a g n 50 r a a 1 T I P M 2 0.5 0 0 0.5 1 1.5 2 2.5 3 2 1 1 150 200 250 300 350 400 450 500 550 600 ~ Opening angle between the leptons m( t ) [GeV] 1 Max Goblirsch (ATLAS) ATLAS Higgs/SUSY 15.12.2014 11 / 17
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