SM Higgs Boson properties ATLAS LHC xs WS

SM Higgs Boson properties - ATLAS LHC xs WS Fabio Cerutti – LBNL On behalf of the ATLAS collaboration December/5/2012 1 F. Cerutti - LHC. xs WS

Outline • Detector status • SM Higgs boson at LHC: • Production modes and decays channels • Results: Discovery + HCP update • Properties measurement: methodology and results • Mass • Couplings • High Luminosity LHC prospect • Conclusions December/5/2012 2 F. Cerutti - LHC. xs WS

Detectors and LHC operation Design Pile-up ! HCP Update 4 th July paper Excellent LHC performance in 2012 LHC operated with 50 ns bunch spacing: Lpeak up to 7. 7 x 1033 cm-2 s-1 at 8 Te. V Lintegrated ~ 23 fb-1 delivered December/5/2012 • 2012 pile-up conditions challenging 3 F. Cerutti - LHC. xs WS

Detectors and LHC operation ATLAS - 2012 • ATLAS sub-detectors in very good shape >96% active channels after 4 years • >90% of delivered luminosity used in physics analysis December/5/2012 4 F. Cerutti - LHC. xs WS

Higgs boson production at LHC Loop – Top coupling BSM contribution ? Tree level W(/Z) V coupling Tree level top coupling Tree level W coupling Tree level Z coupling • Access to top (direct and Loop), W and Z couplings via production cross section • Main production mode: gg. H only via loop December/5/2012 5 F. Cerutti - LHC. xs WS

Higgs boson production at LHC 8 Te. V MH(125 Ge. V) s(fb) d(th)TOT d(th)QCD-Scale d(th)PDF+as ds/d. M(. 5 Ge. V) gg. H 19. 5 x 103 15% 8% 7% 0. 8% VBF 1. 58 x 103 3% 0. 2% 3% 0. 4% WH 697 4% 0. 5% 4% 1. 3% ZH 394 5% 1. 5% 4% 1. 3% tt. H 130 14% 7% 8% 1. 9% • Cross-sections are LARGE • Theory systematics larger for gg. H and tt. H • Important to predict gg. H contamination in “VBF experimental selection” December/5/2012 • Mass dependency very weak 6 F. Cerutti - LHC. xs WS

Higgs boson decay at LHC MH=125 Ge. V • Experimentally accessible: • bb, tt, WW, ZZ, gg, Zg, (mm) Mass dependency: • GH 4 Me. V NOT direct measure at LHC December/5/2012 7 • • d. BR(bb)/0. 5 Ge. V 1% d. BR(gg)/0. 5 Ge. V <1% d. BR(WW)/0. 5 Ge. V 4% d. BR(ZZ)/0. 5 Ge. V 4% F. Cerutti - LHC. xs WS

Higgs Searches ATLAS (and CMS) claimed the discovery of an Higgs-like boson the 4 th of July 2012 December/5/2012 8 F. Cerutti - LHC. xs WS

Clear evidence in mass spectra of ZZ* 4 l and gg channels Supported by WW* lnln results December/5/2012 9 F. Cerutti - LHC. xs WS

The Higgs Boson Discovery CB significance ~6 s December/5/2012 10 F. Cerutti - LHC. xs WS

HCP Update ATLAS updated “low mass resolution” channels by HCP with 13 fb-1 of data at 8 Te. V December/5/2012 11 F. Cerutti - LHC. xs WS

HCP update ATLAS updated: “low mass resolution channels” December/5/2012 12 F. Cerutti - LHC. xs WS

HCP Updated channels tt VH bb WW* ll nn 0+1 Jet 2012 • WW “observation” confirmed with 2012 data • VH bb and tt compatible with SM with (m=1) or without (m=0) Higgs More details on experimental analyses in backup slides December/5/2012 13 F. Cerutti - LHC. xs WS

HCP: The Higgs Boson Signal Strength HCP update • Signal strength m = s/s. SM: • m = 1. 3 ± 0. 3 • In agreement with SM prediction • Precision better then 30% December/5/2012 14 F. Cerutti - LHC. xs WS

HCP: gg vs VBF production WW* gg tt Check in quite model independent way different production modes m. VBF+VHx(BR/BRSM) vs mggx(BR/BRSM) December/5/2012 15 F. Cerutti - LHC. xs WS

Properties Measurement Following slides Based on Published results ONLY (4 th July paper ~10 fb-1) Is the newly discovered Higgs-like Boson the (minimal) SM one ? December/5/2012 16 F. Cerutti - LHC. xs WS

Mass Measurement • Only missing SM parameter • From gg and ZZ*(4 l) mass spectrum • Mass measurement independent on m • MH = 126. 0 ± 0. 4 stat ± 0. 4 sys Ge. V Total Error ~ 0. 6 Ge. V (5 per mill) • Statistical precision at 3 per mill level • Systematics dominated by e/g energy scale: challenging our calibration: • limiting factor in gg channel • Impact of mass error on LHC yields smaller than 5% (WW/ZZ most sensitive) December/5/2012 17 F. Cerutti - LHC. xs WS

Couplings • SM Higgs (GF v= 246 Ge. V) all G predicted once MH measured: proportional to (measured) fermion/boson masses • • Gff GWW GZZ GHH Ggg GZg a (mf /v)2 a (2 MW 2/v)2 a (MZ 2 /v)2 a (MH 2/v)2 a (1. 6 GWW + 0. 07 Gtt – 0. 7 GWt) Wt interference a (1. 1 Gtt + 0. 01 Gbb – 0. 12 Gbt) bt interference a (1. 12 GWW + 0. 003 Gtt – 0. 12 GWt) Wt interference • Gtot (126 Ge. V) = 4. 2 Me. V (dominated by bb ~57%, ferm. >70%) 18

Couplings Two possibilities (1 is more suited to test SM 2 to look for NP) 1) Assume SM Lagrangian CP=0+ + NW approximation to parameterize coupling dependency of measured Yield Test agreement between SM and observed yields 2) Effective Lagrangian expansion (P 2, P 4 operators) Measure effective coupling from observed yields and confront with SM LHC-XS wg 19 Grojean et al.

Couplings Fit • Follow prescription form LHC-XS working group 1) • Assume only one resonance observed • Assume Narrow Width Approximation • Assume SM Lagrangian tensor structure (also implies CP=0+) • Observed yields parameterized SM prediction x coupling scaling factors k 2 • SM equivalent to all k=1 • This simplified approach is sufficient for Today’s available statistics 20

The Couplings fit: Loops • Loop contributions can: • • Expressed as a function of SM couplings No access to total width GH two kind of assumptions • Only SM particles contribute to the total width • Treated as free parameter (assume possible BSM contributions) • Measure ratio of couplings Ggg /Ggg. SM = (1. 6 k 2 W + 0. 07 k 2 t – 0. 67 k. Wkt) LHC-XS wg: ar. Xiv: 1209. 0040 December/5/2012 21 F. Cerutti - LHC. xs WS

Coupling Fits • Basic Ingredient Experimental measurements of Signal Yields/channels: • Production modes: gg, VBF, W/ZH, (tt. H) • Final states: gg, WW, ZZ, bb, tt 22

Couplings Fit • SM theory predictions (at fixed mass) • Production ds/s ~5 -15% • Decay d. BR/BR ~ 3 -6% • VBF << gg. H Important to compute gg. H contamination in VBF experimental selection 23

Global k fit • Several Fits performed with 2011(~4. 8 fb-1) +2012(~5. 9 fb-1) results • Fit global scale factor k: • As expected just ~square root of m = 1. 4 ± 0. 3 • Theory error not dominant yet … but already sizable 24

k. F vs k. V fit • Couplings to Fermion and Vector boson sectors: k. F vs k. V ~k. V 2 ~k. V 4 / k. F 2 • Assumption only SM particles in GH k 2 H(k. F k. V) • All Fermion couplings scale with the same factor k. F • All Boson couplings scale with the same factor k. V December/5/2012 25 F. Cerutti - LHC. xs WS

k. F vs k. V fit • Good compatibility with SM • k. F = 0 (Fermiophobic Higgs) Excluded at >2 s • Thanks to channels that distinguish gg. H from VBF production December/5/2012 26 F. Cerutti - LHC. xs WS

Custodial Symmetry l. WZ = k. W/k. Z • Testing Custodial Symmetry W vs Z couplings • Move to fit of RATIO’s (can relax assumption on total width) • l. WZ = k. W/k. Z • Two additional parameters l. FZ k. ZZ in the fit but with small correlation with l. WZ 27

Custodial Symmetry l. WZ = k. W/k. Z • Testing Custodial Symmetry W vs Z couplings • Move to fit of RATIOs (can relax assumption on total width) • l. WZ = k. W/k. Z • Two additional parameters l. FZ k. ZZ in the fit but with small correlation with l. WZ • dominated by relative WW and ZZ yields and by BRgg that scales mainly as k. W 2 *In this plot l. FZ >0 28

Loop contributions S. Dimopoulos • Couplings to gg and gg expected to proceed via loop: very sensitive to BSM physics • Hierarchy problem related to top loop that are the same that contributes to gg Higgs coupling • Treat gg and gg loops as free parameters (no relationship with SM content assumed) December/5/2012 29 F. Cerutti - LHC. xs WS

Loop Contributions kg vs kg • Assumptions: • Direct Coupling to known SM particles assumed to be as in SM: • kb =k. W =k. Z =kt = …. = 1 • k. H ~ 0. 9 + 0. 1 kg • No extra contributions to Total width (only known SM and gg) • Fitted parameters kg vs kg December/5/2012 30 F. Cerutti - LHC. xs WS

Loop Contributions kg vs kg Still Dominated by statistical uncertainty WO Theory ~20% smaller error December/5/2012 31 F. Cerutti - LHC. xs WS

Prospects: High Luminosity LHC ATLAS submitted a document to Cracow European Strategy symposium: How well can we measure Higgs Boson Properties at LHC ? Main Focus on HL-LHC but first look also at HE-LHC December/5/2012 32 F. Cerutti - LHC. xs WS

The Couplings roadmap • Test structure of SM couplings to accessible particles • Account for correlations between production and decays modes • Start with simple basic tests (depending on available L): • • • L ~ 20 fb-1 Total signal yield m: tested at 30% Today Couplings to Fermions and Vector Bosons Test custodial symmetry W/Z Couplings Test possible BSM contributions to loop-induced couplings Test Down vs Up fermion couplings Test Lepton vs Quark fermion couplings Top Yukawa direct measurement tt. H: kt HL-LHC Test second generation fermion couplings: km L ~ 3000 fb-1 Higgs self-couplings HHH: k. H December/5/2012 33 F. Cerutti - LHC. xs WS

ATLAS studies: m at HL-LHC Signal strength m • Dashed chart Theory Uncertainties Contribution: • Dominant for ZZ and gg final states: hope to improve on that or consider ratios • Extrapolation of WW and tt is more difficult since experimentally dominated by bkg. Systematics: • ZZ, gg, tt ~10% (~5% on k) • Limited by theory errors • tt. H ~20% (~10% on k) November/14/2012 Dm/m = 2 Dk/k 34 F. Cerutti - Higgs Factory

Coupling Ratios Fit at HL-LHC • Fit to coupling ratios: • No assumption BSM contributions to GH • Some theory systematics cancels in the ratios • Loop-induced Couplings gg and gg treated as independent parameter • kg/k. Z tested at 2% • gg loop (BSM) kt/kg at 7 -12% (limited by theory error) • 2 nd generation ferm. km/k. Z at 7% ATLAS DG/G = 2 Dk/k November/14/2012 35 F. Cerutti - Higgs Factory

ATLAS HL-LHC summary Approved LHC 300 fb-1 at 14 Te. V: HL-LHC 3000 fb-1 at 14 Te. V: • Mass: <100 Me. V (statistical) • Mass: ~ <50 Me. V (statistical) • Coupling k rel. precision* • Couplings k rel. precision* • Z, W, b, t 10 -15% • t, m 3 -2 s observation • gg and gg 5 -11% • Z, W, b, t, t, m 2 -10% • gg and gg 2 -5% • H HH >3 s observation (2 Exper. ) *Assuming sizeable (1/2) reduction of theory errors Improvement on gg. H cross-section (QCD scale) ? Improvement on gg (and qq) PDF from LHC data ? Mass Measurement: Several exp/theory challenges to reach 50 Me. V (e/g/m calibration E-scale, Interference, FSR, …) November/14/2012 36 More details on analyses backup F. Cerutti - Higgsslides Factory

Conclusions • ATLAS (and CMS) has discovered a new boson: • “Observed” in 3 final states gg, ZZ and WW and 2 production modes gg and VBF • Measured Mass 126. 0 ± 0. 6 Ge. V • Measured s. BR’s and coupling fits • Global yield agrees at ~30% level with SM • Custodial symmetry verified at ~30% level • No significant deviations from SM in all tests performed • First Spin/CP measurements from ZZ, gg and WW coming(very) soon Higgs boson Precision measurement campaign just started: Final LHC potential can be reached only via strong cooperation between experimental and theory communities ! 37

Backup December/5/2012 38 F. Cerutti - LHC. xs WS

Bibliography of shown results • ATLAS Open Symposium European Strategy- Cracow 2012: • http: //indico. cern. ch/internal. Page. py? page. Id=10&conf. Id=175067 • LHC XSWG: ar. Xiv: 1209: 040 • Higgs discovery paper: • ATLAS: Phys. Lett. B 716 (2012) 1 -29 • ATLAS coupling fit: • ATLAS-CONF-2012 -127 http: //cdsweb. cern. ch/record/1476765/files/ATLAS-CONF 2012 -127. pdf December/5/2012 39 F. Cerutti - LHC. xs WS

December/5/2012 40 F. Cerutti - LHC. xs WS

H gg g g reducible g g Irreducible • Relay in excellent g vs jet (p 0) rejection • g identification and isolation: • high LAr granularity γγ ~ 75 -80% • Background dominated by continuum gg (Irreducible) γj ~ 20% jj ~ 2% 41

H gg • Analysis rely on Mgg spectrum fit • Look for narrow resonance over smooth background: Fully data driven method • M resolution ~1. 6 Ge. V dominated by g. Energy Resolution z • Contribution of gg angle negligible: from calorimeter pointing (+ PV from tracks) • Classify events depending on: • h (different resolution and material), • presence of conversions • transverse momentum (w. r. t. gg thrust axis): • Dedicated VBF tag categories • 2 Jets with Dh>2. 8 and Mjj>400 Ge. V (70% VBF purity) 42

H gg • Great attention in choosing bkg. modeling: • Study effect of possible bias (“fake signal”): Choose bkg model that gives better sensitivity only if signal bias less then 20% its expected statistical error • “Potential Signal Bias” added to bkg systematics • Separate fit for each category • Better representation of observed significance given by the “weighted mass spectrum”: • each category event weighted by wi = ln(1+si/bi) • Local Significance at 126. 5 Ge. V • Observed 4. 5 s ; Expected 2. 5 s • m (126 Ge. V) = s. BR(Obs)/s. BR(SM) = 1. 8 ± 0. 5 43

H ZZ* 4 l • High-purity channel s/b>1 in signal mass window • Statistically limited ! • s(125 Ge. V) x BR(ZZ 4 l) ~2. 8 fb at 8 Te. V • Important experimental ingredients: • Lepton reconstruction efficiency significance ~ e 2 • Mass resolution ~1. 4% for 125 Ge. V Higgs • Non-prompt leptons rejection: • Muons mainly Heavy Flavor decays (Zbb, ttbar) • Electrons: dominated by “Fakes” inside jets (p 0, g conv. , ) • Relay on Calorimetric + Track isolation and Impact Parameter significance (against HF decays) 44

H ZZ* 4 l Backgrounds: • Irreducible ZZ* 4 l: from MC but cross checked with data • Reducible backgrounds: • Z+light flavors e (large) • Z+HF and tt m (small) • Derived from Data M 4 l after final selection 45

H ZZ* 4 l • Excess of events around 125 Ge. V s/b ___ 1. 7 1. 1 0. 6 • Channels kept separated in significance calculation • Local Significance at 125. 0 Ge. V • Observed 3. 6 s ; Expected 2. 7 s m (126 Ge. V) = s. BR(Obs. )/s. BR(SM) = 1. 2 ± 0. 6 46

H WW* nlnl • Small s/b (15 -20%) with the exception of VBF category • Selections divided in 3 categories depending on Jet multiplicity: 0, 1 and 2 Jets (VBF) • Main backgrounds: • Irreducible: WW* (qq and gg productions) • tt and t. W with two W nl decays • W+Jets - Z/g+jets • Main discriminating variables: • Prompt lepton: Reduce W+jets (Huge cross-section) • ET-miss: Reject Z/g+Jets (Huge cross-section) • Transverse mass • DFll against Irreducible WW* (relay on scalar nature of SM Higgs) 47

H WW* nlnl Local Significance at 125. 0 Ge. V Observed 2. 8 s ; Expected 2. 3 s m (126 Ge. V) = 1. 3 ± 0. 5 After MT and DFll cut 48

H tt • Complex analysis • 3 different final states (lep-lep, lep-had, had-had) • Several categories to enhance sensitivity December/5/2012 49 F. Cerutti - LHC. xs WS

H tt • Main discriminating variable mtt (Missing Mass Calculator) • Main irreducible bkg: Z tt December/5/2012 50 F. Cerutti - LHC. xs WS

H tt Most sensitive category VBF Expected = 1. 7 s Observed = 1. 1 s December/5/2012 51 F. Cerutti - LHC. xs WS

VH bb 16 Signal Categories December/5/2012 52 F. Cerutti - LHC. xs WS

VH bb December/5/2012 53 F. Cerutti - LHC. xs WS

VH bb m = -0. 4 ± 0. 7(stat) ± 0. 8(sys) December/5/2012 54 F. Cerutti - LHC. xs WS

HL-LHC mass measurement • Mass measurement: • Statistical error down to ~50 (~15) Me. V in 4 l (gg) /Experiment • Systematics more difficult to predict: • gg: Photon Energy scale at the moment 600 Me. V • 4 l: calibrated with Z ll (Huge statistics) Today 200 Me. V • “Educated guess”: 50 Me. V achievable at HL-LHC December/5/2012 55 F. Cerutti - LHC. xs WS

Spin/CP • Several channels observables sensitive to Spin and CP properties • Production and Decay angles of different final states going to be used (soon) • gg decay angle cosq* • WW* set of angular variables • ZZ* complete set of kinematic variables (8) • Possible other handles/topologies • VBF production DFjj • VH mass • Spin 0+ SM all observable can be predicted: • Strategy: Use SM-0+ as benchmark to test agreement with Spin/CP sensitive observables 56

Spin/CP Prospects (Winter) • Spin: • Expect to test at Test SM-0+ vs several Spin 2 models • Main sensitivity from gg and WW channels, less from ZZ • Expect rejection ~2 s (for the tested models) • CP: • ~2 s sensitivity for simple 0+ vs 0 - models coming mainly form ZZ (WW small sensitivity, gg NO sensitivity) • Long term: study possible CP admixture and CP violation in Higgs sectors 57

Spin/CP • Some spin=2 models can already be rejected with modest luminosity combining several final state • CP in V sector can be studied with H ZZ 4 l • General parameterization of CP amplitude: • Complex form factors ai: • SM tree level a 1=1, a 2=a 3=0 – • Generated at loop level a 2(~few %) and a 3(~10 -10) • CP violation requires (a 1 OR a 2 ≠ 0) AND (a 3 ≠ 0) December/5/2012 58 F. Cerutti - LHC. xs WS

Spin/CP: ATLAS • Sensitivity to CP odd a 3 coupling vs L • High luminosity can allow CP studies in Higgs sector via ZZ to 4 l final state (very robust against pile-up) December/5/2012 59 F. Cerutti - LHC. xs WS

Signal XS evolution 14 Te. V • 8 14 Te. V • Higgs s 2. 6 higher • tt s 3. 9 higher • 8 33 Te. V • Higgs s 9. 2 higher • tt s 22 higher gg HH increases by 6 going from 14 to 33 Te. V December/5/2012 60 F. Cerutti - LHC. xs WS

Up vs Down Fermion sectors • Other additional interesting fits: • Test down vs up sectors Higgs couplings lud = ku/kd • Assumptions: same scaling factor for all down type (kd) and up type (ku) fermions Need bb and/or tt observations Up coupling indirect form gg Loop 61

Lepton vs Quark Fermion Sectors • Other additional interesting fits: • Assumptions same scaling factor for quark couplings (kq) • Test lepton vs quark sectors Higgs couplings llq = kl/kq Need tt observation quark coupling indirect form gg Loop 62

Coupling Fits With Current Data • Via Production we have access to: • In SM framework kt (gg Loop), (kb), k. W/Z • Assuming BSM in loops: kgluon • Via Decay we have access to: • In SM framework k. W (direct and gg Loop), k. Z (direct), kb, kt • Assuming BSM in loops: kgg • No access to total width GH two kind of assumptions • Only SM particles contribute to the total width • Measure ratio of couplings 63

Couplings at HL-LHC: ATLAS • MC Samples at 14 Te. V from Fast-Sim. • Truth with smearing: best estimate of physics objects dependency on pile-up • Validated with full-sim. up to m~70 • Analyses included in ATLAS study: H gg 0 -jet and VBF H tt VBF lep-lep and lep-had tt. H gg H ZZ 4 l H WW lnln 0 -jet and VBF Very Robust channel WH/ZH gg Good S/B tt. H gg (tt. H mm) Direct top Y coupling Statistically limited H mm Second generation fermion coupling F. Cerutti - Higgs Factory November/14/2012 64 • HH bb gg Higgs Self-Couplings • •

km Coupling at HL-LHC H mm Second generation fermion coupling: • Analysis strategy very similar to gg (advantage that DY spectrum is predictable): • Look for a narrow mass peak over continuous Z/DY background • ATLAS and CMS can go (well) above 5 s/Experiment at HL-LHC • km at 10% level/Experiment (statistically limited) November/14/2012 65 F. Cerutti - Higgs Factory

Higgs self-couplings l. HHH • Need to distinguish between HH production via H or V (negative interference) • ATLAS: HH bbgg (under study HH bbtt) • Example ATLAS analysis bbgg – Simple analysis MH=125 Ge. V: • Cuts on Pt 2 g (40/25) and 2 b-jets (25) and relative angles • 50 <Mbb<130 Ge. V - 120 <Mgg<130 Ge. V • Signal[l. HHH=1]=15, Signal[l. HHH=0 ]=26, Background = 24 (mainly tt. H) • 1 experiment: ~2 s observation for l. HHH=1 • Only one channel and very simple CUT-based analysis: we can do better November/14/2012 66 F. Cerutti - Higgs Factory