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Measurements of the Standard Model Higgs parameters at ATLAS

Measurements of the Standard Model Higgs parameters at ATLAS. Lidija Živković Weizmann Institute Israel. Measurements of the Standard Model Higgs parameters. If there is a Higgs boson , it would be found at ATLAS (> 5 s ) over the full mass range after a few months of running.

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Measurements of the Standard Model Higgs parameters at ATLAS

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  1. Measurements of the Standard ModelHiggs parameters at ATLAS Lidija Živković Weizmann Institute Israel

  2. Measurements of the Standard Model Higgs parameters • If there is a Higgs boson, it would be found at ATLAS (> 5s) over the full mass range after a few months of running. • Precision measurement of Higgs parameters will become a major goal • Necessary for better understanding of Standard Model symmetry-breaking mechanism • Refernces for this talk: • Physics TDR • M. Hohlfeld, ATL-PHYS-2001-004 • D. Zeppenfeld, et al., hep-ph/0002036 • M. Dührssen, et al., note in preparation • E. Gross, L. Živković, A. Ito, note in prepeartion • C. P. Buszello, et al, SN-ATLAS-2003-025 (spin and CP) L. Živković Weizmann Institute

  3. The Higgs Mechanism • Essential ingredient of the Standard Model: • complex scalar field with potential • Used to break the el. weak symmetry...... • ..... and to generate fermion masses: • Search for the Higgs Boson is a key issue for experiments at future colliders • Experimental challenges: • Higgs boson discovery • Measurement of Higgs boson parameters (couplings to bosons and fermions) • Measurment of the Higgs self coupling  Higgs potential • Mass limits: lower 114.4 GeV/c2and upper up to 1TeV form theory and ~200 GeV from precision measurement U f2 f1 L. Živković Weizmann Institute

  4. Production … The highest cross-section Two high-pT forward jets gg → H qq → WH qq → qqH High pT lepton for trigger gg,qq → ttH One ortwohigh pT leptons for trigger qq → ZH Reconstruction of one or two top quarks L. Živković Weizmann Institute

  5. 2mZ LEP excluded bb WW ZZ tt cc tt gg gg … and Decays Light Higgs L. Živković Weizmann Institute

  6. SM Higgs Physics TDR ATLAS-PHYS-2003-005 L. Živković Weizmann Institute

  7. Search channels - mass range100 – 1000 GeV L. Živković Weizmann Institute

  8. Measurements of Higgs Mass • Mass: • Direct in the channels where Higgs mass can be reconstructed: • H → gg, • H → bb, • H → ZZ(*)→ 4l • indirect elsewhere: • H → WW → lnln • WH → WWW → lnlnln • VBF channels (t final states) • Errors: statistical, systematic on absolute energy scale (assumed 0.1% for channels with leptons and photons and 1% for jets; goal 0.02% for channels with leptons and photons) • Precission from 0.1% to 1% Physics TDR and ATL-PHYS-2001-004 L. Živković Weizmann Institute

  9. Measurements of Higgs Rates • The cross section times branching ratio: where Є is efficency and h is acceptance. • Erorrs: 5% on background where it can’t be subtracted, neglected otherwise, 5% or 10% on luminosity’ 2% on Є∙h • Relative error: ATL-PHYS-2001-004 ttH gg fusion WH L. Živković Weizmann Institute

  10. Measurements of Higgs Couplings • Couplings and branching ratios • Can be obtained from rate measurements if is known from the theory; • Otherwise: measure ratios of rates for different channels: (errors on the) cross sections, L, G cancel get ratios of couplings • Couplings to bosons (mH < 190 GeV considered so far): • directly from and the same production mode for mH > 150 GeV • indirectly using and • the last one can be checked via with the same production mode (VBF, ttH) L. Živković Weizmann Institute

  11. Measurements of Higgs Couplings • Couplings to fermions: • ttH from • bbH from and • ttH from and L. Živković Weizmann Institute

  12. Measurements of Higgs Couplings • Errors: • K-factors - 20% gluon fusion, 5% VBF • proportionality constant for Higgs decay to gg or gg via loop – 10% • theoretical uncertainties from comparison of two different production modes ATL-PHYS-2001-004 L. Živković Weizmann Institute

  13. Relative branching ratios: Theoretical assumption : only one Higgs-Boson Relative couplings: Additional assumption: only particles of Standard-Model Measurements of Higgs Couplings New results from Physics Workshop in Athens: M. Dührssen L. Živković Weizmann Institute

  14. Measurements of Higgs Width • Width: • direct H → ZZ(*)→ 4l just for mH > 200 GeV because total width GH < GDetector, detector resolution. • Errors: statistical, systematic (detector energy and momentum resolution) ~ 1.5% Physics TDR L. Živković Weizmann Institute

  15. Measurements of Higgs Width • Width: • Indirect measurement at lower masses mH < 200 GeV. • Method proposed by D. Zeppenfeld et al., hep-ph/0002036: • The total width is dominated by bb, cc, WW, ZZ, gg, gg, tt→ most of them partially detectable in this mass range and the part that can’t be measured taken into account by the parameter e: • The H → ZZ* and H → WW* partial widths are related by SU(2): • The ratio of b to t partial widths is connected to their mass ratio: L. Živković Weizmann Institute

  16. Measurements of Higgs Width • Method proposed by D. Zeppenfeld et al., hep-ph/0002036 (continued): • Let us defined: • Then provides lower limit on G(H→WW(*)) = GW • Then • With a knowledge of GW and G, it is easy to obtain the other partial widths H → WW H → tt H → gg gg → H H → WW VBF or VH (V = Z or W) L. Živković Weizmann Institute

  17. Measurements of Higgs Width ATLAS + CMS 100 + 100 fb-1 • Correct assumptions (small e, SM ratios) • Just prediction for VBF processes: D. Zeppenfeld et al., hep-ph/0002036 WW bb ZZ tt L. Živković Weizmann Institute

  18. WW bb ZZ tt Measurements of Higgs Width M. Dührssen • But H→bb can’t really be measured at mH ~ 150 GeV enot so small (~20%) b to t width ratio (y) can’t really be checked • Assumption: BRvisible = 1 – e, e from Standard Model L. Živković Weizmann Institute

  19. Preliminary L = 30 fb-1 Hbb gttH/gttH HW+W- 2030% H+- MH [GeV/c2] MH [GeV/c2] top-Yukawa coupling • ttH → tt tt not included yet • Can improve measurement of top Yukawa coupling M. Dührssen E. Gross, et al. L. Živković Weizmann Institute

  20. f- angle between decay planes in the rest frame of the Higgs. q - angle between leptons and the momentum of the Z in the rest frame of the Z. Azimuthal angle f: Polar angle q: Measurements of Spin SN-ATLAS-2003-025 L. Živković Weizmann Institute

  21. Theoretical prediction Results after background subtraction For mH > 250 GeV all non Standard Model particles are excluded Measurements of Spin mH = 200 GeV SN-ATLAS-2003-025 L. Živković Weizmann Institute

  22. Measurements of Spin • Exclusion of non Standard Model particles through polar angle for higher Higgs masses. • For mH = 200 GeVpseudoscalar is excluded even at 100 fb-1. • The spin 1, CP even can be excluded at 300 fb-1 with significance 6.4s, while for the CP odd case significance is only 3.9s. SN-ATLAS-2003-025 L. Živković Weizmann Institute

  23. Conclusions • Precision measurements: • masses  0.1% - 1% • production rates  10% - 20% • relative branching ratios  15% – 45% • relative coupling ratios  10% - 20% • width  10% - 30% for mH > 150 GeV • For mH > 200 (230) GeV a Spin-0 CP-odd and a Spin-1 (CP-even and CP-odd) Higgs-Boson can be ruled out at 2s(5s) –Level with 100 fb-1 L. Živković Weizmann Institute

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