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Scott McGarvie Determining the CP Properties of a Light Higgs Boson

Scott McGarvie Determining the CP Properties of a Light Higgs Boson. Royal Holloway, University of London. Contents. Introduction Heavy Higgs CP Light Higgs CP Production/Decay Channel Selection procedure CP sensitive variables Conclusions and Future Plans. Introduction

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Scott McGarvie Determining the CP Properties of a Light Higgs Boson

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  1. Scott McGarvie Determining the CP Properties of a Light Higgs Boson Royal Holloway, University of London

  2. Contents • Introduction • Heavy Higgs CP • Light Higgs CP • Production/Decay Channel • Selection procedure • CP sensitive variables • Conclusions and Future Plans

  3. Introduction The search for the Higgs boson is one of the most important tasks for the LHC Demonstrated for the TDR that ATLAS can cover the whole SM parameter space Once the Higgs is discovered, we will need to study its properties

  4. SM Higgs is spin 0 and CP-even • This may not be the case in models with extended Higgs sectors: • general 2HDM • MSSM with complex parameters MSSM predicts 3 neutral Higgs particles. h, H (CP-even) A (CP-odd) Presence of complex phases causes mixing and the mass eigenstates (h1, h2, h3) then have mixed CP Carena, Ellis, Mrenna, Pilaftsis, Wagner. Nucl.Phys. B659 (2003) 145-178 - hep-ph/0211467

  5. Experimental evidence that demonstrates the CP quantum numbers, would be very useful in determining the correct model Making a precision measurement such as this will be very difficult in the messy environment of the LHC

  6. Heavy Higgs CP CP Information is contained in the decay planes of H → ZZ* → 4l • CP even parallel decay planes, • CP odd perpendicular • Buszello, Fleck, Marquard, Van der Bij, SN-ATLAS-2003-025

  7. It was shown that they can distinguish between a CP-even and a CP-odd with 100fb-1, for a Higgs mass  200 GeV The linear collider uses a similar technique to determine the CP Running in the  mode, the polarisation of the photons can be changed from parallel to perpendicular to preferentially produce either a CP-even or CP-odd state

  8. Higgs Decays

  9. Higgs production

  10. Light Higgs CP For a light Higgs the H → ZZ* branching fraction is too small Use H → bb, , + decay channels Using ideas from Gunion, He PRL 76, 24, 4468 (1996) Interaction Lagrangian c is the CP-even coupling and d is the CP-odd coupling SM has c = 1 and d = 0 Only top quark will have significant sensitivity to CP

  11. CP sensitive variables CP information contained in the momenta of the tops

  12. Aims • Use the associated ttH →  channel • Select events with required topology • Reconstruct the physics objects • Select events using a 2 technique, to reduce the combinatorial background • Demonstrate that the CP information is contained with the proposed variables

  13. Comment The ttH →  will probably not be the best channel in which to measure CP • Very small event rate • In the context of the MSSM, the HVV coupling is absent

  14. Comment II the ttH → bb, +- channels have advantages and disadvantages. Much higher signal rate, much higher backgrounds Couplings , Branching fractions increase production cross-section decreases

  15. Selection Procedure • 2 or more light jets • 2 bjets • 2 photons (pT  25 GeV) • 1 electron or 1 muon ( pT  25 GeV) g g

  16. Selection efficiencies For the selected events • Reconstruct a hadronic W from all jet-jet pairs • Assume missing momentum is due to the neutrino, use W mass constraint to fully reconstruct the neutrino momentum. • Reconstruct a leptonic W in events which have 1 or more neutrino solutions • Reconstruct the top quark by combining the b-jet and W 4-vectors

  17. Hadronic W mass from all jj pairs

  18. Hadronic top mass from all bjj

  19. Top Reconstruction Reconstruct a top for all bjj and bl combinations. 4-vectors of the two tops are found by selecting the combination which minimizes the 2 mt = 175 GeV, mw = 80 GeV,  from TDR The selected tops are then used to Determine to values of the CP sensitive variables

  20. Reconstructed hadronicW

  21. Reconstructed hadronictop

  22. Reconstructed semi-leptonictop

  23. CP sensitive variables: a1, a2 CP even CP even CP odd CP odd

  24. CP sensitive variables: b1, b2 CP even CP even CP odd CP odd

  25. CP sensitive variables: b3, b4 CP even CP even CP odd CP odd

  26. Future Plans Several things still to do • Finish the semi-leptonic ttH →  channel and obtain significances for distinguishing between CP-even and CP-odd • Backgrounds • Better operators with greater sensitivity to CP • Sensitivity to a Higgs with mixed CP • Other Decay channels • ttH → , both tops hadronic • ttH →bb • ttH →+- • Combined analysis of different channels • MC@NLO

  27. Conclusions ATLAS does have some sensitivity to the CP properties of a light higgs. A precision measurement like this needs high statistics, and may require a combined ATLAS/CMS analysis

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