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Higgs Physics

The discovery of a Higgs boson at the Large Hadron Collider at CERN, announced on 4 July 2012, constitutes a major milestone for elementary particle physics. This boson could be the key to a long-standing question of the scientific world: the origin of mass itself.
Our CMS Higgs group at DESY has contributed importantly to the historic Higgs discovery paper of CMS, and is deeply involved in key research clarifying the nature and the properties of the observed Higgs itself, and the structure of a possible Higgs sector.

H (125) → ττ
We have analyzed three of the six possible decay patterns of the τ lepton pairs in the H to ττ decay channel. In this decay mode, we have recently established direct evidence of the τ coupling to leptons. Together with the non-observance of muonic decay mode, it gives also direct proof of the non-universality of the Higgs coupling, which is expected in the Standard Model. Once the latter is measured, it will allow a precise investigation of the mass dependence of the Higgs coupling. With the data of the upcoming Run-II of the LHC at 13 TeV, we will also investigate spin correlations within τ pairs as a further probe into the properties of the new boson.
Heavy Higgs Search (H → ττ Channel)
A key question after the initial discovery of a Higgs boson is the structure of the underlying sector. The observed boson could just be a first indication of a new family of new bosons, which might possibly lead into a whole realm of New Physics. The LHC , currently the collider with the largest energy ever achieved, offers unique possibilities as a discovery machine. One scenario involving heavy Higgs bosons is offered by super-symmetric extensions of the Standard Model. Our group has strongly contributed to the latest search for super-symmetric Higgs bosons , which in the meantime extends over a mass range of up to 1.8 TeV.
Heavy Higgs Search (H → bb Channel)
The Higgs decay to a pair of b quarks is the strongest expected decay mode for a wide range of model scenarios and parameters. However, the huge background from QCD multi-jet production makes the analysis of this channel very challenging. Our group has proposed and implemented a dedicated trigger for CMS which allowed recording of a large number of candidates in both the 7 TeV and 8 TeV data-taking periods. With the 7 TeV data alone, we have established the first measurement of this kind at the LHC, and with the full Run I dataset (7 + 8 TeV) we achieved the highest sensitivity for the super-symmetric parameter tan β in this channel. We are now in the process of analyzing the first data taken at 13 TeV, and expect our sensitivity to benefit greatly from the increased energy and luminosity.
Light Higgs Search
Also additional Higgs bosons much lighter than the state discovered at 125 GeV must be considered . Such bosons could be feasible e.g. in the context of the Next-to-Minimal Supersymmetric Model (NMSSM). We are investigating two such scenarios:
  • a pair of light Higgs boson could appear through the decay of the known Higgs boson at 125 GeV. If the mass of the light bosons is below the beauty threshold, each would decay dominantly into a pair of tau leptons.
  • a light Higgs boson below the Z mass could have reduced couplings to W and Z and thus be invisible to the previous searches performed at the LEP collider. Such bosons might then be visible in super-symmetric neutralino cascades only accessible at the LHC.
The analysis has been successfully completed. No signal has been observed (see figure below), and certain NMSSM benchmark scenarios are already excluded by this novel analysis.

Last Updated on 15-11-2016

 

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