Stefan Hesselbach

Exploring the di-photon decay of a light Higgs boson in the MSSM with explicit CP violation

The di-photon decay channel of the lightest Higgs boson is considered as a probe to explore CP violation in the minimal supersymmetric standard model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs–sfermion–sfermion couplings, with and without light sparticles. The impact of a light stop on the decay width and branching ratio (BR) is established through a detailed study of the amplitude of the process H1→γγ. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM parameters, a light stop can change the BR by more than 50% with a CP-violating phase φμ∼90°, while the change is almost nil with a heavy stop.

Studies of spin effects in charged Higgs boson production with an iterative discriminant analysis at the Tevatron and LHC

We report on detailed Monte Carlo comparisons of selection variables to separate tbH± signal events from the standard model tt̄ background using an iterative discriminant analysis (IDA) method. While kinematic differences exist between the two processes whenever

H±W± production in the MSSM at the LHC

m_{H^\pm}{\ne}m_{W^\pm}

Explicit CP violation in the MSSM Higgs sector

, the exploration of the spin difference between the charged Higgs and the W± gauge boson becomes crucial in the particularly challenging case of near degeneracy of the charged Higgs boson mass with the W± mass. The TAUOLA package is used to decay the tau leptons emerging from the charged Higgs and W± boson decays taking the spin difference properly into account. We demonstrate that, even if the individual selection variables have limited discriminant power, the IDA method achieves a significant separation between the expected signal and background. For both Tevatron and LHC energies, the impact of the spin effects and H± mass on the separation of signal and background has been studied quantitatively. The effect of a hard transverse momentum cut to remove QCD background has been studied and it is found that the spin effects remain important. The separation is expressed in purity versus efficiency curves. The study is performed for charged Higgs boson masses between the W± mass and near the top mass.

Di-photon Higgs decay in the MSSM with explicit CP violation

We investigate the viability of observing charged Higgs bosons (H±) produced in association with W bosons at the CERN Large Hadron Collider, using the leptonic decay H+ → and hadronic W decay, within the Minimal Supersymmetric Standard Model. Performing a parton level study we show how the irreducible Standard Model background from W + 2 jets can be controlled by applying appropriate cuts. In the standard mmaxh scenario we find a viable signal for large tan β and intermediate H± mmasses (~ mt).

The scope of the 4 tau channel in Higgs-Strahlung and vector boson fusion for the NMSSM No-Lose theorem at the LHC

We analysed the sensitivity of the process gg→H1→γγ to the explicitly CP‐violating phases φμ and φAf in the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider (LHC), where H1 is the lightest Supersymmetric Higgs boson. We conclude that depending on these phases, the overall production and decay rates of H1 can vary up to orders of magnitude compared to the CP‐conserving case.

CP violation in SUSY particle production and decay

The Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation is studied with the help of the di-photon decay channel of the lightest neutral Higgs boson. Effects of CP violation, entering via the scalar/pseudo-scalar mixing at higher order as well as through the Higgs-sfermion-sfermion couplings at tree-level, are analyzed in the MSSM with and without light sparticles. A light stop may have a strong impact on the decay width and Branching Ratio (BR) of the decay process H1 → γγ, whereas other light sparticles have only little influence. In some regions of the MSSM parameter space with large CP-violating phase μ ~ 90° a light stop can change the BR by more than 50%.