Search for a light charged Higgs boson in top quark decays in pp collisions at √ s = 7 TeVThe CMS collaborationAbstract: Results are presented on a search for a light charged Higgs boson that can be produced in the decay of the top quark t → H + b and which, in turn, decays into τ + ν τ . The analysed data correspond to an integrated luminosity of about 2 fb −1 recorded in protonproton collisions at √ s = 7 TeV by the CMS experiment at the LHC. The search is sensitive to the decays of the top quark pairs tt → H ± W ∓ bb and tt → H ± H ∓ bb. Various final states have been studied separately, all requiring presence of a τ lepton from H + decays, missing transverse energy, and multiple jets. Upper limits on the branching fraction B(t → H + b) in the range of 2-4% are established for charged Higgs boson masses between 80 and 160 GeV, under the assumption that B(H + → τ + ν τ ) = 1.

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Si wafers were preamorphized by either Si or Ge ions at temperatures between 5 and 40°C. The diffusion of low energy 4 keV B implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range EOR region toward the surface. Transient enhanced diffusion TED in the regrown silicon was observed for all implants. Increasing the implantation temperature of the Si implant by as little as 15°C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater for Ge implants. In order to better understand this effect, detailed transmission electron microscopy TEM studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer up to 300 Å occurs when the implantation temperature increases from 5 to 40°C as a result of ion beam induced epitaxial recrystallization. Upon 800°C annealing, two types of defects are observed in the EOR region: 311 defects and dislocation loops. The 311 defects are unstable and the comparison of secondary ion mass spectroscopy and TEM data for annealed samples indicating the dissolution of these 311 defects is at least one of the sources of interstitials for TED in the regrown Si at 800°C. The EOR dislocation loops are stable for the annealing conditions used in this study 800°C for 15 min and there appears to be an exponential dependence of the TED that occurs in regrown Si on the density of the EOR dislocation loops.

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