A. Attikis

The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4 crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4 crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1× 1013 and 1.3× 1014 cm−2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb−1 and 3000 fb−1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. The experimental results obtained can be used to estimate the long term performance of the CMS ECAL.

A search for light charged Higgs bosons is presented, conducted using t t events with the t → bH ± and H ± → τ ± ν τ decay modes, and in the fully hadronic final state.The search was based on 2.3 fb -1 of data, delivered by the LHC and recorded with the CMS detector in 2011, at a centreof-mass energy √ s = 7 TeV.No excess of events was observed over the expected SM background.Model-independent upper limits were calculated for the t → bH ± branching ratio.These limits were translated in the (m H ± , tan β ) parameter space of the MSSM in the maximal mixing scenario (m max h ), excluding a significant region that had previously remained unexplored.

The search for a light charged Higgs boson at the LHC will greatly depend on how well the QCD background can be controlled, especially for the fully hadronic final state where it is expected that QCD is overwhelmingly the dominant source of background.As the QCD production crosssection at the LHC is large and more importantly poorly known, specific methods to suppress and consequently predict the remaining QCD multi-jet background are required.Several methods of suppressing this QCD background and data-driven methods to estimate the remaining in the signal region are discussed for both the lepton+jets and fully hadronic final state signal channels.

An overview of the results from various searches for charged Higgs bosons (H$^{\pm}$) is presented, based on data from proton-proton collisions delivered by the CERN LHC and recorded by the CMS experiment. These include the first running period (Run 1) legacy results at a $\sqrt{s}$ = 8 TeV and corresponding to an integrated luminosity of 19.7 fb$^{-1}$, as well as the most recent results with the second running period Run 2 at $\sqrt{s}$ = 13 TeV and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Model-independent upper limits at 95% confidence level on the branching ratio and/or the production cross section times the branching ratio for various processes are summarised, for charged Higgs bosons in the mass range of 80 GeV up to 3 TeV. For the first time in CMS, the intermediate-mass range near the top quark mass is also explored. A summary of the interpretation of these exclusion limits in the context of the minimal supersymmetric standard model (MSSM) for specific benchmark scenarios is also presented.