Getting ready for Physics at the LHC with the CMS Detector

In order to get ready for physics at the LHC, the CMS experiment has to be set up for data taking. The data have to be well understood before new physics can be investigated. On the other hand, there are standard processes, well known from previous experiments and from simulation, which will help to understand the data of the detector in the early days of the LHC.Comment: presented at Lake Louise Winter Institute 2006, 17-23 February 2006, Alberta, Canad

Comparison of Higgs Boson Mass and Width Determination of the LHC and a Linear Collider

Two important properties of a Higgs boson are its mass and width. They may distinguish the Standard Model (SM) Higgs boson from Higgs bosons of extended models. We show results from a direct mass and width reconstruction for a Higgs boson mass range from 120 to 340 GeV. The mass and width have been reconstructed from the H --> ZZstar --> mu+mu-mu+mu- reaction in an LHC simulation of the CMS detector. The determined mass accuracy has been compared with that obtained from studies for a linear collider (LC). The mass precision from the latter studies is derived by scaling previous LC simulation results according to the expected event rates. For the Higgs boson width we compare a direct determination with indirect methods and find good complementarity.Comment: 4 pages, 4 figure

Searching for Higgs Bosons in Association with Top Quark Pairs in the H -> bb Decay Mode

Search for the Higgs Boson is one of the prime goals of the LHC. Higgs bosons lighter than 130 GeV decay mainly to a b-quark pair. While the detection of a directly produced Higgs boson in the bb channel is impossible because of the huge QCD background, the channel ttH -> lnqqbbbb is very promising in the Standard Model and the MSSM. We discuss an event reconstruction and selection method based on likelihood functions. The CMS detector response is performed with parametrisations obtained from detailed simulations. Various physics and detector performance scenarios are investigated and the results are presented. It turns out that excellent b-tagging performance and good mass resolution are essential for this channel.Comment: 10 pages, 6 figure

Prospects for Higgs Boson Searches in the Channel WH -> lnbb

We present a method how to detect the WH -> lnbb in the high luminosity LHC environment with the CMS detector. This study is performed with fast detector response simulation including high luminosity event pile up. The main aspects of reconstruction are pile up jet rejection, identification of b-jets and improvement of Higgs mass resolution. The detection potential in the SM for m(H) < 130 GeV and in the MSSM is only encouraging for high integrated luminosity. Nevertheless it is possible to extract important Higgs parameters which are useful to elucidate the nature of the Higgs sector. In combination with other channels, this channel provides valuable information on Higgs boson couplings.Comment: 8 pages, 8 figure

Three-loop corrections to the lightest Higgs scalar boson mass in supersymmetry

I evaluate the largest three-loop corrections to the mass of the lightest Higgs scalar boson in the Minimal Supersymmetric Standard Model in a mass-independent renormalization scheme, using effective field theory and renormalization group methods. The contributions found here are those that depend only on strong and Yukawa interactions and on the leading and next-to-leading logarithms of the ratio of a typical superpartner mass scale to the top quark mass. The approximation assumes that all superpartners and the other Higgs bosons can be treated as much heavier than the top quark, but does not assume their degeneracy. I also discuss the consistent addition of the three-loop corrections to a complete two-loop calculation.Comment: 9 page

Bottom-quark fragmentation: comparing results from tuned event generators and resummed calculations

We study bottom-quark fragmentation in e+e- annihilation, top and Higgs decay H -> b bbar, using Monte Carlo event generators, as well as calculations, based on the formalism of perturbative fragmentation functions, which resum soft- and collinear-radiation effects in the next-to-leading logarithmic approximation. We consider the PYTHIA and HERWIG generators, and implement matrix-element corrections to the parton shower simulation of the H -> b bbar process in HERWIG. We tune the Kartvelishvili, string and cluster models to B-hadron data from LEP and SLD, and present results in both x_B and moment spaces. The B-hadron spectra yielded by HERWIG, PYTHIA and resummed calculations show small discrepancies, which are due to the different approaches and models employed and to the quality of the fits to the e+e- data.Comment: 22 pages, 11 colour figures. Minor changes in the text, published versio

Summary of the CMS Discovery Potential for the MSSM SUSY Higgses

This work summarises the present understanding of the expected MSSM SUSY Higgs reach for CMS. Many of the studies presented here result from detailed detector simulations incorporating final CMS detector design and response. With 30 fb-1 the h -> gamma,gamma and h -> bb channels allow to cover most of the MSSM parameter space. For the massive A,H,H+ MSSM Higgs states the channels A,H -> tau,tau and H+ -> tau,nu turn out to be the most profitable ones in terms of mass reach and parameter space coverage. Consequently CMS has made a big effort to trigger efficiently on taus. Provided neutralinos and sleptons are not too heavy, there is an interesting complementarity in the reaches for A,H -> tau,tau and A,H -> chi,chi.Comment: 19 pages, 27 figure

Strong and Yukawa two-loop contributions to Higgs scalar boson self-energies and pole masses in supersymmetry

I present results for the two-loop self-energy functions for neutral and charged Higgs scalar bosons in minimal supersymmetry. The contributions given here include all terms involving the QCD coupling, and those following from Feynman diagrams involving Yukawa couplings and scalar interactions that do not vanish as the electroweak gauge couplings are turned off. The impact of these contributions on the computation of pole masses of the neutral and charged Higgs scalar bosons is studied in a few examples.Comment: 23 pages, 9 figures, revtex4. New paragraph in introduction, more explanation of Figure

pp -> ttH, H->tau tau: toward a model independent determination of the Higgs boson couplings at the LHC

The possibility of detecting a Higgs boson through several production and decay channels is instrumental to the measurement of its couplings. In this paper we study the pp-> ttH(H-> tau tau) channel at the LHC, for the case of a scalar Higgs boson, and use the obtained results to improve on existing strategies toward a model independent determination of the Higgs boson couplings. The case of a scalar Higgs boson with mass below 140 GeV looks particularly promising.Comment: 19 pages, 5 Figures, LaTex, published version, typos corrected, comments added in Sec.