Eduard Boos

Single top quark at future hadron colliders: Complete signal and background study

Inst. de Fis. Teorica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 Sao Paulo

Higgs-Boson Production Induced by Bottom Quarks

Bottom quark‐induced processes are responsible for a large fraction of the LHC discovery potential, in particular for supersymmetric Higgs bosons. Recently, the discrepancy between exclusive and inclusive Higgs boson production rates has been linked to the choice of an appropriate bottom factorization scale. We investigate the process kinematics at hadron colliders and show that it leads to a considerable decrease in the bottom factorization scale. This effect is the missing piece needed to understand the corresponding higher order results. Our results hold generally for charged and for neutral Higgs boson production at the LHC as well as at the Tevatron. The situation is different for single top quark production, where we find no sizeable suppression of the factorization scale. Turning the argument around, we can specify how large the collinear logarithms are, which can be resummed using the bottom parton picture.

The Higgs Working Group: Summary report

In this working group we have investigated the prospects for Higgs boson searches at the Tevatron and LHC and, in particular, the potential of these colliders to determine the Higgs properties once these particles have been found. The analyses were done in the framework of the Standard Model (SM) and its supersymmetric extensions as the minimal (MSSM) and next-to-minimal (NMSSM) supersymmetric extensions. The work for the discovery potential of the LHC mainly concentrated on the difficult regions of previous analyses as those which are plagued by invisible Higgs decays and Higgs decays into supersymmetric particles. Moreover, the additional signatures provided by the weak vector-boson fusion process (WBF) have been addressed and found to confirm the results of previous analyses. A major experimental effort has been put onto charged Higgs boson analyses. The final outcome was a significant improvement of the discovery potential at the Tevatron and LHC than previous analyses suggested. For an accurate determination of Higgs boson couplings, the theoretical predictions for the signal and background processes have to be improved. A lot of progress has been made during and after this workshop for the gluon-fusion gg {yields} H + (0, 1, 2jets) and the associated t{bar t}H production process. A thorough study of the present theoretical uncertainties of signal and background processes has been initialized, culminating in a list of open theoretical problems. A problem of major experimental interest is the proper treatment of processes involving bottom quark densities, which is crucial for some important signal and background processes. Further theoretical improvements have been achieved for the MSSM Higgs boson masses and Higgs bosons in the NMSSM. This report summarizes our work. The first part deals with theoretical developments for the signal and background processes. The second part gives an overview of the present status of Higgs boson searches at the Tevatron. The third part analyzes invisible Higgs boson decays at the LHC and the forth part the Higgs boson search in the WBF channel. Part 5 summarizes the progress that has been achieved for A/H {yields} {tau}{sup +}{tau}{sup -}. decays in the MSSM. In part 6 the status of the Higgs boson search in t{bar t}H production is presented. Finally, part 7 describes the charged Higgs boson analyses in detail.

Sfermion precision measurements at a linear collider

At future e{sup +}e{sup -} linear colliders, the event rates and clean signals of scalar fermion production--in particular for the scalar leptons--allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan {beta} from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.

LIGHT AND INTERMEDIATE HIGGS BOSON SEARCH AT TEVATRON ENERGIES

We study the Higgs boson search possibility at the TEVATRON energies. The detailed analysis of the 4-fermion final state reactions is presented. Among the complete set of Feynman diagrams the main contribution to the final states comes from the Higgs signal WH and ZH, from the backgrounds WZ, ZZ and gluonic background Wbb, Zbb with subssiquent decays of W, Z bosons. It is shown that the important contribution to the background is connected with single top quark production subreactions qq-bar --> tb-bar or t-bar b with the top decay to Wb. As a result of various distributions for Higgs signal and backgrounds a number of optimum cuts has been found. The finaleffective

The top quark (20 years after its discovery)

bbar{b}

The Top Quark

-- pair mass distribution allows to extract the signal from Higgs with mass up to about 100 GeV at 2 TeV C.M. energy and up to about 120 GeV at 4 TeV C.M. energy for the integrated luminosity 1000 inverse pb.

Top-кварк (к 20-летию открытия)

On the twentieth anniversary of the observation of the top quark, we trace our understanding of this heaviest of all known particles from the prediction of its existence, through the searches and discovery, to the current knowledge of its production mechanisms and properties. We also discuss the central role of the top quark in the Standard Model and the windows that it opens for seeking new physics beyond the Standard Model.

Measurement of the electron charge asymmetry in p(p)over-bar -> W + X -> ev plus X decays in p(p)over-bar collisions at root S=1.96 TeV

On the twentieth anniversary of the observation of the top quark, we trace our understanding of this heaviest of all known particles from the prediction of its existence, through the searches and discovery, to the current knowledge of its production mechanisms and properties. We also discuss the central role of the top quark in the Standard Model and the windows that it opens for seeking new physics beyond the Standard Model.

TOP QUARK PHYSICS

On the twentieth anniversary of the observation of the top quark, we trace our understanding of this heaviest of all known particles from the prediction of its existence, through the searches and discovery, to the current knowledge of its production mechanisms and properties. We also discuss the central role of the top quark in the Standard Model and the windows that it opens for seeking new physics beyond the Standard Model.