Branching Fraction Measurements of the SM Higgs with a Mass of 160 GeV at Future Linear \ee Colliders

Assuming an integrated luminosity of 500 fb$^{-1}$ and a center-of-mass energy of 350 GeV, we examine the prospects for measuring branching fractions of a Standard Model-like Higgs boson with a mass of 160 GeV at the future linear \ee collider TESLA when the Higgs is produced via the Higgsstrahlung mechanism, \ee \pfr HZ. We study in detail the precisions achievable for the branching fractions of the Higgs into WW$^*$, ZZ$^*$ and \bb. However, the measurement of BF(H \pfr \gaga) remains a great challence. Combined with the expected error for the inclusive Higgsstrahlung production rate the uncertainty for the total width of the Higgs is estimated.Comment: 17 pages Latex, including 7 figure

Probe of the Wtb coupling in ttˉt \bar t pair production at Linear Colliders

The Wtb vertex can be probed on future colliders in the processes of single top production (LHC, pp mode, NLC, $\gamma e$ mode) and of top pair production (NLC, e^+ e^- mode). We analyse observables sensitive to anomalous Wtb couplings in the top pair production process of e^+ e^- collisions. In particular, forward-backward and spin-spin asymmetries of the top decay products and the asymmetry of the lepton energy spectum are considered. Possible bounds on anomalous couplings obtained are competitive to those expected from the upgraded Tevatron and LHC. The validity of the infinitely small width approximation for the three-body top decay is also studied in detail.Comment: 23 pages, 6 figures, uses axodraw.st

Single Top Production in e+e−e^+ e^-, e−e−e^- e^-, γe\gamma e and γγ\gamma \gamma Collisions

Single top quark cross section evaluations for the complete sets of tree-level diagrams in the $e^+ e^-$, $e^- e^-$, $\gamma e$ and $\gamma \gamma$ modes of the next linear collider with unpolarized and polarized beams are performed within the Standard Model and beyond. From comparison of all possibilities we conclude that the process $\gamma_+ e^-_L \to e^- t \bar b$ is extremely favoured due to large cross section, no $t \bar t$ background, high degrees of beam polarization, and exceptional sensitivities to $V_{tb}$ and anomalous $Wtb$ couplings. Similar reasons favour the process $e^- e^- \to e^- \nu_e \bar t b$ for probing top quark properties despite a considerably lower cross section. Less favourable are processes like $e^+ e^-, \gamma \gamma \to e^- \nu_e t \bar b$. Three processes were chosen to probe their sensitivity to anomalous $Wtb$ couplings, with best bounds found for $\gamma_+ e^-_L \to e^- t \bar b$ and $e^+_R e^-_R \to e^- \nu_e t \bar b$.Comment: 23 pages, 13 figure

Higgs and Top Production in the Reaction γe→νbbˉW\gamma e \to \nu b \bar{b} W at TeV Linear Collider Energies

For an electron-photon collider the complete tree-level cross sections of the reaction $\gamma e \rightarrow \nu b \bar{b} W$ are computed at center-of-mass energies between 0.5 and 2.0 TeV, for top masses of 160 to 200 GeV and Higgs masses between 80 and 140 GeV within the Standard Model. It is shown that most of the $\nu b \bar{b}$ events are due to Higgs and $Z/\gamma^*$ production (with $H, Z/\gamma^* \rightarrow b \bar{b}$ decay) while top production (with $t \rightarrow bW$ decay) is about 50% smaller. Multiperipheral background and interferences are small, respectively negligible, in the energy range studied. By convoluting the basic cross sections with an energy spectrum of the backscattered photon beam, and inserting linear collider luminosities as anticipated in present designs, realistic $\nu b \bar{b} W$ event rates are estimated. This results in large event rates for $\gamma e \rightarrow \nu t b$ and $\gamma e \rightarrow \nu H W$. We estimate that the CKM matrix element $|V_{tb}|$, can be probed from the $\nu t b$ final state to an accuracy of 1-3% at $\sqrt{s_{e^+e^-}} > 1 TeV$. Assuming an effective Lagrangian based on dimension-6 operators we discuss the sensitivity for detecting deviations of the HWW coupling from the Standard Model in the reaction $\gamma e \rightarrow \nu H W$.Comment: 18 pages Latex, including 8 eps-figures To be appear in Zeitschrift f. Physik

Higgs Search in the WW* Decay Mode at Photon Linear Colliders

We present the results of calculations for the process gamma gamma -> W + 2 fermions at a future Photon Linear Collider (PLC). The calculations include at the same time the next-to-leading order Higgs signal and the complete tree level gauge boson background. We present numerical results in the intermediate mass Higgs region 140 GeV < M_H < 2M_W. We propose strategies for the determination of Higgs properties using the leptonic and hadronic final states for both polarized and unpolarized photon beams.Comment: 14 pages, LaTeX (using amsmath.sty), 4 EPS figures include

Probing Anomalous Wtb Coupling via Single Top Production at TeV Energy γ\gamma e Colliders

Results of complete tree level calculations of the single top production reaction $\gamma e \to \nu \bar{t} b$ at the Next Linear Collider, including the contribution of anomalous operators to the Wtb coupling are presented. The sensitivity for probing the structure of the Wtb coupling in a model independent way is analyzed and found to be significantly higher than for comparable measurements at the Tevatron.Comment: 10 Latex pages including 1 ps-figure and 3 eps-figure

QED corrections with partial angular integration to fermion pair production in e+e- - annihilation

Analytic formulae are derived for the complete photon energy spectrum due to QED corrections to fermion pair production in case of a limited angular acceptance for the final state fermions. After a numerical integration over the energy of non-observed photons, this corresponds to typical experimental conditions at LEP/SLC.Comment: 8 pages, Latex, text is unchanged compared to preprint and Journal-re