TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
The TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
hep-ph↗
arXiv subjects
J. A. Aguilar-Saavedra
Publications and source records attributed to J. A. Aguilar-Saavedra.
Probing top flavour-changing neutral couplings at TESLA
We present a comprehensive analysis of the sensitivity of the TESLA e+ e- collider to top flavour-changing neutral couplings to the Z boson and photon. We study single top production and top decay processes, and we consider the cases without beam polarization, with only e- polarization and with e- and e+ polarization. We show that the use of the latter substantially enhances the sensitivity to discover or bound these vertices, and for some of the couplings the expected LHC limits could be improved by factors 2-14 for equal running times.
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Top flavour-changing neutral coupling signals at a linear collider
We present an analysis of the sensitivity of the TESLA e+ e- collider to top flavour-changing neutral couplings to the Z boson and photon. We consider the cases without beam polarization, with only e- polarization and with e- and e+ polarization, showing that the use of the latter substantially enhances the sensitivity to discover or bound these vertices. For some of the couplings the expected LHC limits could be improved up to an order of magnitude for equal running times.
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Probing top flavour-changing neutral scalar couplings at the CERN LHC
Top decays into a light Higgs boson and an up or charm quark can reach detectable levels in Standard Model extensions with two Higgs doublets or with new exotic quarks, and in the Minimal Supersymmetric Standard Model. Using both a standard and a neural network analysis we show that the CERN Large Hadron Collider will give 3 sigma evidence of decays with Br(t -> Hc) >= 6.5 10^-5 or set a limit Br(t -> Hc) <= 4.5 10^-5 with a 95% confidence level if these decays are not observed. We also consider limits obtained from single top production associated with a neutral Higgs boson.
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Unitarity triangles and geometrical description of CP violation with Majorana neutrinos
We generalize the geometrical description of CP violation in the Standard Model in terms of a unitarity triangle. For three left-handed Majorana neutrinos CP violation in the lepton sector is determined by three unitarity triangles. With three additional right-handed neutrinos 15 quadrangles are required to characterize CP violation. We show the relation of the unitarity polygons with physical observables.
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Multilepton production via top flavour-changing neutral couplings at the CERN LHC
Zt and gamma t production with Z -> l+ l- and t -> Wb -> l nu b provides the best determination of top flavour-changing neutral couplings at the LHC. The bounds on tc couplings eventually derived from these processes are similar to those expected from top decays, while the limits on tu couplings are better by a factor of two. The other significant Z and W decay modes are also investigated.
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Computation of confidence intervals for Poisson processes
We present an algorithm which allows a fast numerical computation of Feldman-Cousins confidence intervals for Poisson processes, even when the number of background events is relatively large. This algorithm incorporates an appropriate treatment of the singularities that arise as a consequence of the discreteness of the variable.
hep-ex↗
Zt and γt production via top flavour-changing neutral couplings at the Fermilab Tevatron
Associated single top production with a Z boson or a photon at large hadron colliders provides a precise determination of top flavour-changing neutral couplings. The best way to measure these couplings with the up quark at Tevatron is to search for events with three jets and missing energy or events with a photon, a charged lepton, a jet and missing energy. Other decay channels are also discussed.
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Top mixing
We discuss the existing limits on top flavour-changing neutral couplings in models with new vector-like quarks. Large hadron and e+ e- colliders can improve these bounds by more than one order of magnitude.
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CP violation from new quarks in the chiral limit
We characterize CP violation in the SU(2)xU(1) model due to an extra vector-like quark or sequential family, giving special emphasis to the chiral limit m_{u,d,s}=0. In this limit, CP is conserved in the three generation Standard Model (SM), thus implying that all CP violation is due to the two new CP violating phases whose effects may manifest either at high energy in processes involving the new quark or as deviations from SM unitarity equalities among imaginary parts of invariant quartets (or, equivalently, areas of unitarity triangles). In our analysis we use an invariant formulation, independent of the choice of weak quark basis or the phase convention in the generalized Cabibbo-Kobayashi-Maskawa matrix. We identify the three weak-basis invariants, as well as the three imaginary parts of quartets B_{1-3} which, in the chiral limit, give the strength of CP violation beyond the SM. We find that for an extra vector-like quark |B_i| <= 10^{-4}, whereas for an extra sequential family |B_i| <= 10^{-2}.
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Constraints on top couplings in models with exotic quarks
The extension of the Standard Model with exotic quark singlets and doublets introduces large flavor changing neutral couplings between ordinary fermions. We derive inequalities which translate the precise determination of the diagonal Z couplings, in particular at LEP, into stringent bounds on the off-diagonal ones. The resulting limits can be saturated in minimal extensions with one vector doublet or singlet. In this case, 23 and 6 single top events, respectively, are predicted at LEP2 for an integrated luminosity of 500 1/pb per experiment.
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Measure of the size of CP violation in extended models
In this letter we introduce a possible measure of the size of CP violation in the Standard Model and its extensions, based on quantities invariant under the change of weak quark basis. We also introduce a measure of the ``average size'' of CP violation in a model, which can be used to compare the size of CP violation in models involving extra sequential or vector-like quarks, or left-right symmetry.
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Invariant formulation of CP violation for four quark families
We find a minimal set of constraints which are independent of the choice of weak quark basis and necessary and sufficient for CP conservation for four quark families, including also the case of degenerate quark masses. These invariant conditions are written in the mass eigenstate basis as a function of the fermion masses and charged current mixings. CP violation is then related to the areas of three unitarity quadrangles and the CP violating effects of the fourth family are discussed in the case of small mixings.
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Invariant analysis of CP violation
The invariant formulation of CP violation involves the generation of sets of invariant constraints for CP conservation, the manipulation of their expressions and the identification of complete and minimal subsets of such constraints. In this paper we present a collection of subroutines to deal with these three tasks in a fast, reliable and systematic way, with examples for the leptonic sector.
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Numerical diagonalization of fermion mass matrices
The diagonalization of general mass matrices is a more delicate problem when eigenvalue degeneracies exist. In this case, often overlooked in the literature, some difficulties arise related to the freedom in the choice of basis in degenerate subspaces. Here two simple algorithms are developed to deal with quark and neutrino mass matrices with arbitrary degeneracies.
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Scale dependence of quark mass matrices in models with flavor symmetries
Numerical correlations between fermion masses and mixings could indicate the presence of a flavor symmetry at high energies. In general, the search for these correlations using low-energy data requires an estimate of leading-log radiative corrections. We present a complete analysis of the evolution between the electroweak and the grand unification scales of quark mass parameters in minimal supersymmetric models. We take $M_t=180$ GeV and consider all possible values of $\tan β$. We also analize the possibility that the {\it top} and/or the {\it bottom} Yukawa couplings result from an intermediate quasifixed point (QFP) of the equations. We show that the quark mixings of the third family do {\it not} have a QFP behaviour (in contrast to the masses, the renormalization of all the mixings is linear), and we evaluate the low-energy value of $V_{ub}$ which corresponds to $V_{ub}(M_X)=0$. Then we focus on the renormalization-group corrections to {\it (i)} typical relations obtained in models with flavor symmetries at the unification scale and {\it (ii)} a superstring-motivated pattern of quark mass matrices. We show that in most of the models the numerical prediction for $V_{ub}$ can be {\it corrected} in both directions (by varying $\tanβ$) due to {\it top} or {\it bottom} radiative corrections.
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