Measurement of $A_{FB}^{\mathrm{b}\overline{\mathrm{b}}}$ in hadronic Z decays using a jet charge techniqueal., P. Abreu et
doi: 10.1007/PL00022988pmid: N/A
Abstract. The \(\mbox{b}\bar{\mbox{b}}\) forward-backward asymmetry has been determined from the average charge flow measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992–1995. The measurement is performed in an enriched \(\mbox{b}\bar{\mbox{b}}\) sample selected using an impact parameter tag and results in the following values for the \(\mbox{b}\bar{\mbox{b}}\) forward-backward asymmetry: \( \begin{gathered} A_{FB}^{b\bar b} \left( {89.55 GeV} \right) = 0.068 \pm 0.018 \left( {stat.} \right) \pm 0.0013\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {91.26 GeV} \right) = 0.0982 \pm 0.0047 \left( {stat.} \right) \pm 0.0016\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {92.94 GeV} \right) = 0.123 \pm 0.016 \left( {stat.} \right) \pm 0.0027\left( {syst.} \right) \hfill \\ \end{gathered} \) The \(\mbox{b}\bar{\mbox{b}}\) charge separation required for this analysis is directly measured in the b tagged sample, while the other charge separations are obtained from a fragmentation model precisely calibrated to data. The effective weak mixing angle is deduced from the measurement to be: \( sin^2 \theta _{eff}^1 = 0.23186 \pm 0.00083 \)
The role of resolved virtual photons in the production of forward jets at HERAJung, H.;Jönsson, L.;Küster, H.
doi: 10.1007/s100520050031pmid: N/A
Abstract. The measurement of forward jet cross sections has been suggested as a promising probe of new small x parton dynamics and the question is whether the new HERA data provide an indication of this. In this paper the influence of resolved photon processes has been investigated and it has been studied to what extent the inclusion of such processes in addition to normal deep inelastic scattering leads to agreement with data. It is shown that two DGLAP evolution chains from the hard scattering process towards the proton and the photon respectively, are sufficient to describe effects observed in the HERA data, which have been attributed to BFKL dynamics.
Neutrino textures in light of Super-Kamiokande data and a realistic string modelEllis, J.;Leontaris, G.K.;Lola, S.;Nanopoulos, D.V.
doi: 10.1007/s100520050032pmid: N/A
Abstract. Motivated by the Super-Kamiokande atmospheric neutrino data, we discuss possible textures for Majorana and Dirac neutrino masses within the see-saw framework. There are two main purposes of this paper: first, to gain intuition into this area from a purely phenomenological analysis, and second, to explore to what extent it may be realized in a specific model. We comment initially on the simplified two-generation case, emphasizing that large mixing is not incompatible with a large hierarchy of mass eigenvalues. We also emphasize that renormalization-group effects may amplify neutrino mixing, and we present semi-analytic expressions for estimating this amplification. Several examples are then given of three-family neutrino mass textures, which may also accommodate the persistent solar neutrino deficit, with different assumptions for the neutrino Dirac mass matrices. We comment on a few features of neutrino mass textures arising in models with a U(1) flavour symmetry. Finally, we discuss the possible pattern of neutrino masses in a “realistic” flipped SU(5) model derived from string theory, illustrating how a desirable pattern of mixing may emerge. Both small- or large-angle MSW solutions are possible, while a hierarchy of neutrino masses appears more natural than near-degeneracy. This model contains some unanticipated features that may be relevant in other models also: The neutrino Dirac matrices may not be related closely to the quark mass matrices, and the heavy Majorana states may include extra gauge-singlet fields.
Mixing of two-level unstable systemsCastro, G. López;Muñoz, J.H.;Pestieau, J.
doi: 10.1007/s100520050033pmid: N/A
Abstract. Unstable particles can be consistently described in the framework of quantum field theory. Starting from the full S matrix amplitudes of \(B^+ \rightarrow (2\pi, 3\pi) l^+ \nu\) decays as examples of processes where the \(\rho-\omega\) resonances dominate, we propose a prescription for the mixing of two “quasi-physical” unstable states that differs from the one obtained from the diagonalization of the \(M-\mathrm{i}\Gamma/2\) non-Hermitian Hamiltonian. We discuss some important consequences for CP violation in the \(K_L-K_S\) system.
Higgs production: CP studies in $e^-e^-$ collisionsBøe, C.A.;Ogreid, O.M.;Osland, P.;Zhang, Jian-zu
doi: 10.1007/s100520050034pmid: N/A
Abstract. We review the production of scalar Higgs-like particles in high-energy electron–electron collisions, via the fusion of electroweak gauge bosons. The emphasis is on how to distinguish a CP-even from a CP-odd Higgs particle. Among the more significant differences, we find that in the CP-odd case, the Higgs spectrum is much harder, and the dependence of the total cross section on the product of the polarizations of the two beams much stronger, than in the CP-even case. We also briefly discuss parity violation, and the production of charged Higgs bosons.
Production of light fermion–antifermion pairs in $\gamma\gamma$ collisionsDenner, A.;Dittmaier, S.
doi: 10.1007/s100520050035pmid: N/A
Abstract. The \({\cal O}(\alpha)\) corrections to \(\gamma\gamma \to f\bar f\) in the standard model are calculated for arbitrary light fermions f. The relevant analytical results are listed in a form that is appropriate for practical applications, and numerical results for integrated cross sections are discussed. The corresponding QED corrections are generally of the order of some per mille for arbitrary energies. The weak corrections to \(\gamma \gamma \to{\rm e}^-{\rm e}^+\) are negligible below the electroweak scale, reach the percent level at a few hundred GeV, and grow to about \(-10\%\) at 2 TeV. The weak corrections to \({\rm u \bar u}\) and \({\rm d \bar d}\) production have a shape similar to the one for \({\rm e^-e^+}\), but they are larger by factors of about 1.4 and 3, respectively.
A possible hidden symmetry and geometrical source of the phase in the CKM matrixChen, Jing-Ling;Ge, Mo-Lin;Li, Xue-Qian;Liu, Yong
doi: 10.1007/s100520050036pmid: N/A
Abstract. Based on the present data, the three Cabibbo–Kobayashi–Maskawa (CKM) angles may construct a spherical surface triangle whose area automatically provides a “holonomy” phase. By assuming this geometrical phase to be that in the CKM matrix determined by an unknown hidden symmetry, we compare the theoretical prediction on \(\epsilon\) with experimental data and find the two are consistent within error range. The \(\alpha,\beta,\gamma\) predicted from this symmetry are also consistent with data. Further applications to the B-physics are briefly discussed. We also suggest restrictions for the Wolfenstein parameters explicitly; the agreement will be tested by more precise measurements in the future.
SU(3) analysis of annihilation contributions and CP violating relations in $B\to P P$ decaysHe, X.-G.
doi: 10.1007/s100520050037pmid: N/A
Abstract. Several methods proposed to measure the angle \(\gamma\) in the KM unitarity triangle assumed that the tree contribution to \(B^-\to \pi^-\bar K^0 \) is purely due to annihilation contributions and is negligibly small. This assumption has to be tested in order to have a correct interpretation of the experimental data. In this paper we show that using SU(3) symmetry, the smallness of the tree contribution can be tested in a dynamic model-independent way. We also derive several relations between CP violating rate differences for \(B\to P P\) decays without assuming the smallness of the annihilation contributions. These relations provide important tests for the standard model of CP violation.