arXiv subjects

A. Bartl

Publications and source records attributed to A. Bartl.

At least 91 records · Page 5Linked to original sources

arXiv1999

Polarization and Spin Effects in Neutralino Production and Decay

We study the production of neutralinos e^+ e^- ->chi^0_i χ^0_j with polarized beams and the subsequent decays chi^0_i -> chi^0_k l^+ l^- and chi^0_j -> chi^0_l l^+ l^-, including the complete spin correlations between production and decay. We present analytical formulae for the differential cross section of the combined process of production and decay of neutralinos. We also allow for complex couplings. The spin correlations have a strong influence on the decay angular distributions and the corresponding forward-backward asymmetries. They are very sensitive to the SUSY parameters and depend strongly on the beam polarizations. We present numerical results for the cross section and the electron forward-backward asymmetry for e^+ e^- -> chi^0_1 chi^0_2, chi^0_2 -> chi^0_1 e^+ e^-. We study the dependence on the parameter M' for various mass splittings between tilde{e}_L and tilde{e}_R and different beam polarizations.

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arXiv1999

Large Higgs Boson Exchange Contribution in Three-Body Neutralino Decays

We show that the Higgs boson exchange contribution can be large in three-body decays of neutralinos even in the case of small tan(beta). This enlarges the branching ratios for the decays neutralino_2 -> neutralino_1 b \bar{b} and neutralino_2 -> neutralino_1 tau- tau+. This is the case in the region of the parameter space where the two lightest neutralinos are gaugino-like, the sfermions are heavier than 300 GeV, and m_A0 = 200 GeV or smaller.

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arXiv1999

Impact of bosonic decays on the search for stau_2 and tau-sneutrino

We perform a detailed study of the decays of the heavier tau slepton (stau_2) and tau-sneutrino (snu_tau) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons, i.e. stau_2 -> stau_1 + (h^0, H^0, A^0 or Z^0), stau_2 -> snu_tau + (H^- or W^-), and snu_tau -> stau_1 + (H^+ or W^+), can be very important due to the sizable tau Yukawa coupling and large mixing parameters of stau. Compared to the decays into fermions, such as stau_2 -> tau + neutralino_i and stau_2 -> nu_tau + chargino_j^-, these bosonic decay modes can have significantly different decay distributions. This could have an important influence on the search for stau_2 and snu_tau and the determination of the MSSM parameters at future colliders.

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arXiv1999

Electron and Neutron Electric Dipole Moments in the Constrained MSSM

We analyze the effects of CP-violating phases on the electric dipole moment (EDM) of electron and neutron in the constrained minimal supersymmetric model. We find that the phases phi_μ and phi_{A_0} have to be strongly correlated, in particular for small values of the SUSY mass parameters. We calculate the neutron EDM in two different models, the Quark-Parton Model and the Chiral Quark Model. It turns out that the predictions are quite sensitive to the model used. We show parameter regions in the M_0-M_1/2 plane which are excluded by considering simultaneously the experimental bounds of both electron and neutron EDM, assuming specific values for the phases phi_μ and phi_{A_0}.

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arXiv1998

SUSY-QCD corrections to stop and sbottom decays into Higgs bosons

We calculate the order(α_s) SUSY-QCD corrections to the widths of stop and sbottom decays into Higgs bosons within the Minimal Supersymmetric Standard Model. We give the complete analytical formulae paying particular attention to the on-shell renormalization of the soft SUSY-breaking parameters. We also perform a detailed numerical analysis of both stop and sbottom decays into all Higgs bosons h^0, H^0, A^0, and H^\pm. We find that the SUSY-QCD corrections are significant, mostly negative and of the order of a few ten percent.

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arXiv1998

Bosonic decays of stop_2 and sbottom_2

We perform a detailed study of the decays of the heavier top and bottom squarks (stop_2 and sbottom_2) in the Minimal Supersymmetric Standard Model (MSSM). We show that the decays into Higgs or gauge bosons can be dominant in a wide range of the model parameters due to the large Yukawa couplings and mixings of stops and sbottoms. Compared to the conventional decays into fermions these bosonic decay modes can have significantly different decay structures and distributions. This could have an important impact on the search for stop_2 and sbottom_2 and the determination of the MSSM parameters at future colliders.

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arXiv1998

CP violation in e+e- -> t tbar: Energy Asymmetries and Optimal Observables of b and bbar Quarks

The energy spectra of the b and bbar quarks in e+e- -> t tbar with t -> b W (tbar -> bbar W) are calculated assuming CP violation in the production process. Expressions for the corresponding CP violating asymmetries and optimal observables that determine the imaginary parts of the electric and weak dipole moment form factors of the top are derived. It is shown that polarization of the initial lepton beams is essential to disentangle Im d^γ(s) and Im d^{Z}(s). Numerical results are given in the Minimal Supersymmetric Standard Model with complex phases.

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arXiv1998

Spin Correlations in Production and Decay of Charginos

We study the production of charginos e^+ e^- -> chi^+_i chi^-_j, (i,j=1,2) with polarized beams and the subsequent decays chi^+_i -> chi^0_k ell^+ nu and chi^-_j -> chi^0_l ell^- nu, (k,l=1,...,4), including the complete spin correlations between production and decay. Analytical formulae are presented for the joint spin-density matrix of the charginos, for the chargino decay matrix and for the differential cross section of the combined processes of production and decays. We present numerical results for pair production of the lighter chargino with unpolarized beams and the leptonic decay of chi^+_1 into the lightest neutralino chi^0_1. The lepton angular distribution and the forward-backward asymmetry are studied in four representative scenarios for sqrt{s}=192 GeV and sqrt{s}=200 GeV.

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arXiv1998

Sfermion Pair Production at $μ^+ μ^-$ Colliders

We discuss pair production of stops, sbottoms, staus and tau--sneutrinos at a $μ^+ μ^-$ collider. We present the formulae for the production cross sections and perform a detailed numerical analysis within the Minimal Supersymmetric Standard Model. In particular, we consider sfermion production near $\sqrt{s} = m_{H^0}$ and $\sqrt{s} = m_{A^0}$.

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arXiv1998

CP violating angular asymmetries of b and bbar quarks in e+e- -> t tbar

We obtain analytical formulae for the cross section and the angular distributions of the b(bbar) quarks in the process e+e- -> t tbar, with t -> W+ b (tbar -> W- bbar) assuming CP violation in the γt tbar and Z t tbar vertices. We present CP violating asymmetries, which measure separately the real and imaginary parts of the electroweak dipole moment form factors of the top, d^γ(s) and d^{Z}(s). We give a numerical analysis of these asymmetries within the Minimal Supersymmetric Standard Model with complex parameters. They turn out to be of order <= 10^{-3}.

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arXiv1998

Spin Effects in Neutralino Production in $e^+e^-$ Annihilation with polarized beams

We study the process e^+ e^- -> chi^0_1 chi^0_2 and the subsequent decay chi^0_2 -> chi^0_1 l^{+} l^{-}$ with polarized beams, including the complete spin correlations of chi^0_2$. We present numerical results for the lepton energy and angular distributions, and for the distribution of the opening angle between the leptons for sqrt{s}=500 GeV. The effects of spin correlations are important in the lepton angular distribution, especially for gaugino-like neutralinos. The opening angle distribution is particularly suitable for distinguishing between higgsino- and gaugino-like neutralinos. The polarized cross sections and lepton angular distributions are very sensitive to the mixing of the neutralinos.

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arXiv1998

Electroweak dipole moment form factors of the top quark in supersymmetry

The CP violating electric and weak dipole moment form factors of the top quark appear in the process $e^{+}e^{-} --> t\bar{t}$. We present a complete analysis of these dipole moment form factors within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loop of the $γt\bar{t}$ and $Z t\bar{t}$ vertex. We give the analytic expressions and present numerical results.

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arXiv1997

Gluino Cascade Decays With Broken R--Parity

We study the pattern of gluino cascade decays in a class of supersymmetric models where R-parity is spontaneously broken. The multi-lepton and same-sign dilepton rates in these models are compared with those of the Minimal Supersymmetric Standard Model. We show that these rates can be substantially enhanced in models with broken R-parity.

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arXiv1997

Scalar Top Quark Production at $μ^+ μ^-$ Colliders

We discuss the production of stops at a $μ^+ μ^-$ collider. We present numerical predictions for the cross sections within the Minimal Supersymmetric Standard Model. In particular we consider stop production near $\sqrt{s} = m_{H^0}$ and $\sqrt{s} = m_{A^0}$.

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arXiv1997

SUSY induced CP violation in e+e- to t\bar{t}

The CP violating electric and weak dipole moment form factors of the top quark, $\dgs$ and $\dzs$, appear in the process \mbox{$e^{+}e^{-} \to t \bar{t}$}. We present a complete analysis of these dipole moment formfactors within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loop of the \mbox{$γt\bar{t}$} and \mbox{$Z t\bar{t}$} vertex. We give analytic expressions and present numerical results for the asymmetries that measure these formfactors.

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arXiv1997

Electroweak dipole moment form factors of the top quark in supersymmetry

We present a complete analysis of the electrtic and weak dipole moment form factors of the top quark within the Minimal Supersymmetric Standard Model with complex parameters. We include gluino, chargino, and neutralino exchange in the loops of the $γt\bar{t}$ and $Z t\bar{t}$ vertices.

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arXiv1997

SUSY--QCD Corrections to Higgs Particle Decays into Quarks and Squarks

We study the decays of the Higgs bosons $H^{\pm}$, $H^0$, and $A^0$ within the Minimal Supersymmetric Standard Model. For decays into quarks and squarks we include the supersymmetric QCD radiative corrections. We find that the corrections are significant and can go up to 50%. The supersymmetric decay modes $H^+ \to \tilde t \bar{\tilde b}$ and $H^0 (A^0) \to \tilde t \bar{\tilde t}$ can be dominant in a wide range of the model parameters due to the large Yukawa couplings and mixings of $\tilde t$ and $\tilde b$.

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arXiv1997

SUSY-QCD corrections to squark production and decays in e+e- annihilation

We discuss the supersymmetric O(alpha_s) QCD corrections to e+ e- -> squark_i + antisquark_j (i,j = 1,2) and to squark_i -> q' + chargino_j, q + neutralino_k (i,j = 1,2; k = 1...4) within the Minimal Supersymmetric Standard Model. In particular we consider the squarks of the third generation stop_i and sbottom_i including the left-right mixing. In the on-shell scheme also the mixing angle has to be renormalized. We use dimensional reduction (which preserves supersymmetry) and compare it with the conventional dimensional regularization. A detailed numerical analysis is also presented.

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