Rare Supersymmetric Top Quark Decays

{Two supersymmetric decays of the top quark, \thb and \tstopneu, are discussed within the framework of the Minimal Supersymmetric Standard Model with radiatively induced breaking of $SU(2)\times U(1)$. The present possibility of detecting these decays, given the available bounds on supersymmetric parameters, is compared with the situation a Next $e^+e^-$ Linear Collider would face if supersymmetric particles were still undiscovered after LEP~II. The indirect implications for \thb and \tstopneu of a possible detection of the bottom quark decay \bsgamma at the Standard Model level are taken into account. } % Invited talk presented to the {\it Workshop on Physics and Experiments with Linear $e^+e^-$ Colliders}, Waikoloa, Hawaii, April 1993Comment: 7 pages, with 8 uuencoded PS figures, PREPRINT DESY 93-098; - few sentences added in the introduction, style file change

Lightest-neutralino decays in R_p-violating models with dominant lambda^{prime} and lambda couplings

Decays of the lightest neutralino are studied in R_p-violating models with operators lambda^{prime} L Q D^c and lambda L L E^c involving third-generation matter fields and with dominant lambda^{prime} and lambda couplings. Generalizations to decays of the lightest neutralino induced by subdominant lambda^{prime} and lambda couplings are straightforward. Decays with the top-quark among the particles produced are considered, in addition to those with an almost massless final state. Phenomenological analyses for examples of both classes of decays are presented. No specific assumption on the composition of the lightest neutralino is made, and the formulae listed here can be easily generalized to study decays of heavier neutralinos. It has been recently pointed out that, for a sizable coupling lambda^{prime}_{333}, tau-sleptons may be copiously produced at the LHC as single supersymmetric particles, in association with top- and bottom-quark pairs. This analysis of neutralino decays is, therefore, a first step towards the reconstruction of the complete final state produced in this case.Comment: 40 pages, 11 figures, version to appear in JHE

INCLUSIVE PARTICLE PRODUCTION IN \pbp COLLISIONS

We calculate the inclusive production of charged hadrons in \pbp collisions to next-to-leading order (NLO) in the QCD improved parton model using a new set of NLO fragmentation functions for charged pions and kaons. We predict transverse-momentum distributions and compare them with experimental data from the CERN S\pbpS Collider and the Fermilab Tevatron.Comment: the file containing the figures has been replaced: we correct a mistake in the uuencoding procedure and we give the real Fig 4 instead of the spurious one which was accidentally included in the previous file. the text is unchanged

Inclusive particle production at HERA: Higher-order QCD corrections to the resolved quasi-real photon contribution

We calculate in next-to-leading order inclusive cross sections of single-particle production via resolved photons in $ep$ collisions at HERA. Transverse-momentum and rapidity distributions are presented and the scale dependence is studied. The results are compared with first experimental data from the H1 Collaboration at HERA.Comment: 11 pages with 15 uuencoded PS figures. Preprint DESY 93-03

Measuring R-parity-violating couplings in dilepton production at the LHC

We revisit the issue of probing R-violating couplings of supersymmetric theories at hadronic colliders, particularly at the LHC. Concentrating on dimuon production, an evaluation of the optimal sensitivity to the R-violating coupling is performed through a maximum likelihood analysis. The measurement uncertainties are evaluated through a study of fully generated events processed through a fast simulation of the ATLAS detector. It is found that a host of R-violating couplings can be measured to a statistical accuracy of better than 10%, over a significant part of the m_{tilde f} -- lambda parameter space still allowed by low energy measurements. Since the bounds thus obtained do not simply scale as the squark mass, one can do significantly better at the LHC than at the Tevatron. The same analysis can also be extended to assess the reach of the LHC to effects due to any non-SM structure of the four-fermion amplitude, caused by exchanges of new particles with different spins such as leptoquarks and gravitons that are suggested by various theoretical ideas.Comment: 28 pages, 14 figures (uses JHEP3.cls

Precision Measurements at The Higgs Resonance: A Probe of Radiative Fermion Masses

The possibility of radiative generation of fermion masses from soft supersymmetry breaking chiral flavor violation is explored. Consistent models are identified and classified. Phenomenological implications for electric dipole moments and magnetic moments, as well as collider probes -- in particular those relevant at the Higgs resonance -- are discussed. It is shown that partial widths $\Gamma_{h^{0} \to ff}$ are enhanced compared with the minimal supersymmetric standard model.Comment: 7 pages, 1 figure, aipproc.sty (included). Talk presented by N. Polonsky at the Workshop on Physics at the First Muon Collider and the Front End of a Muon Collider, Fermilab, November 6-9, 199

Gluino Contribution to Radiative B Decays: Organization of QCD Corrections and Leading Order Results

The gluino-induced contributions to the decay b-> s gamma are investigated in supersymmetric frameworks with generic sources of flavour violation. It is shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to contain: i) magnetic and chromomagnetic operators with a factor of alpha_s and weighted by a quark mass m_b or m_c; ii) magnetic and chromomagnetic operators of lower dimensionality, also containing alpha_s; iii) four-quark operators weighted by a factor alpha_s^2. Numerical results are given, showing the effects of the leading order QCD corrections on the inclusive branching ratio for b-> s gamma. Constraints on supersymmetric sources of flavour violation are derived.Comment: 36 pages including 16 postscript figures; uses epsf; journal version: one ref. added; rephrasing of a couple of paragraph

Charged Higgs- and R-Parity-Violating Slepton-Strahlung at Hadron Colliders

It is shown that the radiation of a charged Higgs boson off a third-generation quark (charged-Higgs-strahlung) provides an important channel for the discovery of the charged Higgs at hadron colliders. Equivalently, in supersymmetric models with explicit lepton-number (R-parity) violation, sleptons may also be produced in association with quarks (slepton-strahlung). Higgs- and slepton-strahlung production cross sections are given for both the Tevatron and the LHC. The LHC cross sections imply that heavy ${\cal{O}}$(TeV) charged Higgs bosons can be produced via charged-Higgs-strahlung and that strahlung production of charged sleptons is possible even for small R-parity violating couplings. The possible discovery of sleptons through this channel offers a surprising handle on models of neutrino masses.Comment: 23 pages, LaTex + RevTex, 11 figures (included). Title modified. (Published version.

Bˉ→Xsγ\bar{B}\to X_s \gamma in the Two Higgs Doublet Model up to Next-to-Next-to-Leading Order in QCD

We compute three-loop matching corrections to the Wilson coefficients $C_7$ and $C_8$ in the Two Higgs Doublet Model by applying expansions for small, intermediate and large charged Higgs boson masses. The results are used to evaluate the branching ratio of $\bar{B}\to X_s \gamma$ to next-to-next-to leading order accuracy, and to determine an updated lower limit on the charged Higgs boson mass. We find \mhplus \ge 380 GeV at 95% confidence level when the recently completed BABAR data analysis is taken into account. Our results for the charged Higgs contribution to the branching ratio exhibit considerably weaker sensitivity to the matching scale $\mu_0$, as compared to previous calculations.Comment: 20 pages, 15 figures; v2: minor modifications, matches published version in JHE