3,974 research outputs found

    Searches for Neutral Higgs Boson and Interpretations in the MSSM at LEP

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    This paper discusses recent publications of the LEP collaborations DELPHI, L3 and OPAL on searches for Higgs bosons motivated by MSSM scenarios as well as their interpretation in the MSSM. With the final publication of the LEP collaborations available or awaited, more and more interpretations in different MSSM models, including both CP conserving and CP violating, become available. Also specialized analyses close open areas in the parameter space. In the same time, better theoretical calculations with an increased maximal mass of the Higgs boson were presented. Both the new scenarios as well as the new theoretical limit on mhm_{\mathrm{h}} has consequences for the limits from LEP. The searches, the models in which they are interpreted and the implications of the LEP results for future SUSY searches, especially on the tanβ\tan\beta limit, are presented here.Comment: 3 pages, 2 figures, contribution to the proceedings of the EPS HEP Conference Aachen (2003), Version 2: added reference to section

    SUSY Parameter Measurements with Fittino

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    This article presents the results of a realistic global fit of the Lagrangian parameters of the Minimal Supersymmetric Standard Model with no assumptions on the SUSY breaking mechanism using the fit program Fittino. The fit is performed using the precision of future mass measurements of superpartners at the LHC and mass and polarized topological cross-section measurements at the ILC. Higher order radiative corrections are accounted for wherever possible to date. Results are obtained for a modified SPS1a MSSM benchmark scenario (general MSSM without assumptions on the breaking mechanism) and for a specific mSUGRA scenario. Exploiting a simulated annealing algorithm, a stable result is obtained without any {\it a priori} assumptions on the fit parameters. Most of the Lagrangian parameters can be extracted at the percent level or better if theoretical uncertainties are neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain a stable result.Comment: 3 pages, presented at the 2005 International Linear Collider Physics And Detector Workshop, Snowmass, CO, 14.-27. August 200

    Radiative bdb\to d Penguins

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    This article gives an overview of the recent searches and measurements of bdb\to d penguin transitions with the BaBar experiment. The branching fraction of these decays in the Standard Model (SM) is expected to be a factor of 10 or more lower than the corresponding bsb\to s penguin transitions, but a deviation from the SM prediction would be an equally striking sign of new physics. The exclusive decay BπB\to\pi\ell\ell is searched by BaBar with no excess over the background found. The BaBar measurement of B(ρ,ω)γB\to(\rho,\omega)\gamma provides the first evidence of B+ρ+γB^+\to\rho^+\gamma, is in good agreement with the previous Belle results and provides a measurement of Vtd/Vts|V_{td}/V_{ts}| independent of the one from BsB_s mixing. No deviation from the SM is found.Comment: Prepared for the Rencontres de Moriond EW 2007. 6 pages, 7 figures, 2 tables, replacement due to missing fonts in feynman diagram

    Fittino, a program for determining MSSM parameters from collider observables using an iterative method

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    Provided that Supersymmetry (SUSY) is realized, the Large Hadron Collider (LHC) and the future International Linear Collider (ILC) may provide a wealth of precise data from SUSY processes. An important task will be to extract the Lagrangian parameters. On this basis the goal is to uncover the underlying symmetry breaking mechanism from the measured observables. In order to determine the SUSY parameters, the program Fittino has been developed. It uses an iterative fitting technique and a Simulated Annealing algorithm to determine the SUSY parameters directly from the observables without any a priori knowledge of the parameters, using all available loop-corrections to masses and couplings. Simulated Annealing is implemented as a stable and efficient method for finding the optimal parameter values. The theoretical predictions can be provided from any program with SUSY Les Houches Accord interface. As fit result, a set of parameters including the full error matrix and two-dimensional uncertainty contours are obtained. Pull distributions can automatically be created and allow an independent cross-check of the fit results and possible systematic shifts in the parameter determination. A determination of the importance of the individual observables for the measurement of each parameter can be performed after the fit. A flexible user interface is implemented, allowing a wide range of different types of observables and a wide range of parameters to be used.Comment: 32 pages, 6 figures, accepted by Comp. Phys. Com

    Light pseudoscalar eta and H->eta eta decay in the simplest little Higgs mode

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    The SU(3) simplest little Higgs model in its original framework without the so-called mu term inevitably involves a massless pseudoscalar boson eta, which is problematic for b-physics and cosmological axion limit. With the mu term introduced by hand, the eta boson acquires mass m_eta ~ mu, which can be lighter than half the Higgs boson mass in a large portion of the parameter space. In addition, the introduced mu term generates sizable coupling of H-eta-eta. The Higgs boson can dominantly decay into a pair of eta's especially when mH below the WW threshold. Another new decay channel of H->Z+eta can be dominant or compatible with H -> WW for mH above the Z+eta threshold. We show that the LEP bound on the Higgs boson mass is loosened to some extent due to this new H->eta eta decay channel as well as the reduced coupling of H-Z-Z. The Higgs boson mass bound falls to about 110 GeV for f=3-4 TeV. Since the eta boson decays mainly into a bb pair, H-> eta eta -> 4b and H-> Z eta -> Z bb open up other interesting search channels in the pursuit of the Higgs boson in the future experiments. We discuss on these issues.Comment: major modification considering the simplest little Higgs model with the mu ter

    New HiggsBounds from LEP and the Tevatron

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    We review the program HiggsBounds that tests theoretical predictions of models with arbitrary Higgs sectors against the exclusion bounds obtained from the Higgs searches at LEP and the Tevatron. We explicitly list the bounds that have been added after the first release of HiggsBounds.Comment: 4 pages, talk given at SUSY09, Boston, June 200

    Determination of MSSM Parameters from LHC and ILC Observables in a Global Fit

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    We present the results of a realistic global fit of the Lagrangian parameters of the Minimal Supersymmetric Standard Model assuming universality for the first and second generation and real parameters. No assumptions on the SUSY breaking mechanism are made. The fit is performed using the precision of future mass measurements of superpartners at the LHC and mass and polarized topological cross-section measurements at the ILC. Higher order radiative corrections are accounted for whereever possible to date. Results are obtained for a modified SPS1a MSSM benchmark scenario but they were checked not to depend critically on this assumption. Exploiting a simulated annealing algorithm, a stable result is obtained without any a priori assumptions on the values of the fit parameters. Most of the Lagrangian parameters can be extracted at the percent level or better if theoretical uncertainties are neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain a stable result. The effects of theoretical uncertainties arising from unknown higher-order corrections and parametric uncertainties are examined qualitatively. They appear to be relevant and the result motivates further precision calculations. The obtained parameters at the electroweak scale are used for a fit of the parameters at high energy scales within the bottom-up approach. In this way regularities at these scales are explored and the underlying model can be determined with hardly any theoretical bias. Fits of high-scale parameters to combined LHC+ILC measurements within the mSUGRA framework reveal that even tiny distortions in the low-energy mass spectrum already lead to inacceptable chi^2 values. This does not hold for ``LHC only'' inputs.Comment: 25 pages, 5 figure

    Collider Bounds on Lee-Wick Higgs Bosons

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    We study the constraints on the Lee-Wick Higgs sector arising from direct collider searches. We work in an effective-field theory framework, where all of the Lee-Wick partners are integrated out, with the sole exception of the Lee-Wick Higgs bosons. The resulting theory is a two-Higgs doublet model where the second doublet has wrong-sign kinetic and mass terms. We include the bounds coming from direct Higgs searches at both LEP and Tevatron using the code HiggsBounds, and show the currently excluded parameter space. We also analyze the prospects of LHC Run-I, finding that with a total integrated luminosity of 5 fb 1^{-1} and a center-of-mass energy of 7 TeV, most of the parameter space for the SM-like CP-even Higgs will be probed.Comment: 26 pages, 5 figures, matches version published by PR

    Relic density of neutralino dark matter in the MSSM with CP violation

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    We calculate the relic density of dark matter in the MSSM with CP violation. We analyse various scenarios of neutralino annihilation: the cases of a bino, bino-wino and bino-Higgsino LSP, annihilation through Higgs, as well as sfermion coannihilation scenarios. Large phase effects are found, on the one hand due to shifts in the masses, on the other hand due to modifications of the couplings. Taking special care to disentangle the effects in masses and couplings, we demonstrate that the presence of CP phases can have a significant influence on the neutralino relic abundance. Typical variations in \Omega h^2 solely from modifications in the couplings are O(10%-100%), but can reach an order of magnitude in some cases.Comment: 36 pages, 21 figures (low resolution). A version with high-resolution figures can be downloaded from http://cern.ch/kraml/papers/omc

    Signals of CP Violation Beyond the MSSM in Higgs and Flavor Physics

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    We study an extension of the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM), considering the effects of new degrees of freedom at the TeV scale, and allowing for sources of CP violation beyond the MSSM (BMSSM). We analyze the impact of the BMSSM sources of CP violation on the Higgs collider phenomenology and on low energy flavor and CP violating observables. We identify distinct Higgs collider signatures that cannot be realized, either in the case without CP violating phases or in the CP violating MSSM, and investigate the prospects to probe them at the Tevatron and the LHC. The most striking benchmark scenario has three neutral Higgs bosons that all decay dominantly into W boson pairs and that are well within the reach of the 7 TeV LHC run. On the other hand, we also present scenarios with three Higgs bosons that have masses M_Hi > 150 GeV and decay dominantly into b bbar. Such scenarios are much more challenging to probe and can even lie completely outside the reach of the 7 TeV LHC run. We explore complementary scenarios with standard MSSM Higgs signals that allow to accommodate a sizable B_s mixing phase as indicated by D0, as well as the excess in B_s --> mu+ mu- candidates recently reported by CDF. We find that, in contrast to the MSSM, a minimal flavor violating soft sector is sufficient to generate significant corrections to CP violating observables in meson mixing, compatible with EDM constraints. In particular, a sizable B_s mixing phase, S_psiphi < 0.4, can be achieved for specific regions of parameter space. Such a large B_s mixing phase would unambiguously imply a sizable suppression of S_psiKs with respect to the SM prediction and a BR(B_s --> mu+ mu-) close to the 95% C.L. upper bound reported by CDF.Comment: 58 pages, 15 figures, 2 tables, v2 matches published versio
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