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W. de Boer

Publications and source records attributed to W. de Boer.

At least 55 records · Page 3Linked to original sources

A gobal fit to the anomalous magnetic moment, Higgs limit and b->s gamma in the constrained MSSM

New data on the anomalous magnetic moment of the muon together with the b->s gamma decay rate and Higgs limits are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment.

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A gobal fit to the anomalous magnetic moment, b->s gamma and Higgs limits in the constrained MSSM

New data on the anomalous magnetic moment a_mu of the muon together with the b->s gamma decay rate are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi^2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment a_mu. The newest b->s gamma data deviate 1.7 sigma from recent SM calculations and prefer a similar parameter region as the 2.6 sigma deviation from a_mu.

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The b->sgamma rate and Higgs boson limits in the Constrained Minimal Supersymmetric Model

New NLO b->sgamma calculations have become available using resummed radiative corrections. Using these calculations we perform a global fit of the supergravity inspired constrained minimal supersymmetric model (CMSSM). We find that the resummed calculations show similar constraints as the LO calculations, namely that only with a relatively heavy supersymmetric mass spectrum of the order of 1 TeV the b-τYukawa unification and the b->sgamma rate can coexist in the large tanb scenario. The resummed b->sgamma calculations are found to reduce the renormalization scale uncertainty considerably. The low tanb scenario is excluded by the present Higgs limits from LEP II. The constraint from the Higgs limit in the $m_0,m_{1/2}$ plane is severe, if the trilinear coupling A_0 at the GUT scale is fixed to zero, but is considerably reduced for $A_0\le -2m_0$. The relatively heavy SUSY spectrum required by \besg corresponds to a Higgs mass of $m_h=119\pm 1~ (stop masses)}\pm 2~(theory)~\pm~3 (top mass) GeV $ in the CMSSM.

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Grand Unified Theories and Supersymmetry in Particle Physics and Cosmology

A review is given on the consistency checks of GUT, which unify the electroweak and strong nuclear forces into a single theory. Such theories predict a new kind of force, which could provide answers to several open questions in cosmology. The possible role of such a ``primeval'' force will be discussed in the framework of the Big Bang Theory. Although such a force cannot be observed directly, there are several predictions of GUT's, which can be verified at low energies. The MSSM distinguishes itself from other GUT's by a successful prediction of many unrelated phenomena with a minimum number of parameters. Among them: a) Unification of the couplings constants; b) Unification of the masses; c) Existence of dark matter; d) Proton decay; e) electroweak symmetry breaking at a scale far below the unification scale. A combined fit shows that indeed the MSSM model can satisfy all these constraints simultaneously. The corresponding constraints on the as yet unknown top mass, the strong coupling constant, and all SUSY masses are given within the minimal model, taking into account the complete second order RGE's for the couplings and the one-loop corrected Higgs potential for the calculation of the Z and the Higgs masses.

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MSSM Predictions of the neutral Higgs boson masses and LEP II production cross sections

Within the framework of the Minimal Supersymmetric Standard Model (MSSM) the Higgs masses and LEP II production cross sections are calculated for a wide range of the parameter space. In addition, the parameter space restricted by unification, electroweak symmetry breaking and other low energy constraints is considered in detail, in which case the masses of all SUSY partners can be estimated, so that their contributions to the radiative corrections can be calculated. Explicit analytical formulae for these contribution are derived. The radiative corrections from the Yukawa couplings of the third generation are found to dominate over the contributions from charginos and neutralinos. Large Higgs mass uncertainties are due to the top mass uncertainty and the unknown sign of the Higgs mixing parameter. For the low tanb scenario the mass of the lightest Higgs is found to be below 103 GeV for a top mass below 190 GeV. The cross section at a LEP energy of 192 GeV is sufficient to find or exclude this low tanb scenario for a top mass below 180 GeV. For the high tanb scenario only a small fraction of the parameter space can be covered, since the Higgs mass is predicted between 105 and 125 GeV in most cases. At the theoretically possible LEP II energy of 205 GeV part of the parameter space for the large tanb scenario would be accessible.

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Lorentz angle measurements in irradiated silicon detectors between 77 K and 300 K

Future experiments are using silicon detectors in a high radiation environment and in high magnetic fields. The radiation tolerance of silicon improves by cooling it to temperatures below 180 K. At low temperatures the mobility increases, which leads to larger deflections of the charge carriers by the Lorentz force. A good knowledge of the Lorentz angle is needed for design and operation of silicon detectors. We present measurements of the Lorentz angle between 77 K and 300 K before and after irradiation with a primary beam of 21 MeV protons.

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The b->sgamma decay rate in NLO, Higgs boson limits, and LSP masses in the CMSSM

New NLO b->sgamma calculations have become available. We observe that at large tanbeta the dominant NLO term of the chargino amplitude, which is proportional to mu.tanbeta^2, changes the sign of this amplitude in a large region of the CMSSM parameter space, so that the preferred sign of the Higgs mixing parameter mu now agrees with the preferred sign of b-tau unification. We find that the b->sgamma rate does not constrain the CMSSM anymore, if the higher order contributions and its uncertainties from the incomplete calculations are taken into account. The Higgs boson mass in the CMSSM is found to be between 110 and 120 GeV for a top mass of 175 GeV, if the Higgs mass limit of 107.9 GeV from LEP, which implies tanbeta>3.3, is taken into account The mean Higgs boson mass value and its dominant errors are: m_h=115\pm 3(stop mass) \pm 1.5(stop mixing) \pm 2(theory) \pm 5(top mass) GeV. This Higgs mass range is valid for all tanbeta values above 20 and decreases for lower tanbeta. If the presently claimed evidence for dark matter by the DAMA Collaboration is interpreted as the Lightest Supersymmetric Particle (LSP) of the CMSSM, then it is at the edge of the parameter space allowed by the present Higgs limit of 107.9 GeV from LEP.

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Search for SUSY and Higgs particles

An overview of hints for new physics outside the Standard Model and the status of sparticle and Higgs searches is given. The present limits on Higgs bosons of about 90 GeV as well as the $\bsg$ rate and cosmological constraints severely restrict the available parameter space of the MSSM.

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Higgs Limit and b->s gamma Constraints in Minimal Supersymmetry

New limits on the Higgs mass from LEP and new calculations on the radiative (penguin) decay of the b->s gamma branching ratio restrict the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). We find that for the low tan(beta) scenario only one sign of the Higgs mixing parameter is allowed, while the high tan(beta scenario is practically excluded, if one requires all sparticles to be below 1 TeV and imposes radiative electroweak symmetry breaking as well as gauge and Yukawa coupling unification. For squarks between 1 and 2 TeV high tan(beta) scenarios are allowed. We consider especially a new high tan(beta)=64 scenario with triple unification of all Yukawa couplings of the third generation, which show an infrared fixed point behaviour. The upper limit on the mass of the lightest Higgs in the low (high) tan(beta) scenarios is 97+-6~(120+-2) GeV, where the errors originate predominantly from the uncertainty in the top mass.

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Updated Combined Fit of Low Energy Constraints to Minimal Supersymmetry

The new precise LEP measurements of alphas and the electroweak mixing angle as well as the new LEP II mass limits for supersymmetric particles and new calculations for the radiative (penguin) decay of the b-quark into sgamma allow a further restriction in the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM).

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In Search of SUSY

Electroweak precision tests of the SM and MSSM as well as searches for Supersymmetric Particles and Higgs bosons at LEP II and their significance within the MSSM are discussed. Invited talk presented at the EPIPHANY Conf. in Cracow, Jan. 3-7, 1997.

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The Constrained MSSM Revisited

Within the Constrained Minimal Supersymmetric Model (CMSSM) it is possible to predict the low energy gauge couplings and masses of the 3 generation particles from a few supergravity inspired parameters at the GUT scale. Moreover, the CMSSM predicts electroweak symmetry breaking due to large radiative corrections from the Yukawa couplings, thus relating the $Z^0$ boson mass to the top quark mass via the renormalization group equations (RGE). In addition, the cosmological constraints on the lifetime of the universe are considered in the fits. The new precise measurements of the strong coupling constant and the top mass as well as higher order calculations of the $b \to sγ$ rate exclude perfect fits in the CMSSM, although the discrepancies from the best fit parameters are below the $2σ$ level.

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Global Fits of the SM and MSSM to Electroweak Precision Data

A program including all radiative corrections to the MSSM at the same level as the radiative corrections to the SM has been developed and used to perform global fits to all electroweak data from LEP, SLC and the Tevatron and the radiative b->sgamma decay from CLEO. Values of the strong coupling constant at the M_Z scale and $\sin^2θ_{\overline{MS}}$ are derived, both in the SM and MSSM. Recent updates on ectroweak data, which have been presented at the Warsaw Conference in summer 1996, reduce the R_b anomaly from a 3.2 σto a 1.8 σeffect. In addition, the $b\rightarrow sγ$ decay is 30% below the SM prediction. In the MSSM light stops and light charginos increase R_b and decrease the $b\rightarrow sγ$ rate, so both observations can be brought into agreement with the MSSM for the same region of parameter space. However, the resulting $χ^2$ value for the MSSM fits is only marginally lower and in addition, the splitting in the stop sector has to be unnaturally high.

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Global Fits of the SM and MSSM to Electroweak Precision Data

A program including all radiative corrections to the MSSM at the same level as the radiative corrections to the SM has been developed and used to perform global fits to all electroweak data from LEP, SLC and the Tevatron and the radiative b->sgamma decay from CLEO. Values of the strong coupling constant at the $M_Z$ scale and $\sin^2θ_{\overline{MS}}$ are derived, both in the SM and MSSM. Recent updates on electroweak data, which have been presented at the Warsaw Conference in summer 1996, reduce the R_b anomaly from a 3.2 sigma to a 1.8 sigma effect. In addition, the $b \to sγ$ decay is 30% below the SM prediction. In the MSSM light stops and light charginos increase $R_b$ and decrease the $b \to sγ$ rate, so both observations can be brought into agreement with the MSSM for the same region of parameter space. However, the resulting $χ^2$ value for the MSSM fits is only marginally lower and in addition, the splitting in the stop sector has to be unnaturally high.

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Global Fits of the SM and MSSM to Electroweak Precision Data

The Minimal supersymmetric extension of the Standard Model (MSSM) with light stops, charginos or pseudoscalar Higgs bosons has been suggested as an explanation of the too high value of the branching ratio of the Z0 boson into b quarks (Rb anomaly). A program including all radiative corrections to the MSSM at the same level as the radiative corrections to the SM has been developed and used to perform global fits to all electroweak data from LEP, SLC and the Tevatron. The probability of the global fit improves from 8% in the SM to 18% in the MSSM. Including the b->s gamma rate, as measured by CLEO, reduces the probability from 18% to 15%. In the constrained MSSM requiring unification and electroweak symmetry breaking no improvement of Rb is possible.

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Combined Fit of Low Energy Constraints to Minimal Supersymmetry and Discovery Potential at LEP II

Within the Constrained Minimal Supersymmetric Standard Model it is possible to predict the low energy gauge couplings and masses of the 3. generation particles from a few parameters at the GUT scale. In addition the MSSM predicts elektroweak symmetry breaking due to large radiative corrections from Yukawa couplings, thus relating the Z^0 boson mass to the top quark mass. From a χ^2 analysis, in which these constraints can be considered simultaneously, one can calculate the probability for each point in the MSGUT parameter space. Our fits include full second order corrections for the gauge and Yukawa couplings, low energy treshold effects, contributions of all (s)particles to the Higgs potential and corrections to m_b from qluinos and higgsinos, which exclude (in our notation) positive values of the mixing parameter in the Higgs potential μfor the large tan βregion. Further constraints can be derived from the branching ratio for the radiative (penguin) decay of the b-quark into s γand the lower limit on the lifetime of the universe, which requires the dark matter density due to the Lightest Supersymmetric Particle (LSP) not to overclose the universe. For particles, which are most likely to have masses in the LEP II energy range, the cross sections are given for the various energy scenarios at LEP II. For low tan βthe production of the lightest Higgs boson, which is expected to have a mass below 103 GeV, is the most promising channel, while for large tan βthe production of charginos and/or neutralinos covers the preferred parameter space.

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Higgs Physics at LEP2

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

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