Top Quark Physics at Colliders
We review some recent developments in top quark production and decay at current and future colliders.
hep-ph↗
arXiv subjects
G. Weiglein
Publications and source records attributed to G. Weiglein.
LHC/LC Interplay in the MSSM Higgs Sector
The interplay of prospective experimental information from both the Large Hadron Collider (LHC) and the Linear Collider (LC) in the investigation of the MSSM Higgs sector is analyzed in the SPS~1a and SPS 1b benchmark scenarios. Combining LHC information on the heavy Higgs states of the MSSM with precise measurements of the mass and branching ratios of the lightest CP-even Higgs boson at the LC provides a sensitive consistency test of the MSSM. This allows to set bounds on the trilinear coupling A_t. In a scenario where LHC and LC only detect one light Higgs boson, the prospects for an indirect determination of M_A are investigated. In particular, the impact of the experimental errors of the other SUSY parameters is analyzed in detail. We find that a precision of about 20% (30%) can be achieved for M_A = 600 (800) GeV.
hep-ph↗
Towards Better Constraints on the Higgs Boson Mass: Two-Loop Fermionic Corrections to sin^2(theta_eff)
The complete two-loop electroweak fermionic corrections to the effective leptonic weak mixing angle, sin^2(theta_eff), are now available. Here we shortly present the methods applied and illustrate the implications on indirect prediction for the Higgs boson mass within the standard model.
hep-ph↗
Impact of a precise top mass measurement
The physics impact of a precise determination of the top-quark mass, m_t, at the Linear Collider (LC) is discussed, and the results are compared with the prospective accuracy at the LHC. The importance of a precise knowledge of m_t for electroweak precision observables and for Higgs physics in the MSSM is pointed out in particular. We find that going from hadron collider to LC accuracy in m_t leads to an improvement of the investigated quantities by up to an order of magnitude.
hep-ph↗
Two-loop Fermionic Electroweak Corrections to the Effective Leptonic Weak Mixing Angle in the Standard Model
We give some details of the recently completed calculation of the full two-loop fermionic corrections to the effective leptonic weak mixing angle. Among others, we describe the C++ library DiaGen/IdSolver, which was used to reduce the two-loop light fermion vertex diagrams to linear combinations of master integrals with rational function coefficients.
hep-ph↗
Complete Two-Loop Electroweak Fermionic Corrections to sin^2(theta_eff) and Indirect Determination of the Higgs Boson Mass
We present a complete calculation of the contributions to the effective leptonic weak mixing angle, sin^2theta_eff, generated by closed fermion loops at the two-loop level of the electroweak interactions. This quantity is the source of the most stringent bound on the mass, M_H, of the only undiscovered particle of the Standard Model, the Higgs boson. The size of the corrections with respect to known partial results varies between -4*10^-5 and -8*10^-5 for a realistic range of M_H from 100 to 300 GeV. This translates into a shift of the predicted (from sin^2theta_eff alone) central value of M_H by +19 GeV, to be compared with the shift induced by a recent change in the measured top quark mass which amounts to +36 GeV. Our result, together with all other known corrections is given in the form of a precise fitting formula to be used in the global fit to the electroweak data.
hep-ph↗
Determination of Higgs-boson couplings at the LHC
We investigate the determination of Higgs boson couplings to gauge bosons and fermions at the LHC from data on Higgs boson production and decay. We demonstrate that very mild theoretical assumptions, which are valid in general multi-Higgs doublet models, are sufficient to allow the extraction of absolute values of the couplings rather than just ratios of the couplings. For Higgs masses below 200 GeV we find accuracies of 10-40% for the Higgs couplings and the total Higgs boson width after several years of LHC running. The sensitivity of the Higgs coupling measurements to deviations from the Standard Model predictions is studied for an MSSM scenario.
hep-ph↗
Extracting Higgs boson couplings from LHC data
We show how LHC Higgs boson production and decay data can be used to extract gauge and fermion couplings of Higgs bosons. We show that very mild theoretical assumptions, which are valid in general multi-Higgs doublet models, are sufficient to allow the extraction of absolute values for the couplings rather than just ratios of the couplings. For Higgs masses below 200 GeV we find accuracies of 10-40% for the Higgs boson couplings and total width after several years of LHC running. Slightly stronger assumptions on the Higgs gauge couplings even lead to a determination of couplings to fermions at the level of 10-20%. We also study the sensitivity to deviations from SM predictions in several supersymmetric benchmark scenarios as a subset of the analysis.
hep-ph↗
The Higgs Working Group: Summary Report 2003
Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed.
hep-ph↗
Two-Loop SUSY Corrections to the Anomalous Magnetic Moment of the Muon
We calculate supersymmetric two-loop corrections to the anomalous magnetic moment of the muon, consisting of diagrams with a closed scalar fermion or fermion loop and gauge and/or Higgs boson exchange. We discuss the numerical impact of each subclass of diagrams and determine the leading contributions. We analyze in detail constraints from experimental information on the Higgs boson mass, Delta(rho), and the branching ratios of B -> X_s gamma and B_s -> mu^+ mu^-. If these constraints are taken into account, the largest possible contributions are reduced from more than 2 sigma (in terms of the current experimental error) to ~0.3 sigma. The only exceptions arise in rather extreme parameter scenarios with a strong non-universality between the soft breaking parameters in the stop and sbottom sectors.
hep-ph↗
Les Houches "Physics at TeV Colliders 2003" Beyond the Standard Model Working Group: Summary Report
The work contained herein constitutes a report of the ``Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 26 May--6 June, 2003. The research presented is original, and was performed specifically for the workshop. Tools for calculations in the minimal supersymmetric standard model are presented, including a comparison of the dark matter relic density predicted by public codes. Reconstruction of supersymmetric particle masses at the LHC and a future linear collider facility is examined. Less orthodox supersymmetric signals such as non-pointing photons and R-parity violating signals are studied. Features of extra dimensional models are examined next, including measurement strategies for radions and Higgs', as well as the virtual effects of Kaluza Klein modes of gluons. An LHC search strategy for a heavy top found in many little Higgs model is presented and finally, there is an update on LHC $Z'$ studies.
hep-ph↗
Single Charged MSSM Higgs-boson production at a Linear Collider
In the Minimal Supersymmetric Standard Model we present the calculation of the single charged Higgs-boson production in the gamma W- or Z W-fusion and the charged Higgs strahlung channel, e^+ e^- -> e nu H^\pm. The set of all O(alpha) corrections arising from loops of Standard Model fermions and scalar fermions are taken into account. Contrary to the case of single neutral heavy CP-even Higgs-boson production, for the charged Higgs boson we find for all the parameter space of the typical benchmark scenarios a cross section smaller than \sim 0.01 fb for sqrt(s)/2 \lessim M_H^\pm.
hep-ph↗
Higher-Order Results in the Electroweak Theory
The present status of higher-order results in the electroweak theory is summarised, with particular emphasis on recent two-loop results for the prediction of the W-boson mass in the Standard Model and leading three-loop corrections to the rho parameter. The remaining theoretical uncertainties in the prediction for the W-boson mass and the effective weak mixing angle are discussed.
hep-ph↗
Physics Impact of a Precise Determination of the Top Quark Mass at an e+e- Linear Collider
At a prospective e+e- Linear Collider (LC) a very precise determination of the top quark mass with an accuracy of $δm_t <= 100 MeV$ will be possible. This is to be compared with the envisaged accuracy of $δm_t = 1-2 GeV$ at the Tevatron and the LHC. We discuss the physics impact of such a precise determination of m_t, focusing on the Standard Model (SM) and its minimal supersymmetric extension (MSSM). In particular, we show the importance of a precise knowledge of m_t for electroweak precision observables, and for Higgs physics and the scalar top sector of the MSSM. Taking the mSUGRA model as a specific example, we furthermore demonstrate the importance of a precise m_t value for the prediction of sparticle masses and for constraints on the parameter space allowed by the relic density. The uncertainty in m_t also significantly affects the reconstruction of the supersymmetric high scale theory. We find that going from hadron collider to LC accuracy in m_t leads to an improvement of the investigated quantities by up to an order of magnitude.
hep-ph↗
The lightest Higgs Boson of mSUGRA, mGMSB and mAMSB at Present and Future Colliders: Observability and Precision Analyses
We investigate the physics of the lightest CP-even MSSM Higgs boson at the Tevatron, the LHC, a linear e+e- collider, a gamma gamma collider and a mu+mu- collider. The analysis is performed in the three most prominent soft SUSY-breaking scenarios, mSUGRA, mGMSB and mAMSB. For all colliders the observability and parameter regions with suppressed production cross sections (compared to a SM Higgs boson with the same mass) are investigated. For the lepton and photon colliders the potential is analyzed of precision measurements of the branching ratios of the light CP-even Higgs boson for obtaining indirect bounds on the mass of the CP-odd Higgs boson and the high-energy parameters of the soft SUSY-breaking scenarios. In regions of the parameter space where the LHC can detect the heavy Higgs bosons, precision measurements of the properties of the light Higgs boson at the linear collider can provide valuable information for distinguishing between the mSUGRA, mGMSB and mAMSB scenarios.
hep-ph↗
The MSSM in the Light of Precision Data
The potential of present and anticipated future electroweak precision data, including the Higgs boson and top quark masses, for testing quantum effects of the electroweak theory is investigated in the context of the Minimal Supersymmetric Standard Model (MSSM). The present status of the theoretical predictions is analyzed. The impact of the parametric uncertainties from the experimental errors of the input parameters is studied, and an estimate for the remaining uncertainties from unknown higher-order corrections is given both in the Standard Model (SM) and the MSSM. Examples of electroweak precision tests in the mSUGRA scenario and the unconstrained MSSM are analyzed, and the status of the global fit to all data is discussed.
hep-ph↗
Complete fermionic two-loop results for the M_W-M_Z interdependence
The complete fermionic two-loop contributions to the prediction for the W-boson mass from muon decay in the electroweak Standard Model are evaluated exactly, i.e. no expansion in the top-quark and the Higgs-boson mass is made. The result for the W-boson mass is compared with the previous result of an expansion up to next-to-leading order in the top-quark mass. The predictions are found to agree with each other within about 5 MeV. A simple parameterization of the new result is presented, approximating the full result better than 0.4 MeV for M_H < 1 TeV.
hep-ph↗
Electroweak two-loop corrections to the MW-MZ mass correlation in the Standard Model
Recently exact results for the complete fermionic two-loop contributions to the prediction for the W-boson mass from muon decay in the electroweak Standard Model have been published [hep-ph/0007091]. This paper illustrates the techniques that have been applied for this calculation, in particular the renormalisation procedure and the treatment of IR-divergent QED contributions. Numerical results are presented in terms of simple parametrisation formulae and compared in detail with a previous result of an expansion up to next-to-leading order in the top-quark mass. An estimate of the remaining theoretical uncertainties of the MW-prediction from unknown higher-order corrections is given. For the bosonic two-loop corrections a partial result is presented, yielding the Higgs-mass dependence of these contributions.
hep-ph↗