arXiv subjects

C. Balazs

Publications and source records attributed to C. Balazs.

At least 55 records · Page 3Linked to original sources

arXiv2003

Where is the Higgs boson?

Electroweak precision measurements indicate that the standard model Higgs boson is light and that it could have already been discovered at LEP 2, or might be found at the Tevatron Run 2. In the context of a TeV^-1 size extra dimensional model, we argue that the Higgs boson production rates at LEP and the Tevatron are suppressed, while they might be enhanced at the LHC or at CLIC. This is due to the possible mixing between brane and bulk components of the Higgs boson, that is, the non-trivial brane-bulk `location' of the lightest Higgs. To parametrize this mixing, we consider two Higgs doublets, one confined to the usual space dimensions and the other propagating in the bulk. Calculating the production and decay rates for the lightest Higgs boson, we find that compared to the standard model (SM), the cross section receives a suppression well below but an enhancement close to and above the compactification scale M_c. This impacts the discovery of the lightest (SM like) Higgs boson at colliders. To find a Higgs signal in this model at the Tevatron Run 2 or at the LC with sqrt(s)=1.5 TeV, a higher luminosity would be required than in the SM case. Meanwhile, at the LHC or at CLIC with sqrt(s) ~ 3-5 TeV one might find highly enhanced production rates. This will enable the latter experiments to distinguish between the extra dimensional and the SM for M_c up to about 6 TeV.

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arXiv2003

Yukawa Coupling Unification in Supersymmetric Models

We present an updated assessment of the viability of t-b-tau Yukawa coupling unification in supersymmetric models. For the superpotential Higgs mass parameter mu>0, we find unification to less than 1% is possible, but only for GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m_{H_u}^2 s gamma and (g-2)_mu constraints, there exists tension with the dark matter relic density unless m_{16}<3 TeV. These models offer prospects for a SUSY discovery at the Fermilab Tevatron collider via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino pair production. If mu<0, Yukawa coupling unification to less than 5% can occur for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified models with b->s gamma, (g-2)_mu, and relic density all imply very large values of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection of sparticles may be a challenge even at the LHC.

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arXiv2002

Updated Constraints on the Minimal Supergravity Model

Recently, refinements have been made on both the theoretical and experimental determinations of the i.) mass of the lightest Higgs scalar (m_h), ii.) relic density of cold dark matter in the universe (Omega_CDM h^2), iii.) branching fraction for radiative B decay BF(b \to s γ), iv.) muon anomalous magnetic moment (a_μ), and v.) flavor violating decay B_s \to μ^+μ^-. Each of these quantities can be predicted in the MSSM, and each depends in a non-trivial way on the spectra of SUSY particles. In this paper, we present updated constraints from each of these quantities on the minimal supergravity (mSUGRA) model as embedded in the computer program ISAJET. The combination of constraints points to certain favored regions of model parameter space where collider and non-accelerator SUSY searches may be more focussed.

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arXiv2002

Viable models with non-universal gaugino mediated supersymmetry breaking

Recently, extra dimensional SUSY GUT models have been proposed in which compactification of the extra dimension(s) leads to a breakdown of the gauge symmetry and/or supersymmetry. We examine a particular class of higher-dimensional models exhibiting supersymmetry and SU(5) or SO(10) GUT symmetry. SUSY breaking occurs on a hidden brane, and is communicated to the visible brane via gaugino mediation. Non-universal gaugino masses are developed at the compactification scale as a consequence of a restricted gauge symmetry on the hidden brane. In this case, the compactification scale is at or slightly below the GUT scale. We examine the parameter space of such models where gaugino masses are related due to a Pati-Salam symmetry on the hidden brane. We find limited but significant regions of model parameter space where a viable spectra of SUSY matter is generated. Our results are extended to the more general case of three independent gaugino masses; here we find that large parameter space regions open up for large values of the U(1) gaugino mass M_1. We also find the relic density of neutralinos for these models to be generally below expectations from cosmological observations, thus leaving room for hidden sector states to make up the bulk of cold dark matter. Finally, we evaluate the branching fraction BF(b -> s gamma) and muon anomalous magnetic moment a_μ.

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arXiv2002

The QCD/SM Working Group: Summary Report

This Report documents the results obtained by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of uncertainties in Parton Distribution Functions is reviewed. Progresses in the description of multiparton final states at Next-to-Leading Order and the extension of calculations for precision QCD observables beyond this order are summarized. Various issues concerning the relevance of resummation for observables at TeV colliders is examined. Improvements to algorithms of jet reconstruction are discussed and predictions for diphoton and photon pi-zero production at the LHC are made for kinematic variables of interest regarding searches for a Higgs boson decaying into two photons. Finally, several improvements implemented in Monte-Carlo event generators are documented.

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arXiv2002

Summary: Working Group on QCD and Strong Interactions

In this summary of the considerations of the QCD working group at Snowmass 2001, the roles of quantum chromodynamics in the Standard Model and in the search for new physics are reviewed, with empahsis on frontier areas in the field. We discuss the importance of, and prospects for, precision QCD in perturbative and lattice calculations. We describe new ideas in the analysis of parton distribution functions and jet structure, and review progress in small-$x$ and in polarization.

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arXiv2001

Probing TeV-scale gauge unification by hadronic collisions

Grand unified theories (GUTs) and extra dimensions are potential ingredients of the new physics that may resolve various outstanding problems of the Standard Model. If the inverse size of (one of) the extra dimension(s) is smaller than the GUT scale and standard gauge bosons are allowed to propagate in the bulk then, among other consequences, the evolution of the gauge couplings deviates from the usual logarithmic running somewhat below and between these two scales. In this work, we show that if the compactification scale is the order of 10 TeV, then this modified running may be observable at the CERN Large Hadron Collider in the dijet invariant mass distribution. We also demonstrate that dijets are highly sensitive to the renormalization effects of the extra dimensions, and are potential tools for determining the number of dimensions and the value of the compactification scale.

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arXiv2000

Report of the QCD Tools Working Group

We report on the activities of the ``QCD Tools for heavy flavors and new physics searches'' working group of the Run II Workshop on QCD and Weak Bosons. The contributions cover the topics of improved parton showering and comparisons of Monte Carlo programs and resummation calculations, recent developments in Pythia, the methodology of measuring backgrounds to new physics searches, variable flavor number schemes for heavy quark electro-production, the underlying event in hard scattering processes, and the Monte Carlo MCFM for NLO processes.

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arXiv2000

Higgs Production: A Comparison of Parton Showers and Resummation

The search for the Higgs boson(s) is one of the major priorities at the upgraded Fermilab Tevatron and at the CERN Large Hadron Collider (LHC). Monte Carlo event generators (MCs) are heavily utilized to extract and interpret the Higgs signal, which depends on the details of the multiple soft-gluon emission from the initial state partons in hadronic collisions. Thus, it is crucial to establish the reliability of the MCs used by the experimentalists. In this paper, the MC based parton shower formalism is compared to that of an analytic resummation calculation. Theoretical input, predictions and, where they exist, data for the transverse momentum distribution of Higgs bosons, $Z^0$ bosons, and photon pairs are compared for the Tevatron and the LHC. This comparison is useful in understanding the strengths and the weaknesses of the different theoretical approaches, and in testing their reliability.

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arXiv2000

Higgs Transverse Momentum at the LHC

Resummed QCD corrections to the transverse momentum ($Q_T$) distribution of the Standard Model Higgs boson, produced at the CERN Large Hadron Collider, are presented. The small $Q_T$ factorization formalism is reviewed, which is used to extend the standard hadronic factorization theorem to the low $Q_T$ region, with emphasis on the matching to the standard hadronic factorization. Comparison of the $Q_T$ predictions from the extended factorization and the parton shower method is performed.

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arXiv2000

The QCD and Standard Model Working Group: Summary Report from Les Houches

The Les Houches Workshop on Physics at TeV Colliders took place from June 8-18, 1999. One of the three working groups at Les Houches concentrated on QCD issues, both at the Tevatron Collider and at the LHC. Besides the interest in QCD in its own right, QCD dynamics plays an important role in the production mechanisms for any new physics process that might be observed at either collider, as well as any processes that may form backgrounds to the new physics. This writeup serves both as a pedagogical overview of QCD as well as an update on the current status of the field.

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arXiv2000

QCD

We discuss issues of QCD at the LHC including parton distributions, Monte Carlo event generators, the available next-to-leading order calculations, resummation, photon production, small x physics, double parton scattering, and backgrounds to Higgs production.

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arXiv2000

Diphoton Background to Higgs Boson Production at the LHC with Soft Gluon Effects

The detection and the measurement of the production cross section of a light Higgs boson at the CERN Large Hadron Collider demand the accurate prediction of the background distributions of photon pairs. To improve this theoretical prediction, we present the soft-gluon resummed calculation of the $p p \to γγX$ cross section, including the exact one loop $g g \to γγg$ contribution. By incorporating the known fixed order results and the leading terms in the higher order corrections, the resummed cross section provides a reliable prediction for the inclusive diphoton invariant mass and transverse momentum distributions. Given our results, we propose the search for the Higgs boson in the inclusive diphoton mode with a cut on the transverse momentum of the photon pair, without the requirement of an additional tagged jet.

hep-ph↗

arXiv2000

The Higgs Working Group: Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

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arXiv2000

Higgs Boson Production at the LHC with Soft Gluon Effects

We present results of QCD corrections to Higgs boson production at the CERN Large Hadron Collider. Potentially large logarithmic contributions from multiple soft-gluon emission are summed up to all order in the strong coupling. Various kinematical distributions, including the Higgs transverse momentum, are predicted with O(alpha_s^3) precision. Comparison is made to outputs of the popular Monte Carlo event generator PYTHIA.

hep-ph↗

arXiv1999

Soft Gluon Effects on Electroweak Boson Production in Hadron Collisions

Shortened table of contents: 1. Introduction 1.1 The Standard Model of Elementary Particles 1.2 The Quantum Nature of Gauge Fields 2. Soft Gluon Resummation 2.1 Lepton Pair Production at Fixed Order in $α_s$ 2.2 The Resummation Formalism 3. Vector Boson Production and Decay in Hadron Collisions 3.1 Vector Boson Distributions 3.2 Lepton Distributions 4. Photon Pair Production In Hadronic Interactions 4.1 Diphoton Production at Fixed Order 4.2 Extension of the Resummation Formalism 5. Gauge Boson Pair Production at the Upgraded Tevatron and at the LHC 5.1 Introduction 5.2 Analytical Results 6. Charged Scalar Production at Hadron Colliders 6.1 Introduction 6.2 Charged (Pseudo-)Scalar Production via Charm-Bottom Fusion 6.3 Soft Gluon Resummation 6.4 Hadronic Decays of Charged (Pseudo-)Scalars to $O(α_s)$ 6.5 Neutral (Pseudo-)Scalar Production via $b \bar b$ Fusion A. Probing Higgs Bosons with Large Bottom Yukawa Coupling at Hadron Colliders B. ``Intrinsic $k_T$'' and Soft Gluon Resummation

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arXiv1999

Collider Tests of Compact Space Dimensions Using Weak Gauge Bosons

We present collider tests of the recent proposal for weak-scale quantum gravity due to new large compact space dimensions in which only the graviton ($\G$) propagates. We show that the existing high precision LEP-I $Z$-pole data can impose non-trivial constraints on the scale of the new dimensions, via the decay mode $Z\to f\bar{f}+\G$ ($f=q,\ell$). These bounds are comparable to those obtained at high energy colliders and provide the first sensitive probe of the scalar graviton. We also study $W(Z)+\G$ production and the anomalous $WW(ZZ)$ signal from virtual $\G$-states at the Fermilab Tevatron, and compare them with the LEP-I bound and those from LEP-II and future linear colliders.

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arXiv1998

Probing Higgs Bosons with Large Bottom Yukawa Coupling at Hadron Colliders

The small mass of the bottom quark, relative to its weak isospin partner, the top quark, makes the bottom an effective probe of new physics in Higgs and top sectors. We study the Higgs boson production associated with bottom quarks, ppbar/pp to phi+b+bbar to 4b, at the Fermilab Tevatron and the CERN LHC. We find that strong and model-independent constraints on the size of the phi-b-bbar coupling can be obtained for a wide range of Higgs boson masses. Their implications for the composite Higgs models with strong dynamics associated with the third family quarks (such as the top-condensate/topcolor models with naturally large bottom Yukawa couplings), and for the supersymmetric models with large tan(beta), are analyzed. We conclude that the Tevatron and the LHC can put stringent bounds on these models, if the phi+b+bbar signal is not found.

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