arXiv subjects

T. Han

Publications and source records attributed to T. Han.

At least 37 records · Page 2Linked to original sources

arXiv2008

Flavour physics of leptons and dipole moments

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

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arXiv2007

Tevatron-for-LHC Report: Higgs

The search for Higgs bosons in both the standard model and its extensions is well under way at the Tevatron. As the integrated luminosity collected increases into the multiple inverse femptobarn range, these searches are becoming very interesting indeed. Meanwhile, the construction of the Large Hadron Collider (LHC) and its associated experiments at CERN are nearing completion. In this TeV4LHC workshop, it was realized that any experience at the Tevatron with respect to backgrounds, experimental techniques and theoretical calculations that can be verified at the Tevatron which have relevance for future measurements at the LHC were important. Studies and contributions to these efforts were made in three broad categories: theoretical calculations of Higgs production and decay mechanisms; theoretical calculations and discussions pertaining to non-standard model Higgs bosons; and experimental reviews, analyses and developments at both the Tevatron and the upcoming LHC experiments. All of these contributions represent real progress towards the elucidation of the mechanism of electroweak symmetry breaking.

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arXiv2006

CP Studies and Non-Standard Higgs Physics

There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. These non-standard Higgs scenarios have important implications for collider physics as well as for cosmology, and understanding their phenomenology is essential for a full comprehension of electroweak symmetry breaking. This report discusses the most relevant theories which go beyond the Standard Model and its minimal, CP-conserving supersymmetric extension: two-Higgs-doublet models and minimal supersymmetric models with CP violation, supersymmetric models with an extra singlet, models with extra gauge groups or Higgs triplets, Little Higgs models, models in extra dimensions, and models with technicolour or other new strong dynamics. For each of these scenarios, this report presents an introduction to the phenomenology, followed by contributions on more detailed theoretical aspects and studies of possible experimental signatures at the LHC and other colliders.

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arXiv2006

Toward High Precision Higgs-Boson Measurements at the International Linear e+e- Collider

This report reviews the properties of Higgs bosons in the Standard Model (SM) and its various extensions. We give an extensive overview about the potential of the ILC operated at centre-of-mass energies up to 1 TeV (including the gamma gamma option) for the determination of the Higgs boson properties. This comprises the measurement of the Higgs boson mass, its couplings to SM fermions and gauge bosons, and the determination of the spin and the CP quantum numbers of the Higgs. The extensions of the SM that are analyzed in more detail are heavy SM-like Higgs bosons, heavy Higgs bosons in the framework of Supersymmetry (SUSY) and further exotic scenarios. We review recent theoretical developments in the field of Higgs boson physics. The important question what the ILC can contribute to Higgs boson physics after the LHC, the LHC/ILC interplay and synergy is discussed. The impact of Higgs boson physics on cosmology in several SUSY frameworks is analyzed. The impact of the accelerator and dector performance on the precision of measurements are discussed in detail. We propose a strategy to optimize future analyses. Open questions arising for the various topics are listed, further topics of study and corresponding roadmaps are suggested.

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arXiv2005

Supersymmetry Parameter Analysis: SPA Convention and Project

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e+e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

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arXiv2004

Physics at the CLIC Multi-TeV Linear Collider

This report summarizes a study of the physics potential of the CLIC e+e- linear collider operating at centre-of-mass energies from 1 TeV to 5 TeV with luminosity of the order of 10^35 cm^-2 s^-1. First, the CLIC collider complex is surveyed, with emphasis on aspects related to its physics capabilities, particularly the luminosity and energy, and also possible polarization, γγand e-e- collisions. The next CLIC Test facility, CTF3, and its R&D programme are also reviewed. We then discuss aspects of experimentation at CLIC, including backgrounds and experimental conditions, and present a conceptual detector design used in the physics analyses, most of which use the nominal CLIC centre-of-mass energy of 3 TeV. CLIC contributions to Higgs physics could include completing the profile of a light Higgs boson by measuring rare decays and reconstructing the Higgs potential, or discovering one or more heavy Higgs bosons, or probing CP violation in the Higgs sector. Turning to physics beyond the Standard Model, CLIC might be able to complete the supersymmetric spectrum and make more precise measurements of sparticles detected previously at the LHC or a lower-energy linear e+e- collider: γγcollisions and polarization would be particularly useful for these tasks. CLIC would also have unique capabilities for probing other possible extensions of the Standard Model, such as theories with extra dimensions or new vector resonances, new contact interactions and models with strong WW scattering at high energies. In all the scenarios we have studied, CLIC would provide significant fundamental physics information beyond that available from the LHC and a lower-energy linear e+e- collider, as a result of its unique combination of high energy and experimental precision.

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arXiv2004

Physics Interplay of the LHC and the ILC

Physics at the Large Hadron Collider (LHC) and the International e+e- Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined.

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arXiv2004

Hadron Collider Signatures for New Interactions of Top and Bottom Quarks

One of the main goals for hadron colliders is the study of the properties of the third generation quarks. We study the signatures for new TeV resonances that couple to top or bottom quarks both at the Tevatron Run II and at the LHC. We find that in the simplest production processes of Drell-Yan type at the Tevatron, the signals are overwhelmed by QCD backgrounds. We also find that it is possible to study these resonances when they are produced in association with a pair of heavy quarks or in association with a single top at the LHC.In particular, with an integrated luminosity of 300 fb$^{-1}$ at the LHC, it is possible to probe resonance masses up to around 2 TeV.

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arXiv2004

Bounds on Four-Fermion Contact Interactions Induced by String Resonances

Based on tree-level open-string scattering amplitudes in the low string-scale scenario, we derive the massless fermion scattering amplitudes. The amplitudes are required to reproduce those of the Standard Model at tree level in the low energy limit. We then obtain four-fermion contact interactions by expanding in inverse powers of the string scale and explore the constraints on the string scale from low energy data. The Chan-Paton factors and the string scale are treated as free parameters. We find that data from the neutral and charged current processes at HERA, Drell-Yan process at the Tevatron, and from LEP-II put lower bounds on the string scale M_S >= 0.9-1.3 TeV for typical values of the Chan-Paton factors, which are comparable to Tevatron bounds on Z' and W' masses.

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arXiv2003

TeV resonances in top physics at the LHC

We consider the possibility of studying novel particles at the TeV scale with enhanced couplings to the top quark via top quark pair production at the LHC and VLHC. In particular we discuss the case of neutral scalar and vector resonances associated with a strongly interacting electroweak symmetry breaking sector. We constrain the couplings of these resonances by imposing appropriate partial wave unitarity conditions and known low energy constraints. We evaluate the new physics signals via WW -> tt~ for various models without making approximation for the initial state W bosons, and optimize the acceptance cuts for the signal observation. We conclude that QCD backgrounds overwhelm the signals in both the LHC and a 200 TeV VLHC, making it impossible to study this type of physics in the tt~ channel at those machines.

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arXiv2002

Determining $\tanβ$ with Neutral and Charged Higgs Bosons at a Future $e^+e^-$ Linear Collider

The ratio of neutral Higgs field vacuum expectation values, tan(beta), is one of the most important parameters to determine in either the Minimal Supersymmetric Standard Model (MSSM) or a general type-II Two-Higgs Doublet Model (2HDM). Assuming an energy and integrated luminosity of sqrts=500 GeV and L=2000 fb-1 at a future linear collider (LC), we show that a very accurate determination of tan(beta) will be possible for low and high tan(beta) values by measuring the production rates of Higgs bosons and reconstructing Higgs boson decays. In particular, based on a TESLA simulation, and assuming no other light Higgs bosons and 100<=mA<=200 GeV, we find that the rate for the process e+e- --> bbA --> bbbb provides a good determination of tan(beta) at high tan(beta). In the MSSM Higgs sector, in the sample case of mA = 200 GeV, we find that the rates for e+e- --> bbA+bbH --> bbbb and for e+e- --> HA --> bbbb provide a good determination of tan(beta) at high and low tan(beta), respectively. We also show that the direct measurement of the average total widths of the H and A in e+e- --> HA --> bbbb events provides an excellent determination of tan(beta) at large values. In addition, the charged Higgs boson process e+e- --> H+H- --> tbtb has been studied. The sensitivity to tan(beta) at the LHC obtained directly from heavy Higgs boson production is briefly compared to the LC results.

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arXiv2002

Overview of tan(beta) Determination at a Linear e+e- Collider

The ratio of the vacuum expectation value of the two Higgs doublets, tan(beta), is an important parameter of the general 2-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric extension of the Standard Model (MSSM). The expected uncertainty on the determination of tan(beta) at a Linear Collider (LC) of at least 500 GeV center-of-mass energy and high luminosity is reviewed based on studies of neutral and charged Higgs boson production.

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arXiv2002

Testing radiative neutrino mass generation via R-parity violation at the Tevatron

An R-parity violating SUSY model with lepton-number violating couplings $λ'_{i33}$, i=2,3 can generate a neutrino mass spectrum that explains the recent results from neutrino oscillation experiments. These R-parity violating couplings lead to a clean signal with at least one isolated lepton and at least three tagged $b$ jets that is accessible in chargino and neutralino production at the Tevatron collider. This signature can be probed at $3 σ$ up to $m_{1/2} = 230$ GeV (320 GeV) with an integrated luminosity of $2 fb^{-1}$ ($30 fb^{-1}$).

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arXiv2002

The Snowmass Points and Slopes: Benchmarks for SUSY Searches

The ``Snowmass Points and Slopes'' (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ``Snowmass Workshop on the Future of Particle Physics'' as a consensus based on different existing proposals.

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arXiv2002

Physics at Future Hadron Colliders

We discuss the physics opportunities and detector challenges at future hadron colliders. As guidelines for energies and luminosities we use the proposed luminosity and/or energy upgrade of the LHC (SLHC), and the Fermilab design of a Very Large Hadron Collider (VLHC). We illustrate the physics capabilities of future hadron colliders for a variety of new physics scenarios (supersymmetry, strong electroweak symmetry breaking, new gauge bosons, compositeness and extra dimensions). We also investigate the prospects of doing precision Higgs physics studies at such a machine, and list selected Standard Model physics rates.

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arXiv2002

Determination of $\tanβ$ at a Future $e^+e^-$ Linear Collider

It is widely stated that the ratio of neutral Higgs field vacuum expectation values, $\tanb$, is one of the most difficult parameters to determine in either the Minimal Supersymmetric Standard Model (MSSM) or a general type-II Two-Higgs Doublet Model (2HDM). Assuming an energy and integrated luminosity of $\rts=500\gev$ and $\call=2000\fbi$, we show that a very accurate determination of $\tanb$ will often be possible using Higgs production rates and/or Higgs decays. Based on a TESLA simulation, and assuming no other light Higgs bosons and $100\leq m_A \leq 200\gev$, we find that the rate for the process $\epem\to b\anti b A \to b\anti b b\anti b$ provides an excellent determination of $\tanb$ at high $\tanb$. In the MSSM Higgs sector, the rate for $\epem\to b\anti b A+ b\anti b H \to b\anti b b\anti b$ ($\epem\to HA \to b\anti b b\anti b$) provides a good determination of $\tanb$ at high (low) $\tanb$, respectively, at moderate $m_A$ values. We also show that direct measurement of the average total width of the $H$ and $A$ in $\epem\to HA \to b\anti b b\anti b$ events provides an excellent determination of $\tanb$ at large $\tanb$.

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arXiv2001

Phenomenology of High Energy Neutrinos in Low-Scale Quantum Gravity Models

We show that neutrino telescopes, optimized for detecting neutrinos of TeV to PeV energy, can reveal threshold effects associated with TeV-scale gravity. The signature is an increase with energy of the cross section beyond what is predicted by the Standard Model. The advantage of the method is that the neutrino cross section is measured in an energy region where i) the models are characteristically distinguishable and ii) the Standard Model neutrino cross section can be reliably calculated so that any deviation can be conclusively identified.

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arXiv2001

Physics of Higgs Factories

We outline the unique role of a muon collider as a Higgs factory for Higgs boson resonance production in the $s$-channel. Physics examples include: the precision measurements of the Higgs mass and total width, and the resulting ability to discriminate between the SM-like Higgs bosons of different models such as between a light SM Higgs boson and the light Higgs boson of the MSSM; the determination of the spin and coupling via the $h\to \tautau$ decay mode; differentiation of two nearly degenerate heavy Higgs bosons by an energy scan; and the ability to explore a general extended Higgs sector, possibly with CP-violating couplings. The muon collider Higgs factory could perform measurements that would be highly complementary to Higgs studies at the LHC and LC; it would be likely to play a very crucial role in fully understanding the Higgs sector.

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