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T. Han

Publications and source records attributed to T. Han.

At least 91 records · Page 5Linked to original sources
arXiv1996

Particle Physics Opportunities at $μ^+μ^-$ Colliders

We discuss the capabilities of future muon colliders to resolve important particle physics questions. A collider with c.m. energy $\sqrt s = 100$ to 500~GeV offers the unique opportunity to produce Higgs bosons in the $s$-channel and thereby measure the Higgs masses, total widths and several partial widths to high precision. At this same machine, $t\bar t$ and $W^+W^-$ threshold studies would yield superior precision in the determination of $m_t$ and $m_W$. A multi-TeV $μ^+μ^-$ collider would open up the realm of physics above the 1 TeV scale, allowing, for example, copious production of supersymmetric particles up to the highest anticipated masses or a detailed study of the strongly-interacting scenario of electroweak symmetry breaking.

hep-ph↗
arXiv1996

Top-Quark Decay Via the Anomalous Coupling $\bar t c γ$ at Hadron Colliders

We determine the constraints on the anomalous top-quark coupling associated with the flavor-changing neutral current vertex $\bar t c γ$ from the limits on the $b$-quark rare decay $b\rightarrow s γ$ and non-standard top-quark decays. Based on these constraints, we discuss the experimental observability of the rare decay mode $t \rightarrow c γ$, both at the Fermilab Tevatron with a luminosity-upgrade and at the LHC.

hep-ph↗
arXiv1996

Higgs Boson Physics in the $s$-channel at $μ^+μ^-$ Colliders

Techniques and strategies for discovering and measuring the properties of Higgs bosons via $s$-channel production at a $μ^+μ^-$ collider, and the associated requirements for the machine and detector, are discussed in detail. The unique feature of $s$-channel production is that, with good energy resolution, the mass, total width and partial widths of a Higgs boson can be directly measured with remarkable accuracy in most cases. For the expected machine parameters and luminosity the Standard Model (SM) Higgs boson $\hsm$, with mass $\lsim 2\mw$, the light $\hl$ of the minimal supersymmetric Standard Model (MSSM), and the heavier MSSM Higgs bosons (the CP-odd $\ha$ and the CP-even $\hh$) can all be studied in the $s$-channel, with the heavier states accessible up to the maximal $\sqrt s$ over a large fraction of the MSSM parameter space. In addition, it may be possible to discover the $\ha$ and $\hh$ by running the collider at full energy and observing excess events in the bremsstrahlung tail at lower energy. The integrated luminosity, beam resolution and machine/detector features required to distinguish between the $\hsm$ and $\hl$ are delineated.

hep-ph↗
arXiv1996

Higgs Boson And $W_L W_L$ Scattering At $e^-e^-$ Colliders

We discuss the Standard-Model Higgs boson production in the channels $e^-e^-\to e^-e^- H$, $e^-νW^- H$, and $e^-e^- ZH We also illustrate the enhancements in the $W^-W^-$ cross section that would result from a strongly-interacting Higgs sector or from a $H^{--}$ resonance in a doublet + triplet scalar field model.

hep-ph↗
arXiv1995

Study of Anomalous Couplings at a $500$~GeV $e^+e^-$ Linear Collider with Polarized Beams

We consider the possibility of observing deviations from the Standard Model gauge-boson self-couplings at a future $500$~GeV $e^+ e^-$ linear collider. We concentrate on the case in which the electroweak symmetry breaking sector is strongly interacting and there are no new resonances within reach of the collider. We find a sensitivity to the anomalous couplings that is two orders of magnitude higher than that achievable at LEP II. We also show how a polarized electron beam extends the reach of the collider, allowing experiments to probe different directions in parameter space.

hep-ph↗
arXiv1995

QCD Corrections and Non-standard Three Vector Boson Couplings in $W^+W^-$ Production at Hadron Colliders

The process $p\,p\hskip-7pt\hbox{$^{^{(\!-\!)}}$} \rightarrow W^{+} W^{-} + X \rightarrow \ell^+_1 ν_1 \ell^-_2 \bar ν_2 + X$ is calculated to ${\cal O}(α_s)$ for general $C$ and $P$ conserving $WWV$ couplings ($V=γ,\, Z$). The prospects for probing the $WWV$ couplings in this reaction are explored. The impact of ${\cal O}(α_s)$ QCD corrections and various background processes on the observability of non-standard $WWV$ couplings in $W^+ W^-$ production at the Tevatron and the Large Hadron Collider (LHC) is discussed in detail. Sensitivity limits for anomalous $WWV$ couplings are derived at next-to-leading order for the Tevatron and LHC center of mass energies, and are compared to the bounds which can be achieved in other processes. Unless a jet veto or a cut on the total transverse momentum of the hadrons in the event is imposed, the ${\cal O}(α_s)$ QCD corrections and the background from top quark production decrease the sensitivity of $p\,p\hskip-7pt\hbox{$^{^{(\!-\!)}}$} \rightarrow W^{+} W^{-} + X \rightarrow \ell^+_1 ν_1 \ell^-_2 \bar ν_2 + X$ to anomalous $WWV$ couplings by a factor two to five.

hep-ph↗
arXiv1995

LHC Analysis of the Strongly Interacting $WW$ System: Gold-Plated Modes

We study the gold-plated purely leptonic signal and background rates at the LHC for the $ZZ,$ $W^{+}W^-,$ $W^\pm Z$ and $W^\pm W^\pm$ final states associated with strongly interacting electroweak symmetry breaking. We work at an energy of $\sqrt s = 14$ TeV, and develop a combination of back-to-back leptonic, central-jet-vetoing and forwaring cuts that suppresses the Standard-Model backgrounds. We find that the LHC with an annual luminosity of 100 fb$^{-1}$ will achieve a reasonably good sensitivity to the physics of strongly interacting electroweak symmetry breaking.

hep-ph↗
arXiv1995

Top-Quark Decay Via Flavor-Changing Neutral Currents at Hadron Colliders

We study low energy experimental constraints on an anomalous top-quark coupling associated with the flavor-changing neutral current vertex $Z \bar t c$. In view of these constraints, we discuss the experimental observability of the induced rare decay mode $t \rightarrow Zc$, both at the Fermilab Tevatron (with the Main Injector or a luminosity-upgrade) and at the LHC.

hep-ph↗
arXiv1995

$s$-Channel Higgs Boson Production at a Muon-Muon Collider

High luminosity muon-muon colliders would provide a powerful new probe of Higgs boson physics through $s$-channel resonance production. We discuss the prospects for detection of Higgs bosons and precision measurements of their masses and widths at such a machine.

hep-ph↗
arXiv1995

ANOMALOUS GAUGE BOSON INTERACTIONS

We discuss the direct measurement of the trilinear vector boson couplings in present and future collider experiments. The major goals of such experiments will be the confirmation of the Standard Model (SM) predictions and the search for signals of new physics. We review our current theoretical understanding of anomalous trilinear gauge boson self-interactions. If the energy scale of the new physics is $\sim 1$ TeV, these low energy anomalous couplings are expected to be no larger than ${\cal O}(10^{-2})$. Constraints from high precision measurements at LEP and low energy charged and neutral current processes are critically reviewed.

hep-ph↗
arXiv1995

Physics Goals of a $μ^+μ^-$ Collider

This working group report focuses on the physics potential of $μ^+μ^-$ colliders beyond what can be accomplished at linear $e^+e^-$ colliders and the LHC. Particularly interesting possibilities include (i)~$s$-channel resonance production to discover and study heavy Higgs bosons with $ZZ$ and $WW$ couplings that are suppressed or absent at tree-level (such as the $H$ and $A$ Higgs bosons of supersymmetric models), (ii)~study of the strongly interacting electroweak sector, where higher energies give larger signals, and (iii)~measurements of the masses and properties of heavy supersymmetric particles.

hep-ph↗
arXiv1995

Probing Strongly-interacting Electroweak Dynamics through $W^+W^-/ZZ$ Ratios at Future $e^+e^-$ Colliders

We point out that the ratio of $W^+ W^- \to W^+ W^-$ and $W^+W^- \to ZZ$ cross sections is a sensitive probe of the dynamics of electroweak symmetry breaking, in the CM energy region $\sqrt {s_{\rm ww}^{}} \agt 1$~TeV where vector boson scattering may well become strong. We suggest ways in which this ratio can be extracted at a 1.5 TeV $e^+e^-$ linear collider, using $W^\pm,Z \to jj$ hadronic decays and relying on dijet mass resolution to provide statistical discrimination between $W^\pm$ and $Z$. $WW$ fusion processes studied here are unique for exploring scalar resonances of mass about 1 TeV and are complementary to studies via the direct channel $e^+ e^- \rightarrow W^+W^-$ for the vector and non-resonant cases. With an integrated luminosity of 200 fb$^{-1}$, the signals obtained are statistically significant. Comparison with a study of $e^-e^- \rightarrow ννW^-W^-$ process is made. Enhancements of the signal rate from using a polarized electron beam, or at a 2 TeV $e^+e^-$ linear collider and possible higher energy $μ^+μ^-$ colliders, are also presented.

hep-ph↗
arXiv1994

$WZ$ Production at Hadron Colliders: Effects of Non-Standard $WWZ$ Couplings and QCD Corrections

The process $p\,\pbar \rightarrow W^{\pm}Z + X \rightarrow \ell^\pm_1 ν_1 \ell_2^+ \ell_2^- + X$ is calculated to ${\cal O}(α_s)$ for general $C$ and $P$ conserving $WWZ$ couplings. At the Tevatron center of mass energy, the QCD corrections to $WZ$ production are modest. At Large Hadron Collider (LHC) energies, the inclusive QCD corrections are large, but can be reduced significantly if a jet veto is imposed. Sensitivity limits for the anomalous $WWZ$ couplings are derived from the next-to-leading order $Z$ boson transverse momentum distribution for Tevatron and LHC energies. Unless a jet veto is imposed, next-to-leading order QCD corrections decrease the sensitivity to anomalous $WWZ$ couplings considerably at LHC energies, but have little influence at the Tevatron. We also study, at next-to-leading order, rapidity correlations between the $W$ and $Z$ decay products, and the $ZZ/WZ$ and $WZ/Wγ$ cross section ratios. These quantities are found to be useful tools in searching for the approximate zero present in the Standard Model $WZ$ helicity amplitudes. The prospects for observing the approximate amplitude zero at the Tevatron and the LHC are critically assessed.

hep-ph↗
arXiv1994

Production of Weak Bosons and Higgs Bosons at e-e- Colliders

We present calculations of cross sections for single $W^-$ and $Z$ production and $W^-W^-, W^-Z, W^-γ, ZZ$, and $W^+W^-$ pair production within the Standard Model at $e^-e^-$ linear colliders. We evaluate Standard-Model Higgs boson production in the channels $e^-e^- \to e^-e^- H$, $e^-νW^- H$, and $e^-e^- ZH$. We also illustrate the enhancements in the $W^-W^-$ cross section that would result from a strongly-interacting Higgs sector or from a $H^{--}$ resonance in a Higgs doublet + triplet model.

hep-ph↗
arXiv1994

Standard Model Higgs Physics at a 4 TeV Upgraded Tevatron

We compute an array of Standard Model Higgs boson ($\hsm$) signals and backgrounds for a possible upgrade of the Tevatron to $E_{\rm cm}=4\tev$. Taking $\mt\geq 140\gev$, and assuming a total accumulated luminosity of $L=30\fbi$, we find that a Standard Model Higgs boson with $\mhsm\lsim 110\gev$ could almost certainly be detected using the $\wpm\hsm\rta lνb\anti b$ mode. A Higgs boson with mass between $\sim 120\gev$ and $\sim 140\gev$ or above $\sim 230-250\gev$ almost certainly would not be seen. A Higgs boson with $\mhsm\sim 150\gev$ or $200\lsim\mhsm\lsim 230-250\gev$ has a decent chance of being detected in the $ZZ\rta 4l$ mode. There would also be some possibility of discovering the $\hsm$ in the $WW\rta lνjj$ mode for $150\lsim\mhsm\lsim 200\gev$. Finally, hints of an event excess in the $WW\rta ll νν$ mode due to the $\hsm$ might emerge for $140\lsim\mhsm\lsim 180\gev$. Given the difficult nature of the Higgs boson signals for $\mhsm$ values beyond the reach of LEP-200, and the discontinuous $\mhsm$ range that could potentially be probed, justification of an upgrade of the Tevatron to $4\tev$ on the basis of its potential for Standard Model Higgs boson discovery would seem inappropriate.

hep-ph↗
arXiv1994

Search for Anomalous Couplings at $eγ$ Colliders

We consider the possibility of observing deviations from the Standard Model gauge-boson self-couplings at future $eγ$ colliders. We concentrate on the process $e^-γ\rightarrow νW^- Z$, which is particularly sensitive to the parity violating coupling $g_5^Z$ at high energies. We find that a 2~TeV $e^+ e^-$ collider operating in the $e^- γ$ mode could reach a sensitivity of order $5\times 10^{-3}$ to $g_5^Z$.

hep-ph↗
arXiv1994

Amplitude Zeros in $W^\pm Z$ Production

We demonstrate that the Standard Model amplitude for $f_1 \bar f_2 \rightarrow W^\pm Z $ at the Born-level exhibits an approximate zero located at $\cosθ= (g^{f_1}_{-} + g^{f_2}_{-}) / (g^{f_1}_{-} - g^{f_2}_{-})$ at high energies, where the $g^{f_i}_{-}$ ($i=1,2$) are the left-handed couplings of the $Z$-boson to fermions and $θ$ is the center of mass scattering angle of the $W$-boson. The approximate zero is the combined result of an exact zero in the dominant helicity amplitudes ${\cal M}(\pm,\mp)$ and strong gauge cancelations in the remaining amplitudes. For non-standard $WWZ$ couplings these cancelations no longer occur and the approximate amplitude zero is eliminated.

hep-ph↗