arXiv subjects

Kingman Cheung

Publications and source records attributed to Kingman Cheung.

262 records · Page 15Linked to original sources

arXiv1993

Perturbative QCD Fragmentation Functions for $B_c$ and $B_c^*$ Production

The dominant production mechanism for ${\bar b} c$ bound states in high energy processes is the production of a high energy ${\bar b}$ or $c$ quark, followed by its fragmentation into the ${\bar b} c$ state. We calculate the fragmentation functions for the production of the S-wave states $B_c$ and $B_c^*$ to leading order in the QCD coupling constant. The fragmentation probabilities for ${\bar b} \rightarrow B_c$ and ${\bar b} \rightarrow B_c^*$ are approximately $2.2 \times 10^{-4}$ and $3.1 \times 10^{-4}$, while those for $c \rightarrow B_c$ and $c \rightarrow B_c^*$ are smaller by almost two orders of magnitude.

hep-ph↗

arXiv1993

Detecting an Intermediate Mass Charged Higgs at $γγ$ Colliders

The detection of an intermediate mass charged Higgs boson at $\gamgam$ colliders via the modes $\gamgam \to H^+ H^- \to ντ^+ \barν τ^-,~ c \bar{s} \bar{c} s,~$ and $ ντ^+ \bar{c}s + c \bar{s} \barν τ^-$ is considered. $W^+ W^-$ boson pair production is the dominant background for these modes. The three modes may be used in a complementary fashion to detect a charged Higgs boson. The mixed leptonic-hadronic mode may be used to determine the charged Higgs mass by reconstructing the invariant hadronic mass. The sensitivity of Br$(H^+ \rightarrow c\bar s,\,ντ^+)$ on the discovery limit of the charged Higgs boson is also discussed.

hep-ph↗

arXiv1993

Search for the intermediate Mass Higgs Signal at TeV $eγ$ colliders

The intermediate mass Higgs (IMH) can be abundantly produced through the process $e^-γ\rightarrow W^-Hν$ at TeV $e^-γ$ colliders, which are realized by the laser back-scattering method. We search for the signature of $W^-H \rightarrow (jj)(b\bar b)$ plus missing transverse momentum, with and without considering the $b$-tagging. We also analyse all the potential backgrounds from $e^-γ\rightarrow W^-Zν,\,W^-W^+e^-,\,ZZe^-,\, \bar t bν$ and $t\bar t e^-$. With our selective acceptance cuts these backgrounds are reduced to a manageable level. We find that for the entire intermediate mass range 60 -- 150~GeV the Higgs discovery should be viable. We also present detail formulas for the helicity amplitudes of these processes.

hep-ph↗

arXiv1993

Z^0 Decay into Charmonium via Charm Quark Fragmentation

In decays of the $Z^0$, the dominant mechanism for the direct production of charmonium states is the decay of the $Z^0$ into a charm quark or antiquark followed by its fragmentation into the charmonium state. We calculate the fragmentation functions describing the splitting of charm quarks into S-wave charmonium states to leading order in the QCD coupling constant. Leading logarithms of $M_Z/m_c$ are summed up using Altarelli-Parisi evolution equations. Our analytic result agrees with the complete leading order calculation of the rate for $Z^0 \rightarrow ψc {\bar c}$. We also use our fragmentation functions to calculate the production rate of heavy quarkonium states in $W^\pm$, top quark, and Higgs decays.

hep-ph↗

arXiv1993

$WZ$, $Wγ$, $WW$ and $ZZ$ pair productions at TeV $eγ$ colliders

We calculate the gauge-boson pairs $W^-Z$, $W^-γ$, $W^+W^-$, $ZZ$ productions in the $e^- γ$ collisions, where the photon beam is realized by the laser back-scattering method. These processes are important tests for the non-abelian gauge sector of the standard model (SM). Precise calculations of these processes can therefore probe the anomalous gauge-boson interactions. Besides, these processes are important potential backgrounds for the intermediate mass Higgs (IMH) search in the $eγ\rightarrow WHν$ production.

hep-ph↗

arXiv1993

Detection of the heavy Higgs boson at $γγ$ colliders

We consider the possibility of detecting a heavy Higgs boson ($m_H>2m_Z$) in proposed $γγ$ colliders through the semi-leptonic mode $γγ\rightarrow H \rightarrow ZZ \rightarrow q\bar q \ell^+\ell^-$. We show that due to the non-monochromatic nature of the photon beams produced by the laser-backscattering method, the resultant cross section for Higgs production is much smaller than the on-resonance cross section and generally {\it decreases} with increasing collider energy. Although continuum $ZZ$ production is expected to be negligible, we demonstrate the presence of and calculate sizeable backgrounds from $γγ\rightarrow \ell^+\ell^-Z,\,q\bar qZ$, with $Z\rightarrow q\bar q,\,\ell^+\ell^-$, respectively, and $γγ\rightarrow t\bar t\rightarrow b\bar b\ell^+\ell^-ν\barν$. This channel may be used to detect a Higgs of mass $m_H$ up to around 350~GeV at a 0.5~TeV $e^+e^-$ collider, assuming a nominal yearly luminosity of 10--20~fb$^{-1}$.

hep-ph↗

arXiv1992

Associated production of Intermediate Higgs or Z-boson with $t \bar t$ pair in $γγ$ collision

Photon-photon linear colliders can be realized by laser back-scattering technique on the next generation linear $e^+e^-$ colliders. Here the associated productions of an intermediate mass Higgs (IMH) or Z-boson with $t \bar t$ pair in $γγ$ collisions are studied. Since IMH is very unlikely to decay into $t\bar t$ pair, $t\bar tH$ production is the only direct channel to probe the Higgs-top Yukawa coupling in case of an IMH. $t\bar tZ$ production can be a potential background to $t\bar tH$ if the Higgs mass is close to $m_Z$. As an alternative to its parent $e^+e^-$ collider, $γγ\to t\bar tH(Z)$ productions are compared with the corresponding productions in the $e^+e^-$ collisions.

hep-ph↗

arXiv1992

Collider discovery limits for supersymmetric Higgs bosons

The prospects for discovery of the five Higgs bosons of the minimal supersymmetric standard model are assessed for existing and planned future colliders, including LEP\,I, LEP\,II, LHC and SSC. As a benchmark for comparisons, we take a top-quark mass $m_t= 150\,$GeV and squark mass parameter $\tilde m= 1\,$TeV in evaluating one-loop radiative corrections; some results for other $m_t$ values are also given. Searches based on the most promising production and decay channels are taken into account. For large regions in parameter space, detectable signals are predicted for one or more of the Higgs bosons, but there remains a region for which no signals would be visible at the above colliders.

hep-ph↗

arXiv1992

What $e^+e^-$ collider could make a ``no-lose'' search for MSSM Higgs bosons?

The lightest CP-even Higgs boson $h$ in the minimum supersymmetric standard model (MSSM) has a mass upper bound depending on the top quark and squark masses. An $e^+e^-$ collider with enough energy and luminosity to produce $h+Z$ at measurable rates up to the maximum $h$ mass would cover the entire MSSM parameter space, if $h+A$ production was also searched for. We explore the energy and/or luminosity needed for various top quark and squark masses. For $m_t=150$\,GeV and 1\,TeV SUSY mass scale, a 230\,GeV collider with 10\,fb$^{-1}$ luminosity would suffice.

hep-ph↗

arXiv1992

Intermediate and Heavy Higgs Boson Physics at a 0.5 TeV e^+ e^- Collider

We explore the potential of a future e^+ e^- collider in the 0.5 TeV center-of-mass energy range to detect intermediate or heavy Higgs bosons in the Standard Model. We first briefly assess the production cross sections and update the decay branching fractions for a Higgs boson of intermediate mass, with M_Z < m_H < 2M_W. We then study in detail the possibility of detecting a heavy Higgs boson, with m_H > 2M_W, through the production of pairs of weak bosons. We quantitatively analyze the sensitivity of the process e^+ e^- --> nu nubar W^+ W^- (ZZ) to the presence of a heavy Higgs-boson resonance in the Standard Model. We compare this signal to various backgrounds and to the smaller signal from e^+ e^- --> ZH --> mu^+ mu^- W^+ W^- (ZZ), assuming the weak-boson pairs to be detected and measured in their dominant hadronic decay modes W^+ W^- (ZZ) --> 4jets. A related Higgs-boson signal in 6-jet final states is also estimated. We show how the main backgrounds from e^+ e^- W^+ W^- (ZZ), e nu WZ, and t tbar production can be reduced by suitable acceptance cuts. Bremsstrahlung and typical beamstrahlung corrections are calculated. These corrections reduce Higgs-boson production by scattering mechanisms but increase production by annihilation mechanisms; they also smear out some dynamical features such as Jacobian peaks in p_T(H). With all these corrections included, we conclude that it should be possible to detect a heavy Higgs-boson signal in the nu nubar W^+ W^-(ZZ) channels up to mass m_H=350 GeV.

hep-ph↗