arXiv subjects
Publications and source records attributed to Kingman Cheung.
The muon-proton ($μp$) collider is an interesting option of the muon collider. Here we discuss the physics potential of the $μp$ collider; especially, leptoquarks and contact interactions. We calculate the sensitivity reach for the second generation leptoquarks and leptogluons, $R$-parity violating squarks, and $μq$ contact interactions for the $μp$ colliders of various energies and luminosities.
We study in the framework of R-parity violating supersymmetric theories the effect of R-parity violation due to the operator L_i L_j \bar{E_k} on the (V-A) structure of the muon decay. The precisely measured muon decay parameters can constrain a product of R-parity violating couplings: |λ_{232}λ_{131}| < 0.022 at the 90% CL, which is complementary to the previous limits obtained by the e-μuniversality in τdecay.
We perform a global fit of data relevant to $eeqq$ contact interactions, including deep inelastic scattering at high $Q^2$ from ZEUS and H1, atomic physics parity violation in Cesium from JILA, polarized $e^-$ on nuclei scattering experiments at SLAC, Mainz and Bates, Drell-Yan production at the Tevatron, the total hadronic cross section $σ_{had}$ at LEP, and neutrino-nucleon scattering from CCFR. With only the new HERA data, the presence of contact interactions improves the fit compared to the Standard Model. When other data sets are included, the size of the contact contributions is reduced and the overall fit represents no real improvement over the Standard Model.
We consider $e e q q$ contact interactions as a possible origin of an excess of events above Standard Model predictions in $e^+ p \to e^+ jet$ at high $Q^2$ observed by the H1 and ZEUS collaborations at HERA. The HERA data prefer chirality RL or LR contact terms and atomic physics parity violation measurements severely limit parity-odd contact terms. With equal left-right and right-left chirality interactions at an effective scale of order 3 TeV we are able to reproduce the main features of the HERA data and still be consistent with Drell-Yan pair production at the Tevatron and hadron production at LEP 2 and TRISTAN.
We summarize results of the 1996 Snowmass workshop on future prospects for discovering dynamical electroweak symmetry breaking, compositeness, and anomalous couplings of quarks at colliders. We present the mass reach of the Tevatron to a color singlet or octet technirho, and to a topgluon or topcolor Z' from topcolor assisted technicolor. We explore the sensitivity of the Tevatron, LHC, NLC, and VLHC to contact interactions and excited fermions. Finally we investigate the possibility of seeing anomalous couplings of quarks at the Tevatron and LHC.
Top spin correlation has been shown to be nontrivial in hadronic top-pair production, and can be realized by the asymmetries of the decay products of the top quark and antiquark. We show in this work that the top spin correlation is a sensitive probe to the anomalous top-quark couplings beyond the standard model. Specifically, we look at the anomalous chromomagnetic and chromoelectric dipole moments, as well as a right-handed component in the weak decay of the top quark. We found a few measurable asymmetries formed by the decay products of the top-quark pair that vary in accord with the spin correlation.
Prompt photon production is sensitive to the anomalous couplings of gluons to quarks, because it is mainly produced by quark-gluon scattering. We will examine the effects of the anomalous chromoelectric and chromomagnetic dipole moment couplings of quarks on prompt photon production. Using the data collected by CDF and D0 at the Fermilab Tevatron we put a bound on these anomalous couplings. We also estimate the sensitivity of various future high energy collider experiments to these anomalous couplings.
The statistical limits on detectability of an anomalous chromomagnetic moment of a quark coupling to a gluon are projected to higher luminosities at the Tevatron at Fermilab, and to the LHC. They roughly scale as the energy, and are not strongly improved with increasing lumonisity.
Prompt photon production has been known to be a sensitive probe to the gluon luminosity inside a hadron because it is mainly produced by quark-gluon scattering. For the same reason prompt photon production should also be sensitive to the anomalous couplings of gluons to quarks. We will examine the effects of two specific anomalous couplings -- chromoelectric and chromomagnetic dipole moments of quarks -- on the prompt photon production. Using the data collected by CDF and D0 at the Tevatron we put a bound on the these anomalous couplings.
The conventional color-singlet model was challenged by the recent data on quarkonium production. Discrepancies in production rates were observed at the Tevatron, at LEP, and in fixed-target experiments. The newly advocated color-octet mechanism provides a plausible solution to the anomalous quarkonium production observed at the Tevatron. The color-octet mechanism should also affect other quarkonium production channels. In this paper we will summarize the studies of quarkonium production in $Z^0$ and $Υ$ decays.
The mixing of a new $Z'$ boson with the $Z$ significantly improves the fit to the LEP precision electroweak data, provided that the $Z'$ couples mainly to quarks. If $M_{Z_2}<200$~GeV, the $s$-channel $Z_2$ production and $(W,Z,γ)Z_2$ pair production cross sections at the Tevatron give an excess above QCD of $b\bar b$ and $(W,Z,γ)b\bar b$ events, respectively, with invariant mass $m(b\bar b)\approx M_{Z_2}$, which provide viable signals for detection of the $Z_2$. The interference of the $Z_2$ with $γ,Z_1$ in $e^+e^-\to \bar bb(\bar cc)$ at LEP\,1.5 energies is correlated with $R_b(R_c)$ and may be observable.
We study the effects of the anomalous chromoelectric and chromomagnetic dipole moments of the top quark on the top-pair production, on the top-pair plus 1jet production, and on their ratios, as well as their dependence on the transverse momenta of the top quark and the jet. We also construct CP-odd and $\hat T$-odd observables to probe the dispersive part of the chromoelectric form factor of the top quark, and compare their sensitivities in both top-pair and top-pair plus 1 jet production.
The direct production rate of $ψ$ in the $Υ$ decay is shown to be dominated by the process $ Υ\to ggg^*$ followed by $g^* \to ψ$ via the color-octet mechanism proposed recently to explain the anomalous prompt charmonium production at the Tevatron. We show that this plausibly dominant process has a branching ratio compatible with the experimental data. Further experimental study in this channel is important to test the significance of the color-octet component of $c\bar c$ pair inside the $ψ$ system.
The production rates and transverse momentum distributions of the strange-beauty mesons $B_s$ and $B_s^*$ at $p\bar p$ colliders are calculated assuming fragmentation is the dominant process. Results are given for the Tevatron in the large transverse momentum region, where fragmentation is expected to be most important.
The direct production rate of $J/ψ$ via the color-octet mechanism is calculated at the $Z$ resonance. The color-octet production process $Z\to J/ψq \bar q$ is shown to have a substantial branching ratio as well as a distinctive energy spectrum, which can be used as a powerful tool to distinguish from the color-singlet direct production of the $J/ψ$.
At hadron colliders the dominant production mechanism of $(\bar bc)$ mesons with large transverse momentum is due to parton fragmentation. We compute the rates and transverse momentum spectra for production of S-wave and P-wave $(\bar b c)$ mesons at the Tevatron via the direct fragmentation of the bottom antiquark as well as the Altarelli-Parisi induced gluon fragmentation. Since all the radially and orbitally excited $(\bar b c)$ mesons below the $BD$ flavor threshold will cascade into the pseudoscalar ground state $B_c$ through electromagnetic and/or hadronic transitions, they all contribute to the inclusive production of $B_c$. The contributions of the excited S-wave and P-wave states to the inclusive production of $B_c$ are 58 and 23\%, respectively, and hence significant.
At the large transverse momentum region, the production of heavy-heavy bound-states such as charmonium, bottomonium, and $\bar bc$ mesons in high energy $e^+e^-$ and hadronic collisions is dominated by parton fragmentation. We calculate the heavy quark fragmentation functions into the D-wave quarkonium and $\bar bc$ mesons to leading order in the strong coupling constant and in the non-relativistic expansion. In the $\bar b c$ meson case, one set of its D-wave states is expected to lie below the open flavor threshold. The total fragmentation probability for a $\bar b$ antiquark to split into the D-wave $\bar b c$ mesons is about $2 \times 10^{-5}$, which implies that only 2\% of the total pseudo-scalar ground state $B_c$ comes from the cascades of these orbitally excited states.
With the recent discovery of a heavy top quark $(m_t \approx 175 - 200$ GeV), the top quark opens an window to electroweak symmetry breaking. We propose the study of four-top, $t\bar t t\bar t$, production at hadronic supercolliders as a probe to electroweak symmetry breaking.