Search

To test the standard model (SM) precisely and to look for the clues deviating from SM, a proposal for determining the effective electro-weak mixing angles sin2 θeff (particularly f = lept, c, b) is proposed. It is via observing the asymmetries (the forward-backward one AFB, the left-right one ALR and the combined left-right forward-backward one ALRFB ) of the doubly heavy-flavored hadrons in the production at a super Z-factory (an e+e− collider designed with a luminosity as high as possible for modern-day techniques runs around the center-of-mass energy $$\sqrt s = {m_Z}$$ ). To see the sensitivity, uncertainties as well as the event accumulation precisely, the observables for describing the asymmetries of the produced hadrons are computed numerically with varying effective mixing angles, and based on the result analyses, it is concluded that the proposal may offer an independent complement determination of the effective mixing angles.

The semileptonic decays \(B_c^ + \to P(V) + \ell ^ + + \bar \nu _\ell \) and the nonleptonic decays Bc+ → P(V) + L, where P(V) denotes a pseudoscalar (vector) charmonium or \((\bar bs)\)-meson, and L denotes a light meson, are studied in the framework of improved instantaneous Bethe-Salpeter (BS) equation and the Mandelstam formula. The numerical results (width and branching ratio of the decays) are presented in tables, and in order to compare conveniently, those obtained by other approaches are also put in the relevant tables. Based on the fact that the ratio \(\frac{{\mathcal{B}\mathcal{R}(B_c^ + \to \psi (2S)\pi ^ + )}} {{\mathcal{B}\mathcal{R}(B_c^ + \to J/\psi \pi ^ + )}} = 0.24_{ - 0.040}^{ + 0.023} \) estimated here is in good agreement with the observation by LHCb \(\frac{{\mathcal{B}\mathcal{R}(B_c^ + \to \psi (2S)\pi ^ + )}} {{\mathcal{B}\mathcal{R}(B_c^ + \to J/\psi \pi ^ + )}} = 0.250 \pm 0.068(stat) \pm 0.014(syst) \pm 0.006(\mathcal{B}) \), one may conclude that with respect to the decays the present framework works quite well.

The production of $B_c$ and $B_c^*$ mesons at a $Z$-factory (an $e^+e^-$ collider operating at energies around the $Z$ pole) is calculatedup to the next-to-leading order (NLO) QCD accuracy. The results show that the dependence of the total cross sections on the renormalization scale $\mu$ is suppressed by the corrections, and the NLO corrections enhance the total cross sections of $B_c$ by $52%$ and of $B_c^*$ by $33%$ when the renormalization scale is taken at $\mu=2m_b$. To observe the various behaviors of the production of the mesons $B_c$ and $B_c^*$, such as the differential cross section vs. the out-going angle, the forward-backward asymmetry, and the distribution vs. the energy fraction $z$ up to NLO QCD accuracy as well as the relevant $K$-factor (NLO to LO) for the production, are calculated, and it is pointed out that some of the observables obtained in the present work may be used as a specific precision test of the standard model.

Considering the possibility to build an $e^+e^-$ collider at the energies around $Z$-boson resonance with a luminosity so high as ${\cal L} \propto 10^{34}cm^{-2}s^{-1}$ (even higher) and the abilities of a modern synthesis detector, we systematically calculate the exclusive two body processes: $e^+e^-$ annihilates into a heavy quarkonium and a photon (initiate state radiation i.e. ISR is involved), at the energies around the $Z$-boson resonance. Since the couplings of $Z$-boson to quarks contain axial vector as well as vector, so here the produced heavy quarkonium may stand for a charmonium such as ${J/\psi,\eta_c,h_c,\chi_{cJ}}\cdots$ and a bottomonium such as ${\Upsilon,\eta_b,h_b,\chi_{bJ}}\cdots$ respectively. If we call such a collider with so high luminosity and running around the $Z$-boson resonance as a $Z$-factory, then our results obtained here indicate that experimental studies at a $Z$-factory about the various heavy quarkona (their ground and excited states) via the two-body processes, especially, the production of the bound states with quantum number $J^{PC}=1^{--}$ via ISR, have outstanding advantages., Comment: 11 page, 3 figures

The magnetic dipole transitions between the vector mesons $B_c^*$ and their relevant pseudoscalar mesons $B_c$ ($B_c$, $B_c^*$, $B_c(2S)$, $B_c^*(2S)$, $B_c(3S)$ and $B_c^*(3S)$ etc, the binding states of $(c\bar{b})$ system) of the $B_c$ family are interesting. To see the `hyperfine' splitting due to spin-spin interaction is an important topic for understanding the spin-spin interaction and the spectrum of the the $(c\bar{b})$ binding system. The knowledge about the magnetic dipole transitions is also very useful for identifying the vector boson $B_c^*$ mesons experimentally, whose masses are just slightly above the masses of their relevant pseudoscalar mesons $B_c$ accordingly. Considering the possibility to observe the vector mesons via the transitions at $Z^0$ factory and the potentially usages of the theoretical estimate on the transitions, we fucus our efforts on calculating the magnetic dipole transitions, i.e. precisely to calculate the rates for the transitions such as decays $B_c^*\to B_c\gamma$ and $B_c^*\to B_c e^+e^-$, and particularly work in the Behte-Salpeter framework. In the estimate, as a typical example, we carefully investigate the dependance of the rate $\Gamma(B_c^*\to B_c\gamma)$ on the mass difference $\Delta M=M_{B_c^*}-M_{B_c}$ as well.

The uncertainties in estimating the hadronic production of the $B_c$ meson are studied under the framework of the complete $\alpha_s^4$ approach of the perturbative QCD and the gluon-gluon fusion mechanism. Quantitative comparisons on the production at TEVATRON and LHC are made. Considering the detectors at TEVATRON and LHC, we have also estimated the production with proper kinematic cuts. Based on the results, we conclude that the experimental studies of the $B_c$ meson at the two colliders will be complimentary and stimulative. We find that as c.m. energy is increasing from RUN-I to RUN-II at TEVATRON, the production cross-section increases about 20%.

The properties of the meson B-c are outlined. The leptonic radiative decays for B-c meson are presented. An outlook on the studies of the meson is given.

The minimum supersymmetric standard model with bilinear R-parity violation is studied systematically. Considering low-energy supersymmetry, we examine the structure of the bilinear R-parity violating model carefully. We analyze the mixing such as Higgs bosons with sleptons, neutralinos with neutrinos and charginos with charged leptons in the model. Possible and some important physics results such as the lightest Higgs may heavy than the weak Z-boson at tree level etc are obtained. The Feynman rules for the model are derived in $'$t Hooft- Feynman gauge, which is convenient if perturbative calculations are needed beyond the tree level., 50 pages, includes 12 figs, revised some formulaes, accepted by EPJC

Based on the nonvalence quark-antiquark and gluon constituent structure of mesons we give a reasonable dynamical mechanism which can induce the hairpin diagram without violating the well-observed OZI rule. We calculate the hairpin amplitudes of D(o)-->KBAR(o)eta and KBAR(o)eta' normalized D(o)-->KBAR(o)pi(o) and have found that the hairpin diagram can give rise to substantial contributions to the decays where a meson with a SU(3) flavor singlet component is involved in the final state. In this scenario, we also obtain the branching ratio of D(o)-->KBAR(o)phi as 0.55% in comparison with the experimental data of 0.83%.