Searching for Flavor-Changing Neutral-Current Signalsvia e+e-(γγ) → t\bar{c}h0t in Topcolor-Assisted Technicolor Model

In the context of the top-color-assisted technicolor (TC2) model, the flavor-changing neutral-current (FCNC) interaction induced by the top-higgs (h⁰_t) are predicted at tree level. We study the relevant processes of e⁺e^-(γγ)→ t\bar{c}h⁰_t at the International Linear Collider (ILC). It is found that these rare processes production rates can be enhanced significantly in the TC2 model. Especially for the process γγ → t\bar{c}h⁰_t, the total cross section will reach a few fb in the reasonable parameter space. We also calculate the distributions of transverse momenta, pseudo-rapid and invariant mass of the top-higgs. In view of the main decay modes of top-higgs for m_h⁰t<2m_t, we find that there will be several hundreds FCNC events produced at the ILC with annuallyintegral luminosity of 500 fb^-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.     

SU（3） Simple Group Model and New Z＇ Properties in Future Linear Colliders

In the SU（3） simple group model, the new neutral gauge boson Z＇ couples to pairs of SM fermions with couplings fixed in terms of the SM gauge couplings and depending only on the choice of the fermion embedding. In this paper, we calculate the contributions of this new particle to the processes e^＋e^-→l^＋l^-, bb^-, and cc^- and study the possibility of detecting this new particle via these processes in the future high-energy linear e^＋e^- collider（LC） experiments with √s= 500 GeV and ￡int= 340 fb^-1. We find that the new gauge boson Z＇ is most sensitive to the process e^＋e^-→b^＋b^-. As long as Mz,≤2 TeV , the absolute values of the relative correction parameter are larger than 5%. We calculate the forward-backward asymmetries and left-right asymmetries for the process e^＋e^-→c^＋c^-, with both the universal and anomaly-free fermion embeddings. Bounds on Z＇ masses are also estimated within 95% confidence level.     

Exclusive Semi-leptonic Decays b→s(d)ν\bar{ν} in the Standard Model with Fourth Generation

We consider the effects of the fourth generation quarks on the rareBdecay processes described by the b→ s(d)ν \bar{ν} processes at the quark level. We find that the values of the branching ratios for some of these rare decay processes are much larger than the standard model (SM) predictions.
These processes can be used to constrain the relevant free parameters.     

Top Quark Polarization and Spin Correlation in the Littlest Higgs Model with T-Parity at the ILC

In the framework of the littlest Higgs model with T-parity(LHT),we study the top quark spin correlation and polarization at the International Linear Collider(ILC).We find that the top quark polarization asymmetry δP t and the left-right asymmetry δA LR can respectively reach-35% and-37.5% for s～(1/2)=500 GeV and s～(1/2)=1000 GeV via e+e-collision,which can reach the observable level at the ILC.By contrast,the spin correlation δC is smaller.The correlation behaviors of these observables at the e+e-collision and the γγ collision will be helpful to distinguish different models and test the LHT model at the ILC.     

Study on Charged Top-Pion Decay Processes

In the framework of top-color assisted technicolor (TC2) theory, we study the four decay processes of charged top-pion, i.e., Π⁺_t→ t\bar{b}, Π⁺_t→ c\bar{b}, Π⁺_t→ W⁺γ, Π⁺_t→ W⁺Z⁰. The decay branching ratio of these modes are calculated. The results show that the main decay channels of charged top-pion are the tree level modes: Π⁺_t → t\bar{b} and Π⁺_t → c\bar{b}. Light Π⁺_t is easier to be detected than heavy one at future coliders. So, the study provides us with some useful informations to search for charged top-pion.     

Single Charged Top-Pion Production at the Next Generation e+e- Colliders

The single charged top-pion production processes e⁺e^-→t\bar{b}Π_t^- and e⁺e^-→ W⁺Π_t^- are studied in the framework of top-color-assisted technicolor (TC2) model. Our studies show that the cross section σ(e⁺e^-→t\bar{b}Π_t^-) reaches the level of tens of fb and σ(e⁺e^-→W⁺Π_t^-) reaches the level of a few fb. With the yearly integrated luminosity of L～500 fb^-1 expected at the planned colliders, one could collect thousands of charged top-pion of events via the process e⁺e^-→t\bar{b}Π_t^- and hundreds of events via the process e⁺e^-→W⁺Π_t^-. The flavor changing decay mode Π_t^-→b\bar{c} is the best channel to detect charged top-pion due to the clean SM background. With a large number of events and the clean background, the charged top-pion should be observable at the planned colliders. Therefore, our studies in this paper can help us to search for charged top-pion, and furthermore, to test the TC2 model.     

Production of Top-Pions Associated with W Boson at Next Generation γγ Colliders

In the context of topcolor-assisted technicolor (TC2) model, we study the charged and neutral top-pions production process γγ→W⁺ Π_t^-Π_t⁰. We find that the production cross section is larger than that of the process γγ→W⁺H^-H in the minimal supersymmetric standard model. With reasonable values of the parameters in the TC2 model, the cross section can reach the level of a few fb. Furthermore, the flavor-changing (FC) decay mode Π_t⁰ → t\bar{c} is the best channel to detect theneutral top-pion due to the clean SM background. With a large number of events and the clean background, the neutral top-pion should be observable at future linear colliders operating in γγ mode at the TeV energy scale.     

Probing signals of the littlest Higgs model via the WW fusion processes at the high energy e + e- collider

In the framework of the littlest Higgs (LH) model, we consider the processes and , and we calculate the contributions of new particles to the cross sections of these processes in the future high energy e ⁺ e^- collider (ILC) with TeV. We find that, with reasonable values of the free parameters, the deviations of the cross sections for the processes from their SM values might be comparable to the future ILC measurement precision. The contributions of the light Higgs boson H⁰ to the process are significantly large in all of the parameter space preferred by the electroweak precision data, which might be detected in the future ILC experiments. However, the contributions of the new gauge bosons B_H and Z_H to this process are very small.Received: 22 February 2005, Revised: 27 April 2005, Published online: 6 July 2005PACS: 12.60.Cn, 14.70.Pw, 14.80.Cp     

Probing vector-like top partner from same-sign dilepton events at the LHC

The standard model is a successful theory but is lacking a mechanism for neutrino mass generation as well as a solution to the naturalness problem. In the models that are proposed to simultaneously solve the two problems, heavy Majorana neutrinos and top partners are usually predicted to lead to a new decay mode of the top partner mediated by the heavy Majorana neutrinos: $T\to b\,{W}^{+}\to b\,{{\ell }}^{+}{{\ell }}^{+}q\bar{q^{\prime} }$. In this paper, we will study the observability of such a new signature via the pair production process of a top partner ${pp}\to T\bar{T}\to 2b+{{\ell }}^{\pm }{{\ell }}^{\pm }+4j$ in a model independent way. By performing Monte Carlo simulations, we present the 2σ exclusion limits of the top partner mass and mixing parameters at the HL-LHC.     

Flavor Changing Top Quark Decay and Bottom-Strange Production in the Littlest Higgs Model with T-parity

Flavor changing effects on the processes t → ch, e+e- → bs, e+e-→ bsh and pp → bs in the LHT model are investigated in this paper. We calculate the one-loop level contributions from the T-parity odd mirror fermions and gauge bosons. The results show that the top quark rare decay t → ch in the LHT model can be significantly enhanced relative to that in the SM. The bs production at linear colliders in the LHT model can enhance the SM cross section a lot and reach 0.1 fb in some parameter space allowed in the experiment. But the heavy gauge boson and mirror fermion loops have small contribution to the processes pp → bs and e+e-→ bsh. So the LHT effect on e+e-→ bs might be detected at future linear colliders, while it is too small to be seen for the e+e-→ bsh and pp → bs processes at future linear colliders and LHC.     

Helicity Amplitude Analysis of ηc Decays into Hyperon-Antihyperon Pairst

The helicity amplitudes for the processes of e^＋e^- →J/ψ→γηc→γYY（Y： hyperon） are presented, together with the joint angular distributions for ηc decays into ∧∧,∑^0 ∑^0, and [1]-[1]＋. The sensitivities to measure the hyperon decay parameters in these decays are evaluated based on the helicity amplitudes. The prospects to test the Bell inequality in experiment using the decay of ηc→∧∧ are discussed.     

Single top partner production in the tZ channel at eγ collision in the littlest Higgs model with T-parity

Introducing the top partner is a common way to cancel the largest quadratically divergent contribution to the Higgs mass induced by the top quark. In this work, we study single top partner production in the tZ channel at eγ collision in the littlest Higgs model with T-parity(LHT). Since it is well known that polarized beams can enhance the cross section, we analyze the signal via polarized electron beams,and photon beams. we have selected two decay modes for comparison, based on the leptonic or the hadronic decays of the W and Z from the top partner. We then construct a detailed detector simulation, and choose a set of cuts to enhance signal significance. For mode A(B), the capacity for exclusion in this process at s~(1/2)=3TeV is comparable to the current experimental limits with L=1000(500) fb~(-1). If the integrated luminosity can be increased to 3000 fb~(-1), the top partner mass+mTcan be excluded up to 1350(1440) GeV at 2σ level. We also considered the initial state radiation effect, and find that this effect reduces the excluding ability of the eγ collision on the the top partner mass by approximately 10 GeV. Moreover, the ability to exclude the LHT parameter space at eγ collision complements the existing research.     

$W^{\pm}\pi_t^{\mp}$ Associated Production at Large Hadron Collider

In this paper we calculate the production of a charged top pion in association with a $W$ boson at the CERN Large Hadron Collider (LHC) in the context of the topcolor assisted technicolor model. We find that the cross section of $pp \rightarrow b\bar{b} \rightarrow W^{\pm}\pi_t^{\mp}$ is roughly corresponding to the result of the process $pp \rightarrow b\bar{b} \rightarrow W^{\pm}H^{\mp}$ in the minimal supersymmetric standard model, and for reasonable ranges of the parameters, the cross section can reach a few hundred fb. The $W^{\pm}\pi_t^{\mp}$ signal should be clearly visible at LHC unless $\pi_t^{\pm}$ is very heavy.     

Study of semileptonic decay of ${\bar{B}}_{s}^{0} \rightarrow \phi {l}^{+}{l}^{-}$ in QCD sum rule

In this work we study the semileptonic decay of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) with the QCD sum rule method. We calculate the ${\bar{B}}_{s}^{0}\to \phi $ translation form factors relevant to this semileptonic decay, then the branching ratios of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) decays are calculated with the form factors obtained here. Our result for the branching ratio of ${\bar{B}}_{s}^{0}\to \phi {\mu }^{+}{\mu }^{-}$ agree very well with the recent experimental data. For the unmeasured decay modes such as ${\bar{B}}_{s}^{0}\to \phi {e}^{+}{e}^{-}$ and ${\bar{B}}_{s}^{0}\to \phi {\tau }^{+}{\tau }^{-}$, we give theoretical predictions.     

Covalent hadronic molecules induced by shared light quarks

After examining Feynman diagrams corresponding to the ${\bar{D}}^{(* )}{{\rm{\Sigma }}}_{c}^{(* )}$, ${\bar{D}}^{(* )}{{\rm{\Lambda }}}_{c}$, ${D}^{(* )}{\bar{K}}^{* }$, and ${D}^{(* )}{\bar{D}}^{(* )}$ hadronic molecular states, we propose a possible binding mechanism induced by shared light quarks. This mechanism is similar to the covalent bond in chemical molecules induced by shared electrons. We use the method of QCD sum rules to calculate its corresponding light-quark-exchange diagrams, and the obtained results indicate a model-independent hypothesis: the light-quark-exchange interaction is attractive when the shared light quarks are totally antisymmetric so they obey the Pauli principle. We build a toy model with four parameters to formulize this picture and estimate binding energies of some possibly-existing covalent hadronic molecules. A unique feature of this picture is that the binding energies of the (I)J^P = (0)1⁺ $D{\bar{B}}^{* }/{D}^{* }\bar{B}$ hadronic molecules are much larger than those of the (I)J^P = (0)1⁺ ${{DD}}^{* }/\bar{B}{\bar{B}}^{* }$ ones, while the (I)J^P = (1/2)1/2⁺ $\bar{D}{{\rm{\Sigma }}}_{c}/\bar{D}{{\rm{\Sigma }}}_{b}/B{{\rm{\Sigma }}}_{c}/B{{\rm{\Sigma }}}_{b}$ hadronic molecules have similar binding energies.     

{Q\bar{s}}{\bar{Q}(') s} Molecular States in QCD Sum Rules

We systematically investigate the mass spectra of {Q\bar{s}}{bar{Q}^(')s}molecular states in the framework of QCD sum rules. The interpolating currents representing the molecular states are proposed. Technically, contributions of the operators up to dimension six are included in operator product expansion (OPE). The masses for molecular states with various{Q\bar{s}} {\bar{Q}^(')s} configurations are presented. The result 4.36±0.08 GeV for the D^*_s\bar{D}^*_s0 molecular state is consistent withthe mass 4350^+4.6_-5.1 ± 0.7 MeV of the newly observed X(4350), which could support X(4350) interpreted as a D^*_s\bar{D^}*_s0 molecular state.     

Charged Top-Pion Production at Hadron Colliders

We studied the charged top-pion in the topcolor assisted technicolor model (TC2). If the charged top-pions are heavy, m_πt >m_t+m_b, they will decay mainly via the channel π⁺_t → t \bar{b}. We also calculated the production ofcharged top-pion at the Tevatron and LHC. The cross section can reach to 100 fb at the Tevatron and dozens of pb at the LHC depending on the mass of the top-pion.     

Use of W-boson longitudinal-transverse interferencein top quark spin-correlation functions

Most of this paper consists of the derivation of general beam-referenced stage-two spin-correlation functions for the analysis of top-antitop pair production at the Tevatron, at the Large Hadron Collider, and/or at an International Linear Collider. However, for the charged-lepton plus jets reaction , there is a simple three-angle spin-correlation function for the determination of the relative sign of or for the measurement of a possible non-trivial phase between the two dominant λ_b=-1/2 helicity amplitudes for the t → W⁺b decay mode. For the CP-conjugate case, there is an analogous function and tests for decay. These results make use of W-boson longitudinal-transverse interference. Received: 24 June 2005, Revised: 10 August 2005, Published online: 3 November 2005     

A measurement of the forward-backward asymmetry of e+e?→bb by applying a jet charge algorithm to lifetime tagged events

The forward-backward asymmetry of has been measured using approximately 2.15 million hadronicZ ⁰ decays collected at the LEP e⁺e^– collider with the OPAL detector. A lifetime tag technique was used to select an enriched event sample. The measurement of the asymmetry was then performed using a jet charge algorithm to determine the direction of the primary quark. Values of:

Measurement of A_{FB}^{\mathrm{b}\overline{\mathrm{b}}} in hadronic Z decays using a jet charge technique

The b[`b]\mbox{b}\bar{\mbox{b}} forward-backward asymmetry has been determined from the average charge flow measured in a sample of 3,500,000 hadronic Z decays collected with the DELPHI detector in 1992–1995. The measurement is performed in an enriched b[`b]\mbox{b}\bar{\mbox{b}} sample selected using an impact parameter tag and results in the following values for the b[`b]\mbox{b}\bar{\mbox{b}} forward-backward asymmetry: $ \begin{gathered} A_{FB}^{b\bar b} \left( {89.55 GeV} \right) = 0.068 \pm 0.018 \left( {stat.} \right) \pm 0.0013\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {91.26 GeV} \right) = 0.0982 \pm 0.0047 \left( {stat.} \right) \pm 0.0016\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {92.94 GeV} \right) = 0.123 \pm 0.016 \left( {stat.} \right) \pm 0.0027\left( {syst.} \right) \hfill \\ \end{gathered} $ \begin{gathered} A_{FB}^{b\bar b} \left( {89.55 GeV} \right) = 0.068 \pm 0.018 \left( {stat.} \right) \pm 0.0013\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {91.26 GeV} \right) = 0.0982 \pm 0.0047 \left( {stat.} \right) \pm 0.0016\left( {syst.} \right) \hfill \\ A_{FB}^{b\bar b} \left( {92.94 GeV} \right) = 0.123 \pm 0.016 \left( {stat.} \right) \pm 0.0027\left( {syst.} \right) \hfill \\ \end{gathered} The b[`b]\mbox{b}\bar{\mbox{b}} charge separation required for this analysis is directly measured in the b tagged sample, while the other charge separations are obtained from a fragmentation model precisely calibrated to data. The effective weak mixing angle is deduced from the measurement to be: $ sin^2 \theta _{eff}^1 = 0.23186 \pm 0.00083 $ sin^2 \theta _{eff}^1 = 0.23186 \pm 0.00083