Study of ππ production in two-photon collisions at Belle

We have measured the cross section for π+π- production in two-photon collisions using a data sample with an integrated luminosity of 85.9 fb-1 collected with the Belle detector. The f0(980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ→π0π0 with two-photon center-of-mass energies ranging from 0.6 to 4.0 GeV, based on a 95 fb-1 data sample. We find at least four resonant structures including a peak from f0(980). In addition, there is evidence for Xc0 production. We also make a preliminary discussion of the angular dependence and cross section ratio of γγ→π+π- and γγ→π0π0.     

Recent results on light hadron spectroscopy from BESⅡ

We reported the observation of Y(2175) in φ f₀(980) mass spectrum in J/ψ→η π f₀(980) with f₀(980)→π⁺π^－ and the observation of a broad 1^－ resonance of K⁺     

Measuring D0-D0 mixing in D→f0(980) K and more

We investigate the D⁰-D⁰ mixing through the doubly Cabibbo suppressed (DCS) channel D0→f₀(980)K^*0 and its charge conjugate channel, in which the K^*0 meson is reconstructed in both K⁺π^－ and K_Sπ⁰ final state. Although the decay D⁰→f₀(980)K^* has a small branching ratio, the final state mesons are relatively easy to identify. The f₀(980) meson can be replaced by the S-wave π⁺π^－ state, or a longitudinally polarized vector meson ρ⁰. All mixing parameters, including the mass difference and decay width difference, can be extracted by studying the time-dependent decay width of these channels. We show that the method is valid in all regions for mixing parameters and it does not depend on the strong phase difference.     

Searching for a neutral top-Higgs in association with top-quark pairs at an e~+e~- collider in the TC2 model

We investigate the associated production of the neutral top-Higgs h_t⁰ with a pair of top-quarks in the context of the topcolor-assisted technicolor (TC2) model at the future e⁺e^- Linear Colliders (LC) i.e. e⁺e^- → tt h_t⁰. We calculate the production rate and present the distributions of the transverse momenta of top-Higgs and top-quarks. The results show that the total cross section is typically of the order of 1.0-7.5 fb in the energy range between 1000 GeV and 2000 GeV of the LC for the whole top-Higgs mass region of interest. It should be distinctly possible that hundreds or even thousands of h_t⁰ signals can be produced per year at the LC given the luminosity L=500 fb^-1.     

Searches for the technicolor signatures via gg → W±πt± at the Large Hadron Collider

In this paper, we calculate the production of a charged top pion in association with a W boson via gg fusion at CERN's Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the total cross section of pp → gg → W^±π_t is several dozen femtobarns with reasonable values of the parameters, and the total cross section of pp → W^±π_t can reach a few hundred femtobarns when we consider the sum of the contributions of these two parton subprocesses, gg → W^±π_t and bb → W^±π_t.     

Charm mixing from BABAR

We present recent results from BABAR experiment for D⁰－D⁰ mixing measurements. Mixing parameters can be measured in different ways using different D⁰ decay modes, here we discuss the most sensitive analyses such as D⁰→K⁺π^－ where we had the first evidence of charm mixing, the measurement of the ratio of lifetimes of the decays D0→K⁺K^－ and D⁰→π⁺π^－ relative to D⁰→K^－π⁺, the time dependent Dalitz plot analysis of D⁰→K⁺π^－π⁰. New limits on CP-violating time-integrated asymmetries in D0→K⁺K^－ and D0→π⁺π^－ are also discussed. The analyses presented are based on 384 fb^－1 data collected with the BABAR detector at the PEP-II asymmetric B Factory.     

A simulation study on the measurement of D0-D0 mixing parameter y at BESⅢ

We established a method on measuring the D⁰-D⁰ mixing parameter y for BESⅢ experiment at the BEPCⅡ e⁺e^－ collider. In this method, the doubly tagged π(3770) →D⁰-D⁰ events, with one D decays to CP-eigenstates and the other D decays semileptonically, are used to reconstruct the signals. Since this analysis requires good e/π separation, a likelihood approach, which combines the dE/dx, time of flight and the electromagnetic shower detectors information, is used for particle identification. We estimate the sensitivity of the measurement of y to be 0.007 based on a 20fb^-1 fully simulated MC sample.     

Study of Λ decay parameter in J/ψ→ΛΛ decay

The helicity amplitudes for J/ψ→ΛΛ and the relevant background decays are presented for measuring the Λ decay parameter α₊(Λ→pπ⁺) in J/ψ→ΛΛ . The Monte Carlo (MC) simulations based on the helicity amplitudes information are carried out. The likelihood fit method to determine the Λ decay parameter is presented. Based on the MC generated sample, the sensitivity of the measurement for α₊ has been estimated, which shows that the J/ψ→ΛΛ channel can be used to measure the Λ decay parameter α₊(Λ→pπ⁺) well.     

Temperature-dependent cross sections for πφ and ρφ nonresonant reactions in hadronic matter

With a potential of which the large-distance part reflects lattice gauge results and of which the short-distance part is given by one gluon exchange plus perturbative one- and two-loop corrections, the Schrödinger equation brings about temperature dependence of meson masses and mesonic quark-antiquark relative-motion wave functions. The ground-state meson masses drop with increasing temperature. The transition amplitude calculated from the potential, the meson masses and the wave functions gives temperature-dependent cross sections for the five nonresonant reactions πφ→KK^* (or K^*K), πφ→K^*K^*,ρφ→KK,ρφ→KK^*(orK^*K) and ρφ→K^*K^*. The numerical temperature-dependent cross sections are parametrized. The peak cross section of either πφ→KK^* or πφ→K^*K^* increases from T=0 to T=0.75T_c and decreases with further increasing temperature. The cross section for ρφ→KK,ρφ→KK^* and ρφ→K^*K^* has a decreasing trend while the temperature increases from 0.75T_c.     

Monte Carlo Simulation on Measurements of Branching Fractions for Some Exclusive Semileptonic Decays of Neutral D Mesons on BES-III

Using the Monte Carlo samples of about 800 pb^-1 and 500pb^-1 generated at and around 3.773GeV with BOSS (BESIII Offline Software System) 6.0.2 and BOSS 6.1.0, we have studied the branching fractions for D⁰ →K^-l⁺ν_l and D⁰ →πi^-l⁺ν_l (l=e, μ). According to the simulation results, the expected precision of these measurements for 20fb^-1 ψ(3770) data which will be collected on BESIII are well estimated.     

D+ → η(')l+νl semileptonic decays in light-cone sum rules

We calculate the D → η transition form factor in light-cone sum rules by taking improved current correlators to avoid the pollution from the twist-3 wave function. We get consistent results of the D⁺ → η^(')l⁺ν_l decays with the experimental data. By comparing the difference between the results of the branching ratios of D⁺ → η^(')l⁺ν_l from a two-pole parameterization model and from a BZ parameterization model, we find that the two-pole model and the BZ model are comparably believable. One way is supposed for the determination of the η-η' mixing angle from the dependence of the branching ratios of D⁺ → η^(')l⁺ν_l decays on the η-η' mixing angle.     

Comprehensive analysis of e+e-→γηc(2S)

We discuss the production of η_c(2S) through the process e⁺e^-→γη_c(2S), where the leading contribution originates from 1-loop electroweak corrections. Adopting some reasonable light-cone distribution amplitudes, we analyze the cross section of this process. As the electron-positron center of mass energy √s=3770 MeV, the typical production cross section of this process is about 1 fb.     

Production of a neutral scalar associated with a photon at the LHC in the topcolorassisted technicolor model

In the context of the topcolor-assisted technicolor (TC2) model, we consider the production of the neutral scalar S(π_t⁰ or h_t⁰) associated with a photon at the LHC and compare our results with those given by the minimal supersymmetric extension of the Standard Model (MSSM). We find that its production cross section is larger or smaller than that of the scalar particle predicted by the MSSM model, depending on the values of the relevant free parameters.     

γγ interactions with KLOE

Studies of γγ interactions are performed with the KLOE detector, without tagging of the outgoing e^＋e^-. The data sample is from an integrated luminosity of 240 pb^-1. It was collected at the φ-factory DAONE with e^＋e^- beams colliding at √s ≌1 GeV, below the φ resonance peak. We present preliminary results concerning the observation of the γγ→η process and the evidence for γγ→π^0π^0 production at low π^0π^0 invariant masses.     

γγ interactions with KLOE

Studies of γγ interactions are performed with the KLOE detector,without tagging of the outgoing e+e-.The data sample is from an integrated luminosity of 240 pb-1.It was collected at the φ-factory DAΦNE with e+e-beams colliding at s～(1/2) 1 GeV,below the φ resonance peak.We present preliminary results concerning the observation of the γγ→η process and the evidence for γγ→π0π0 production at low π0π0 invariant masses.     

Two-photon processes at Belle

We review recent measurements of pure neutral final state production in the two-photon processes, γγ→π^0π^0 and ηπ^0 at the Belle experiment. In the lower invariant mass region, properties of light scalar mesons are measured by partial wave analysis. In the higher energy region the total and differential cross section are compared with QCD models.     

Study of charmonium(-like) states via ISR at Belle

The cross sections for e⁺e－→π⁺π^－J/ψ, π⁺π^－ψ(2S), K⁺K^－J/ψ, DD, D⁰D^－+π⁺+c.c., D^*D+c.c., and D^*D^* are measured using data sample collected on or near the Υ(4S) resonance with the Belle detector at KEKB. A peak near 4.25GeV/c², corresponding to the so called Y(4260), is observed in π⁺π^－J/ψ final state. In addition, there is another cluster of events at around 4.05GeV/c². Two resonant structures are observed in the π⁺π^－ψ(2S) invariant mass distribution, one at 4361±9±9MeV/c² with a width of 74±15±10MeV/c², and another at 4664±11±5MeV/c² with a width of 48±15± 3MeV/c². The rich structures observed in all these final states indicate that our understanding of the vector charmonium states above the open charm threshold is still poor, let alone the other possible dynamics such as charmonium hybrids or final state re-scattering and so on.     

Photodetachment of a Negative Hydrogen Molecular Ion near an Interface

Photodetachment of a negative hydrogen molecular ion near an interface is studied by using the two-centre model and the closed orbit theory. The calculation results show that the photodetachment cross section is related to the distance between the two centres in the H₂^- and different molecular ion-interface distances. The comparison between the cross section of H₂^- near an interface with the section of Hˉ shows that at the equilibrium distance of two centres and at low photon energy, the photodetachment cross section of H₂^- is about twice the cross section of Hˉ, which shows that the interference of the two nuclei is very strong; when the distance between the two centres is large, the section of H₂^- is almost the same as the cross section of Hˉ near one interface, which indicates that the interference effect of the two centres anishes.     

Branching fraction of the isospin violating process φ→ωπ^0

We have examined the parametrization of the e⁺e^- → ωπ⁰ cross section in the vicinity of the φ resonance and the extraction of the branching fraction of the isospin violating process φ → ωπ⁰ from experimental data. We found that there are two possible solutions of the branching fraction: one is 4 × 10^-5, and the other is 7 × 10^-3. The latter is two orders of magnitude higher than the former, which is the commonly accepted one.