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In this work, we find a Critical Energy induced Enhancement (CEE) mechanism for the general three-body open-charm process at the $e^+e^-$ collisions, which utilizes the peculiar kinematic behavior of the $e^+e^-$ annihilation process involving three-body final states. We present a general analysis of a three-body process $e^+e^-to BCto B(Cto DE)$. When the center-of-mass (CM) energy of the $e^+e^-$ collision satisfies a critical relation $sqrt{s}=m_B+m_C$, there clearly exists the reflection peak of an intermediate $C$ state near the threshold of the invariant mass distribution of $m_{BE}$ or $m_{BD}$, whose formation is very sensitive to the CM energy. The reflection enhancement phenomenon induced at the critical energy means that a new cluster of charmoniumlike structures can be experimentally mapped. Taking an example of $e^+e^-to D_s^{*-}D_{s2}^*(2573)^+ to D_s^{*-}(D^0K^+)$, we further illustrate this novel phenomenon when $sqrt{s}=4.680$ GeV. What is more important is that a series of optimal CM energy points to search for new charmoniumlike structures in three-body open-charm processes from $e^+e^-$ annihilation are suggested, which can be accessible at BESIII and further BelleII as a new research topic.
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$J/Psi$ particles are abundantly produced at the Beijing Electron Positron Collider (BEPC). The $J/Psi$ decays provide an excellent place for studying $N^*$ resonances. For $J/Psitobar NNpi$ and $bar NNpipi$, the $pi N$ and $pipi N$ systems are limited to be pure isospin 1/2 due to isospin conservation. This is a big advantage in studying $N^*$ resonances from $J/Psi$ decays, compared with $pi N$ and $gamma N$ experiments which suffer difficulty on the isospin decomposition of 1/2 and 3/2. All other $N^*$ decay channels which are presently under investigation at CEBAF(JLab, USA), ELSA(Bonn,Germany) and GRAAL(Grenoble, France) with real photon or space-like virtual photon can also be studied at BEPC complementally with the time-like virtual photon. The process $J/Psitobar NN^*$ or $Nbar N^*$ provides a new way to probe the internal structure of the $N^*$ resonances. The recent results and outlook of our new $N^*$ program at BEPC are presented.
We study the pair production of scalar top quarks in e+e- collisions with the subsequent decay of the top squarks into b-quarks and charginos. We simulate this process using PYTHIA6.4 for beam energies 2E_beam = 350, 400, 500, 800, 1000 GeV. Proposing a set of criteria we obtain a good separation of the signal stop events from top quark pair production which is the main background. The number of stop production events obtained with the proposed cuts for different energies is calculated for an integrated luminosity of 1000 1/fb. We propose a method to reconstruct the mass of the top squark, provided the mass of the lightest neutralino is known, and estimate the error of the mass determination for the case sqrt{s} = 500 GeV.
We study the process e+e- to pi+pi-J/psi at a center-of-mass energy of 4.260 GeV using a 525 pb^{-1} data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9pm 1.9pm 3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c^2 in the pi^pm J/psi mass spectrum, which we refer to as the Z_c(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the pi^pm J/psi invariant mass spectrum, neglecting interference, results in a mass of (3899.0pm 3.6pm 4.9) MeV/c^2 and a width of (46pm 10pm 20) MeV. Its production ratio is measured to be R=frac{sigma(e+e- to pi^pm Z_c(3900)^mp to pi+pi-J/psi))} {sigma(e+e- to pi+pi-J/psi)}=(21.5pm 3.3pm 7.5)%. In all measurements the first errors are statistical and the second are systematic.
Using a data sample of 921.9 fb$^{-1}$ collected with the Belle detector, we study the process of $e^+e^-to D^+_sD_{s1}(2536)^-+c.c.$ via initial-state radiation. We report the first observation of a vector charmoniumlike state decaying to $D^+_sD_{s1}(2536)^-+c.c.$ with a significance of 5.9$sigma$, including the systematic uncertainties. The measured mass and width are $(4625.9^{+6.2}_{-6.0}({rm stat.})pm0.4({rm syst.}))~{rm MeV}/c^{2}$ and $(49.8^{+13.9}_{-11.5}({rm stat.})pm4.0({rm syst.}))~{rm MeV}$, respectively. The product of the $e^+e^-to D^+_sD_{s1}(2536)^-+c.c.$ cross section and the branching fraction of $D_{s1}(2536)^-to{bar D}^{*0}K^-$ is measured from the $D_s bar{D}_{s1}(2536)$ threshold to 5.59~GeV.
In this paper we study transverse polarization of $Lambda$ hyperons in single-inclusive leptonic annihilation. We show that when the transverse momentum of the $Lambda$ baryon is measured with respect to the thrust axis, a transverse momentum dependent (TMD) factorization formalism is required and the polarization is generated by the TMD polarizing fragmentation function (TMD PFF), $D_{1T}^perp$. However, when the transverse momentum of the $Lambda$ baryon is measured with respect to the momentum of the initial leptons, a collinear twist-3 formalism is required and the polarization is generated by the intrinsic collinear twist-3 fragmentation function $D_{T}$. Thus while these measurements differ from one another only by a change in the measurement axis, they probe different distribution functions. Recently, Belle measured a significant polarization in single-inclusive $Lambda$ baryon production as a function of the transverse momentum with respect to the thrust axis. However, this data can in principle be re-analyzed to measure the polarization as a function of the transverse momentum of the $Lambda$ baryon with respect to the lepton pair. This observable could be the first significant probe of the function, $D_{T}$. In this paper, we first develop a TMD formalism for $Lambda$ polarization; we then present a recent twist-3 formalism that was established to describe $Lambda$ polarization. Using the TMD formalism, we demonstrate that the $Lambda$ polarization at OPAL and Belle can be described using the twist-2 TMD factorization formalism. Finally, we make a theoretical prediction for this polarization in the collinear twist-3 formalism at Belle.
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