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Register a new userTwo-photon exchange effects in $e^+ e^-rightarrowpi^+pi^-$ at small $ sqrt{s}$
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In this work, the two-photon-exchange (TPE) effects in $e^+e^- rightarrow pi^+ pi^-$ at small $sqrt{s}$ are discussed within a hadronic model. In the limit $m_erightarrow 0$, the TPE contribution to the amplitude can be described by one scalar function $overline{c}_{1}^{(2gamma)}$. The ratio between this function and the corresponding contribution in one-photon exchange $c_{1}^{(1gamma)}$ reflects all the information of the TPE corrections. The numerical results on this ratio are presented and an artificial function is used to fit the numerical results. The latter can be used conveniently in the further experimental data analysis. The numerical results show the asymmetry of the differential cross sections in $e^+e^- rightarrow pi^+ pi^-$ is about $-4%$ at $sqrt{s}sim 0.7$ GeV.
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We report results on studies of the e+e- annihilation into three-body Y(nS)pi+pi- (n=1,2,3) final states including measurements of cross sections and the full amplitude analysis. The cross sections measured at sqrt(s)=10.865 GeV and corrected for the initial state radiation are sigma(e+e-=>Y(1S)pi+pi-)=(2.27+-0.12+-0.14) pb, sigma(e+e-=>Y(2S)pi+pi-)=(4.07+-0.16+-0.45) pb, and sigma(e+e-=>Y(3S)pi+pi-)=(1.46+-0.09+-0.16) pb. Amplitude analysis of the three-body Y(nS)pi+pi- final states strongly favors I^G(J^P)=1^+(1^+) quantum-number assignments for the two bottomonium-like Zb+- states, recently observed in the Y(nS)pi+- and hb(mP)pi+- (m=1,2) decay channels. The results are obtained with a $121.4 1/fb data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider.
In this work, the two-photon-exchange (TPE) effects in $eprightarrow enpi^+$ at small $-t$ are discussed within a hadronic model. The TPE contributions to the amplitude and the unpolarized differential cross section are both estimated and we find that the TPE corrections to the unpolarized differential cross section are about $-4%sim-15%$ at $Q^2=1$GeV$^2sim1.6$GeV$^2$. After considering the TPE corrections to the experimental data sets of unpolarized differential cross section, we analyse the TPE corrections to the separated cross sections $sigma_{textrm{L,T,LT,TT}}$. We find that the TPE corrections (at $Q^2=1$GeV$^2sim1.6$GeV$^2$) to $sigma_{textrm{L}}$ are about $-10%sim -20%$, to $sigma_{textrm{T}}$ are about $20%$ and to $sigma_{textrm{LT,TT}}$ are much larger. By these analysis, we conclude that the TPE contributions in $eprightarrow enpi^+$ at small $-t$ are important to extract the separated cross sections $sigma_{textrm{L,T,LT,TT}}$ and the electromagnetic magnetic form factor of $pi^+$ in the experimental analysis.
We report the analysis of the three-body e+e- => B B-bar pi, B B*-bar pi, and B* B*-bar pi processes, including the first observation of the Zb+-(10610) =>[B B*-bar+c.c.]+- and Zb+-(10650) => [B*B*-bar]+- transitions. We measure visible cross sections for the three-body production of sigma_vis(e+e- => [B B*-bar+c.c.]+-pi-+=(11.2+-1.0(stat.)+-1.2(syst.)) pb and sigma_vis(e+e- => [B*B*-bar]+-pi-+)=(5.61+-0.73(stat.)+-0.66(syst.)) pb and set a 90% C.L. upper limit of sigma_vis(e+e- => [BB-bar]+-pi-+)<2.1 pb. The results are based on a 121.4 1/fb data sample collected with the Belle detector at a center-of-mass energy near the Y(5S) peak.
We evaluate the two-photon exchange corrections to the Lamb shift and hyperfine splitting of S states in electronic hydrogen relying on modern experimental data and present the two-photon exchange on a neutron inside the electronic and muonic atoms. These results are relevant for the precise extraction of the isotope shift as well as in the analysis of the ground state hyperfine splitting in usual and muonic hydrogen.
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.
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