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Register a new userRadiative muon (pion) pair production in high energy electron-positron annihilation process
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Process of muon (pion) pair production with small invariant mass in the electron-positron high-energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Dell-Yan picture for differential cross section is valid in the charge-even experimental set-up. Radiative corrections both for electron block and for final state block are taken into account.
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The muon collider represents one of the most promising solutions for a future machine exploring the high energy frontier, but several challenges due to the 2.2 $mu$sec muon lifetime at rest have to be carefully considered. The LEMMA project is investigating the possibility of producing low emittance muon/antimuon pairs from the e$^+$e$^-$ annihilation process at threshold energy, resulting in small transverse emittance beams without any additional beam cooling. However most of the measurements available are performed at higher $sqrt{s}$ values. It is therefore necessary to measure muons production in positron annihilation at threshold energy and compare the experimental results with the predictions in this specific energy regime. Apart from being a topic of physical interest by itself, these near to threshold measurements can have a sizeable impact on the estimation of the ultimate luminosity achievable in a muon collider with the LEMMA injection scheme.
Using a sample of $1.31times 10^9$ $J/psi$ events collected with the BESIII detector, we report the first observation of spin polarization of $Lambda$ and $barLambda$ hyperons from the coherent production in the $J/psitoLambdabarLambda$ decay. We measure the phase between the hadronic form factors to be $DeltaPhi=(42.4pm0.6pm0.5)^circ$. The decay parameters for $Lambdato ppi^-$ ($alpha_-$), $barLambdatobar ppi^+$ ($alpha_+$) and $barLambdatobar npi^0$ ($baralpha_0$) are measured to be $alpha_-=0.750pm0.009pm0.004$, $alpha_+=-0.758pm0.010pm0.007$ and $baralpha_0=-0.692pm0.016pm0.006$, respectively. The obtained value of $alpha_-$ is higher by $(17pm 3)%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006pm0.012pm0.007$ is extracted with substantially improved precision. The ratio $bar{alpha}_0/alpha_{+} = 0.913pm 0.028 pm 0.012$ is also measured.
In this work we study the e^{+}e^{-}tophi K^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the gamma*phi K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies using Rchi PT supplemented with the anomalous term for the VVP interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in Uchi PT in the former case and the ones extracted from recent data on e^{+}e^{-}to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(Xto phi f_{0})Gamma (Xto e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}to phi K^{+}K^{-} around 2.2 GeV.
This paper presents the high-precision theoretical predictions for $e^+e^- to l^-l^+$ scattering. Calculations are performed using the {tt SANC} system. They take into account complete one-loop electroweak radiative corrections as well as longitudinal polarization of initial beams. Reaction observables are obtained using the helicity amplitude method with taking into account initial and final state fermion masses. Numerical results are given for the center-of-mass energy range $sqrt{s}=250-1000$ GeV with various degrees of polarization.
The cross section for muon pair productions by electrons scattering over photons, $sigma_{MPP}$, is calculated analytically in the leading order. It is pointed out that for the center-of-mass energy range, $s geq 5 m^{2}_{mu}$, the cross section for $sigma_{MPP}$ is less than $1 mu $b. The differential energy spectrum for either of the resulting muons is given for the purpose of high-energy neutrino astronomy. An implication of our result for a recent suggestion concerning the high-energy cosmic neutrino generation through this muon pair is discussed.
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