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Register a new userSearch for a strangeonium-like structure $Z_s$ decaying into $phi pi$ and a measurement of the cross section $e^+e^-rightarrowphipipi$
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Using a data sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 108 pb$^{-1}$ collected with the BESIII detector at a center-of-mass energy of 2.125 GeV, we study the process $e^+e^-rightarrow phipipi$ and search for a strangeoniumlike structure $Z_s$ decaying into $phipi$. No signal is observed in the $phipi$ mass spectrum. Upper limits on the cross sections for $Z_s$ production at the 90% confidence level are determined. In addition, the cross sections of $e^+e^-rightarrowphipi^{+}pi^{-}$ and $e^+e^-rightarrowphipi^{0}pi^{0}$ at 2.125 GeV are measured to be $(436.2pm6.4pm30.1)$ pb and $(237.0pm8.6pm15.4)$ pb, respectively, where the first uncertainties are statistical and the second systematic.
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We study the process e+e- -> pi+pi-pi+pi-gamma, with a photon emitted from the initial-state electron or positron, using 454.3 fb^-1 of data collected with the BABAR detector at SLAC, corresponding to approximately 260,000 signal events. We use these data to extract the non-radiative sigma(e+e- ->pi+pi-pi+pi-) cross section in the energy range from 0.6 to 4.5 Gev. The total uncertainty of the cross section measurement in the peak region is less than 3%, higher in precision than the corresponding results obtained from energy scan data.
We report the results of a search for a light pseudoscalar particle $a$ that couples to electrons and decays to $e^+e^-$ performed using the high-energy CERN SPS H4 electron beam. If such pseudoscalar with a mass $simeq 17$ MeV exists, it could explain the ATOMKI anomaly. We used the NA64 data samples collected in the visible mode configuration with total statistics corresponding to $8.4times 10^{10}$ electrons on target (EOT) in 2017 and 2018. In order to increase sensitivity to small coupling parameter $epsilon$ we used also the data collected in 2016-2018 in the invisible mode configuration of NA64 with a total statistics corresponding to $2.84times 10^{11}$ EOT. A thorough analysis of both these data samples in the sense of background and efficiency estimations was already performed and reported in our previous papers devoted to the search for light vector particles and axion-like particles (ALP). In this work we recalculate the signal yields, which are different due to different cross section and life time of a pseudoscalar particle $a$, and perform a new statistical analysis. As a result, the region of the two dimensional parameter space $m_a - epsilon$ in the mass range from 1 to 17.1 MeV is excluded. At the mass of the ATOMKI anomaly the values of $epsilon$ in the range $2.1 times 10^{-4} < epsilon < 3.2 times 10^{-4}$ are excluded.
The cross section of the process e+e- -> pi+pi- has been measured using about 114000 events collected by the CMD-2 detector at the VEPP-2M e+e- collider in the center-of-mass energy range from 0.61 to 0.96 GeV. Results of the pion form factor determination with a 0.6% systematic uncertainty are presented. Implications for the hadronic contribution to the muon anomalous magnetic moment are discussed.
Using a data set with an integrated luminosity of 2.93 fb$^{-1}$ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider, we extract the $e^+e^-rightarrow pi^+pi^-$ cross section and the pion form factor $|F_pi|^2$ in the energy range between 600 and 900 MeV. We exploit the method of initial state radiation for this measurement, yielding a systematic uncertainty of 0.9%. We calculate the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to $(g-2)_mu$.
We search for the process $e^{+}e^{-}rightarrow pi ^{+}pi ^{-} chi_{cJ}$ ($J=0,1,2$) and for a charged charmonium-like state in the $pi ^{pm} chi_{cJ}$ subsystem. The search uses data sets collected with the BESIII detector at the BEPCII storage ring at center-of-mass energies between 4.18 GeV and 4.60 GeV. No significant $pi ^{+}pi ^{-} chi_{cJ}$ signals are observed at any center-of-mass energy, and thus upper limits are provided which also serve as limits for a possible charmonium-like structure in the invariant $pi ^{pm} chi_{cJ}$ mass.
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