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Register a new userSearch for direct production of the $f_1(1285)$ resonance in $e^+e^-$ collisions
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A search for direct production of the $f_1(1285)$ resonance in $e^+e^-$ annihilation is performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The analysis is based on data with an integrated luminosity of 15.1 pb$^{-1}$ accumulated in the center-of-mass energy range 1.2--1.4 GeV. Two $e^+e^-to f_1(1285)$ candidate events are found at the peak of the resonance and zero events beyond the resonance. The significance of the $e^+e^-to f_1(1285)$ signal is $2.5sigma$. The cross section at the maximum of the resonance is found to be $sigma(e^+e^-to f_1)=45^{+33}_{-24}$ pb. The corresponding branching fraction $B(f_1(1285)to e^+e^-)=(5.1^{+3.7}_{-2.7})times 10^{-9}$. We consider this result as a first indication of the process $e^+e^-to f_1(1285)$. The measured branching fraction is consistent with the theoretical prediction.
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A search for direct production of C-even resonances a2(1320) and f2(1270) in e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The upper limits of electronic widths of these mesons were obtained at 90% confidence level: Gamma(a2(1320) to e+e-) < 0.56 eV, Gamma(f2(1270) to e+e-) < 0.11 eV.
Decays of Bs and B0 mesons into J/psi pi +pi -pi +pi - final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3/fb collected with the LHCb detector. B^0_(s) -> Jpsi f_1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and non-strange components of its wave function in the q-qbar structure model is determined to be pm (24.0^{+3.1+0.6}_{-2.6-0.8}) degrees. Implications on the possible tetraquark nature of the f_1(1285) are discussed.
The $f_1(1285)$ meson with mass $1281.0 pm 0.8$ MeV/$c^2$ and width $18.4 pm 1.4$ MeV (FWHM) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the $etapi^{+}pi^{-}$, $K^+bar{K}^0pi^-$, and $K^-K^0pi^+$ decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the $etapi^{+}pi^{-}$ final-state Dalitz distribution are consistent with the axial-vector $J^P=1^+$ $f_1(1285)$ identity, rather than the pseudoscalar $0^-$ $eta(1295)$. The production mechanism is more consistent with $s$-channel decay of a high-mass $N^*$ state, and not with $t$-channel meson exchange. Decays to $etapipi$ go dominantly via the intermediate $a_0^pm(980)pi^mp$ states, with the branching ratio $Gamma(a_0pi text{ (no} bar{K} Ktext{)}) / Gamma(etapipi text{(all)}) = 0.74pm0.09$. The branching ratios $Gamma(K bar{K} pi)/Gamma(etapipi) = 0.216pm0.033$ and $Gamma(gammarho^0)/Gamma(etapipi) = 0.047pm0.018$ were also obtained. The first is in agreement with previous data for the $f_1(1285)$, while the latter is lower than the world average.
We present a search for the direct production of a light pseudoscalar $a$ decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process ${e^+e^-togamma a, a togammagamma}$ in the mass range ${0.2} ,< m_a < {9.7},{text{GeV/$c$}^2}$ using data corresponding to an integrated luminosity of $(445pm 3),text{pb}^{-1}$. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axion-like particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength $g_{agammagamma}$ of ALPs to photons at the level of $10^{-3},{text{GeV}^{-1}}$. The limits are the most restrictive to date for $0.2,<,m_a,<,1,{text{GeV/$c$}^2}$.
We present results of a direct search for the decay K_S->e+e- with the KLOE detector, obtained with a sample of e+e- -> phi -> K_S K_L events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.9 fb-1. The Standard Model prediction for this decay is BR(K_S->e+e-) = 2 x 10^-14. The search has been performed by tagging the K_S decays with simultaneous detection of a K_L interaction in the calorimeter. Background rejection has been optimized by using both kinematic cuts and particle identification. At the end of the analysis chain we find BR(K_S->e+e-) < 9.3 x 10^-9 at 90% CL, which improves by a factor of ~15 on the previous best result, obtained by CPLEAR experiment.
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