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Register a new userPhotoproduction of the $f_1(1285)$ Meson
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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.
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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.
An experimental study of $omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $gamma ptoomega p$ differential cross sections are measured from threshold to the incident-photon energy $E_gamma=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_gamma$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $omega N$ scattering length $alpha_{omega p}$ is provided.
The quark structure of the $f_2(1270)$ meson has, for many years, been assumed to be a pure quark-antiquark ($qbar{q}$) resonance with quantum numbers $J^{PC} = 2^{++}$. Recently, it was proposed that the $f_2(1270)$ is a molecular state made from the attractive interaction of two $rho$-mesons. Such a state would be expected to decay strongly to final states with charged pions, due to the dominant decay $rho to pi^+ pi^-$, whereas decay to two neutral pions would likely be suppressed. Here, we measure for the first time the reaction $gamma p to pi^0 pi^0 p$, using the CLAS detector at Jefferson Lab for incident beam energies between 3.6-5.4~GeV. Differential cross sections, $dsigma / dt$, for $f_2(1270)$ photoproduction are extracted with good precision, due to low backgrounds, and are compared with theoretical calculations.
We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $vec gamma vec ptoeta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.
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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