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تسجيل مستخدم جديدGeneralized two-point tree-level amplitude $jf to j^{, prime} f^{, prime}$ in a magnetized medium (extended version)
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The tree-level two-point amplitudes for the transitions $jf to j^{, prime} f^{, prime}$, where $f$ is a fermion and $j$ is a generalized current, in a constant uniform magnetic field of an arbitrary strength and in charged fermion plasma, for the $jf$ interaction vertices of the scalar, pseudoscalar, vector and axial-vector types have been investigated. The particular cases of a very strong magnetic field, and of the coherent scattering off the real fermions without change of their states (the forward scattering) have been analysed.
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The tree-level two-point amplitudes for the transitions $jf to j^{, prime} f^{, prime}$, where $f$ is a fermion and $j$ is a generalized current, in a constant uniform magnetic field of an arbitrary strength and in charged fermion plasma, for the $jf
f$ interaction vertices of the scalar, pseudoscalar, vector and axial-vector types have been calculated. The generalized current $j$ could mean the field operator of a boson, or a current consisting of fermions, e.g. the neutrino current. The particular cases of a very strong magnetic field, and of the coherent scattering off the real fermions without change of their states (the forward scattering) have been analysed. The contribution of the neutrino photoproduction process, $gamma eto e u bar u$, to the neutrino emissivity has been calculated with taking account of a possible resonance on the virtual electron.
We have measured several branching ratios for $psi^prime$ decay using the data collected by FNAL E835 experiment during year 2000, obtaining ${cal B}(psi^prime to e^+ e^-) = 0.0068pm0.0001pm0.0004$, ${cal B}(psi^prime to J/psi pi^+ pi^-) = 0.292pm0.0
05pm0.018$, ${cal B}(psi^prime to J/psi pi^0 pi^0) = 0.167pm0.005pm0.014$ and ${cal B}(psi^prime to J/psi eta) = 0.028pm0.002pm0.002$. We also present a measurement of the dipion mass distribution in the decays $psi^prime to J/psi pi pi$.
Using a sample of $1.31times10^{9} ~J/psi$ events collected with the BESIII detector, we perform a study of $J/psitogammaetaetaeta^{prime}$ to search for the $X(2370)$ and $eta_{c}$ in the $etaetaeta^{prime}$ invariant mass distribution. No significa
nt signal for the $X(2370)$ is observed, and we set an upper limit for the product branching fraction of ${cal B}(J/psitogamma X(2370)cdot{cal B}(X(2370)toetaetaeta^{prime}) < 9.2times10^{-6}$ at the 90% confidence level. A clear $eta_{c}$ signal is observed for the first time, yielding a product branching fraction of ${cal B}(J/psito gammaeta_{c})cdot{cal B}(eta_{c}to etaetaeta^{prime}) = (4.86pm0.62~({rm stat.})pm0.45~({rm sys.}))times10^{-5}$.
We present a search for the dark photon $A^{prime}$ in the $B^0 to A^{prime} A^{prime}$ decays, where $A^{prime}$ subsequently decays to $e^+ e^-$, $mu^+ mu^-$, and $pi^+ pi^-$. The search is performed by analyzing $772 times 10^6$ $Boverline{B}$ eve
nts collected by the Belle detector at the KEKB $e^+ e^-$ energy-asymmetric collider at the $Upsilon (4S)$ resonance. No signal is found in the dark photon mass range $0.01~mathrm{GeV}/c^2 le m_{A^{prime}} le 2.62~mathrm{GeV}/c^2$, and we set upper limits of the branching fraction of $B^0 to A^{prime} A^{prime}$ at the 90% confidence level. The products of branching fractions, $mathcal{B}(B^0 to A^{prime} A^{prime}) times mathcal{B}(A^{prime} to e^+ e^-)^2$ and $mathcal{B}(B^0 to A^{prime} A^{prime}) times mathcal{B}(A^{prime} to mu^+ mu^-)^2$, have limits of the order of $10^{-8}$ depending on the $A^{prime}$ mass. Furthermore, considering $A^{prime}$ decay rate to each pair of charged particles, the upper limits of $mathcal{B}(B^0 to A^{prime} A^{prime})$ are of the order of $10^{-8}$-$10^{-5}$. From the upper limits of $mathcal{B}(B^0 to A^{prime} A^{prime})$, we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of $10^{-2}$-$10^{-1}$ at $m_{h} simeq m_{B^0} pm 40~mathrm{MeV}/c^2$ and $10^{-1}$-$1$ at $m_{h} simeq m_{B^0} pm 3~mathrm{GeV}/c^2$.
We observe the process $psi(3686) to p bar{p} eta^{prime}$ for the first time, with a statistical significance higher than 10$sigma$, and measure the branching fraction of $J/psi to p bar{p} eta^{prime}$ with an improved accuracy compared to earlier
studies. The measurements are based on $4.48 times 10^8$ $psi(3686)$ and $1.31 times 10^{9}$ $J/psi$ events collected by the BESIII detector operating at the BEPCII. The branching fractions are determined to be $B(psi(3686) to p bar{p} eta^{prime}) = (1.10pm0.10pm0.08)times10^{-5}$ and $B(J/psi to p bar{p} eta^{prime})=(1.26pm0.02pm 0.07)times10^{-4}$, where the first uncertainties are statistical and the second ones systematic. Additionally, the $eta-eta^{prime}$ mixing angle is determined to be $-24^{circ} pm 11^{circ}$ based on $psi(3686) to p bar{p} eta^{prime}$, and $-24^{circ} pm 9^{circ}$ based on $J/psi to p bar{p} eta^{prime}$, respectively.
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