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Register a new userAnnihilation of $bar p+pto e^++e^-+ pi^0$ and $bar p+pto gamma + pi^0$ through $omega$-meson intermediate state
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The s-channel annihilation of proton and antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such mechanism is expected to play a role at moderate values of the total energy $sqrt{s}$, when the pion is emitted around $90^{circ}$ in the center of mass. A fair comparison with the existing data is obtained taking into account scattering and annihilation channels. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.
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A measurement of the double-polarization observable $E$ for the reaction $gamma pto pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_gamma =600$~MeV to $E_gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
The spin density matrix of the $omega$ has been determined for the reaction $bar{p} p , rightarrow , omega pi^0$ with unpolarized in-flight data measured by the Crystal Barrel LEAR experiment at CERN. The two main decay modes of the $omega$ into $pi^0 gamma $ and $pi^+ pi^- pi^0$ have been separately analyzed for various $bar{p}$ momenta between 600 and 1940 MeV/c. The results obtained with the usual method by extracting the matrix elements via the $omega$ decay angular distributions and with the more sophisticated method via a full partial wave analysis are in good agreement. A strong spin alignment of the $omega$ is clearly visible in this energy regime and all individual spin density matrix elements exhibit an oscillatory dependence on the production angle. In addition, the largest contributing orbital angular momentum of the $bar{p}p$ system has been identified for the different beam momenta. It increases from $L^{max}_{bar{p}p}$ = 2 at 600 MeV/c to $L^{max}_{bar{p}p}$ = 5 at 1940 MeV/c.
We study the decay $bar{B}^{0}rightarrowLambda_{c}^{+}bar{p}pi^{+}pi^{-}$, reconstructing the Lambda_{c}^{+} baryon in the $p K^{-}pi^{+}$ mode, using a data sample of $467times 10^{6}$ $Bbar{B}$ pairs collected with the BaBar detector at the PEP-2 storage rings at SLAC. We measure branching fractions for decays with intermediate $Sigma_{c}$ baryons to be ${cal B}[bar{B}^{0}rightarrowSigma_{c}(2455)^{++}bar{p}pi^{-}]=(21.3 pm 1.0 pm 1.0 pm 5.5) times 10^{-5}$, ${cal B}[bar{B}^{0}rightarrowSigma_{c}(2520)^{++}bar{p}pi^{-}]=(11.5pm 1.0 pm 0.5 pm 3.0)times 10^{-5}$, ${cal B}[bar{B}^{0}rightarrowSigma_{c}(2455)^{0}bar{p}pi^{+}]=(9.1 pm 0.7 pm 0.4 pm 2.4)times10^{-5}$, and ${cal B}[bar{B}^{0}rightarrowSigma_{c}(2520)^{0}bar{p}pi^{+}]= (2.2 pm 0.7 pm 0.1pm 0.6) times 10^{-5}$, where the uncertainties are statistical, systematic, and due to the uncertainty on the $Lambda_{c}^{+}rightarrowprotonKmpi^{+}$ branching fraction, respectively. For decays without $Sigma_{c}(2455)$ or $Sigma_{c}(2520)$ resonances, we measure ${cal B}[bar{B}^{0}rightarrowLambda_{c}^{+}bar{p}pi^{+}pi^{-}]_{mathrm{non-Sigma_{c}}}=(79 pm 4 pm 4 pm 20)times10^{-5}$. The total branching fraction is determined to be ${cal B}[bar{B}^{0}rightarrowLambda_{c}^{+}bar{p}pi^{+}pi^{-}]_{mathrm{total}}=(123 pm 5 pm 7 pm 32)times10^{-5}$. We examine multibody mass combinations in the resonant three-particle $Sigma_{c}bar{p}pi$ final states and in the four-particle $Lambda_{c}^{+}bar{p}pi^{+}pi^{-}$ final state, and observe different characteristics for the $bar{p}pi$ combination in neutral versus doubly-charged $Sigma_{c}$ decays.
We have searched for proton decay via $pto e^+pi^0$ and $pto mu^+pi^0$ modes with the enlarged fiducial volume data of Super-Kamiokande from April 1996 to May 2018, which corresponds to 450 kton$cdot$years exposure. We have accumulated about 25% more livetime and enlarged the fiducial volume of the Super-Kamiokande detector from 22.5 kton to 27.2 kton for this analysis, so that 144 kton$cdot$years of data, including 78 kton$cdot$years of additional fiducial volume data, has been newly analyzed. No candidates have been found for $pto e^+pi^0$ and one candidate remains for $pto mu^+pi^0$ in the conventional 22.5 kton fiducial volume and it is consistent with the atmospheric neutrino background prediction. We set lower limits on the partial lifetime for each of these modes: $tau/B(pto e^+pi^0) > 2.4 times 10^{34}$ years and $tau/B(pto mu^+pi^0) > 1.6 times 10^{34}$ years at 90% confidence level.
The $e^+e^- to omega pi^0 to pi^0 pi^0 gamma$ process was investigated in the SND experiment at the VEPP-2M collider. A narrow energy interval near the $phi$-meson was scanned. The observed cross-section reveals, at the level of three standard deviation, the interference effect caused by $phi to pi^0pi^0gamma$ decay. The cross-section parameters, as well as the real and imaginary parts of the $phi$-meson related amplitude, were measured.
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