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Register a new userDetecting the pure triangle sigularity effect through the $psi(2S) to p bar{p} eta / p bar{p} pi^0$ process
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In this work, the triangle singularity mechanism is investigated in the $psi(2S) to p bar{p} eta / p bar{p} pi^0$ process. The triangle loop composed by $J/psi$, $eta$ and $p$ has a singularity in the physical kinematic range for the $psi(2S) to p bar{p} eta / p bar{p} pi^0$ process, and it would generate a very narrow peak in the invariant mass spectrum of $peta (pi)$ around $1.56387$ GeV, which is far away from both the threshold and relative resonances. In these processes, all the involved vertices are constrained by the experimental data. Thus, we can make a precise model independent prediction here. It turns out that the peak in the $peta$ invariant mass spectrum is visible, while it is very small in the $ppi^0$ invariant mass spectrum. We expect this effect shown in $p bar{p} eta$ final state can be observed by the Beijing Spectrometer (BESIII) and Super Tau-Charm Facility (STCF) in the future.
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Using a sample of $1.06 times 10^{8}$ $psi(2S)$ events collected with the BESIII detector at BEPCII, the decay $psi(2S) to p bar{p}eta$ is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of $1524pm5^{+10}_{-4}$ MeV/$c^2$ and a width of $130^{+27+57}_{-24-10}$ MeV/$c^2$ is dominant in the decay; the product branching fraction is determined to be $B(psi(2S) to N(1535)bar{p})times B(N(1535)to peta)+c.c. = (5.2pm0.3^{+3.2}_{-1.2})times 10^{-5}$. Furthermore, the branching fraction of $psi(2S) to eta p bar{p}$ is measured to be $(6.4pm0.2pm0.6)times 10^{-5}$.
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.
Nucleon pole contributions in $J/psi to N bar N pi$, $p bar p eta$, $p bar p eta^{prime}$ and $p bar{p} omega$ decays are re-studied. Different contributions due to PS-PS and PS-PV couplings in the $pi$-N interaction and the effects of $NNpi$ form factors are investigated in the $J/psi to N bar N pi$ decay channel. It is found that when the ratio of $|F_0| /|F_M|$ takes small value, without considering the $NNpi$ form factor, the difference between PS-PS and PS-PV couplings are negligible. However, when the $NNpi$ form factor is included, this difference is greatly enlarged. The resultant decay widths are sensitive to the form factors. As a conclusion, the nucleon-pole contribution as a background is important in the $J/psito Nbar{N}pi$ decay and must be accounted. In the $J/psito Nbar{N}eta$ and $Nbar{N}eta$ decays, its contribution is less than 0.1% of the data. In the $J/psito Nbar{N}omega$ decay, it provides rather important contribution without considering form factors. But the contribution is suppressed greatly when adding the off-shell form factors. Comparing these results with data would help us to select a proper form factor for such kind of decay.
An amplitude analysis of flavour-untagged $B_s^0 to J/psi p bar{p}$ decays is performed using a sample of $797pm31$ decays reconstructed with the LHCb detector. The data, collected in proton-proton collisions between 2011 and 2018, correspond to an integrated luminosity of 9 $text{fb}^{-1}$. Evidence for a new structure in the $J/psi p$ and $J/psi bar{p}$ systems with a mass of $4337 ^{+7}_{-4} ^{+2}_{-2}~text{MeV}$ and a width of $29 ^{+26}_{-12} ^{+14}_{-14}~text{MeV}$ is found, where the first uncertainty is statistical and the second systematic, with a significance in the range of 3.1 to 3.7 $sigma$, depending on the assigned $J^P$ hypothesis.
Provided the enhancement in the $p bar{p}$ spectrum in radiative decay $J/psi to gamma p bar{p}$ observed by the BES collaboration is due to an existence of a $p bar{p}$ molecular state, we calculate its binding energy and lifetime in the linear $sigma$ model. We consider a possibility that the enhancement is due to a $p bar p$ resonance which is in either S-wave or P-wave structure and compare our results with the data.
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