Kavli Affiliate: Ke Wang
| First 5 Authors: Ke Wang, Rong Li, Bo-Chao Liu, ,
| Summary:
In this work, we study the role of triangle singularity in the $J/psi to
gamma bar{p} Delta$ decay. We find that through a triangle mechanism,
involving a triangle loop composed by $omega$, $pi$ and $p$, this decay may
develop a triangle singularity and produce a visible peak in the invariant mass
$M_{gammaDelta}$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle
mechanism may also cause significant spin effects on the final $Delta$, which
can be detected by measuring its spin density matrix elements. Our calculations
show that the branching ratios due to the triangle mechanism is Br($J/psito
gamma bar pDelta,Deltato pi p$)=$1.058times 10^{-6}$. Hopefully, this
reaction can be investigated at BESIII and future experiments, e.g. Super
Tau-Charm Facility, and the narrow width of the induced structure, the moving
TS position and the distinct features of the spin density matrix elements of
the $Delta$ may serve as signals for the triangle singularity mechanism.
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