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Register a new userIsoscalar Single-Pion Production in the Region of Roper and $d^*(2380)$ Resonances
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Exclusive measurements of the quasi-free $pn to pppi^-$ and $pp to pppi^0$ reactions have been performed by means of $pd$ collisions at $T_p$ = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region $T_p = 0.95 - 1.3$ GeV ($sqrt s$ = 2.3 - 2.46 GeV), which includes the regions of $Delta(1232)$, $N^*(1440)$ and $d^*(2380)$ resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below $T_p$ = 1 GeV. We observe a substantial increase of this cross section above 1 GeV, which can be related to the Roper resonance $N^*(1440)$, the strength of which shows up isolated from the $Delta$ resonance in the isoscalar $(Npi)_{I=0}$ invariant-mass spectrum. No evidence for a decay of the dibaryon resonance $d^*(2380)$ into the isoscalar $(NNpi)_{I=0}$ channel is found. An upper limit of 90 $mu$b (90 $%$ C.L.) corresponding to a branching ratio of 5 $%$ has been deduced.
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In arxiv: 2102.05575 a two-step process $pn to (pp) pi^- to (Delta N) pi^- to (d pi^+) pi^-$ was calculated by using experimental total cross sections for the single-pion production processes $pn to pp pi^-(I=0)$ and $pp to d pi^+$. As a result the authors obtain a resonance-like structure for the total $pn to dpi^+pi^-$ cross section of about the right size and width of the observed $d^*(2380)$ peak at an energy about 40 MeV below the $d^*(2380)$ mass. We object both the results of the sequential process calculation and its presentation as an alternative to the dibaryon interpretation.
New data on quasifree polarized neutron-proton scattering, in the region of the recently observed $d^*$ resonance structure, have been obtained by exclusive and kinematically complete high-statistics measurements with WASA at COSY. This paper details the determination of the beam polarization, checks of the quasifree character of the scattering process, on all obtained $A_y$ angular distributions and on the new partial-wave analysis, which includes the new data producing a resonance pole in the $^3D_3$-$^3G_3$ coupled partial waves at ($2380pm10 - i40pm5$) MeV -- in accordance with the $d^*$ dibaryon resonance hypothesis. The effect of the new partial-wave solution on the description of total and differential cross section data as well as specific combinations of spin-correlation and spin-transfer observables available from COSY-ANKE measurements at $T_d$ = 2.27 GeV is discussed.
We report the first large-acceptance measurement of the beam-spin asymmetry for deuteron photodisintegration ($vec{gamma} dto pn$) in the photon energy range $400<E_{gamma}<630$~MeV. The measurement provides important new constraints on the mechanisms of photodisintegration above the delta resonance and on the photocoupling of the recently discovered $d^*(2380)$ hexaquark.
Based on measurements the branching ratios for the decay of the recently discovered dibaryon resonance $d^*(2380)$ into two-pion production channels and into the $np$ channel are evaluated. Possibilities for a decay into the isoscalar single-pion channel are discussed. Finally also the electromagnetic decay of $d^*(2380)$ is considered.
The purpose of the present study was to explore the possibility of accommodating the $d^*(2380)$ and its flavor SU(3) partners in a diquark model. Proposing that $d^*(2380)$ is composed of three vector diquarks, its mass is calculated by use of an effective Hamiltonian approach and its decay width is estimated by considering the effects of quark tunneling from one diquark to the others and the decays of the subsequent two-baryon bound state. Both the obtained mass and decay width of $d^*(2380)$ are in agreement with the experimental data, with the unexpected narrow decay width being naturally explained by the large tunneling suppression of a quark between a pair of diquarks. The masses and decay widths of the flavor SU(3) partners of $d^*(2380)$ are also predicated within the same diquark scenario.
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