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Register a new userComment on Sequential Single-Pion Production Explaining the Dibaryon $d^*(2380)$ Peak
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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.
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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.
The $DeltaDelta$ dibaryon resonance $d^ast (2380)$ with $(J^P, I)=(3^+, 0)$ is studied theoretically on the basis of the 3-flavor lattice QCD simulation with heavy pion masses ($m_pi =679, 841$ and $1018$ MeV). By using the HAL QCD method, the central $Delta$-$Delta$ potential in the ${}^7S_3$ channel is obtained from the lattice data with the lattice spacing $asimeq 0.121$ fm and the lattice size $Lsimeq 3.87$ fm. The resultant potential shows a strong short-range attraction, so that a quasi-bound state corresponding to $d^ast (2380)$ is formed with the binding energy $25$-$40$ MeV below the $DeltaDelta$ threshold for the heavy pion masses. The tensor part of the transition potential from $DeltaDelta$ to $NN$ is also extracted to investigate the coupling strength between the $S$-wave $DeltaDelta$ system with $J^P=3^+$ and the $D$-wave $NN$ system. Although the transition potential is strong at short distances, the decay width of $d^ast (2380)$ to $NN$ in the $D$-wave is kinematically suppressed, which justifies our single-channel analysis at the range of the pion mass explored in this study.
MiniBooNE [1] and MINERvA [2] charge current {pi} + production data in the Delta region are discussed. It is argued that despite the differences in neutrino flux they measure the same dynamical mechanism of pion production and should be strongly correlated. The correlation is clearly seen in the Monte Carlo simulations done with NuWro generator but is missing in the data. Both normalization and the shape of the ratio of measured differential cross sections in pion kinetic energy are different from the Monte Carlo results, in the case of normalization a discrepancy is by a factor of 1.49.
The narrow peak recently found in various pionic double charge exchange (DCX) cross sections can be explained by the assumption of a universal resonance at 2065 MeV, called d. We calculate the mass of a six-quark system with J^P=0^-, T=0 quantum numbers employing a cluster model and a shell model basis to diagonalize the nonrelativistic quark model Hamiltonian.
We calculate the mass and structure of a J^P=0^-, T=0 six-quark system using a colored diquark-tetraquark cluster wave function and a nonrelativistic quark model Hamiltonian. The calculated mass is some 350 MeV above the empirical value if the same confinement strength as in the nucleon is used. If the effective two-body confinement strength is weaker in a compound six-quark system than in a single baryon, as expected from a simple harmonic oscillator model, one obtains M_d = 2092 MeV close to experiment.
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