Branching Ratios for the Decay of d∗(2380)d^*(2380)

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

Examination of the Nature of the ABC Effect

Recently it has been shown by exclusive and kinematically complete experiments that the appearance of a narrow resonance structure in double-pionic fusion reactions is strictly correlated with the appearance of the so-called ABC effect, which denotes a pronounced low-mass enhancement in the $\pi\pi$-invariant mass spectrum. Whereas the resonance structure got its explanation by the $d^*(2380)$ dibaryonic resonance, a satisfactory explanation for the ABC effect is still pending. In this paper we discuss possible explanations of the ABC effect and their consequences for the internal structure of the $d^*$ dibaryon

Measurement of np->npπ0π0 reaction in search for the recently observed d*(2380) resonance

Exclusive measurements of the quasi-free np →npπ0π0reaction have been performed by means of dpcollisions at Td=2.27GeVusing the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region √s=(2.35–2.46)GeV, which includes the region of the ABC effect and its associated d∗(2380)resonance. Adding the d∗resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Fäldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e.the low-mass enhancement in the π0π0-invariant mass spectrum, is found to be very modest – if present at all, which might pose a problem to some of its interpretations

The ABC Effect in Double-Pionic Nuclear Fusion and a pn Resonance as its Possible Origin

The ABC effect -- a long-standing puzzle in double-pionic fusion -- has been reexamined by the first exclusive and kinematically complete measurements of solid statistics for the fusion reactions $pn \to d\pi^0\pi^0$, $pd \to ^3$He$\pi\pi$ and $dd \to ^4$He$\pi\pi$ using the WASA detector, first at CELSIUS and recently at COSY -- the latter with a statistics increased by another two orders of magnitude. In all cases we observe a huge low-mass enhancement in the $\pi\pi$-invariant mass accompanied by a pronounced $\Delta\Delta$ excitation. For the most basic fusion reaction, the $pn \to d\pi^0\pi^0$ reaction, we observe in addition a very pronounced resonance-like energy dependence in the total cross section with a maximum 90 MeV below the $\Delta\Delta$ mass and a width of only 50 MeV, which is five times smaller than expected from a conventional $t$-channel $\Delta\Delta$ excitation. This reveals the ABC effect to be the consequence of a s-channel resonance with the formfactor of this dibaryonic state being reflected in the low-mass enhancement of the $\pi\pi$-invariant mass. From the fusion reactions to $^3$He and $^4$He we learn that this resonance is robust enough to survive even in nuclei.Comment: conference proceedings PANIC 0

Systematic Study of Two-Pion Production in NN Collisions -- from Single-Baryon to Di-Baryon Excitations

The two-pion production in nucleon-nucleon collisions has been studied by exclusive and kinematically complete experiments from threshold up to $T_p$ = 1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential distributions for the $\pi^+\pi^-$ and $\pi^0\pi^0$ channels are dominated by Roper excitation and its decay into $N\sigma$ and $\Delta\pi$ channels. At beam energies $T_p >$ 1.1 GeV the $\Delta\Delta$ excitation governs the two-pion production process. In the $\pi^+\pi^+$ channel evidence is found for the excitation of a higher-lying I=3/2 resonance, favorably the $\Delta(1600)$. The isovector fusion processes leading to the deuteron and to quasi-stable $^2$He, respectively, %with the production of an isovector pion-pair exhibit no or only a modest ABC-effect, {\it i.e.} low-mass enhancement in the $\pi\pi$-invariant mass spectrum, and can be described by conventional $t$-channel $\Delta\Delta$ excitation. On the other hand, the isoscalar fusion process to the deuteron %with the production of an isoscalar pion-pair exhibits a dramatic ABC-effect correlated with a narrow resonance-like energy dependence in the total cross section with a width of only 50 MeV and situated at a mass 90 MeV below the $\Delta\Delta$ mass.Comment: Proceedings HADRON0

Baryon Resonance Analysis from SAID

We discuss the analysis of data from piN elastic scattering and single pion photo- and electroproduction. The main focus is a study of low-lying non-strange baryon resonances. Here we concentrate on some difficulties associated with resonance identification, in particular the Roper and higher P11 states.Comment: 4 pages, 6 figures; Nstar2009 Conf Proceedings; small revisio

Nature of S\bm{S}-wave NN\bm{NN} interaction and dibaryon production at nucleonic resonance thresholds

Phase shifts and inelasticity parameters for $NN$ scattering in the partial-wave channels ${}^3S_1$--${}^3D_1$ and ${}^1S_0$ at energies $T_{\rm lab}$ from zero to about 1 GeV are described within a unified $NN$ potential model assuming the formation of isoscalar and isovector dibaryon resonances near the $NN^*(1440)$ threshold. Evidence for these near-threshold resonances is actually found in the recent WASA experiments on single- and double-pion production in $NN$ collisions. There, the excitation of the Roper resonance $N^*(1440)$ exhibits a structure in the energy dependence of the total cross section, which corresponds to the formation of dibaryon states with $I(J^\pi)=0(1^+)$ and $1(0^+)$ at the $NN^*(1440)$ threshold. These two $S$-wave dibaryon resonances may provide a new insight into the nature of the strong $NN$ interaction at low and intermediate energies.Comment: 10 pages, 8 figure

Encounters with di-baryons - from the ABC effect to a new resonance?

The ABC effect, an intriguing low-mass enhancement in the $\pi\pi$ invariant mass spectrum, is known from inclusive measurements of two-pion production in nuclear fusion reactions to the few-body systems d, $^{3}$He and $^{4}$He. It was first observed 1960 by Abashian, Booth and Crowe in the inclusive pd $\to$ $^{3}$He X reaction. Its explanation has been a puzzle since then. In an effort to solve this long-standing problem by exclusive and kinematically complete high-statistics experiments, we have measured the fusion reactions to d, $^{3}$He and $^{4}$He with WASA-at-COSY. These measurements cover the full energy region, where the ABC effect has been observed previously in inclusive reactions. In a recent kinematically complete measurement of the $pn \to d\pi ^{0}\pi ^{0}$ reaction we have shown that the ABC effect in this basic double-pionic fusion reaction is correlated with a narrow structure in the total cross section with quantum numbers I(J$^{P}$) = 0(3$^{+}$), a mass of 2.37 GeV and a width of about 70 MeV. The mass is about 90 MeV below 2 times the mass of $\Delta$, the mass of a $\Delta\Delta$ system, and the width is three times narrower than expected from a conventional t-channel $\Delta\Delta$ process. In the double-pionic fusion reaction to the helium isotope $dd \to ^{4}$He$\pi ^{0}\pi ^{0}$ again the ABC effect is observed to be correlated with the appearance of a resonance-like structure in the total cross section at the same excess energy. From a previous exclusive experiment at CELSIUS-WASA it is known that the double-pionic fusion to $^{3}$He also exhibits a pronunced ABC effect. New data from COSY on the $pd \to ^{3}$He$\pi ^{0}\pi ^{0}$ reaction scanning the full ABC region are presented as well as the status of measurements in other reaction channels, where the new resonance might contribute

Experimental and theoretical evidences for an intermediate σ\sigma-dressed dibaryon in the NN interaction

Numerous theoretical and experimental arguments are presented in favor of the generation of intermediate $\sigma$-dressed dibaryon in $NN$ interaction at intermediate and short distances. We argue that this intermediate dibaryon can be responsible for the strong intermediate-range attraction and the short-range repulsion in the $NN$ interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the $\sigma$-dressing of the dibaryon is identical to that which explains the Roper resonance structure, its dominant decay modes and its extraordinary low mass. A similar transformation mechanism from the glue to the scalar field was discovered in $J/\Psi$ decays. The new experimental data on 2$\pi$-production in the scalar-isoscalar channel produced in $pn$- and $pd$-collisions and in particular the very recent data on $\gamma\gamma$ correlations in $p$C and $d$C scattering in the GeV region seems to corroborate the existence of the $\sigma$-dressed dibaryon in two- and three nucleon interactions.Comment: 14 pages,4 figure