Two-pion production in proton–proton collisions — experimental total cross sections and their isospin decomposition

Skorodko, T.; Bashkanov, M.; Bogoslawsky, D.; Calén, H.; Clement, H.; Doroshkevich, E.; Demiroers, L.; Ekström, C.; Fransson, K.; Gustafsson, L.; Höistad, B.; Ivanov, G.; Jacewicz, M.; Jiganov, E.; Johansson, T.; Khakimova, O.; Keleta, S.; Koch, I.; Kren, F.; Kullander, S.; Kupść, A.; Marciniewski, P.; Meier, R.; Morosov, B.; Pauly, C.; Petrén, H.; Petukhov, Y.; Povtorejko, A.; Ruber, Roger; Schönning, K.; Scobel, W.; Shwartz, B.; Steṕaniak, J.; Thörngren-Engblom, P.; Tikhomirov, V.; Wagner, G. J.; Wolke, M.; Yamamoto, A.; Zabierowski, J.; Złomańczuk, J.

doi:10.1016/j.physletb.2009.07.012

Cited by 59 publications

(69 citation statements)

References 26 publications

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“…On the contrary the basic isovector fusion process pp → dπ + π 0 exhibits neither an ABC effect nor a narrow resonance structure [14,15] in this particular energy region -in agreement with the observations in all other two-pion channels of pp initiated reactions [16][17][18][19][20][21][22][23][24][25][26][27], i.e. of isovector reactions.…”

Section: Introductionsupporting

confidence: 80%

ABC Effect in Double-Pionic Fusion – a New Resonance?

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Bashkanov

Clement

et al. 2012

EPJ Web of Conferences

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Abstract. The ABC effect, an intriguing low-mass enhancement in the ππ invariant mass spectrum -known since more than 50 years from inclusive measurements of double-pionic fusion reactions -is reexamined. To this end exclusive and kinematically complete high-statistics experiments of the fusion reactions to d, 3 He and 4 He have been carried out with WASA at COSY. These measurements cover the full energy region, where the ABC effect has been observed previously. They also complement the systematic measurements of nucleon-nucleon induced two-pion production. An isospin decomposition of all three basic double-pionic fusion reactions leading to the deuteron uniquely shows that solely the isoscalar reaction part exhibits the ABC effect tightly correlated with a narrow resonance structure in the total cross section. The peak energy of the resonance structure is about 90 MeV below the nominal ∆∆ threshold of 2 m ∆ and its width of only 70 MeV is much less than the 2 Γ ∆ expected from the conventional t-channel ∆∆ process. Based on angular distributions the quantum numbers I(J P ) = 0(3 + ) have been assigned. In the double-pionic fusion reaction dd → 4 Heπ 0 π 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 this we conclude that this resonance structure obviously is strong enough to survive even in nuclei.

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Section: Introductionsupporting

confidence: 80%

ABC Effect in Double-Pionic Fusion – a New Resonance?

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Bashkanov

Clement

et al. 2012

EPJ Web of Conferences

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“…Isospin decomposition according to Refs. [53][54][55] gives roughly half of the background processes to be isovector, i.e. about 15% of the total cross section.…”

Section: Description Of the D * (2380) Resonance Processmentioning

confidence: 99%

Examination of the nature of the ABC effect

2017

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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 ππ-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. To this end we examine and review a variety of proposed explanations for the ABC effect, add a new hypothesis and confront all of them with the experimental results for the np → dπ 0 π 0 and np → npπ 0 π 0 reactions, which are the most challenging ones for this topic.

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“…[16] this reaction is reasonably well described by conventional t-channel ∆∆ excitation, which is known to be the leading process in all pp induced, i.e. isovector two-pion production channels at beam energies above 1 GeV [18,19].…”

Section: Experiments and Resultsmentioning

confidence: 99%

Isospin Decomposition of the Basic Double-Pionic Fusion in the Region of the ABC Effect

Bashkanov

Clement

Doroshkevich

et al. 2012

EPJ Web of Conferences

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Abstract.With a proton beam of T p = 1.2 GeV incident on the deuterium pellet target of the WASA detector setup all three basic double-pionic fusion reactions have been measured simultaneously. By use of quasifree kinematics the energy range 2.3 GeV ≤ √ s < 2.5 GeV could be covered, which just coincides with the energy region, where the ABC effect and its associated resonance structure has been observed. From the isospin decomposition we see that the resonance effect is solely in the isoscalar part of the reaction process, whereas the isovector part exhibits a monotonic smoothly rising energy dependence and no ABC effect.

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Two-pion production in proton–proton collisions — experimental total cross sections and their isospin decomposition

Cited by 59 publications

References 26 publications

ABC Effect in Double-Pionic Fusion – a New Resonance?

ABC Effect in Double-Pionic Fusion – a New Resonance?

Examination of the nature of the ABC effect

Isospin Decomposition of the Basic Double-Pionic Fusion in the Region of the ABC Effect

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