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Yonnet, Jean‐Paul; Tatischeff, B.; Boivin, M.; Comets, M. P.; Courtat, P.; Gacougnolle, R.; Bornec, Y. Le; Loireleux, E.; Reide, F.; Willis, N.

doi:10.1103/physrevc.63.014001

Cited by 9 publications

(13 citation statements)

References 45 publications

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“…Surprisingly, the basic pp → ppπ 0 π 0 reaction in the ∆∆ region also shows an ABC-like low-ππ mass enhancement which deserves special attention. It confirms the earlier result in [19] where the analyzing powers and cross sections for the ABC enhancement production were measured for the reaction pp → p + p + X 0 in the missing mass range m 0 π < M X 0 < m η . However, the big difference was observed in the width of the resonance cross section and it was concluded that the observed width in the isoscalar channel is not obviously just a simple result of the binding between the two ∆ states.…”

Section: Introductionsupporting

confidence: 91%

Resonance structure in the γγ invariant mass spectrum in pC- and dC-interactions

Abraamyan¹,

Baznat²,

Friesen³

et al. 2010

Phys. Part. Nuclei

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Along with π 0 and η mesons, a resonance structure in the invariant mass spectrum of two photons at M γγ = 360 ± 7 ± 9 MeV is observed in the reaction dC → γ + γ + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are Γ = 63.7 ± 17.8 MeV and σ γγ = 98 ± 24 +93 −67 µb, respectively. The collected statistics amount to 2339 ± 340 events of 1.5 · 10 6 triggered interactions of a total number ∼ 10 12 of dC-interactions. This resonance structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed. * ) abraam@sunhe.jinr.ru Accepted for publication in Phys.Rev.C

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Section: Introductionsupporting

confidence: 91%

Resonance structure in the γγ invariant mass spectrum in pC- and dC-interactions

Abraamyan¹,

Baznat²,

Friesen³

et al. 2010

Phys. Part. Nuclei

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“…This has recently been overcome by measuring the quasi-free pd → dπ 0 π 0 p sp reaction semi-exclusively at beam energies of T p = 1.03 and 1.35 GeV, with just the spectator proton p sp escaping detection [6]. The only published study of the ABC effect in proton-proton collisions was carried out at T p = 1.52 and 1.81 GeV [7], though this concentrated on possible substructure.…”

mentioning

confidence: 99%

Observation of an “ABC” Effect in Proton-Proton Collisions

et al. 2009

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The cross section for inclusive multipion production in the pp → ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasi-particle is in the 1 S0 state. At the three higher energies the missing mass MX spectra show a strong enhancement at low MX , corresponding to an ABC effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with MX and beam energy are consistent with two-pion production being mediated through the excitation of two ∆(1232) isobars, coupled to S-and D-states of the initial pp system. The ABC effect is a sharp enhancement of the twopion invariant mass spectrum near its threshold that has puzzled hadron physicists for almost fifty years. First observed in a pd → 3 HeX missing-mass experiment [1], and subsequently confirmed using a deuteron beam [2], it was seen most spectacularly in the dd → 4 HeX reaction [3,4]. The ABC typically manifests itself as a peak at an invariant mass M X ≈ 310 − 330 MeV/c 2 and it was first even speculated that it might be a scalar meson with isospin I = 0. However, the fact that the mass and width varied with experimental conditions [2] suggests that the ABC is a kinematic enhancement. This is consistent with the smooth behavior of the isoscalar ππ phase shifts at low energies. To understand the nature of the ABC it is necessary to investigate the effect in simpler systems.The ABC showed up very clearly in the zero-degree momentum spectrum of the deuteron from np → dX [5].Here it leads to two peaks, i.e. forward and backward production in the c.m. system, though the momentum spread of the neutron beam degraded the missing-mass resolution. This has recently been overcome by measuring the quasi-free pd → dπ 0 π 0 p sp reaction semi-exclusively at beam energies of T p = 1.03 and 1.35 GeV, with just the spectator proton p sp escaping detection [6]. The only published study of the ABC effect in proton-proton collisions was carried out at T p = 1.52 and 1.81 GeV [7], though this concentrated on possible substructure.Studies of the energy dependence of the pd → 3 HeX and dd → 4 HeX cross sections showed that the ABC effect is most prominent for energies where the maximum missing mass is about 600 MeV/c 2 [3]. Since this corresponds to the mass difference between two ∆(1232) isobars and two nucleons, it is tempting to suppose that the two-pion production is mediated by the excitation and decay of two separate ∆ isobars. Such a model with π [8] and then π + ρ exchange [9] had semi-quantitative success in describing the existing np → dX data. The dominant contribution to the cross section arises when the two ∆ are in a relative S-wave. For the production of an I ππ = 0 pion pair, isospin conservation requires I ∆∆ = 0. It follows from the generalized Pauli principle that the two isobars must then couple to a total spin of S ∆∆ = 1 or 3. In contrast, for pp → ∆∆ → ppππ, I...

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“…Narrow structures in dibaryons [3], in baryons [4], and in mesons at larger masses [5] [6] were already previ- ously observed . Mesonic structures appeared in the missing mass of the same reaction, pp→ppX but in different kinematical conditions from those discussed here.…”

Section: A Possible Mass Relation Between Mesons and Baryonsmentioning

confidence: 85%

Search for low-mass exotic mesonic structures: II. Attempts to understand the results

Tatischeff

Tomasi–Gustafsson

2008

Phys. Part. Nuclei Lett.

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Our previous paper, part I of the same study, shows the different experimental spectra used to conclude on the genuine existence of narrow, weakly excited mesonic structures, having masses below and a little above the pion (M=139.56 MeV) mass. This work [1] was instigated by the observation, in the Σ + disintegration: Σ + →pP 0 , P 0 → µ − µ + [2], of a narrow range of dimuon masses. The authors conclude on the existence of a neutral intermediate state P0, with a mass M=214.3 MeV ± 0.5 MeV. We present here some attempts to understand the possible nature of the structures observed in part I.

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ABCresonance in thep→p→

Cited by 9 publications

References 45 publications

Resonance structure in the γγ invariant mass spectrum in pC- and dC-interactions

Resonance structure in the γγ invariant mass spectrum in pC- and dC-interactions

Observation of an “ABC” Effect in Proton-Proton Collisions

Search for low-mass exotic mesonic structures: II. Attempts to understand the results

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