Bound two-pion Cooper pairs in nuclei?

Schuck, Peter; Nörenberg, W.; Chanfray, G.

doi:10.1007/bf01287274

Cited by 46 publications

(72 citation statements)

References 5 publications

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“…Whereas in vacuum the low energy ππ interaction in the I = J = 0 channel, although attractive, is too weak to admit a bound state, it was soon realized that the nuclear medium attraction of the pions could lead to the accumulation of some strength close to the two pion threshold, or even to the appearance of a new bound state [7]. A similar conclusion has been reached in Ref.…”

Section: Introductionsupporting

confidence: 56%

Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction

Vacas

Oset

1999

Phys. Rev. C

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The reaction A(π, ππ)X has been studied at low energies, paying particular attention to the interaction of the two final pions in the scalar isoscalar (I=J=0) channel. We have developed a microscopic model for the pion production, and then implemented the two pion final state interaction by using the results of a non-perturbative unitary coupled-channels method based in the standard chiral Lagrangians. The resulting model, describes well the reaction on the nucleon for all different isospin channels. Finally, we have considered the reaction in nuclei. Our calculation takes into account Fermi motion, Pauli blocking, pion absorption, and also the strong modification of the ππ interaction in the nuclear medium.13.60. Le,13.75.Lb,13.75.Gx,21.65+f,25.80.Hp

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Section: Introductionsupporting

confidence: 56%

Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction

Vacas

Oset

1999

Phys. Rev. C

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“…3.2. The appearance of pole doubling and bound states has been also analyzed in other works [30,32,33]. (7).…”

Section: 2mentioning

confidence: 99%

“…In contrast, finite temperature analyses show that this state remains broad even near the chiral phase transition despite the proximity of the pole to the two-pion threshold [12,30,32], which in practice does not produce any sizable enhancement in the scattering amplitude or cross section. A striking possibility to be explored is that by increasing further the medium strength, the σ could become a ππ bound state, as suggested earlier in [33] and confirmed recently in [12,30,32].…”

Section: Introductionmentioning

confidence: 99%

Chiral symmetry and light resonances in hot and dense matter

2008

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Abstract. We present a study of the ππ scattering amplitude in the σ and ρ channels at finite temperature and nuclear density within a chiral unitary framework. Meson resonances are dynamically generated in our approach, which allows us to analyze the behavior of their associated scattering poles when the system is driven towards chiral symmetry restoration. Medium effects are incorporated in three ways: (a) by thermal corrections of the unitarized scattering amplitudes, (b) by finite nuclear density effects associated to a renormalization of the pion decay constant, and complementarily (c) by extending our calculation of the scalar-isoscalar channel to account for finite nuclear density and temperature effects in a microscopic many-body implementation of pion dynamics. Our results are discussed in connection with several phenomenological aspects relevant for nuclear matter and Heavy-Ion Collision experiments, such as ρ mass scaling vs broadening from dilepton spectra and chiral restoration signals in the σ channel. We also elaborate on the molecular nature of ππ resonances. PACS

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“…Hence, these models predict a significant drop in the mass of the σ. A measurement of the inmedium σ→ ππ mass distribution might be essential for the understanding of the mechanism of chiral-symmetry breaking.Alternatively, the in-medium σ mode can be considered to be a resonant state of two pions [6,7,8,9]. In vacuum, the ππ system is mildly attractive.…”

mentioning

confidence: 99%

“…Alternatively, the in-medium σ mode can be considered to be a resonant state of two pions [6,7,8,9]. In vacuum, the ππ system is mildly attractive.…”

mentioning

confidence: 99%

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

et al. 2002

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Differential cross sections of the reactions (γ, π • π • ) and (γ, π • π +/− ) have been measured for several nuclei ( 1 H, 12 C, and nat Pb) at an incident-photon energy of Eγ =400-460 MeV at the taggedphoton facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the ππ invariant-mass distribution is found in the π • π • channel. This dependence is not observed in the π • π +/− channel and is consistent with an in-medium modification of the ππ interaction in the I=J=0 channel. The data are compared to π-induced measurements and to calculations within a chiral-unitary approach.One of the challenges in nuclear physics is to study the properties of hadrons and the modification of these properties when the hadron is embedded in a nuclear manybody system. Although much has been learned about the properties of hadrons in free space, there is a lack of information for particles in a dense environment. In this Letter, an experiment is described which has measured correlated pion pairs photoproduced on nuclei in the scalar-isoscalar J=I=0 channel, also known as the σ mode. In Ref.[1] the σ meson is identified as the f 0 (400-1200). The large natural width in free space of Γ=400-500 MeV [2] makes it doubtful that this particle is a mesonic state, and has initiated many discussions on its nature. An in-medium study of the I=J=0 channel could provide a better insight into the nature of the σ meson.Within some theoretical approaches of quantum chromodynamics (QCD) [3,4,5], the σ is treated as a pure qq state (J P =0 + ) and regarded as the chiral partner of the pion (J P =0 − ). Chiral symmetry is spontaneously broken in the QCD vacuum, resulting in a mass difference between the pion and the σ. For large baryon densities, it is predicted that chiral symmetry is partially restored, leading to a degeneracy in mass of the pion and the σ. Since the pion approximates a Goldstone boson, the pion mass is not expected to change dramatically with increasing nuclear density ρ. Hence, these models predict a significant drop in the mass of the σ. A measurement of the inmedium σ→ ππ mass distribution might be essential for the understanding of the mechanism of chiral-symmetry breaking.Alternatively, the in-medium σ mode can be considered to be a resonant state of two pions [6,7,8,9]. In vacuum, the ππ system is mildly attractive. However, in the nuclear medium the ππ interaction strength could increase, thereby changing width and pole position of the resonant state. Experimental data on the density dependence of pion-pair interactions in the nuclear medium can provide evidence for this phenomenon.The first measurement of the in-medium ππ mass was obtained by a pion-induced experiment by the CHAOS collaboration [10,11,12]. A rising accumulation of strength at low π + π − mass was observed with increasing nuclear mass whereas such an enhancement was not seen in the π + π + -mass distributions. This effect was interpreted as a signature for an in-medium modification of the ππ interaction in the I=J=0 chann...

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Bound two-pion Cooper pairs in nuclei?

Cited by 46 publications

References 5 publications

Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction

Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction

Chiral symmetry and light resonances in hot and dense matter

In-Medium Modifications of theππInteraction in Photon-Induced Reactions

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