Meson exchange in the weak decay of Λ hypernuclei and the Γn/Γp ratio

Jido, Daisuke; Oset, E.; Palomar, J.E.

doi:10.1016/s0375-9474(01)01085-5

Cited by 80 publications

(170 citation statements)

References 57 publications

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“…We compare our results with the nuclear matter calculations done in Refs. [26,17]. In the first work a partial wave expansion of the nuclear matter plane waves is done.…”

Section: Calculations IImentioning

confidence: 99%

Nonmesonic weak decay of Λ hypernuclei within a nuclear matter formalism

Bauer

Krmpoti

2003

Nuclear Physics A

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The nonmesonic weak decay of Λ hypernuclei using nonrelativistic nuclear matter is studied. As the basic building block we use the Polarization Propagator Method developed by Oset and Salcedo. It is shown that the exact calculation of exchange terms is required. Using the Local Density Approximation we evaluate the nonmesonic decay width for 12 Λ C and compare the result with a finite nucleus calculation, obtaining a qualitative agreement.PACS number: 21.80.+a, 25.80.Pw.

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“…We compare our results with the nuclear matter calculations done in Refs. [26,17]. In the first work a partial wave expansion of the nuclear matter plane waves is done.…”

Section: Calculations IImentioning

confidence: 99%

Nonmesonic weak decay of Λ hypernuclei within a nuclear matter formalism

Bauer

Krmpoti

2003

Nuclear Physics A

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“…Such a component is two orders higher in the chiral expansion than the corresponding single-pion exchange piece. Also, previous studies [17] found such contributions to be small due to significant cancellations between the correlated and uncorrelated 2 exchanges.…”

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confidence: 90%

ΛN→NNweak interaction in effective-field theory

2004

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The nonleptonic weak ͉⌬S͉ =1 ⌳N interaction, responsible for the dominant nonmesonic decay of all but the lightest hypernuclei, is studied in the framework of an effective-field theory. The long-range physics is described through tree-level exchange of the SU(3) Goldstone bosons, while the short-range potential is parametrized in terms of the lowest-order contact terms. We obtain reasonable fits to available weak hypernuclear decay rates and quote the values for the parity-violating asymmetry as predicted by the present effective-field theory. For the past 50 years, ⌳ hypernuclei, systems of one or more ⌳ hyperons bound to a core nucleus, have been used to extend our knowledge of both the strong and the weak baryon-baryon interaction from the NN case into the SU(3) sector. The nonmesonic hypernuclear weak decay, facilitated via the ͉⌬S͉ = 1 four-fermion interaction, thus complements the weak ⌬S =0 NN case, which allows the study of only the parity-violating amplitudes.In analogy to NN phenomenology, the nonmesonic hypernuclear decay has traditionally been modeled using a mesonexchange approach [1]. The long-range part of the interaction is naturally explained by one-pion exchange, which could approximately reproduce the total (one-nucleoninduced) nonmesonic decay rate, ⌳N → NN, but not the partial rates, the proton-induced ⌳p → np rate ⌫ p , and the neutron-induced ⌳n → nn rate ⌫ n [2]. Due to the ⌳N mass difference, the process ⌳N → NN produces nucleons with momenta around Ϸ420 MeV, suggesting that the short-range part of the interaction cannot be neglected. These contributions have been described either through the exchange of vector mesons [3,4], whose production thresholds are too high for the free ⌳ decay, or through direct quark exchange [5].In contrast to previous theoretical studies, we present an exploratory study in order to determine the possible efficacy of the use of effective-field theory (EFT) methods in hypernuclear decay. Studies in this direction have already begun in Ref. [6], where a Fermi ͑V-A͒ interaction was added to the one-pion-exchange (OPE) mechanism to describe the weak ⌳N → NN transition. The present approach is motivated by the remarkable success of EFT techniques based on chiral expansions in the (nonstrange) SU(2) sector [7-10], which suggests its extension to the SU(3) realm, even though stability of the chiral expansion is less clear for the SU(3) sector, due to the significant degree of SU(3) symmetry breaking. A well-known example of the problems facing the SU(3) chiral perturbation theory has been the prediction [11][12][13][14] The EFT approach is based on the existence of wellseparated scales in the physical process under study. Formally, the high-momentum (short-distance) modes in the four-baryon interaction Lagrangian are replaced by contact operators, compatible with the underlying physical symmetries, of increasing dimension. Built in such a way, the Lagrangian will contain an infinite number of terms, and a consistent power-counting scheme is needed in order to trunca...

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“…The ad-dition of σ and a 1 exchanges does not effectively change the Γ n /Γ p ratio, but proves to be significant in the calculation of the Λ asymmetry parameter as discussed below. Earlier calculations by Jido, Oset, and Palomar (2001), using a chiral-interaction EFT approach, gave a very similar result, Γ n /Γ p = 0.53 in 12 Λ C. Shown also in Table XIII are Λ C, perhaps due to the increased role of the 2N branch which was not included in the calculation. However, earlier calculations using the same exchanges, but with somewhat different couplings and with different prescriptions for the short-range behavior of the OME exchanges, were able to produce values Itonaga, Ueda, and Motoba, 2002;Barbero et al, 2003).…”

Section: Transitionmentioning

confidence: 61%