Excitation of giant electric isovector resonances in pion charge exchange reactions

Auerbach, N.; Klein, Amir

doi:10.1103/physrevc.28.2075

Cited by 28 publications

(9 citation statements)

References 37 publications

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“…The excitation energy observed for the IVMR is approximately consistent with the theoretical prediction, i.e., E x 23.1 MeV [1]. Both the excitation energy and width for the IVMR presently observed are, within errors, consistent with the result observed in the pion chargeexchange reaction [4,12].…”

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confidence: 83%

“…Thus, such simultaneous observations of the DS 0 and DS 1 spectra may allow one to get evidence for isovector resonances with the DS 0 and DS 1 modes by distinguishing them from the underlying continuum. We investigated separately the singles, the DS 0, and the DS 1 spectra in the excitation energy ͓E x ͑IVMR͒ 23.1 MeV͔ region where the isovector resonances were theoretically predicted [1]. Their multipolarities were discussed by comparing the angular distributions of the differential cross sections with microscopic distorted-wave-approximation (DWBA) calculations.…”

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confidence: 99%

“…These resonances are also characterized by the electric ͑DS 0͒ and magnetic ͑DS 1͒ modes which correspond to coherent motions of the spin-nonflip and spin-flip oscillations, respectively. Resonances with various multipolarities have been theoretically predicted [1]. Among them, the monopole resonances play a crucial role in astrophysics [2].…”

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Isovector Electric Monopole Resonance in60Ni

et al. 1999

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The isovector electric monopole resonance (IVMR) was studied by the 60 Ni͑ 7 Li, 7 Be͒ 60 Co reaction at 65A MeV and at forward scattering angles including zero degrees. We confirmed the existence of the IVMR at an excitation energy of 20 6 2 MeV with a width of 10 6 2 MeV in 60 Co, which is an analog of the T 0 1 1 isospin component of the IVMR estimated at E x ഠ 31 MeV in 60 Ni. The result presently obtained is consistent with previous results using the pion charge-exchange reaction. PACS numbers: 25.70.Kk, 24.30.Cz, 27.50. + e Isovector resonances ͑DT 1͒ in nuclei are collective motions in which protons oscillate in opposite phase with respect to neutrons. These resonances are also characterized by the electric ͑DS 0͒ and magnetic ͑DS 1͒ modes which correspond to coherent motions of the spin-nonflip and spin-flip oscillations, respectively. Resonances with various multipolarities have been theoretically predicted [1]. Among them, the monopole resonances play a crucial role in astrophysics [2]. Concerning the isoscalar mode ͑DT 0͒, the electric monopole resonance (GMR; DT 0, DS DL 0) has been well established in various inelastic scatterings. The GMR was unambiguously identified due to a sharp enhancement at u L 0 ± [3]. On the other hand, the existence of the isovector electric monopole resonance (IVMR; DT 1, DS DL 0) has been reported only by the pion charge-exchange reaction [4]. The IVMR has also been searched for by using other reaction probes such as electron scattering [5] and the ͑ 13 C, 13 N͒ reaction [6]. Confirmation of the IVMR is, however, still very desirable because of the inconclusive data from these reactions.One of the major reasons for the inconclusive data is due to a difficulty in determining the multipolarity of the resonance. The resonance is, in general, observed as a broad bump riding on a large underlying background mainly caused by a quasielastic scattering. One meets another serious difficulty when one uses hadron reaction probes with spins like ͑p, n͒ and ͑ 3 He, t͒. These reactions allow simultaneous DS 0 and DS 1 excitations, differing from the case of the pion charge-exchange reaction which proceeds only via the DS 0 transition. There is no nuclear probe allowing only the DS 0 excitation. In this respect, the ͑ 13 C, 13 N͒ reaction is expected to be a promising probe for observing isovector electric resonances because of its large Fermi matrix element ͑M F ͞M GT ϳ 5͒ [6]. In this reaction, a resonance has been observed at the relevant excitation energy, but its multipolarity is not consistent with the DL 0 assumption.In the present work, we started with the following question: Can we observe the IVMR reported by the pion charge-exchange reaction? To answer this question, we employed the ͑ 7 Li, 7 Be͒ reaction at 65A MeV on a 60 Ni target which is the target studied by various other ͑n, p͒-like reactions [4,6,7]. The ͑ 7 Li, 7 Be͒ reaction is chosen for the following two reasons. One is that the reaction predominantly proceeds via a one-step process at 65A MeV and at forward an...

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Isovector Electric Monopole Resonance in60Ni

et al. 1999

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“…Returning to the question of the possible experimental determination of Ω M , we note that the charge-exchange IVMR was first observed in pion single charge exchange reactions [9,10]. Recently, the IVMR has been studied in various charge-exchange reactions:…”

Section: The Charge-dependent Isospin-breaking Interaction Is Dominatmentioning

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Relation between isospin-symmetry-breaking correction to superallowedβdecay and the energy of the charge-exchange giant monopole resonance

Rodin

2013

Phys. Rev. C

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After application of an analytical transformation, a new exact representation for the nuclear isospin-symmetry breaking correction δ C to superallowed beta decay is obtained. The correction is shown to be essentially the reciprocal of the square of an energy parameter Ω M which characterizes the charge-exchange monopole strength distribution. The proportionality coefficient in this relation is determined by basic properties of the ground state of the even-even parent nucleus, and should be reliably calculable in any realistic nuclear model. Therefore, the single parameter Ω M contains all the information about the properties of excited 0 + states needed to describe δ C . This parameter can possibly be determined experimentally by charge-exchange reactions. Basic quantities of interest are calculated within the isospin-consistent continuum random phase approximation, and the values of δ C are compared with the corresponding results from other approaches.

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“…We compare the properties of both resonances with random-phase, distorted-wave impulse approximation (RPA-DWIA) calculations. 2 The availability of such a large data set enabled us to establish the systematic behavior of the nonresonant background. We searched for the isovector quadrupole resonance, for which some evidence has been given, 3 and we determine upper limits for its cross sections.…”

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Properties of the Isovector Monopole and Other Giant Resonances in Pion Charge Exchange

et al. 1984

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We present the energies, widths, and cross sections of the isovector monopole resonance in nuclei between 40 Ca and 208 Pb excited by the (TT ± ,TT°) reactions. We also give results for the giant dipole resonance. Both resonances exhaust the same substantial fraction of the cross section calculated in a random-phase, distorted-wave impulse-approximation model. No isovector quadrupole resonance was observed.PACS numbers: 21.10. Re, 24.30.Cz, 25.80.Fm Recently, we have reported the observation of the isovector monopole resonance 1 (IVMR) in 120 Sn and 90 Zr in the (TT -,^0) reaction. The study of this new collective excitation is fundamental to our understanding of basic ingredients of nuclear theory, such as the isovector part of the residual interaction and Coulomb and isospin mixings in nuclear states. Among the requisite properties of giant resonances in nuclei are a smooth A dependence of cross sections, excitation energies, and widths, and an exhaustion of a large fraction of the sum rule. Here we present the results of an extensive study of the (TT ± ,TT°) reactions at 165 MeV on ^Ca, 60 Ni, 90 Zr, 120 Sn, 140 Ce, and 208 Pb establishing the IVMR in a wide range of nuclei with two related probes. We also give results for the T+l and T-1 components of the giant dipole resonance (GDR). We compare the properties of both resonances with random-phase, distorted-wave impulse approximation (RPA-DWIA) calculations. 2 The availability of such a large data set enabled us to establish the systematic behavior of the nonresonant background. We searched for the isovector quadrupole resonance, for which some evidence has been given, 3 and we determine upper limits for its cross sections.The experiment was carried out at the LEP channel at the Clinton P. Anderson Meson Physics Facility (LAMPF) with the 7T° spectrometer. Double differential cross sections were measured from 4° to 33°. Experimental details are given elsewhere. 1,4 In Fig. 1, we show energy spectra at (a) 4° near the peak of the IVMR cross section, (b) 7° where both IVMR and GDR have considerable strength, (c) 15° near the minimum of the IVMR cross section and the maximum of the GDR cross section, and (d) 28° where both the IVMR and GDR are small.An examination of the data shows an IVMR excitation centered at 142 MeV and a GDR excitation centered at 154 MeV, superimposed on an approximately isotropic background. The GDR is clearly seen in the energy spectrum at 15°. In order to identify the broader IVMR peak, we must consider the angular variation as well as the energy variation of the cross section. Figure 2(a) demonstrates the presence of a forward-peaked monopole signal in a wide range of nuclei for the (7r",7r°) reaction. We plot the ratios of the cross sections integrated over the expected monopole region to the cross sections integrated over the whole spectrum, versus the squared momentum transfer q in the quasifree 7r~p-+iT 0 n reaction [q -2k n -sin(0/2)]. At small q 2 there is an excess cross section above the linearly extrapolated background. The ...

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Excitation of giant electric isovector resonances in pion charge exchange reactions

Cited by 28 publications

References 37 publications

Isovector Electric Monopole Resonance in60Ni

Isovector Electric Monopole Resonance in60Ni

Relation between isospin-symmetry-breaking correction to superallowedβdecay and the energy of the charge-exchange giant monopole resonance

Properties of the Isovector Monopole and Other Giant Resonances in Pion Charge Exchange

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