Candidate for the 2+excited Hoyle state atEx∼10 MeV in12<

Abstract

Inelastic scattering from12 C has been measured at the extremely forward angles including 0• using 386 MeV α particles to study the α-cluster states around Ex ∼ 10 MeV, especially the 2 + state predicted by the α-cluster model. We have analyzed the (α,α ′ ) cross-section data using both the peak-fitting and the multipole decomposition techniques. A 2 + state at Ex = 9.84 ± 0.06 MeV with a width of 1.01 ± 0.15 MeV is found to be submerged in the broad 0 + state at Ex = 9.93 ± 0.03 MeV with a width of 2.71 ± 0.08 MeV. This 2 + state may be interpreted as the 2 + excitation of the Hoyle state and the α-condensate state.

Isoscalar dipole transition as a probe for asymmetric clustering

“…(B1) can be comparable or even larger than the last two terms of Eq. (12). We conclude that, if the cluster nucleus has the rotational or vibrational ground band with an enhanced E2 transition, the internal excitation of the cluster from 0 + to 2 + can have a large contribution to IS dipole excitation.…”

“…In Ref. [31], taking 12 C and 16 O as examples, it was shown that the IS monopole transition matrix from the ground state to the nodal excited cluster states is large.…”

“…(B1) does not vanish and can be very large. A typical example is the 12 is proportional to the large E2 matrix element, Eq. (B1) can be comparable or even larger than the last two terms of Eq.…”

“…The observed electric monopole (E0) and isoscalar (IS) monopole strength distributions of light nuclei [1][2][3][4][5][6][7][8][9][10][11][12][13][14] show that a considerable amount of the strength fractions appears at relatively small excitation energy as sharp resonances. It was known that many of those resonances are associated with the α cluster states such as the Hoyle state of 12 C [15][16][17][18][19][20][21][22][23][24], the α + 12 C cluster states in 16 O [25,26], the α + 16 O cluster states in 20 Ne [27], and the α + α + t cluster state in 11 B [28][29][30].…”

“…In a recent experimental study [35], the observed low-lying resonances in 32 S are conjectured to be the α + 28 Si cluster states, because of their enhanced IS dipole transition strength from the ground state. Very recently, Kanada-En'yo also discussed the enhancement of the IS dipole transition strength of the α cluster states in 12 C based on a theoretical calculation [56]. However, the excitation mechanism of the IS dipole transition and the relationship to the cluster states are still unclear and must be clarified to promote theoretical and experimental studies.…”