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SUMMARY:Near-threshold states in dissociation of relativistic nuclei
DTSTART;VALUE=DATE-TIME:20261030T142500Z
DTEND;VALUE=DATE-TIME:20261030T144000Z
DTSTAMP;VALUE=DATE-TIME:20261103T142633Z
UID:indico-contribution-6351@cern.ch
DESCRIPTION:Speakers: Pavel Zarubin (Joint Institute for Nuclear Research)
 \nJoint Institute for Nuclear Research\, Dubna\, Russia\nThe use of nuclea
 r emulsions (NEs) in beams of relativistic nuclei expands the study of nuc
 lear clustering and\, above all\, resonance states near α-particle separa
 tion thresholds [nsr-2026]. The current focus is on searching for extremel
 y low-energy α-particle states\, described as Bose-Einstein condensates. 
 Following the 2α-state of 8Be(0+) and the 3α-state of Hoyle 12C(0+2)\, t
 he excitation of 16O(0+6) at 15.1 MeV or 296 keV above the 12C(0+2)α thre
 shold has been proposed as a 4α-condensate. In general\, decays of unstab
 le states can be identified in distributions of invariant masses Q\, defin
 ed as sums of the scalar products of the fragment 4-momenta. For convenien
 ce\, the masses of the fragments or the parent nucleus are subtracted from
  Q. In the relativistic case\, the 4-momenta are determined with sufficien
 t accuracy in the approximation of conservation of momentum per nucleon of
  the parent nucleus from their emission angles. In the dissociation of 12C
  and 16O nuclei\, the assumption that He fragments correspond to α partic
 les is justified. Due to their minimal energy\, their decays can manifest 
 themselves as ensembles of relativistic He fragments with the smallest sca
 ttering angles.\nThe contribution of the 8Be(0+)α channel at Q2α ≤ 200
  keV to the dissociation of 12C → 3α at 3.65 GeV per nucleon was determ
 ined to be 43%\, including 26% through 12C(0+2) at Q3α ≤ 700 keV. The c
 ontribution of 12C(0+2) to the coherent dissociation of 16O → 4α at 3.6
 5 GeV per nucleon was 22%\, significantly increasing compared to the case 
 of 12C (11%). However\, 16O(0+6) at Q4α ≤ 1 MeV did not manifest itself
  in the 12C(0+2)α and 28Be(0+) channels. Such suppression can be explaine
 d by the extremely small energy difference between 16O(0+6) and 12C(0+2)α
 \, leading to a decay width of only 10-9 MeV . At the same time\, the stru
 cture of 16O(0+6 as 12C(0+2)α\, makes possible the internal conversion of
  12C(0+2) to the ground state 12C(0+1) with a width of 0.2 MeV. By allowin
 g 16O(0+6) to be considered as an excitation near the 4α threshold\, this
  scenario motivated the search for binary decays 16O(0+6) → 12C(0+1)α p
 resented here.\nThe distribution over invariant mass of 12Cα pairs produc
 ed in the dissociation of 16O indicates decays of the excited state 16O(0+
 6). An estimate of the probabilities of the 12C(0+1)α and 12C(0+2)α chan
 nels indicates a dominance of the former with a factor of about 20. It sup
 ports the hypothesis of decay of the 16O(0+6) state via internal conversio
 n of its substructure 12C(0+2) to 12C(0+1). This makes it possible to synt
 hesize the isotope 12C through the decay 16O(0+6) → 12C(0+2)α → 12C(0
 +1)α without a radiative transition as an addition to the known 3α-proce
 ss.\nThe study of binary dissociation of 16O nuclei stimulated a reanalysi
 s of data on the α-particle dissociation of 22Ne nuclei for observations 
 of near-threshold resonances\, as follows. The invariant mass distribution
  of 18Oα pairs produced in the dissociation of 22Ne at 3.22 GeV per nucle
 on exhibits a peak that can be interpreted as 22Ne excitation with a mean 
 value of approximately 11.6 MeV. Corresponding to sub barrier fusion of 18
 O + α\, this observation provides further evidence for the feasibility of
  nucleosynthesis reactions in the fragmentation cone of relativistic nucle
 i.\n\n[nsr-2026] D.А. Artemenkov\, A.A. Zaitsev\, P.I. Zarubin “The 8Be
  nucleus and the Hoyle state in dissociation of relativistic nuclei” Nat
 ural Sci. Rev. 3 200603 (2026)\nhttps://doi.org/10.54546/NaturalSciRev.200
 603\; arXiv:260121425.\n\nhttps://indico.particle.mephi.ru/event/626/contr
 ibutions/6351/
LOCATION: Conference Hall 1
URL:https://indico.particle.mephi.ru/event/626/contributions/6351/
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