a particle correlations for studying Nuclear Structure and Dynamics

Abstract:  The investigation of the structure of light nuclei assumes an important role in the description of nuclear forces and their properties. Particle-particle and multi-particle correlations in nucleus­ nucleus collisions are a powerful probe for these aspects. They allow to explore the structure of unbound states, including their interplay with collision dynamics, in stable and unstable nuclei produced in direct reactions as well as under extreme conditions of temperature and density attained in heavy ion collisions [1,2]. Indeed, one can investigate spectroscopic properties of nuclei (like branching ratios and spin [3,4]) and the dynamic properties of nuclear collisions (such as space-time properties of nuclear reactions [5,6]) via the study of the decay of resonant states produced in the collision itself. In presence of clustering phenomena, these tools become particularly important since light particle emissions (cluster) dominate the decay of resonances. In this scenario, a-a and multi-a correlations a re a very special case; they provide information on clustering phenomena in self-conjugated nuclei and allow to investigate the dynamical phases of an Heavy Ion Collision (HIC) with large statistics [1]. By using correlation techniques of a particles applied to spectroscopy, we have studied the 3a disintegration of the Hoyle state in 12C [7]. Our high precision experiment was developed to shed light on its non-resonant decay branch [8], a topic of fundamental importance in Nuclear Structure [9-11] and Astrophysics [11-13]. We observed a fully sequential decay mechanism providing a new upper limit to non-resonant decays [14] which is about a factor 5 lower than previous works [8,11]. Similar correlation are also studied in Heavy Ion Collisions (HICs), in the colliding system 36Ar+58Ni at different incident energies (32-95 AMeV) with the INDRA 4Jt multi-detector. The aim of this study consists of building an in-flight decay simulation code based on the thermal model of two-particle correlations in Heavy Ion Collision (HIC), commonly used to extract temperatures from the population of unbound states and spins in some spectroscopic applications. Regardless the limited angular resolution of the array, not built specifically for light particle correlation measurements, it is shown that some information about the validity of attainment of thermal population of internal states in 8Be can be inferred from a-a correlation functions [15]. Hypothesis on the reaction mechanism and on the time scale of the process will be also discussed by also looking at the shape of IMF-IMF correlation functions. The simulation code is meant to be used in high resolution correlation experiments that can be performed with the FAZIA detector or with silicon strip detector arrays, such as HiRA or MUST2. References: [1] D.H. Boal et al., Rev. Mod. Phys. 62 (1990) 553. [2] G. Verde et al., Eur. Phys. J. A 30 (2006) 81. [3] R.J. Charity et al., Phys. Rev. C 75 (2007) 051304(R}. [4] D. Dell\'Aquila et al., Phys. Rev. C 93, 024611 (2016}. [5] S.E. Koonin et al.,Phys. Lett. B 70 (1977) 43. [6] M.A. Lisa et al., Phys. Rev. Lett. 70 (1993) 2545. [7] D. Dell\'Aquila et al., in press on J. Phys.: Cont.Ser. [8] M. ltoh et al.,Phys. Rev. Lett. 113 (2014) 102501. [9] W. von Oertzen, Zeit. Phys. A 357, 355 (1997). [10] E. Uegaki,S. Okabe, Y. Abe, and H. Tanaka, Prag. Theor. Phys. 57, 1262 (1977). [11] 0. S. Kirsebom et al., Phys. Rev. Lett. 108 {2012) 202501. [12] K. Nomoto, F.-K. Thielemann, and S. Miyaji,Astron. Astrophys. 149, 239 (1985). [13] K. Langanke, M. Wiescher, and F.K. Thielemann, Z. Physik A - Atomic Nuclei 324, 147 (1986). [14] D. Dell\'Aquila et al., in press on Phys. Rev. Lett. [15] J. Pochodzalla et al., Phys. Rev. C 35 {1987) 1695.