Nuclear matter at high density: Phase transitions, multiquark states, and supernova outbursts

Phase transition from hadronic matter to quark-gluon matter is discussed for various regimes of temperature and baryon number density. For small and medium densities, the phase transition is accurately described in the framework of the Field Correlation Method, whereas at high density predictions are less certain and leave room for the phenomenological models. We study formation of multiquark states (MQS) at zero temperature and high density. Relevant MQS components of the nuclear matter can be described using a previously developed formalism of the quark compound bags (QCB). Partial-wave analysis of nucleon-nucleon scattering indicates the existence of 6QS which manifest themselves as poles of $P$-matrix. In the framework of the QCB model, we formulate a self-consistent system of coupled equations for the nucleon and 6QS propagators in nuclear matter and the G-matrix. The approach provides a link between high-density nuclear matter with the MQS components and the cumulative effect observed in reactions on the nuclei, which requires the admixture of MQS in the wave functions of nuclei kinematically. 6QS determine the natural scale of the density for a possible phase transition into the MQS phase of nuclear matter. Such a phase transition can lead to dynamic instability of newly born protoneutron stars and dramatically affect the dynamics of supernovae. Numerical simulations show that the phase transition may be a good remedy for the triggering supernova explosions in the spherically symmetric supernova models. A specific signature of the phase transition is an additional neutrino peak in the neutrino light curve. For a Galactic core-collapse supernova, such a peak could be resolved by the present neutrino detectors. The possibility of extracting the parameters of the phase of transition from observation of the neutrino signal is discussed also.Comment: 57 pages, 22 figures, 7 tables; RevTeX 4; submitted to Phys. Atom. Nuc

Elastic scattering angular distribution for the 18O+48Ti collision at 275 MeV within the NUMEN project

In the context of the NUMEN project, the 18O + 48Ti collision at 275 MeV incident energy was studied for the first time. In the adopted multichannel approach, the elastic scattering was measured in order to deduce the initial state interaction and the corresponding optical potential. The angular distribution of elastic scattering was determined across a wide range of scattering angles

One-neutron transfer reaction in the 18^{18}O + 48^{48}Ti collision at 275 MeV

The present article reports new data on the $^{48}$Ti($^{18}$O,$^{17}$O)$^{49}$Ti reaction at 275 MeV incident energy as part of the systematic research pursued within the NUMEN project. Supplementary measurements of the same reaction on $^{16}$O and $^{27}$Al targets were also performed in order to estimate the background arising from the use of a composite target (TiO$_{2}$ + $^{27}$Al). These data were analyzed under the same theoretical framework as those obtained with the titanium target in order to reinforce the conclusions of our analysis. Differential cross-section angular distribution measurements for the $^{17}$O$^{8+}$ ejectiles were performed in a wide angular range by using the MAGNEX large acceptance magnetic spectrometer. The experimental results were analyzed within the distorted-wave and coupled-channels Born Approximation frameworks. The optical potentials at the entrance and exit channels were calculated in a double folding approach adopting the S\~ao Paulo potential, and the spectroscopic amplitudes for the projectile and target overlaps were obtained from large-scale shell model calculations. The differential cross-sections are well-described by the theoretical calculations, where a weak coupling to collective excitations of projectile and target is inferred. The sensitivity of transfer cross-sections on different model spaces adopted in nuclear structure calculations, is also discussed

One-proton transfer reaction for the O 18 + Ti 48 system at 275 MeV

Single-nucleon transfer reactions are processes that selectively probe single-particle components of the populated many-body nuclear states. In this context, recent efforts have been made to build a unified description of the rich nuclear spectroscopy accessible in heavy-ion collisions. An example of this multichannel approach is the study of the competition between successive nucleon transfer and charge exchange reactions, the latter being of particular interest in the context of single and double beta decay studies. To this extent, the one-proton pickup reaction Ti48(O18,F19)Sc47 at 275 MeV was measured for the first time, under the NUMEN experimental campaign. Differential cross-section angular distribution measurements for the F19 ejectiles were performed at INFN-LNS in Catania by using the MAGNEX large acceptance magnetic spectrometer. The data were analyzed within the distorted-wave and coupled-channels Born approximation frameworks. The initial and final-state interactions were described adopting the São Paulo potential, whereas the spectroscopic amplitudes for the projectile and target overlaps were derived from shell-model calculations. The theoretical cross sections are found to be in very good agreement with the experimental data, suggesting the validity of the optical potentials and the shell-model description of the involved nuclear states within the adopted model space

A constrained analysis of the 40Ca(18O,18F)40K direct charge exchange reaction mechanism at 275 Mev

The40 Ca(18 O,18 F)40 K single charge exchange (SCE) reaction is explored at an incident energy of 275 MeV and analyzed consistently by collecting the elastic scattering and inelastic scattering data under the same experimental conditions. Full quantum-mechanical SCE calculations of the direct mechanism are performed by including microscopic nuclear structure inputs and adopting either a bare optical potential or a coupled channel equivalent polarization potential (CCEP) constrained by the elastic and inelastic data. The direct SCE mechanism describes the magnitude and shape of the angular distributions rather well, thus suggesting the suppression of sequential multi-nucleon transfer processes

Investigation of 76Se(18O, 17O)75Se and 76Se(18O, 19F)75As transfer reactions at 15 MeV/u in a multi-channel approach within the NUMEN project

. - A full-comprehensive study of heavy-ion induced nuclear reac-tions is a powerful tool to characterize nuclear mean-field features as well as few-nucleon correlations in low-lying nuclear states. In this context, the investigation of 76Se(18O,17O)75Se and 76Se(18O,19F)75As transfer reactions was performed with the NUMEN project, aiming at providing data-driven information to constrain nu-clear structure models for the 76Se nucleus. This nucleus is under investigation since it is the daughter nucleus of 76Ge in the neutrinoless double beta decay (0 nu 1313) pro-cess. The experiment was performed at INFN-LNS where the 18O beam impinged the 76Se target and the reaction ejectiles were momentum analyzed by the MAGNEX magnetic spectrometer

The NUMEN heavy ion multidetector for a complementary approach to the neutrinoless double beta decay

Neutrinos are so far the most elusive known particles, and in the last decades many sophisticated experiments have been set up in order to clarify several questions about their intrinsic nature, in particular their masses, mass hierarchy, intrinsic nature of Majorana or Dirac particles. Evidence of the Neutrinoless Double-Beta Decay (NDBD) would prove that neutrinos are Majorana particles, thus improving the understanding of the universe itself. Besides the search for several large underground experiments for the direct experimental detection of NDBD, the NUMEN experiment proposes the investigation of a nuclear mechanism strongly linked to this decay: the Double Charge Exchange reactions (DCE). As such reactions share with the NDBD the same initial and final nuclear states, they could shed light on the determination of the Nuclear Matrix Elements (NMEs), which play a relevant role in the decay. The physics of DCE is described elsewhere in this issue, while the focus of this paper will be on the challenging experimental apparatus currently under construction in order to fulfil the requirements of the NUMEN experiment. The overall structure of the technological improvement to the cyclotron, along with the newly developed detection systems required for tracking and identifying the reaction products and their final excitation level are described

The NUMEN heavy ion multidetector for a complementary approach to the neutrinoless double beta decay

Neutrinos are so far the most elusive known particles, and in the last decades many sophisticated experiments have been set up in order to clarify several questions about their intrinsic nature, in particular their masses, mass hierarchy, intrinsic nature of Majorana or Dirac particles. Evidence of the Neutrinoless Double-Beta Decay (NDBD) would prove that neutrinos are Majorana particles, thus improving the understanding of the universe itself. Besides the search for several large underground experiments for the direct experimental detection of NDBD, the NUMEN experiment proposes the investigation of a nuclear mechanism strongly linked to this decay: the Double Charge Exchange reactions (DCE). As such reactions share with the NDBD the same initial and final nuclear states, they could shed light on the determination of the Nuclear Matrix Elements (NMEs), which play a relevant role in the decay. The physics of DCE is described elsewhere in this issue, while the focus of this paper will be on the challenging experimental apparatus currently under construction in order to fulfil the requirements of the NUMEN experiment. The overall structure of the technological improvement to the cyclotron, along with the newly developed detection systems required for tracking and identifying the reaction products and their final excitation level are described

Recent results on Heavy-Ion induced reactions of interest for 0νββ decay

An updated overview of recent results on Heavy-Ion induced reactions of interest for neutrinoless double beta decay is reported in the framework of the NUMEN project. The NUMEN idea is to study heavy-ion induced Double Charge Exchange (DCE) reactions with the aim to get information on the nuclear matrix elements for neutrinoless double beta (0νββ) decay. Moreover, to infer the neutrino average masses from the possible measurement of the half- life of 0νββ decay, the knowledge of the nuclear matrix elements is a crucial aspec

Recent results on heavy-ion direct reactions of interest for 0νββ decay at INFN LNS

Neutrinoless double beta decay of nuclei, if observed, would have important implications on fundamental physics. In particular it would give access to the effective neutrino mass. In order to extract such information from 0νββ decay half-life measurements, the knowledge of the Nuclear Matrix Elements (NME) is of utmost importance. In this context the NUMEN and the NURE projects aim to extract information on the NME by measuring cross sections of Double Charge Exchange reactions in selected systems which are expected to spontaneously decay via 0νββ. In this work an overview of the experimental challenges that NUMEN is facing in order to perform the experiments with accelerated beams and the research and development activity for the planned upgrade of the INFN-LNS facilities is reported