Bimodalities: A survey of experimental data and models

Abstract

Abstract. Bimodal distributions of some chosen variables measured in nuclear collisions were recently proposed as a non ambiguous signature of a first order phase transition in nuclei. This section presents a compilation of both theoretical and experimental studies on bimodalities performed so far, in relation with the liquid-gas phase transition in nuclear matter.After a formulation of the theoretical bases of bimodality, world-wide experimental results will be reviewed and discussed, as well as the occurrence of some kind of bimodality in models. Finally conclusions on the perspectives of such analyses in the near future and the possible connections to other proposed signals of the liquid-gas phase transition in nuclear matter will be given.

Distributions of the largest fragment size in multifragmentation: Traces of a phase transition

“…Bimodality in distributions of the largest fragment size or other quantities expected to be closely correlated with the order parameter is considered as a promising signature of first-order phase transition [18,59,60]. Experimental examinations of the largest-fragment charge distribution have, however, not ascertained yet such a signal up to now.…”

“…Besides the characteristic evolution of its mean-value, event-to-event fluctuations reflected in the probability distribution of the largest fragment size are of considerable interest. Experimental examinations have focused on the appearance of particularly large fluctuations [6,9,[11][12][13][14][15], on bimodal characteristics representative of a two-phase coexistence [6,8,10,[16][17][18], on so-called ∆-scaling features [1, 5,6,8], and on the connection with dynamical observables as, e.g., radial flow [19].…”

Onset of quenching of the giant dipole resonance at high excitation energies

“…In particular, in the last decade, the study of the nuclear caloric curve, i.e., the relation between the system temperature and its excitation energy, has yielded evidence of a trend that is reminiscent of liquid water heating to the boiling point, the plateau region being interpreted as a liquid-gas phase transition in nuclear matter [43,53]. Other possible signatures of a liquid-gas phase transition or critical behavior in nuclei were found by using different experimental probes and theoretical approaches [54][55][56][57]. It has been proposed that the presence of collective states can be a signature of the existence of a compound nucleus and that the disappearance of the collective motion at high excitation energies could therefore provide further evidence for a phase transition in nuclei [58,59].…”

Shear viscosity of hot nuclear matter by the mean free path method

“…At ρ ∼ 1 2 ρ0, a minimum of η/s is seen at around T = 10 MeV and a maximum of the multiplicity of intermediate mass fragment (MIMF) is also observed at the same temperature which is an indication of the liquid-gas phase transition.Due to van der Waals nature of nuclear force, liquidgas phase transition (LGPT) occurs in heavy ion collisions (HIC) at energy around hundred MeV/nucleon [1][2][3][4][5][6][7][8]. Studies on the phenomena of LGPT and its probes, like fragment size distribution, caloric curve, bimodality etc., have become the most important subjects in HIC at intermediate energies in the past years [3,4,[9][10][11][12].Viscosity describes fluid's internal resistance to flow and may be thought of as a measure of fluid friction. In ultra-relativistic HIC, hydrodynamic model has been used to study the Quark Gluon Plasma (QGP) phase and critical phenomenon [13][14][15][16][17][18].…”

“…PACS numbers: 51.20.+d, 51.10.+y, 24.10.-i Due to van der Waals nature of nuclear force, liquidgas phase transition (LGPT) occurs in heavy ion collisions (HIC) at energy around hundred MeV/nucleon [1][2][3][4][5][6][7][8]. Studies on the phenomena of LGPT and its probes, like fragment size distribution, caloric curve, bimodality etc., have become the most important subjects in HIC at intermediate energies in the past years [3,4,[9][10][11][12].…”