Critical behavior in the variation of GDR width at low temperature

TL;DR

This study investigates the temperature-dependent behavior of the GDR width in nuclei around 1 MeV, revealing a critical point influenced by GDR-induced quadrupole moments, which challenges existing models.

Contribution

It introduces the concept of a critical point in GDR width evolution due to quadrupole moments, enhancing the phenomenological understanding of GDR behavior.

Findings

GDR widths are below model predictions at low temperatures.

A critical point in GDR width increase is identified.

GDR-induced quadrupole moments influence width evolution.

Abstract

We present the first experimental giant dipole resonance (GDR) width systematics, in the temperature region 0.8 $\sim$ 1.2 MeV for $^{201}$Tl, a near Pb nucleus, to investigate the evolution of the GDR width in shell effect & pairing dominated region. The extracted GDR widths are well below the predictions of shell effect corrected thermal shape fluctuation model (TSFM) and thermal pairing included phonon damping model. A similar behavior of the GDR width is also observed for $^{63}$Cu measured in the present work and $^{119}$Sb, measured earlier. This discrepancy is attributed to the GDR induced quadrupole moment leading to a critical point in the increase of the GDR width with temperature. We incorporate this novel idea in the phenomenological description based on the TSFM for a better understanding of the GDR width systematics for the entire range of mass, spin and temperature.