Angular Dependence in Proton-Proton Correlation Functions in Central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ Reactions

TL;DR

This study investigates how proton-proton correlation functions vary with angle in central calcium nuclear reactions at 80 MeV/A, revealing significant angular dependence linked to reaction dynamics and comparing results with BUU model predictions.

Contribution

It provides the first detailed analysis of angular dependence in proton-proton correlations in these reactions, highlighting differences between participant zones and projectile remnants.

Findings

Significant angular dependence in p-p correlation functions observed.

Backward angles reflect participant zone characteristics.

Forward angles show expanding, fragmenting projectile remnants.

Abstract

The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$\pi$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and expected isospin dependent difference between the neutron-rich and neutron-deficient systems. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The decrease of the size of the source with increasing momentum is observed at backward angles while a weaker trend in the opposite direction is observed at forward angles. The results are compared to the theoretical calculations using the BUU transport model.