[Paper Review] {Coherent Dissociation $^{12}$C~$ ightarrow$~3$α$ in Lead-Enriched Emulsion at 4.5 GeV/$c$~per Nucleon

V. V. Belaga, A. A. Benjaza+3 more|arXiv (Cornell University)|Sep 5, 2011

High-Energy Particle Collisions Research4 citations

TL;DR

This study investigates coherent dissociation of 12C into three α particles at 4.5 GeV/c per nucleon in lead-enriched emulsion, using transverse momentum and correlation analyses to show that the statistical model of rapid fragmentation fails to describe the data. The key finding is that angular momentum transfer to the carbon nucleus during collision explains the observed azimuthal collinearity of α particles, with decay temperatures of 3.4–4.0 MeV, significantly lower than nucleon binding energy.

ABSTRACT

The transverse-momentum distributions and correlation characteristics of relativistic $α$ particles from the coherent dissociation of a carbon nucleus into three $α$ particles at 4.5 GeV/$c$ are studied in lead-enriched emulsion. Comparative analysis of data obtained in ordinary and lead-enriched emulsion stacks is performed. It is shown that the statistical model of rapid fragmentation does not describe the momentum and correlation characteristics of a $α$ particles in the rest frame of the carbon nucleus. The estimated decay temperature of $^{12}$C is weakly dependent on the target atomic mass. It is shown that the carbon nucleus undergoing fragmentation acquires angular momentum in the collision.

Motivation & Objective

• To investigate coherent dissociation of relativistic 12C nuclei into three α particles in lead-enriched emulsion.
• To determine whether the statistical model of rapid fragmentation accurately describes momentum and correlation characteristics of α particles in the rest frame of 12C.
• To assess the role of target nuclear mass and Coulomb interaction in coherent dissociation mechanisms.
• To examine the influence of angular momentum transfer on the spatial correlation of decay products.
• To quantify decay temperature and transverse momentum distributions in coherent 12C → 3α processes.

Proposed method

• Scanning of nuclear emulsion stacks enriched with lead (1 Pb atom per 5 Ag atoms) to detect three relativistic doubly charged fragments with z = 2.
• Measurement of α particle angles using a method that minimizes distortion effects from multiple scattering.
• Comparison of transverse momentum distributions and correlation functions in ordinary vs. lead-enriched emulsions to isolate coherent processes.
• Application of statistical models (Rayleigh distribution) to describe pT spectra and ε*ij correlations under the assumption of fast statistical decay.
• Monte Carlo simulation of the cascade decay path 12C → 8Be + α → 3α to compare with experimental data and assess contribution of sequential decay.
• Use of momentum transfer q² and effective mass M* to evaluate coherence conditions and threshold constraints for dissociation.

Experimental results

Research questions

• RQ1 Does the statistical model of rapid fragmentation accurately describe the transverse momentum and correlation distributions of α particles from 12C → 3α dissociation?
• RQ2 How does the target atomic mass (Pb vs. ordinary emulsion) affect the cross section and characteristics of coherent 12C dissociation?
• RQ3 What is the decay temperature of 12C in coherent dissociation, and how does it compare to nucleon binding energy?
• RQ4 Why do the experimental pT and ε*ij distributions deviate from the Rayleigh and statistical model predictions?
• RQ5 What is the role of angular momentum transfer in shaping the azimuthal collinearity of the three α particles?

Key findings

• The decay temperature of 12C in coherent dissociation is estimated at 3.4–4.0 MeV, significantly lower than the nucleon binding energy in carbon.
• The statistical model of rapid fragmentation fails to describe the observed transverse momentum and correlation distributions of α particles, indicating non-thermal dynamics.
• The mean cross section for 12C → 3α increases by a factor of approximately 2 in lead-enriched emulsion, indicating dominance of the Coulomb mechanism on high-Z targets.
• The azimuthal-collinearity coefficient B* exceeds theoretical predictions for both direct and cascade decay models, suggesting angular momentum transfer to the dissociating nucleus.
• Deviations in pT² and ε*ij distributions from statistical models are not due to target composition but likely due to final-state interactions and angular momentum effects.
• The coherence condition is satisfied, with low momentum transfer qL < μ/B¹/³, confirming the dominance of diffraction or Coulomb mechanisms in peripheral collisions.