SciPost Phys. Proc. 8, 160 (2022) ·
published 14 July 2022
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· pdf
To study quantum properties of the hadron wavefunction at small x, we derived
the reduced density matrix for soft gluons in the CGC framework. We explicitly
showed that the reduced density matrix is not diagonal in the particle number
basis. The off-diagonal components are usually ignored in the conventional
parton model. We thus defined the density matrix of ignorance by keeping only
the part of the reduced density matrix which can be probed in a limited set of
experimental measurements. We calculated Von Neumann entropy for both the
reduced and ignorance density matrices. The entropy of ignorance is always
greater than the entanglement entropy (computed drom the reduced density
matrix) of gluons. Finally, we showed that the CGC reduced density matrix for
soft gluons can be diagonalized in a thermal basis with Boltzmann weights
suggesting thermalization of new quasi-particle states which we dubbed
entangolons.
