Entanglement refers to the phenomenon of two quantum mechanical objects correlated with each other at large distances and proposed to affect quantum criticality, the critical point of a quantum phase transition and governed by non-thermal control parameters such as magnetic field H. C12D14CuN4O5, a good representation of a one dimensional spin ½ Heisenberg antiferromagnetic with an exchange coupling constant J/kB ~ 3.2 K, has been shown to be quantum critical with respect to H. Measurement of magnetic susceptibility showed a variation of J/kB across the critical field, and hence, a non-monotonic field variation of entanglement. Such a field dependent variation of J/kB has not been previously observed. We want to investigate the spinon spectrum by inelastic neutron scattering experiments at different temperatures down to 100 mK as well as estimate J/kB at H = 0 using LET spectrometer.