Constraining the density dependence of the symmetry energy at low density using new observables from neck fragmentation mechanism, E. De Filippo for the EXOCHIM collaboration, INFN Catania, Italy − We present comparisons between experimental data for the systems 35 A. MeV 124Ni + 64Ni (neutron rich) and 112Sn + 58Ni (neutron poor) studied in inverse (Reverse experiment) and direct kinematics (Timescale experiment) and Stochastic Mean Field (SMF) + GEMINI calculations.  We have correlated the emission timescale at mid-velocity of intermediate mass fragments (IMF) with their isotopic composition: prompt emitted particles show larger value of asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in distributions respect those produced in sequential emission.  By comparison the data with calculations we show that these new observables add valuable constraint on the symmetry energy term of EOS at subsaturation density and can constitute a robust probe for dynamical models (SMF, QMD) predictions.