Search for missing materials in the LHCb simulation

The disagreement between data and Monte Carlo in the multiplicity distribution of downstream detectors is an open question in the LHCb group. The previous studies indicate that in the downstream area, there might be some materials not taken into consideration in the simulation. To validate the material description in MC simulation, the data/MC comparison for the hit map (hit distribution) of sub detectors are made, and a method called tomography is used to study in detail. With the tomography method, the interaction between high energy particles and materials in the detectors are reconstructed, and the distribution of the interaction vertices can reflect the material distribution in both real detectors and MC models.