Abstract: Background: The change of hadron properties in nuclear medium is a very active field for both experimental and theoretical research. The study of hypernuclei plays an important role in nuclear physics. Purpose: We aim to study the properties of Lambda hypernuclei and the medium modifications of baryon properties. The quark degrees of freedom are explicitly considered in the model, which enables us to investigate the medium modifications of baryons in a nuclear many-body system and provide a reasonable description of the system in a consistent manner. Methods: We use the Friedberg-Lee (FL) model to describe the nucleon and hyperon in nuclear matter and hypernuclei. The baryon is described as a bound state of three quarks in a nontopological soliton formed by a scalar composite gluon field. The baryons interact through the self-consistent exchange of scalar and vector mesons. The mesons couple directly to the quarks inside the baryons. Results: The properties of baryons are significantly modified in nuclear medium. At normal nuclear matter density, the nucleon radius increases by 13% or so with the parameter Set B, while the Lambda radius increases by 9% or so. The Lambda single-particle energies in hypernuclei are very close to the experimental values. Conclusion: It is shown that the present model is able to provide a reasonable description of Lambda hypernuclei without adjusting parameters, and at the same time it predicts a significant increase of the baryon radius in nuclear medium.

Key words: Friedberg-Lee (FL) model, Nuclear matter, Medium effect, Hypernuclei