Belong to the students themselves. Postgraduate dissertations are created independently by students, who are the real authors, and the copyright should also belong to the students themselves.

Although the tutor has played a great role in the final completion of the thesis and should not enjoy any copyright, the author can mention the thesis tutor and his contribution in the publication in an appropriate way. In fact, in practice, many schools default that the author is the only right holder with the right of signature, but require the author to indicate the instructor on the cover of the paper, and the author himself will take the initiative to mention the teacher's guidance and help in the paper.

If you can provide detailed information, you can give a more detailed answer.