std::thread pass by reference calls copy constructor

std::thread takes its arguments by value. You can get reference semantics back by using std::reference_wrapper:

std::thread newThread(session, &sock, std::ref(logger));

Obviously you must make sure that logger outlives the thread.

I get a compiler error when I try to pass the logger (or the socket) to the thread by reference

It is not sufficient for the thread's entrypoint function to take a reference type: the thread object itself takes its arguments by value. This is because you usually want a copy of objects in a separate thread.

To get around this, you may pass std::ref(logger), which is a reference wrapper hiding reference semantics under a copyable object.