Why does behaviors of "assigning an object(pointer points to base class) to an variable" and "assigning it to a reference" differ?

Question

Here's the code:

class Base {
public:
    virtual void f() {
        std::cout << "Base::f()" << std::endl;
        std::cout << std::endl;
    };
};
class Derived : public Base {
public:
    void f() override {
        std::cout << "Derived::f()" << std::endl;
        std::cout << std::endl;
    };
};

int main(int argc, char** argv) {
    Base* d           = new Derived();
    Base  without_ref = *d;
    Base& with_ref    = *d;
    without_ref.f();
    with_ref.f();
}

Here's the result:

Base::f()

Derived::f()

Could anybody explains this? In my opinion, they should have the same behavior.