Why I am able to change member of an object which is passed as constant reference?

class Student {
private:
    int age;
public:
    char *name;
    Student(int age,char*name) {
        this->age=age;
        this->name=new char[strlen(name)+1];
        strcpy(this->name,name);
    }
    Student(Student const &s1) {
        this->age=s1.age;
        this->name=new char[strlen(s1.name)+1];
        strcpy(this->name,s1.name);
        s1.name[0]='x';
    }
    void display() {
        cout<<age<<" "<<name<<endl;
    }
};
int main() {
    char name[]="abcd";
    Student s1(10,name);
    s1.display();
    Student s2(s1);
    s2.name[0]='x';
    s1.display();
    s2.display();
}

I have passed s1 as a constant reference but I am able to change s1.name[0] and the program compiles successfully. Why I am able to change s1.name[0]?enter image description here