C++ Setting a private class member with function after the object is initialized via a constructor

I am trying to set a private class member after I have created the object with a constructor. This constructor set a bunch of public members but doesn't touch the private member.

class Tower {
  std::vector<Tower> jtowers;
public:
  Double_t E;
  Double_t Et;

void SetJTowers( std::vector<Tower> );
std::vector<Tower> GetJTowers() { return jtowers; }

Tower ();
Tower (TLorentzVector,std::vector<Double_t>);   //For jTowers
Tower (TLorentzVector,std::vector<Double_t>,std::pair<bool,bool>); //For gTowers
Tower (TLorentzVector,std::vector<Double_t>,std::pair<bool,bool>,std::vector<Tower>); //For seed gTowers
};

The constructor looks like this:

Tower::Tower (TLorentzVector FourVec,
              std::vector<Double_t> otherTowerInfo,
              std::pair<bool,bool> SeedRho_info) {
  E = FourVec.E();
  Et = FourVec.Et();
};

void Tower::SetJTowers (std::vector<Tower> constJTowers) {
  jtowers = constJTowers;
};

I then call a function that accepts a reference to a Tower object, does some fun stuff, and then attempts to set the jtowers member.

void AngularResolution :: ConstituentJTowers ( Tower& gT ) {
  // Find constituent jTowers
  std::vector<Tower> constJTowers;
  // code to fill constJTowers

  std::cout << constJTowers.size() << std::endl;  // This will a nonzero size
  gT.SetJTowers(constJTowers);
  std::cout << gT.GetJTowers().size() << std::endl;  // As will this

}

But when I attempt to check the contents of gT.GetJTowers() later in my code, I still find that it is empty, as if the original object is not being modified.

Any help is appreciated thanks!