angularjs service not populating

Why is the $sope.b not being populated?

I'm trying to reach to the JSON that is received from the $http in the service through the service but it appears always as undefined I've added a snapshot of the output.

var app= angular.module("myApp");
app.service('RepoService', function($http){
   this.data= function(callBack){
    $http.get('/Data/list.json')
        .then(function(response){
            console.log(response.data);
            callBack(response.data);
        })
    }
 })
 var myApp = angular.module('myApp');
 myApp.controller('listCtrl',function($scope,RepoService){
   RepoService.data(function(callBack){
   console.log(callBack) 
   $scope.b = callBack   
 });
  console.log("this is b =" +$scope.b);
 })
 [Somehow its always 'undefined'][1]