Closing a child view which is from another controller

Titanium Studio 3.2.3 IOS 7

This is my main window:

index.xml

<Alloy>
    <Window id="mainWin">
         <Button title="Load Sizes" onClick="loadSize"></Button>
    </Window>
</Alloy>

function loadSize()
   {
         var newview = Alloy.createController('sizes').getView();
         $.mainWin.add(newview);
   }

<Alloy>
   <View>
          <Label title="List of Sizes"></Label>
   </View>
</Alloy>