Added dedicated roman pot constructor.

new file: ForwardRomanPot_geo.cpp

ip6/B0_tracker.xml

@@ -6,7 +6,7 @@
       Far Forward B0 Tracker Parameters
       ---------------------------------
     </comment>
-    <constant name="B0Tracker_zpos" value="B0PF_CenterPosition + B0PF_Length/2.0 + 20.0*cm"/>
+    <constant name="B0Tracker_zpos" value="B0PF_CenterPosition + B0PF_Length/2.0 - 50.0*cm"/>
   </define>
 
   <detectors>
@@ -18,16 +18,20 @@
       insideTrackingVolume="true"
       reflect="false"
       vis="AnlRed">
-      <position x="0" y="0" z="B0Tracker_zpos"/>
+      <position x="100*mm" y="0" z="B0Tracker_zpos"/>
       <layer id="1" 
         vis="AnlBlue"
-        x="20.0*cm" 
-        y="10.0*cm" >
-        <slice material="Air" thickness="1.0*cm" vis="AnlBlue" sensitive="true" />
-        <slice material="Air" thickness="1.0*cm" vis="AnlBlue" sensitive="true" />
+        x="15.0*cm" 
+        y="5.0*cm" >
         <slice material="Air" thickness="1.0*cm" vis="AnlBlue" sensitive="true" />
+      </layer>
+      <layer id="2" 
+        vis="AnlBlue"
+        x="15.0*cm" 
+        y="5.0*cm" >
         <slice material="Air" thickness="1.0*cm" vis="AnlBlue" sensitive="true" />
       </layer>
+
     </detector>
   </detectors>