add new CF as a function of q_abs_lcms and q_inv

Author: Steffimro

PWGEM/PhotonMeson/Tasks/photonhbt.cxx

@@ -981,6 +981,10 @@ struct Photonhbt {
 
     fRegistryCF.addClone("Pair/same/", "Pair/mix/");
 
+    // New CF idea
+
+    fRegistryCF.add("Pair/same/CF_QLcms_Qinv", "diphoton CF |q|_{LCMS} vs. q_{inv}", kTHnSparseD, {axisQabsLcms, axisQinv, axisKt}, true);
+
     fRegistryCF.add("Pair/mix/hDiffBC", "diff. global BC in mixed event;|BC_{current}-BC_{mixed}|", kTH1D, {{10001, -0.5, 10000.5}}, true);
   }
   // ─── CF: PairSep  ────────────────────────
@@ -1985,6 +1989,11 @@ struct Photonhbt {
         fRegistryCF.fill(HIST("Pair/mix/CF_1D"), hbtanalysis.cfgUseLCMS ? qabs_lcms : qinv, kt, weight);
       }
     }
+    if constexpr (ev_id == 0) {
+      fRegistryCF.fill(HIST("Pair/same/CF_QLcms_Qinv"), qabs_lcms, std::fabs(qinv), kt, weight);
+    } else {
+      fRegistryCF.fill(HIST("Pair/mix/CF_QLcms_Qinv"), qabs_lcms, std::fabs(qinv), kt, weight);
+    }
     float deta_pair = v1.Eta() - v2.Eta();
     float dphi_pair = v1.Phi() - v2.Phi();
     dphi_pair = RecoDecay::constrainAngle(dphi_pair, -o2::constants::math::PI);