update qhl ratio

1 files changed, 20 insertions, 2 deletions

diff --git a/src/dc.h b/src/dc.h
index 248a6e0..5984687 100644
--- a/src/dc.h
+++ b/src/dc.h
@@ -78,8 +78,26 @@
  * and charge. */
 #define MUON_OWL_NEARBY_DISTANCE 300.0
 
-/* QvNHIT ratio threshold. */
-#define QRATIO_THRESHOLD 0.25
+/* QvNHIT ratio threshold.
+ *
+ * Note: This is defined as 0.25 in the SNO documentation and in the code, but
+ * there is a major bug in the implementation. On line 174 of flt_qnhit_cut.for
+ * it does:
+ *
+ *     * check if pmt terminator is blown
+ *     if( .not. btest(ccc_info(KCCC_STATUS,iccc), KCCC_B_75OHM) )then
+ *        qhl_work(nhit_cal)=  qhl
+ *     else
+ *        qhl_work(nhit_cal)=  qhl/2.0
+ *     endif
+ *
+ * I *think* it's always evaluating the qhl/2.0 branch even though the docs and
+ * Neil Mccauley's thesis don't say that.
+ *
+ * I verified this by looking at the QHL over nhit ratio for neutrons in Monte
+ * Carlo which peaked around 0.9 whereas the ratio for the N16 events in Neil
+ * Mccauley's thesis peaks around 0.5. */
+#define QRATIO_THRESHOLD 0.5
 
 int is_itc(event *ev);
 int is_fts(event *ev);