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--- 2013:groups:tools:substructure [2013/06/06 11:34]
loch.peter [Software version 1]
+++ 2013:groups:tools:substructure [2013/06/06 11:51]
gregory.soyez [Methods]
@@ Line 66: / Line 66: @@
 ===== Methods =====
+The idea is to test filtering/grooming techniques as a way to reduce the sensiticity to bsoft backgrounds (initially the filter used with the BDRS tagger was meant to reduce the sensitivity to the UE).
+Following the Filter tool in FastJet3, we need (i) a jet definition to break the jet into subjets and (ii) a selection criterion that decides what subjets are kept. We'll consider 3 options:
+  * "Filtering":
+    * cluster with Cambridge/Aachen, $R_{\rm filt} = \eta_{\rm filt} R_{\rm jet}$ [$\eta_{\rm filt}$ between 1/3 and 1/2 sounds about right]
+    * keep the $n_{\rm filt}$ hardest subjets [$n_{\rm filt}$=2.3.4]
+  * "Trimming":
+    * cluster with Cambridge/Aachen, $R_{\rm filt} = 0.2$
+    * keep all subjets with $p_{t,\rm sub} > f p_{t,jet}$ [$f$ between 0.01 and 0.05 should be fine]
+  * "Area-filtering":
+    * cluster with Cambridge/Aachen, $R_{\rm filt} = 0.2$
+    * keep all subjets with $p_{t,\rm sub} > \rho A_{\rm sub} + n \sigma \sqrt{A_{\rm sub}}$ [$n$ between 2 and 5]
+The 3rd option is new and based on the idea that the PU scales $\rho$ and $\sigma$ should set the scale of the PU/noise removal.
+For pileup sutraction, one usually want to first subtract the average PU contamination ($\rho A_{\rm sub}$) from each subjet before deciding which subjets are to be kept. This is implemented in the fastjet::Filter. Note that with "Area-filtering" you should then cut with   $p_{t,\rm sub} > n \sigma \sqrt{A_{\rm sub}}$ since the baseline has already been subtracted.

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