Changes between Initial Version and Version 1 of WorkBook/PileUp

Timestamp:

Mar 6, 2013, 11:26:19 AM (12 years ago)

Author:

Michele Selvaggi

Comment:

--

WorkBook/PileUp

@@ +1 @@
+= Pile-up implementation in Delphes =
+
+Multiple particle interactions per bunch-crossing are now implemented in Delphes. The procedure is divided in two main parts: 
+
+* mixing pile-up events with the main interaction
+* pile-up subtraction with the fast jet area method
+
+== Mixing pile-up ==
+
+The mixing procedure is done via the PileUpMerger module. The user can specify 4 parameters: PileUpFile, MeanPileUp, ZVertexWidth, ZVertexResolution.
+
+*PileUpFile: 
+
+the event sample containing pile-up events in binary format. This format allows for faster random event access compared to root trees. Basic information about the event is contained (particle 4-momenta, vertex position, and Particle ID)
+
+This sample has to be generated in advance with an event generator (typically Pythia6/8 or HERWIG) and then converted into binary format.
+
+* MeanPileUp:
+
+the average amount of pile-up events per bunch-crossing. For each hard scattering, N pile-up events will be randomly chosen from the PileUp file, where N is a random number following Poisson statistics with a mean MeanPileUp.
+
+*ZVertexWidth:
+
+Pile-up events randomly populate the z-axis. The position of each pile-up event is generated from a gaussian distribution with a standard deviation ZveterxWidth.
+
+*ZVertexResolution
+
+For |z|< ZVertexResolution the hard interaction vertex cannot be distinguished from pile-up vertices. For such pile-up events both charged and neutrals are then merged in the event (no charged particle subtraction).
+For |z|> ZVertexResolution the hard interaction vertex can be distinguished from pile-up vertices. For such pile-up events only neutrals are merged in the event (total charged particle subtraction), which assumes perfect vertex resolution and efficiency.
+
+== Pile-up contamination ==
+
+The density (in GeV/A) of pile-up contamination (rho) per event is computed within the FastJetFinder module if the following parameters are defined:
+
+{{{
+set ComputeRho true
+set OutputArrayRho rho
+}}}
+
+The method for the area calculation can also be specified (active area, passive area, Voronoi …) via the parameter AreaAlgorithm. 
+
+== Pile-up subtraction ==
+
+Since charged particle have already been subtracted to some extent, pile-up contamination only affects the jet energy resolution and the lepton and photon isolations.
+
+* Jet pile-up subtraction is done via the JetPileUpSubtractor module that takes as input the jet collection and rho:
+
+{{{
+set JetInputArray FastJetFinder/jets
+set RhoInputArray rho
+}}}
+
+* Isolation subtraction is done inside the Isolation module itself just by adding the line in the delphes card:
+
+{{{
+set RhoInputArray rho
+}}}
+
+
+
+= Running Delphes with Pile-Up = 
+
+
+