ATLAS vertexing group

Conveners: Graham Richard Lee and Federico Meloni

Welcome to the ATLAS vertexing group. The tasks of our group are:

• Development and support of algorithms for finding the primary vertices of events, including the pile-up;
• Provide tools for the evaluation of the performance of the primary vertex reconstruction.

General

Our meetings take place each Wednesday at 09:00
E-group atlas-vertexing
List of tasks considered by the Vertex Reconstruction group for the Run-2 ( OPEN )
Tutorial on using vertexing software in Run 2
The Paper describing the vertexing algorithm in Run I
Collection of papers and notes on vertex reconstruction
Useful datasets for the algorithm development and performance checks

List of tasks considered by the Vertex Reconstruction group for the LS1 ( CLOSED )

Current activity

New seeding strategy for Primary vertex finding in RunII
Other developments and improvements of the vertexing code
Optimization of track selection for primary vertex reconstruction
Transition of vertexing code to the new xAOD format
Optimization of split-vertex and re-merging algorithms
Primary vertex selection for different physics tasks
Re-weighting of z-position of primary vertex
InclusiveSecondaryVertexFinder

Run 2 Recommendations

The choice of the primary vertex may be analysis dependent, especially for those analyses for which the signal process has low track multiplicity.

• Hard-scattering (HS) vertex selection
  • Hard-scattering vertex is selected by default from highest sum p_T²
  • Select HS vertex requiring: xAOD::Vertex­>vertexType() == xAOD::VxType::PriVtx; This will not be guaranteed in the future to always be the first reconstructed vertex in the container.
  • Automatically ensures at least 2 tracks (no further selection on the number of tracks should be applied)

• Pile-up vertex selection
  • Select vertices requiring xAOD::Vertex­>vertexType() == xAOD::VxType::PileUp
  • Automatically ensures at least 2 tracks at vertex

• IP resolution
  • As of Spring 2017, oversight of this work is being transferred to the Vertexing group.
  • Recent work on release 20.7 and 21 recommendations is documented here.
  • Updates to follow.

Public Plots

Comparison of release 20.7 to release 21.0: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/IDTR-2017-006/

Plots for ICHEP 2016: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/IDTR-2016-007/

Number of Reconstructed Vertices vs Mu: https://cds.cern.ch/record/2220099

Data from 2016: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/IDTR-2016-003/

Public Talks

CHEP 2016: https://indico.cern.ch/event/505613/contributions/2230823/

https://cds.cern.ch/record/2211054/files/ATL-COM-PHYS-2016-1212.pdf

https://cds.cern.ch/record/2210180/files/ATL-COM-PHYS-2016-1187.pdf

Notes and Publications

Full list: Collection of papers and notes on vertex reconstruction

Data from 2015: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2015-026/

Image Seeding Description: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2015-008/

Old links

Tutorial on using vertexing software in Release 17

Expected performance for mu=60

Number of tracks at each reconstructed vertex

Number of reconstructed vertices per event

Hard-scatter pT efficiency

Fraction of reconstructed hard-scatter vertex's pT from tracks coming from the true hard-scatter event.

Hard-scatter pT impurity

Fraction of reconstructed hard-scatter vertex's pT from tracks coming from true pileup events.

Update given at Vertex Reconstruction Meeting, 22/3/17 - https://indico.cern.ch/event/605644/contributions/2525007/attachments/1431707/2199525/AMorris_Vertexing_2017-03-22.pdf