Identification of SUSY events with displaced vertices
Project Description
This project consists of performing physics analysis tasks
with the ATLAS detector of the Large Hadron Collider at CERN.
A number of interaction terms that may appear in
supersymmetric models allow the lightest supersymmetric particle to decay.
Since the couplings involved are probably small such decays may lead
to spectacular signatures of several high pT jets and/or leptons not
originating from the main interaction point.
The aim of this project is to identify such events in terms
of their acceptance in the trigger and the reconstruction of
their characteristic properties.
Studies will focus on decays in the inner detector allowing
to reconstruct the tracks of the particles produced in the decay.
The tasks include activities in the areas of Trigger and Reconstruction.
Tasks
Work on the Reconstruction
Due to the special nature of the considered events
detailed studies of the ATLAS tracking capabilities and
vertex finding algorithms have to be performed.
The main background will come from
secondary vertices as resulting from QCD events.
The central task in the reconstruction of the signal events is
the identification of the displaced vertices.
Up to now, one of the standard vertex finding algorithms of the ATLAS software
has been optimized for the identification of displaced vertices as present in the signal events.
However, its ability to reject background events was found to be limited with
varying results depending on internal parameters.
Therefore, the preformence of a topological vertex finding algorithm should be explored.
It will be neccessary to adjust the vertex preselection for this algorithm
and optimize its internal parameters to keep the rate of misidentified
fake vertices as small as possible
while assuring a high signal efficiency.
Finally, the application of these techniques
to the signal and ways to separate it from the Standard Model
background have to be explored.
Work on the Trigger
For most analyses in the ATLAS experiment the trigger system is a crucial ingredient.
It has to selects events online with the LHC bunch crossing rate
and must therefore operate extremely fast. Its purpose is to reject uninteresting
events and keep only the relevant ones. In our scenario we are interested in events
with long-lived lightest supersymmetric particles which travel across many layers of the
inner detector before they decay into lighter stable particles.
The resulting displaced decay vertex
is a characteristic signature in this supersymmetric scenario that can be used
to trigger on such events. Assessing the efficiency of the currently availably tracking
trigger algorithms using displaced vertices will help to optimize the selection cuts and
also the performance of the tracking trigger algorithms. A mandatory boundary condition
of all trigger algorithms is that it has to be fast. Therefore improving the discrimination
power of a trigger algorithm should not introduce additional processing time. In the
inner detector this is particularly challenging due to the high number of readout elements
and the large background from pile-up events.
What you will learn
Supersymmetry;
Details of the ATLAS trigger/reconstruction algorithms;
Analysis techniques and
analysis tools (ROOT + Atlas specific tools).
Required Knowledge
No prior knowledge of supersymmetry is required.
Introductory knowledge of particle physics and programming
experience (especially in C++) would be advantageous.
Contacts
Ignacio Aracena
Claus Horn
Last modified: Tu March 5 15:16:47 PDT 2007