Experiments:CERN-LHC-ATLAS
Deadline: 2018-01-15
Region: Europe
Job description:
This program proposes to Chinese students with at least 4 years of physics study at the university to join a French master program in Particle Physics (Master 2 NPAC) and then accomplish a PhD at Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE Paris) to search for Dark Matter inside the ATLAS experiment. The selected student will be offered a full living tuition for the period of the full program through a CSC fellowship.
An application can be made through the following site :
http://self.parisdescartes.fr/cgi-bin/WebObjects/RecDoctor.woa
This project is identified with the reference ED 560 SS-P7-ED560-PhysiqueParticules-1
Here is the motivation of the whole project and a description of the PhD that could start in fall 2019.
The current understanding of elementary particles and their interactions is based on the Standard Model (SM). This is the theory of electromagnetic, weak and strong forces between quarks and leptons, which has been confirmed experimentally over a wide range of energies, from atomic scales to the TeV energy scale. Despite this remarkable success, we know that the SM is incomplete.
Cosmological and astrophysical pieces of evidence suggest that either general relativity (GR) is wrong or the SM describes only about 5% of the energy content of the known Universe, failing to account for a needed so-called dark matter (DM) component, which amounts to roughly 27%. The severe constraints on GR theory from solar system observations make very difficult to built modified gravity theories being able to account for DM gravitational effects at the various scales of interest. It is thus rather likely that there should be new particles and dynamic degrees of freedom beyond the SM, generally referred to as physics beyond the Standard Model (BSM).
The Large Hadron Collider (LHC) and the related ATLAS experiment offer a unique occasion to search for possible DM particles in a complementary way to direct and indirect detection experiments by selecting events with elusive DM particles produced in the final state giving rise to large missing transverse energy (MET). This allows in particular to study a possible coupling of the top quark with DM with both leptonic and hadronic decays of the W boson.
A missing transverse energy high-level trigger using jets and tracks is one of the most promising options to foster the trigger rate reduction while keeping a high signal efficiency at large collision pileup met at the High Luminosity LHC. The algorithm used currently in ATLAS sums over all the jets which are reconstructed from calorimetric clusters and is highly pileup dependent. With the addition of track information, both soft-term and pileup suppression can be addressed and significant improvement can be achieved in high pileup conditions. Furthermore, using the new ATLAS Fast-TracKer system (FTK), a hardware-based system that can quickly reconstruct the charged particle trajectories from the pixel and silicon detectors and provide these track information for high-level trigger decision, should allow further improving the pileup suppression using the same algorithm, and will be a good candidate for the main trigger after LHC Long Shutdown 2.
The student working on this project will first address the question of how to develop a new MET trigger algorithm integrating FTK tracks to improve the rate reduction while keeping a high signal efficiency at high pileup. Based on these improvements, the student will improve the sensitivity of the ATLAS experiment to search for dark matter particle candidates. The candidate will study the possible coupling of the top quark with DM using both leptonic and hadronic decays of the W boson. The obtained results will be interpreted in terms of constraints on different DM models relevant to LHC physics. The candidate will also perform fiducial differential cross section measurements in the regions relevant for DM search so that these legacy run II measurements can be used to put constraints on any new possible model after the publication of these results. The candidate will work with the complete data set of LHC Run2 which will reach a planned integrated luminosity of 300/fb.
The project will benefit from the long-standing activity of the LPNHE group inside the ATLAS collaboration and will work in a group composed of several experts of DM searches at the LHC. The student will be directed by a senior mentor which already trained several PhD and demonstrated to be able to design appropriate objectives and timetables for his students.
The LHC is the facility where the most promising searches regarding direct production and detection of new particles can be performed. Any positive result in the search covered in this PhD would bring a major update to our understanding of the universe.
The forecast timetable for the PhD project is the following,:
months 1-12 :
- qualification task in the ATLAS experiment to become an ATLAS author. That work will be connected to the trigger activity and to related performance issues.
- Study of the DM models and tools to study their properties (Monte Carlo)
- Discovery of the ATLAS computing framework and setup of the analysis framework based on the LPNHE group activity already involved in DM search.
months 13-24 :
- work on the performance aspect of the project
- apply the improved performance to the top + MET search
- contribute to the ATLAS DM group activity on a regular basis
months 25-30 :
- produce the final Run II results and prepare a paper for the ATLAS collaboration
months 31-36 :
- write up of the PhD and defense.
More Information:http://self.parisdescartes.fr/cgi-bin/WebObjects/RecDoctor.woa