A novel muon identification method for dileptons from the initial stages of collisions at the LHC

Full description

At the Large Hadron Collider (LHC) in Geneva, collisions of lead nuclei are used to create a thermodynamic system described by fluid dynamics under extreme conditions. This system evolves from a deconfined state of matter, known as the Quark-Gluon Plasma (QGP), where quarks and gluons move freely and interact via the strong force, to a state of partons in thermal and chemical equilibrium. It then expands and cools until the temperature for the transition to a hadron gas is reached.

Experimentally, the early stages of heavy-ion collisions are difficult to access. One possibility to investigate this initial phase is using dileptons emission, such as prompt muon pairs. Prompt muons are produced at the beginning of the collision and their propagation is not affected by the presence of the QGP.
To use these dileptons effectively, an high-purity muon identification is necessary to distinguish prompt muon pairs from other background particles produced.

The internship’s goal is to develop a kink finder algorithm to reduce background muons, with the aim to improve the signal over background for prompt dileptons.

The QGP laboratory inside the department of nuclear physics of CEA Saclay is actively involved at all levels of experimental exploration of the QGP with the ALICE and LHCb experiments at LHC. Currently, one part of the group investigates novel probes and new detectors for QGP studies with the LHCb experiment, such as dilepton production.

The proposed internship consists of developing an algorithm capable of identifying muons originating from the weak decays of charged pions and kaons, commonly referred to as in-flight decays. These muons at the moment represent non-negligible source of background in analyses involving prompt muons, such as those done for studying the QGP with dileptons measurements. Since they are real muons tracks within the muon system, the in-flight muons cannot be reduced by improvements based on the muon system identification algorithm itself.
However, the trajectories of these background leptons exhibit a kink topology at the decay position. Therefore, the comparison of their position and slope in different subdetectors can be used to improve significantly the rejection of muons from decays in flight.

The selected student will work within a Python/C++ framework developed by the lQGP group at CEA and the LHCb Collaboration to implement a dedicated kink finder algorithm aimed at improving background muon identification. Once validated the algorithm, the extracted features could be used as input to a neural network, with the goal of enhancing the performance of existing muon identification techniques.

During the internship, the student will gain familiarity with the physics of the QGP, learn about detector physics and develop skills in data analysis and track reconstruction techniques.
The project offers the opportunity to develop or strengthen programming skills in Python/C, depending on the student’s background and interest, while contributing to the group ongoing studies to improve muon identification performance with the LHCb experiment.

Location

Saclay

Internship conditions

• Internship duration: 6 months
• Level of study: Bac+5
• Training: Master 1
• Continuation in PhD thesis: No
• Application deadline: 25 avril 2026

Useful methods and technics:
Relativistic kinematics, programming, MC simulations

Computer languages and software:
Python/C++

Supervisor

ARATA Carolina
Phone: 01 69 08 73 57
Email :

Head of the laboratory DPhN / LQGP

Phone: