Search for new physics on the FASER experiment at the LHC

Detailed analysis of first FASER data through multi-variate techniques to improve sensitivity to new physics models by way of a establishing a global particle ID that will improve signal-background separation.
Institution: University of Liverpool 

FASER (ForwArd Search ExpeRiment) is a new CERN-based experiment designed primarily to search for light and weakly-interacting BSM particles with a significant lifetime (long-live particles, LLP). Located 480m downstream of the proton-proton interaction point (IP) used by the ATLAS experiment, the detector is a cylindrical spectrometer, consisting primarily of a tracker and a calorimeter, immersed in a 0.6T magnetic field. It successfully started data-taking in Summer 2022 during Run 3 of the LHC and has collected approximately 40/fb of data so far. Run 3 will last until 2025 and FASER will collect more than 200/fb of data. 

The student will work on the analysis of the data, focusing on searches for long-lived dark photons. These are characterised by a signature with two oppositely charged tracks with very high energy (∼TeV) that emanate from a common vertex inside the detector, and which have a combined momentum that points back through 10 m of concrete and 90 m of rock to the ATLAS IP. By the time the student joined, first data had been analysed using simple and basic techniques, and early results have been released. The student will work on expanding these first analyses to improve the dark-photon sensitivity and probe other new physics models, such as axion-like particles. 

Using multi-variate techniques such as neural networks, they will develop sophisticated analyses aimed to get the most out of the FASER data in terms of signal selection and background reduction.  In particular, they will combine the output of the individual detector components to establish a first global particle ID that will significantly improve the signal-background separation. The student will utilise these to play a pivotal role in the analysis of the full Run 3 dataset, producing the final legacy publications. They will have the opportunity of a long-term attachment at CERN and as such you will be able to support operations of the FASER experiment. 

In addition, the student will have the opportunity to perform feasibility studies on a proposed upgrade of the FASER experiment, consisting of an entirely new detector in a brand-new facility, which will collect a significantly larger dataset at the High-Luminosity LHC. 

Throughout the project the student will have access to targeted training in data science provided by the University of Liverpool with the Centre for Doctoral Training LIV.INNO. They will also be given the opportunity to carry out an industry placement of six months to broaden your wider research and career skills. 

This project will be carried out over 48 months, supported by a standard RKUK PhD stipend. 

Student: Sinead Eley