Maximiliano Sioli

Study of quantum nature of high energy top quarks

Our nature is astonishing: we are not subject to the laws of classical mechanics but live in a quantum universe. Among the most extraordinary effects of quantum mechanics, entanglement stands out: the capacity of two states to influence each other even when they area causally-disconnected.

Numerous experiments have been conducted to observe entanglement in different systems, but there is still no experimental proof of entanglement between particles at very high energy, such as those created in the Large Hadron Collider. However, in recent years, there has been a tremendous interest in attempting to observe entanglement for the first time in this fascinating context, and the most promising channel is the production of pairs of top quarks.

The entanglement between top quarks can be studied in two regions: the threshold region, where the energy is sufficient to create the quark pair, or the "boosted" region, where the top quarks are generated with incredibly high momentum. It is precisely this latter region that represents the most challenging task but also the most sensitive to quantum correlations.

The main obstacles we encounter in the "boosted" region concern the individual reconstruction of all the decay products of the top quark, which are collimated and difficult to separate. The reconstruction of the entire system is essential to observe entanglement.

The objective of this thesis project is to develop a strategy to measure observables sensitive to entanglement, using ATLAS data and simulations. We aim to be the first to observe quantum entanglement between high-energy top quarks.

But that's not all: measuring the quantum properties of fundamental particles also offers an unexplored opportunity to investigate the presence of new physics that could modify quantum correlations. This innovative approach represents a direction of research that is still relatively unexplored and differs from the traditional methods used for discovering new phenomena. The phenomenology group at the University of Bologna is a true pioneer in this field and is actively collaborating with the ATLAS experimental group to push forward research in this area.

Summary:

The student will analyze data collected from the ATLAS experiment, located at the CERN's Large Hadron Collider (LHC), in order to study the quantum correlations between pairs of top quarks. The objective is to develop an analysis method that allows for the first observation of entanglement between high-energy particles created in a collider. The thesis work will involve the development and comparison of different approaches for the reconstruction and measurement of the high-energy top-antitop systems. The approach will be optimized toward the precision with which variables sensitive to the presence of entanglement, "entanglement witnesses," can be measured. This thesis project is suitable for master's degree students and can be adapted for bachelor's degree students as well. The main activities involve data analysis and programming, so basic knowledge of a programming language (C++/Python) is preferable but not necessary.