LHCb top asymmetry

Lead Research Organisation: University of Liverpool
Department Name: Physics

Abstract

The Large Hadron Collider is the most powerful particle accelerator ever constructed. LHCb, one of its four major experiments, provides unique detector coverage of proton beam collisions. Specialised for particle identification, utilising advanced tracking and mass determination; the full detector is layered perpendicular to the beams in one 'forward' direction from the interaction point, where the incoming beams define the forward-backward axis. As a result, LHCb can contribute to unprecedented forward region studies.
Matter and antimatter are frequently produced together from the energies accessible in accelerator experiments. Quarks, the building blocks of subatomic matter making up protons, are produced alongside anti-quarks in high energy interactions. The expected angular distributions of the particles being emitted differs between matter and anti-matter; quarks tend to fall closer to the beam-line by comparison. Measuring the direction of these pairs allows us to quantify the differences, or asymmetry, between matter and antimatter.
The top quark has a very short lifetime, so any measurable asymmetry would rely on charge reconstruction through its decay products. Only accessible through quantum mechanical interference, the mechanism for the asymmetry, predicted to be largest in the forward region, is sensitive to new physics. Top quarks are the heaviest known fundamental particle, making them, too, particularly sensitive. As a result, they are anticipated to play a key role in physics beyond the Standard Model.
LHCb observed top production through decays to a bottom quark and a muon using Run I data, becoming the fifth experiment to observe top production and the first in the forward region. In performing angular differential cross section measurements for top and anti-top, this analysis will probe the production asymmetry in this same channel using Run II data. The resultant fourfold increase in statistics and improved to signal to background ratio may determine if first signs of new physics appear.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/N504142/1 01/10/2015 30/09/2020
1796908 Studentship ST/N504142/1 01/10/2016 31/03/2020 James Vincent Mead