Disentangling QCD and new physics with charmonium resonances at LHCb

The Standard Model (SM) of particle physics describes the properties and interactions of all known particles and forces (except gravity). It tells us that there are 12 fundamental particles and their anti-particles: the 6 quarks, the electron and its heavier cousins the muon and tau as well as their three associated neutrinos. These particles interact with each other via the exchange of the force-carrying bosons: the photon of the electromagnetic interaction; the W and Z particles of the weak interaction that are responsible for radioactive decay; and the gluons of the strong interaction that bind the quarks into the protons and neutrons that compose atomic nuclei.

The last piece of the puzzle, the Higgs boson that gives all particles their bare mass, was discovered in 2012 at the Large Hadron Collider (LHC) at CERN, Geneva. Despite this amazing success we know that the SM jigsaw is incomplete as there remain some holes in our knowledge of the Universe. For example, how do we explain gravity, the dominance of matter over anti-matter and how do we account for all of the Dark Matter that we believe exists in the Universe but has so far evaded our detection? The experiments being performed at the LHC are probing the SM at an unprecedented level of energy and precision, trying to test every corner of it to look for signs of where it breaks down. We are searching for something unexpected that may be the first signs of a new theory that gives a more complete picture of the Universe.

The LHCb experiment at CERN has recently made some very interesting measurements in the decays of B mesons (particles composed of an anti-bottom (b) quark and a down (d) quark), something that it was designed to do with high precision. The decays of interest are rare, happening only once for every 10^8 B mesons produced, but is is precisely because they are rare that makes them sensitive to potential new physics effects that could appear in the quantum mechanical process that controls the decay. Viewed together, these measurements have hinted that non-SM physics could be playing a role, which has generated significant interest and excitement in the particle physics community, giving rise to different predictions for the source of these effects. However, it is also possible that these anomalies are due to some property of Quantum Chromodynamics (QCD), the part of the SM that explains how the gluons and quarks interact. In particular, B meson decay amplitudes may be modified by unknown effects from resonances of a charm and anti-charm quark (charmonium) that can interfere with the signal process, perhaps mimicking some signs of new physics.

Given the complicated nature of QCD, it is important that we try to approach and constrain the problem from many directions. The proposed research will use the data recorded (and soon to be recorded) by LHCb to perform new measurements to understand these new and intriguing anomalies by disentangling the complicated effects of QCD and potential new physics. The LHCb experiment is best placed to perform these studies owing to the efficient triggering system that it uses to select the B decays of interest and the excellent particle identification that is used to suppress backgrounds. In collaboration with particle theorists, we will be able to expand our understanding of these B meson decays and, depending upon what we find, can set the direction for the next programme of measurements that should be made during future data taking periods of the LHC.

Particle physics has the ability to inspire the next generation of researchers by attempting to tackle some of the big unanswered questions of science. The research proposed here has the potential to enhance the research capacity, knowledge and skills of public and private sector organisations.

1. Education and teaching

It is known that undergraduate and postgraduate students are attracted to learning about and, in some cases, working directly on problems at the forefront of particle physics with the researchers themselves. During this project, the PDRA and myself will teach courses to junior-Honours students on particle physics research methods and computational analysis techniques as part of the University teaching schedule. This will build upon the material that I developed for these courses in previous years. We will supervise MPhys and summer students to perform small, self-contained projects that support the research proposed here and in my own fellowship. The skills learned will be highly relevant to their future careers, whether it be in academia or industry.

2. Public outreach

Similarly to the above, engagement with school children is enhanced when done by active particle physics researchers. During the course of this proposal, myself and the PDRA will continue the excellent public outreach work of the Edinburgh group through the use of in-school roadshows, museum demonstrations and social media such as Google Hangouts and Twitter. We also enthusiastically support organisations such as the Sutton Trust that are trying to improve access to higher education for children from disadvantaged backgrounds. The PDRA and myself will continue to search for future outreach activities, leaning on the support offered by the Edinburgh-based Beltane public outreach organisation.

Edinburgh is home to the largest annual cultural festival in the world, which provides an excellent platform for further engagement with the general public through participation in science-inspired shows and public lectures from academics. This provides clear pathways for communicating the results of this research to the general public and special interest groups.

3. Economic impact

This physics described in this application is clearly contributing to a high profile project (the CERN LHC) and, as such, it is hoped that the research will be seen as a cultural enrichment towards Scottish and UK society. While this proposal does not have any direct industrial links, it can potentially have the knock-on effect of attracting further R&D investment to the University research group which contributes to a wider section of the CERN programme. There are options to engage with existing and start-up businesses via our links with technology incubators in Edinburgh and with the newly formed Scottish centre of excellence for sensor and imaging systems (CENSIS). Furthermore, the benefits to society can be leveraged by closer engagement with the Scottish government (based in Edinburgh), which could potentially lead to a greater influence on the national science spending policies.