Croucher Scholar at CERN

24 November 2013

Faye Cheung, who is currently pursuing a advanced research degree (DPhil) in Particle Physics at the University of Oxford, is reconstructing B-meson decays with data taken at CERN’s Large Hadron Collider Beauty experiment (LHCb).

The LHCb is one of the seven particle physics detector experiments at the Large Hadron Collider (LHC); it detects the products of proton-proton collisions conducted there.

Cheung is attempting to obtain a precision measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix angle Gamma through the study of B to DK, D to multi-body, tree-level decays.

This matrix parameterises the probability with which quarks can change flavours when they interact with the weak force. The angle Gamma is part of the Unitary Triangle, an assumed mathematical property of the matrix.

According to Cheung, Gamma is the least experimentally constrained parameter of the Unitary Triangle, and a precise measurement of it can be used to test the validity of the Standard Model.

“Currently in particle physics, we still do not have the complete picture,” she says,

“The Standard Model only makes up about 5 per cent of what we know and there is still 95 per cent unaccounted for. However, in order to expand our knowledge, we need to first ascertain that what we know is accurate and make sure our assumptions are correct.”

Gamma is also one of the parameters that quantifies the amount of Charge Parity (CP) violation in the Standard Model.

CP violation describes the asymmetry between matter and anti-matter in the visible universe, in which it has been found that if a particle is replaced with its antiparticle (charge conjugation) and then its spatial coordinates are inverted (parity), the laws of Physics remain only mostly unchanged, unlike the postulated idea of CP symmetry.

The slight asymmetry, which has been discovered in K-mesons, anti-K-mesons and B-mesons, is thought to be useful in explaining why the universe is made up of matter instead of antimatter.

Researchers at the LHC reached a breakthrough last year – confirming the existence of the Higgs boson, a new sub-atomic ‘elementary’ particle, after a forty-year search.

At CERN, Cheung also participates in “working group meetings”, which bring together people from different institutions who are working on similar analyses in LHCb, as well as Colloquia, talks on results from other CERN experiments and the 53rd Analysis and Software Week for LHCb, with a joint workshop for experimentalists and theorists.

She will be working with the LHCb till June 2014.


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