My research is based on the data from the LHCb experiment at CERN's Large Hadron Collider. The LHCb experiment is an international collaboration of ~600 physicists from ~40 institutes that is designed to study B decays.
I am particularly interested in the use of rare decay modes as probe for physics beyond the current "Standard Model" of particle physics. From January 2012-March 2014 I lead the "Rare Decays" working group at LHCb which is responsible for making measurements of such decays. We have made a number of world class tests of the Standard Model, showing that new physics particles must be much heavier than was previously supposed. Highlights from the group include:
- The world's first evidence for the rare decay Bs0→mu+mu- at a branching fraction of 3.2×10-9. The decay has been sought for more than 25 years and the measurements strongly constrain new scalars and pseudoscalars that are predicted in e.g. supersymmetric extensions of the Standard Model. Our paper was published in Physics Review Letters and was selected as a ''Focus'' article by the editors;
- The world's best measurements of the rare decay Bd0→K*0mu+mu-. I led the sub-group that made the first LHCb measurements of this decay and our paper was again published in Physics Review Letters. Our measurements refuted indications of new physics from previous experiments. Our subsequent paper constrains generically flavour violating new physics vectors or axial vectors to be at mass scales of more than 15TeV and a further paper demonstrates that in some regions there is some tension with the SM predictions;
- The world's first observation of the decay B+→pi+mu+mu-. This is the first b→dmu+mu- decay that has even been observed at 5sigma level and allows us to constrain the parameters |Vts/Vtd|2 which are sensitive to new heavy particles and allow us to test the minimal flavour violation hypothesis in such decays for the first time. Our paper was published in JHEP;
- The observation of a significant isospin asymmetry in B→Kmu+mu- decays. This analysis involved the first rare decay studied at LHCb with a long-lived particle. Our paper show some tension with the SM predictions and was published in JHEP.
I have also made new searches for Majorana neutrinos (paper published in PRL and an update which makes searches for long-lived neutrinos at lifetimes of up to 1000ps and branching fractions <10-8) and the world's first search for B→mu+mu-mu+mu- decays (again published in PRL). As well as leading the rare decay working group, I have served as UK physics coordinator for LHCb and am presently a member of the Heavy Flavour Averaging Group (HFAG) - our latest combination of rare decay properties can be found here. My interests outside of rare decays include measuring the ratio of branching fractions of the semileptonic processes B→ Dtaunu and B→ Dmunu, where previous experiments have results that show considerable tension with the Standard Model. Given the neutrinos, selecting such decays in the hadronic environment of LHCb is extremely challenging. Together with one of my Ph.D. students, I have developed new inclusive reconstruction algorithms that enable these events to be isolated. The tools are now being applied in other analyses such as the measurement of Vub using ΛB→pmunu decays.
I am also investigating the application of search engine software to rare decay searches with the Russian company, Yandex. See an article about our work in BusinessWeek here and an interview with my colleague, visiting researcher at Imperial and Yandex employee, Andrey Ustyuzhanin here.
On the hardware-side I have been active in LHCb's Ring Imaging CHerenkov (RICH) detectors. See papers on our test-beam programme here and the full detector description here. For the future LHCb experiment upgrade, I am working with colleagues from Imperial to design an upgraded RICH detector.
For further in the future, I am developing the design of a new experiment we propose to build at CERN, SHiP, which will make a next generation search for "hidden sector" particles. Our 'expression of interest' which was submitted to CERN's SPSC can be found here.
et al., 2018, Search for the rare decay Lambda(+)(c) -> p mu(+ )mu(-), Physical Review D, Vol:97, ISSN:2470-0010, Pages:15-24
et al., 2018, Search for B<inf>c</inf><sup>+</sup>decays to two charm mesons, Nuclear Physics B, Vol:930, ISSN:0550-3213, Pages:563-582
et al., 2018, Test of lepton flavor universality by the measurement of the B-0 -> D*(-) tau(+) nu(tau) branching fraction using three-prong tau decays, Physical Review D, Vol:97, ISSN:2470-0010