Searches for physics beyond the Standard Model are at the research frontier of particle physics experiments. LHCb is particularly sensitive to new physics in flavour observables. Sensitivity arises either through precision studies of well-predicted flavour observables within the Standard Model, or through the search of rare decays. Both venues have been pursued by the PPD-LHCb group. Since the start of LHCb data-taking, PPD has contributed to the single-experiment most precise measurement of the CKM angle gamma, which is one of the main goal of LHCb, and has pioneered studies of the rare FCNC processes B+→K+ll, with l=e,μ.
Currently, we are studying charged lepton flavour violation and lepton flavour unitary violation in the decays of hadrons with a b-quark content. Both phenomena are forbidden in the Standard Model, and observation of any of them would be a revolutionary discovery. These phenomena, which may be related in some new physics models, have recently sparked new excitement thanks to hints of
possible deviations found in two classes of B-meson decays.
Lepton Flavour Violation and Lepton Flavour Unitarity
Physicists in the PPD-LHCb group are leading authors in the first observed anomaly in the RK observable: the ratio of branching fraction of B+→K+μ-μ+ and B+→K+e-e+ (https://arxiv.org/abs/1406.6482, Phys.Rev.Lett. 113, 151601(2014)). In addition, we are taking active part in the following analyses:
- Lepton flavour unitarity tests in the ratio of branching fractions between Λb→Kpμμ and Λb→Kpee
- Search for lepton flavour violation in the decay of B0→K*0eμ and B0s→φeμ. To be extended to all B→V0eμ decays.
Measurement of CKM angle γ
The CKM angle γ is the only unitarity triangle angle that can be measured with tree-level decays, of the type B→DK. In absence of penguin contribution, both theoretical uncertainties and new physics contributions are expected to be negligible. This is a precision SM test, where the main uncertainties are the statistical ones, due to the small branching fractions of the sensitive processes involved.
Comparison between this measurement and other CKM measurements where new physics contributions can be involved is a powerful way to look for new physics. Sufficient precision is achieved by combining many different B→DK decay channels. The PPD-LHCb group has contributed by studying B0 decays to D0K*0
- "First observation of the decay Bs→D0K*0", [LHCb Collaboration], Physics Letters B, Volume 706, Issue 1, 30 November 2011, Pages 32-39,
- "Measurement of CP observables in B0→DK*0 with D→K+K-", [LHCb Collaboration], JHEP03 067 (2013).
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"Measurement of CP violation parameters in B→DK* decays", [LHCb Collaboration], Phys. Rev. D 90, 112002 (2014)
- PPD-LHCb members have first proposed the possibility of measuring g with
Bs→D0ϕ decays at LHCb and conducted sensitivity studies [LHCB-PUB-2010-005] and published the first observation of this decay mode [“Observation of the decay Bs→D0ϕ", [LHCb Collaboration], Phys. Lett. B, 727 (2013) 403-411.]
In addition we have contributed within the CLEO-UK collaboration, to measurements of hadronic observables needed to reduce the systematic uncertainties on the determination of γ [“Model-independent determination of the strong-phase difference between D0 and D0bar to K0_{S,L} h+ h- (h=pi,K) and its impact on the measurement of the CKM angle γ/φ3”, Phys.Rev.D82:112006,2010]
Other physics studies
LHCb papers with PPD authors
For a list of all papers published by the PPD LHCb group,
click here.
