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Run 2 promises a harvest of beauty for LHCb

13 January 2017


The first b-physics analysis using data from LHC Run 2, which began in 2015 with proton–proton collisions at an energy of 13 TeV, shows great promise for the physics programme of LHCb. During 2015 and 2016, the experiment collected a data sample corresponding to an integrated luminosity of about 2 fb–1. Although this value is smaller than the total integrated luminosity collected in the three years of Run 1 (3 fb–1), the significant increase of the LHC energy in Run 2 has almost doubled the production cross-section of beauty particles. Furthermore, the experiment has improved the performance of its trigger system and particle-identification capabilities. Once such an increase is taken into account, along with improvements in the trigger strategy and in the particle identification of the experiment, LHCb has already more than doubled the statistics of beauty particles on tape with respect to Run 1.

LHCb

The new analysis is based on 1 fb–1 of available data, aiming to measure the angle γ of the CKM unitarity triangle using B D0K*– decays. While B D0K decays have been extensively studied in the past, this is the first time the B D0K*– mode has been investigated. The analysis, first presented at CKM2016 (see “Triangulating in Mumbai” in Faces & Places), allows the LHCb collaboration to cross-check expectations for the increase of signal yields in Run 2 using real data. A significant increase, roughly corresponding to a factor three, is observed per unit of integrated luminosity. This demonstrates that the experiment has benefitted from the increase in b-production cross-section, but also that the trigger of the detector performs better than in Run 1. Although the statistical uncertainty on γ from this measurement alone is still large, the sensitivity will be improved by the addition of more data, as well as by the use of other D-meson decay modes. This bodes well for future measurements of γ to be performed in this and other decay modes with the full Run 2 data set.

Measurements of the angle γ are of great importance because it is the least well-known angle of the unitarity triangle. The latest combination from direct measurements with charged and neutral B-meson decays and a variety of D-meson final states, all performed with Run 1 data, yielded a central value of 72±7 degrees. LHCb’s ultimate aim, following detector upgrades relevant for LHC Run 3, is to determine γ with a precision below 1°, providing a powerful test of the Standard Model.

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