LHCb finds early surprises at Run 2

16 September 2016

The bumper data harvest at LHC Run 2 continues for the LHCb experiment. In mid-August, the collaboration celebrated the milestone of 1 fb–1 integrated luminosity collected so far during 2016, with significantly more expected to come during the remainder of the year. This corresponds to the production of around 1012 beauty hadrons, of which the most interesting decays have been selected and recorded for offline analysis. The stupendous performance of the LHC has been central to this success. Indeed, the LHCb operations team has had to adjust trigger and offline procedures to prevent the torrent of incoming data from overflowing the experiment’s data-storage resources.

The ratio of differential cross-sections for b-hadron production with respect to pseudorapidity, η, measured at collision energies of 13 and 7 TeV. Data are compared to predictions described in Eur. Phys. J C 75 610.

With LHCb’s physics programme centred around painstaking precision measurements, the most eagerly awaited results from the Run 2 data set will not begin to appear until early next year. However, the first glimpses into the new sample are already revealing surprising results. For example, a measurement of the production cross-section of beauty hadrons at 13 TeV has shown unexpected behaviour when compared to what was observed at 7 TeV during Run 1. Although the ratio of the cross-sections at the two energies is roughly equal to two, as predicted, there is a clear dependence on pseudorapidity (which is related to the angle of production) that differs markedly from the current model expectations. The ratio in the data is significantly higher at low values of pseudorapidity, which corresponds to the more central regions of production (see figure).

This result, which was first shown at the ICHEP conference in Chicago in August, is still being digested by theorists. Although it is too early to speculate on the causes of this intriguing behaviour, and indeed the consequences for other measurements, it is hoped that many other surprises lurk in the Run-2 data set.


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