Speaker
Dr
Vladislav Balagura
(CNRS / LLR - Ecole polytechnique)
Description
Luminosity measurements at LHCb are of pivotal importance.
They have been used in about 50 LHCb publications of production cross section results.
The interaction rate at LHCb is continuously monitored by several luminosity counters
(like the number of reconstructed tracks) measuring the fraction of "empty" events,
i.e. events which fall below a chosen threshold of a given luminosity counter.
Using the law of Poisson statistics, an average interaction rate per bunch crossing
is derived from the "empty" events fraction.
The absolute calibration of the luminosity counters is performed a few times per year
(typically for each new beam energy and beam types), mostly in dedicated LHC fills.
Two techniques are employed for the direct luminosity measurement.
The first one is the classic van der Meer scan method which is used by all four LHC
experiments. The second one is unique to LHCb. Here, the beam
profiles and their overlap integral are determined from the
beam "images" recorded with beam-gas interactions. Both
techniques give similar accuracy but have different
systematics. Their combination has allowed us to obtain in LHC Run I the
most precise luminosity measurement ever achieved at a bunched hadron
collider.
In this talk, we give an overview of the LHCb experience with the luminosity calibration,
present several recent calibration results and outline the developments which
are being pursued to obtain a better understanding of the calibrations.
Primary author
Dr
Marco Gersabeck
(The University of Manchester)
Co-author
Dr
Vladislav Balagura
(CNRS / LLR - Ecole polytechnique)
