Main Image
Volume 270 - International Symposium on Grids and Clouds (ISGC) 2016 (ISGC 2016) - HEP
LHCb experience during the LHC 2015 run
C. Haen* on behalf of the LHCb collaboration
*corresponding author
Full text: pdf
Published on: 2017 January 11
LHCb is one of the four high energy physics experiments currently in operation at the Large
Hadron Collider at CERN, Switzerland. After a successful first running period (Run1 from 2011
to 2013), the LHC just entered the second exploitation phase (Run2, 2015-2018).
The technical break between these two running periods, known as Long Shutdown 1 (LS1), was
the opportunity for LHCb to adapt, among other area of development, its data acquisition and
computing models.
The operational changes on the data acquisition aspect include a clear split of the High Level
Trigger (HLT) software in two distinct entities, running in parallel and in an asynchronous mode
on the filtering farm, allowing a higher output rate to the final offline storage for further physics
analysis. A very challenging and innovative system performing full calibration and reconstruction
in real time has been put in place. Thanks to this system, a fraction of the output of the HLT can
be used directly for physics, without any intermediate step: this output is named “Turbo stream”.
Many changes were operated on the offline computing side as well. Besides the use of more modern
and/or more scalable tools for the pure data management aspect, the computing model itself
and the processing workflow were revisited in order to cope with the increased load and amount of
data. The new Turbo stream requires new operational management compared to the other “standard”
streams. The clear separation between the different levels of Tiers (0, 1 and 2) has been
abandoned for a more flexible, dynamic and efficient “Mesh” processing model, in which any site
can process data stored at any other site. Validation and probing procedures were established and
automatized before the start of massive Monte Carlo Simulation. This paper presents the changes
that were operated, and gives some feedback on their usage during the running period in 2015
Open Access
Creative Commons LicenseCopyright owned by the author(s) under the term of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.