1–5 Sept 2014
Faculty of Civil Engineering
Europe/Prague timezone

The LHCb trigger and its upgrade

1 Sept 2014, 14:00
25m
C217 (Faculty of Civil Engineering)

C217

Faculty of Civil Engineering

Faculty of Civil Engineering, Czech Technical University in Prague Thakurova 7/2077 Prague 166 29 Czech Republic
Oral Computing Technology for Physics Research Computing Technology for Physics Research

Speaker

Gerhard Raven (NIKHEF (NL))

Description

The current LHCb trigger system consists of a hardware level, which reduces the LHC inelastic collision rate of 30 MHz to 1 MHz, at which the entire detector is read out. In a second level, implemented in a farm of 20k parallel-processing CPUs, the event rate is reduced to about 5 kHz. We review the performance of the LHCb trigger system, focusing on the High Level Trigger, during Run I of the LHC. Special attention is given to the use of multivariate analyses in the Hight Level Trigger and their importance in controlling the output rate. We demonstrate that despite its excellent performance to date, the major bottleneck in LHCb's trigger efficiencies for hadronic heavy flavour decays is the hardware trigger. The LHCb experiment plans a major upgrade of the detector and DAQ system in the LHC shutdown of 2018. In this upgrade, a purely software based trigger system is being developed, which will have to process the full 30 MHz of inelastic collisions delivered by the LHC. We demonstrate that the planned architecture will be able to meet this challenge, particularly in the context of running stability and long term reproducibility of the trigger decisions. We discuss the use of disk space in the trigger farm to buffer events while performing run-by-run detector calibrations, and the way this real time calibration and subsequent full event reconstruction will allow LHCb to deploy offline quality multivariate selections from the earliest stages of the trigger system. We discuss the cost-effectiveness of such a software-based approach with respect to alternatives relying on custom electronics. We discuss the particular importance of multivariate selections in the context of a signal-dominated production environment, and report the expected efficiencies and signal yields per unit luminosity in several key physics benchmarks the LHCb upgrade.

Primary authors

Gerhard Raven (NIKHEF (NL)) Johannes Albrecht (Technische Universitaet Dortmund (DE)) Vladimir Gligorov (CERN)

Presentation materials