CERN Accelerating science

ATLAS Note
Report number	ATLAS-CONF-2013-087
Title	Performance and Validation of Q-Jets at the ATLAS Detector in pp Collisions at $\sqrt{s}$=8 TeV in 2012
Corporate Author(s)	The ATLAS collaboration
Imprint	13 Aug 2013. - 20 p.
In:	5th International Workshop on Boosted Object Phenomenology, Reconstruction, and Searches, Flagstaff, Arizona, AZ, USA, 12 - 16 Aug 2013
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Abstract	The Q-jets technique introduces the idea of interpreting jets through multiple sets of possible showering histories. This approach allows jet observables, such as the jet mass, to be evaluated not simply as single values, but rather as distributions. The resulting distributions can be interpreted statistically to form new observables, allowing the separation of boosted, hadronically-decaying particles from light quark and gluon backgrounds. We present a study of Q-jets in boosted, hadronically-decaying $W$ boson and dijet samples, demonstrating the discriminating power of this technique. Different Q-jet parameters and observables are studied, and an optimal configuration based on physics performance and computational efficiency is proposed, leading to a factor of 15 in dijet rejection at a 50% efficiency for jets from boosted, hadronically decaying $W$ bosons. The impact of pile-up on the performance of this method is tested and found to be weak up to an average of 40 additional interactions per event. A performance comparison between the Q-jets algorithm and $N$-subjettiness, a previously measured substructure observable which determines the compatibility of a jet with the $N$-subjet hypothesis, is presented.

Corresponding record in: Inspire