Measurement of the flavour composition of dijet events in pp collisions at √s =7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at root s = 7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb(-1). Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity vertical bar y vertical bar < 2.1. The fit results agree with the predictions of leading-and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e. g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions.
Bibliographic reference
ATLAS Collaboration Cabrera Urbán, Susana Castillo Giménez, María Victoria Costa Mezquita, María José Fassi, Farida Ferrer Soria, Antonio Fiorini, Luca Fuster Verdú, Juan A. García García, Carmen García Navarro, José Enrique González de la Hoz, Santiago Hernández Jiménez, Yesenia Higón Rodríguez, Emilio Irles Quiles, Adrián Kaci, Mohammed Lacasta Llácer, Carlos Lacuesta Miquel, Vicente March Ruiz, Luis Martí García, Salvador Miñano Moya, Mercedes Mitsou, Vasiliki Moles Valls, Regina Moreno Llácer, María Oliver García, Elena Pedraza López, Sebastián Pérez García-Estañ, María Teresa Romero Adam, E. Ros Martínez, Eduardo Salt Cairols, José Sánchez Martínez, V. Soldevila, U. Sánchez, J. Torró Pastor, Emma Valero Biot, Alberto Valladolid Gallego, E. Valls Ferrer, Juan Antonio Villaplana Pérez, Miguel Vos, Marcel 2013 Measurement of the flavour composition of dijet events in pp collisions at √s =7 TeV with the ATLAS detector European Physical Journal C 73 2 2301-1 2301-30