Quark and Gluon Jet Response from Dijet and Z/Gamma + Jet Events at ATLAS

Synopsis

The most common objects in the ATLAS detector are jets, cones of particles spreading out from the proton-proton collision point. Jets develop from the constituent quarks and gluons of protons. The ATLAS calorimeters measure much of the energy of these jets, but not all. This measured fraction is known as the response, and jets initiated by quarks have a different response than those initiated by gluons. The quark/gluon response can be determined by comparing the responses of various kinds of collision events and the fractions of quarks and gluons present. Three kinds of events are analyzed here: Photon + jet, Z boson + jet, and Dijet. The jet responses of Z boson/γ + jet events can be easily determined using well-established techniques, while Dijet events must be modified. A study of jet variables is undertaken to correct Dijet events, allowing the Dijet response to be determined. Then, the responses of the different events are used together to determine the quark and gluon responses.