Abstract
Measurements of K_S^0 and Lambda ^0 production in tbar{t} final states have been performed. They are based on a data sample with integrated luminosity of 4.6 mathrm {fb}^{-1} from proton–proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tbar{t} dileptonic events is found to be well described by current Monte Carlo models for K_S^0 and Lambda ^0 production within jets, but not for those produced outside jets.
Highlights
Background subtractionIn order to take into account the background due to fake candidates in) mass distributions, a simple sideband subtraction in the reconstructed mass distribution is used
The aim of this paper is to extend the studies to ttproduction, which is known to be a copious source of high- pT jets, especially b-jets
Neutral strange particle production is studied as a function of the transverse momentum pT, the energy E, the pseudorapidity η, the transverse flight distance Rxy and the multiplicity and production inside jets, the energy fraction, xK, = EK, /Ejet, is considered
Summary
The ATLAS detector is described in detail in Ref. [47]. All of its subsystems are relevant for this analysis, including the inner detector (ID), the electromagnetic and hadronic calorimeters and the muon spectrometer. The muon spectrometer, located inside a toroidal magnetic field, provides triggering and muon tracking capabilities in the ranges |η| < 2.4 and |η| < 2.7 respectively. This allows identification of muons with momenta above 3 GeV and precision determination of the muon transverse momentum up to 1 TeV. In this analysis muons reconstructed in the muon spectrometer are matched with well-measured tracks from the inner detector. The EF triggers use offline data reconstruction algorithms For this analysis, events are required to pass a single-electron or single-muon trigger
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