2 research outputs found
Medium modification of the shape of small-radius jets in central Pb-Pb collisions at root s(NN)=2:76 TeV
No full textWe present the measurement of a new set of jet shape observables for track-based jets in central Pb-Pb collisions at √sNN = 2.76 TeV. The set of jet shapes includes the first radial moment or angularity, g; the momentum dispersion, pTD; and the difference between the leading and sub-leading constituent track transverse momentum, LeSub. These observables provide complementary information on the jet fragmentation and can constrain different aspects of the theoretical description of jet-medium interactions. The jet shapes were measured for a small resolution parameter R = 0.2 and were fully corrected to particle level. The observed jet shape modifications indicate that in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by PYTHIA calculations, which were validated with the measurements of the jet shapes in proton-proton collisions at √s=7 TeV. The comparison of the measured distributions to templates for quark and gluon-initiated jets indicates that in-medium fragmentation resembles that of quark jets in vacuum. We further argue that the observed modifications are not consistent with a totally coherent energy loss picture where the jet loses energy as a single colour charge, suggesting that the medium resolves the jet structure at the angular scales probed by our measurements (R = 0.2). Furthermore, we observe that small-R jets can help to isolate purely energy loss effects from other effects that contribute to the modifications of the jet shower in medium such as the correlated background or medium response
Technical Design Report for the Upgrade of the ALICE Inner Tracking System
No full textALICE (A Large Ion Collider Experiment) is preparing a major upgrade of its experimental apparatus, planned for installation in the second long LHC shutdown (LS2) in the years 2018-2019. These plans are presented in the ALICE Upgrade Letter of Intent submitted to the LHCC in September 2012. A key element of the upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System based on monolithic pixel detectors. This Technical Design Report is an update of the Conceptual Design Report for the Upgrade of the ALICE Inner Tracking System, which was presented to the LHCC in September 2012. The primary focus of the ITS upgrade is on the improved performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di-electrons emitted by the QGP. The Conceptual Design Report demonstrated that it is possible to build a new silicon tracker with greatly improved features in terms of determination of the distance of closest approach to the primary vertex, tracking efficiency at low transverse momenta, and read-out rate capabilities. This document presents an update of R&D activities, with particular focus on the technical implementation of the main detector components, and detector and physics performance. The detector performance and physics studies are based on Monte Carlo simulations that include the transport of particles in a detailed model of the new detector
