Measurement of event-shape observables in Z→ℓ+ℓ− events in pp collisions at √ s=7 TeV with the ATLAS detector at the LHC

Event-shape observables measured using charged particles in inclusive $Z$-boson events are presented, using the electron and muon decay modes of the $Z$ bosons. The measurements are based on an integrated luminosity of $1.1 {\rm fb}^{-1}$ of proton--proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy $\sqrt{s}=7$ TeV. Charged-particle distributions, excluding the lepton--antilepton pair from the $Z$-boson decay, are measured in different ranges of transverse momentum of the $Z$ boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and $\mathcal{F}$-parameter, which are in particular sensitive to properties of the underlying event at small values of the $Z$-boson transverse momentum. The Sherpa event generator shows larger deviations from the measured observables than Pythia8 and Herwig7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high $Z$-boson transverse momenta than at low $Z$-boson transverse momenta and for the observables that are less sensitive to the number of charged particles in the event.Comment: 36 pages plus author list + cover page (54 pages total), 14 figures, 4 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2014-0

Condensation of a 50/50 Blend of R-32/R-125 in Horizontal Tubes with and Without Oil

This study examined local condensation heat transfer and pressure drop for a pure 50/50% mixture of R- 32/125 and for R-32/125 mixed with approximately 1%, 3%, and 5% concentrations of an ester oil. An apparatus was built to simulate conditions found in the condenser sections of domestic refrigerators/freezers. Experiments were performed to measure the internal heat transfer coefficients and pressure drops inside a 0.277 in. (7.0 mm) o.d. smooth, horizontal copper tube. It was observed from the oil samples that the oil concentration of the oil-refrigerant mixtures flowing through the test section changed for different mass fluxes and qualities. The data for the heat transfer coefficients were compared with existing correlations and the Dobson correlation demonstrated the best accuracy for the pure R-32/125 and predicted the performance of oil-refrigerant mixtures with less than 20% error when used with the Schlager enhancement factor. The experiments showed that oil addition degraded the heat transfer coefficient at vapor qualities greater than 50% and increased the pressure drop by as much as 25% at high mass fluxes