The production of mesons containing strange quarks (, φ) and both singly and doubly strange baryons (, , and ) are measured at mid-rapidity in pp collisions at \(\sqrt{s}\) = 0.9 \({\rm TeV}\) with ...the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields (〈dN/dy〉) of 0.184±0.002(stat.)±0.006(syst.) for and 0.021±0.004(stat.)±0.003(syst.) for φ. For baryons, we find 〈dN/dy〉=0.048±0.001(stat.)±0.004(syst.) for , 0.047±0.002(stat.)±0.005(syst.) for and 0.0101±0.0020(stat.)±0.0009(syst.) for . The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.
The phenomenon of transgranular stress corrosion cracking is observed in buried pipelines operating in contact with diluted solutions under disbonded coatings. It was proposed that this kind of ...cracking is explained by the evolution and permeation of hydrogen at the crack tip, as observed in nuclear pressure-vessel steels and other low-alloy steels. We discuss the mechanism of transgranular stress corrosion cracking. The combined effect of hydrogen permeation and anodic dissolution is experimentally investigated by imposing different levels of cathodic protection: from the free corrosion potential -750 mV (SCE) to -1300 mV (SCE). The comparison of the experimental and literature data shows that both anodic dissolution and hydrogen permeation are active and their (synergic) combination gives rise to this particular kind of cracking. Anodic dissolution is active in the crack enclave. At the same time, the cathodic discharge of protons produces hydrogen which enters steel at the crack tip. This phenomenon is intensified for more electronegative potentials. In addition, inside the cracks, the environment becomes more acid than in the bulk and the rates of both anodic and cathodic reactions increase. Hydrogen penetrating into steel increases its brittleness, which depends on the microstructure of the metal and the stress-strain field. This effect was corroborated in our experiments by monitoring the variations of the hardness (brittleness) of steel, observing the formation of internal cracks by optical microscopy, and examining fracture surfaces by scanning electron microscopy. Material: X65 steel.
The charged particle multiplicity distributions measured by two experiments, WA97 and NA57, in Pb+Pb collisions at 158 A GeV/c have been analyzed in the framework of the Wounded Nucleon Model (WNM). ...We obtain a good description of the data within the centrality range of our samples. This allows us to make use of the measured multiplicities to estimate the number of wounded nucleons of the collision.
The Time Projection Chamber is the main tracking detector in the central barrel of the ALICE experiment. The task of large acceptance tracking in a heavy ion experiment is similar to that encountered ...in the NA49 and STAR experiments at the SPS and RHIC respectively. However, the extreme multiplicities of ion collisions at the LHC set qualitatively and quantitatively new demands making new designs indispensable. In this paper we present an overview of the main components, with special focus on the front-end and readout electronics, and some of the most crucial aspects addressed by the R&D activities that have preceded the design and construction of the ALICE TPC.
The pseudorapidity density and multiplicity distribution of charged particles produced in proton–proton collisions at the LHC, at a centre-of-mass energy
TeV, were measured in the central ...pseudorapidity region |
η
|<1. Comparisons are made with previous measurements at
TeV and 2.36 TeV. At
TeV, for events with at least one charged particle in |
η
|<1, we obtain
. This corresponds to an increase of
relative to collisions at 0.9 TeV, significantly higher than calculations from commonly used models. The multiplicity distribution at 7 TeV is described fairly well by the negative binomial distribution.
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