Observation of a centrality-dependent dijet asymmetry in lead-lead collisions at sqrt[S(NN)] =2.76 TeV with the ATLAS detector at the LHC.

Albert-Ludwigs-Universität, Fakultät für Mathematik und Physik, Hermann-Herder Strasse 3, D-79104 Freiburg i.Br., Germany.
Physical Review Letters (Impact Factor: 7.73). 12/2010; 105(25):252303.
Source: PubMed

ABSTRACT By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

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    ABSTRACT: Objective.This study was designed to explore relationships of resonance frequency analysis (RFA)—assessed implant stability (ISQ values)with bonemorphometric parameters and bone quality in an ex vivomodel of dental implants placed in human femoral heads and to evaluate the usefulness of this model for dental implant studies. Material and Methods. This ex vivo study included femoral heads from 17 patients undergoing surgery for femoral neck fracture due to osteoporosis (OP) (𝑛 = 7) or for total prosthesis joint replacement due to severe hip osteoarthrosis (OA) (𝑛 = 10). Sixty 4.5 × 13mm Dentsply Astra implants were placed, followed by RFA. CD44 immunohistochemical analysis for osteocytes was also carried out. Results. As expected, the analysis yielded significant effects of femoral head type (OAversusOA) (𝑃 < 0.001), but not of the implants (𝑃 = 0.455) or of the interaction of the two factors (𝑃 = 0.848). Bonferroni post hoc comparisons showed a lower mean ISQ for implants in decalcified (50.33 ± 2.92) heads than in fresh (66.93 ± 1.10) or fixated (70.77 ± 1.32) heads (both 𝑃 < 0.001). The ISQ score (fresh) was significantly higher for those in OA (73.52 ± 1.92) versus OP (67.13 ± 1.09) heads. However, mixed linear analysis showed no significant association between ISQ scores and morphologic or histomorphometric results (𝑃 > 0.5 in all cases), and no significant differences in ISQ values were found as a function of the length or area of the cortical layer (both 𝑃 > 0.08). Conclusion. Although RFA determined ISQ values are not correlated with morphometric parameters, they can discriminate bone quality (OP versus OA). This ex vivo model is useful for dental implant studies.
    BioMed Research International 06/2014; DOI:10.1155/2014/535929 · 2.71 Impact Factor
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    Dataset: 1212.1599
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    ABSTRACT: Dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 150 inverse microbarns is analyzed. Jets are reconstructed using combined information from tracking and calorimetry. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found, while more central collisions show a strong imbalance of leading and subleading jet transverse momenta attributed to the jet-quenching effect. The dijet momentum imbalance in central collisions is found to persist for leading jet transverse momenta up to the highest values studied.

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