Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.

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.

No abstract

Proton-proton collisions at √ s = 7 TeV and heavy ion collisions at √ s NN = 2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the evolution of the system during 2010 and the performance of the trigger system components and selections based on the 2010 collision data are shown. A brief outline of plans for the trigger system in 2011 is presented.

The ATLAS IBL CollaborationDuring the shutdown of the CERN Large Hadron Collider in 2013-2014, an additional pixel layer was installed between the existing Pixel detector of the ATLAS experiment and a new, smaller radius beam pipe. The motivation for this new pixel layer, the Insertable B-Layer (IBL), was to maintain or improve the robustness and performance of the ATLAS tracking system, given the higher instantaneous and integrated luminosities realised following the shutdown. Because of the extreme radiation and collision rate environment, several new radiation-tolerant sensor and electronic technologies were utilised for this layer. This paper reports on the IBL construction and integration prior to its operation in the ATLAS detector.The ATLAS [1] general purpose detector is used for the study of proton-proton (pp) and heavy-ion collisions at the CERN Large Hadron Collider (LHC) [2]. It successfully collected data at pp collision energies of 7 and 8 TeV in the period of 2010-2012, known as Run 1. Following an LHC shutdown in 2013-2014 (LS1), it has collected data since 2015 at a pp collision energy of 13 TeV (the so-called Run 2).The ATLAS inner tracking detector (ID) [1, 3] provides charged particle tracking with high efficiency in the pseudorapidity 1 range of |η| < 2.5. With increasing radial distance from the interaction region, it consists of silicon pixel and micro-strip detectors, followed by a transition radiation tracker (TRT) detector, all surrounded by a superconducting solenoid providing a 2 T magnetic field.The original ATLAS pixel detector [4,5], referred to in this paper as the Pixel detector, was the innermost part of the ID during Run 1. It consists of three barrel layers (named the B-Layer, Layer 1 and Layer 2 with increasing radius) and three disks on each side of the interaction region, to guarantee at least three space points over the full tracking |η| range. It was designed to operate for the Phase-I period of the LHC, that is with a peak luminosity of 1 × 10 34 cm −2 s −1 and an integrated luminosity of approximately 340 fb −1 corresponding to a TID of up to 50 MRad 2 and a fluence of up to 1 × 10 15 n eq /cm 2 NIEL. However, for luminosities exceeding 2 × 10 34 cm −2 s −1 , which are now expected during the Phase-I operation, the read-out efficiency of the Pixel layers will deteriorate. This paper describes the construction and surface integration of an additional pixel layer, the Insertable B-Layer (IBL) [6], installed during the LS1 shutdown between the B-Layer and a new smaller radius beam pipe. The main motivations of the IBL were to maintain the full ID tracking performance and robustness during Phase-I operation, despite read-out bandwidth limitations of the Pixel layers (in particular the B-Layer) at the expected Phase-I peak luminosity, and accumulated radiation damage to the silicon sensors and front-end electronics. The IBL is designed to operate until the end of Phase-I, when a full tracker upgrade is planned [7] for high luminosity LHC (HL-LHC) operation from approximately ...