Phys. Lett. B

Decays of b hadrons into final states containing a D0 meson and a muon are used to measure the bb¯ production cross-section in proton–proton collisions at a centre-of-mass energy of 7 TeV at the LHC. In the pseudorapidity interval 2<η<6 and integrated over all transverse momenta we find that the average cross-section to produce b -flavoured or b¯ -flavoured hadrons is (75.3±5.4±13.0) μb .

Eur. Phys. J. C

Muons from cosmic-ray interactions in the atmosphere provide a high-statistics source of particles that can be used to study the performance and calibration of the ATLAS detector. Cosmic-ray muons can penetrate to the cavern and deposit energy in all detector subsystems. Such events have played an important role in the commissioning of the detector since the start of the installation phase in 2005 and were particularly important for understanding the detector performance in the time prior to the arrival of the first LHC beams. Global cosmic-ray runs were undertaken in both 2008 and 2009 and these data have been used through to the early phases of collision data-taking as a tool for calibration, alignment and detector monitoring. These large datasets have also been used for detector performance studies, including investigations that rely on the combined performance of different subsystems. This paper presents the results of performance studies related to combined tracking, lepton identification and the reconstruction of jets and missing transverse energy. Results are compared to expectations based on a cosmic-ray event generator and a full simulation of the detector response.

Phys.Rev.Lett.

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 underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is 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, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

Phys. Rev. C

Measurements of states excited by nuclear resonance fluorescence in Np237 were performed using a bremsstrahlung beam. Fifteen new states were observed in the region of 1.7 to 2.5 MeV. They can be used to detect or assay Np237 nondestructively for applications in security and safeguards. The states are populated with similar strength as those states found previously in U235 and Pu239 but are spread out more in energy.

Phys.Lett.B

The energy dependence of the photon–proton total cross section, σtotγp , was determined from e+p scattering data collected with the ZEUS detector at HERA at three values of the center-of-mass energy, W , of the γp system in the range 194