Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Methylation-Dependent Binding of the Epstein-Barr Virus BZLF1 Protein to Viral Promoters

The switch between latent and lytic Epstein-Barr virus (EBV) infection is mediated by the viral immediate-early (IE) protein, BZLF1 (Z). Z, a homologue of c-jun that binds to AP1-like motifs (ZREs), induces expression of the BRLF1 (R) and BRRF1 (Na) viral proteins, which cooperatively activate transcription of the Z promoter and thereby establish a positive autoregulatory loop. A unique feature of Z is its ability to preferentially bind to, and activate, the methylated form of the BRLF1 promoter (Rp). To date, however, Rp is the only EBV promoter known to be regulated in this unusual manner. We now demonstrate that the promoter driving transcription of the early BRRF1 gene (Nap) has two CpG-containing ZREs (ACGCTCA and TCGCCCG) that are only bound by Z in the methylated state. Both Nap ZREs are highly methylated in cells with latent EBV infection. Z efficiently activates the methylated, but not unmethylated, form of Nap in reporter gene assays, and both ZREs are required. Z serine residue 186, which was previously shown to be required for Z binding to methylated ZREs in Rp, but not for Z binding to the AP1 site, is required for Z binding to methylated Nap ZREs. The Z(S186A) mutant cannot activate methylated Nap in reporter gene assays and does not induce Na expression in cells with latent EBV infection. Molecular modeling studies of Z bound to the methylated Nap ZREs help to explain why methylation is required for Z binding, and the role of the Z Ser186 residue. Methylation-dependent Z binding to critical viral promoters may enhance lytic reactivation in latently infected cells, where the viral genome is heavily methylated. Conversely, since the incoming viral genome is initially unmethylated, methylation-dependent Z activation may also help the virus to establish latency following infection

Measurement of the cross-section for b-jets produced in association with a Z boson at root s=7 TeV with the ATLAS detector ATLAS Collaboration

A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of root s = 7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb(-1). The event selection requires a Z boson decaying into high P-T electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum p(T) > 25 GeV and rapidity vertical bar y vertical bar < 2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order

Adsorbent particle size effects in the separation of air by rapid pressure swing adsorption

Experimental and theoretical investigations into air separation by rapid pressure swing adsorption over zeolite 5A are presented. These concentrate on the effect of adsorbent particle size on the separation performance of the unit undergoing simple cycles consisting of pressurisation and depressurisation steps. An optimum particle size for maximum cyclic equilibrium product oxygen purity is shown to exist; this is accurately predicted by model simulation. Calculations indicate that for beds containing very small particles, a poor separation results from ineffective pressure swing, and for beds containing very large particles from intraparticle diffusional limitations. For the zeolite 5A adsorbent used in this work, theoretical calculations indicate that the rate limiting intraparticle diffusion is described by a parallel combination of molecular and Knudsen diffusion within the macropores of the adsorbent particles. Axial dispersion within the bed is also shown to have a significant effect upon the cyclic equilibrium value of the cycle-average product oxygen purity. In addition to measurements at the cyclic equilibrium, temporal profiles of the product oxygen purity during the approach to cyclic equilibrium are shown. Under certain operating conditions, an overshoot of oxygen purity is found to exist. This behaviour can be attributed to ineffective pressure swing within the product end region of the bed, and thus to the poor utilisation of adsorbent in this region. © 1994

Simulation of rapid pressure swing adsorption and reaction processes

A general model for non-isothermal adsorption and reaction in a rapid pressure swing process is described. Several numerical discretisation methods for the solution of the model are compared. These include the methods of orthogonal collocation, orthogonal collocation on finite elements, double orthogonal collocation on finite elements, and cells-in-series. Computationally, orthogonal collocation on finite elements is found to be the most efficient of these. The model is applied to air separation for oxygen production. Calculations confirm the formation of a concentration shock when an adsorbent bed is pressurised with air. The form and propagation of the shock over short times is found to be in excellent agreement with the exact similarity transformation solutions derived for an infinitely long bed. For air separation, novel experimental measurements, showing an optimum particle size for maximum product oxygen purity, are accurately described by the model. Calculations indicate that a poor separation results from ineffective pressure swing for beds containing very small particles, and from intraparticle diffusional limitations for beds containing very large particles. For adsorption coupled with reaction, finite rate and reversible reactions are considered. These include both competitive and non-competitive reaction schemes. For the test case of a dilute reaction A &.rlhar2; B + 3C, with B the only adsorbing species, bed pressurisation calculations are found to be in excellent agreement with the solutions obtained by the method of characteristics. © 1993

Adsorbent particle size effects in the separation of air by rapid pressure swing adsorption

Experimental and theoretical investigations into air separation by rapid pressure swing adsorption over zeolite 5A are presented. These concentrate on the effect of adsorbent particle size on the separation performance of the unit undergoing simple cycles consisting of pressurisation and depressurisation steps. An optimum particle size for maximum cyclic equilibrium product oxygen purity is shown to exist; this is accurately predicted by model simulation. Calculations indicate that for beds containing very small particles, a poor separation results from ineffective pressure swing, and for beds containing very large particles from intraparticle diffusional limitations. For the zeolite 5A adsorbent used in this work, theoretical calculations indicate that the rate limiting intraparticle diffusion is described by a parallel combination of molecular and Knudsen diffusion within the macropores of the adsorbent particles. Axial dispersion within the bed is also shown to have a significant effect upon the cyclic equilibrium value of the cycle-average product oxygen purity. In addition to measurements at the cyclic equilibrium, temporal profiles of the product oxygen purity during the approach to cyclic equilibrium are shown. Under certain operating conditions, an overshoot of oxygen purity is found to exist. This behaviour can be attributed to ineffective pressure swing within the product end region of the bed, and thus to the poor utilisation of adsorbent in this region. © 1994

Simulation of rapid pressure swing adsorption and reaction processes

A general model for non-isothermal adsorption and reaction in a rapid pressure swing process is described. Several numerical discretisation methods for the solution of the model are compared. These include the methods of orthogonal collocation, orthogonal collocation on finite elements, double orthogonal collocation on finite elements, and cells-in-series. Computationally, orthogonal collocation on finite elements is found to be the most efficient of these. The model is applied to air separation for oxygen production. Calculations confirm the formation of a concentration shock when an adsorbent bed is pressurised with air. The form and propagation of the shock over short times is found to be in excellent agreement with the exact similarity transformation solutions derived for an infinitely long bed. For air separation, novel experimental measurements, showing an optimum particle size for maximum product oxygen purity, are accurately described by the model. Calculations indicate that a poor separation results from ineffective pressure swing for beds containing very small particles, and from intraparticle diffusional limitations for beds containing very large particles. For adsorption coupled with reaction, finite rate and reversible reactions are considered. These include both competitive and non-competitive reaction schemes. For the test case of a dilute reaction A &.rlhar2; B + 3C, with B the only adsorbing species, bed pressurisation calculations are found to be in excellent agreement with the solutions obtained by the method of characteristics. © 1993