Measurement of the flavour composition of dijet events in pp collisions at root s=7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at √s=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y|<2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions

Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector

A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at s√=7TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb−1. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles

Search for pair-produced massive coloured scalars in four-jet final states with the ATLAS detector in proton-proton collisions at s=7\sqrt{s}=7 TeV

A search for pair-produced massive coloured scalar particles decaying to a four-jet final state is performed by the ATLAS experiment at the LHC in proton-proton collisions at sqrt(s) = 7 TeV. The analysed data sample corresponds to an integrated luminosity of 4.6 /fb. No deviation from the Standard Model is observed in the invariant mass spectrum of the two-jet pairs. A limit on the scalar gluon pair production cross-section of 70 pb (10 pb) is obtained at the 95% confidence level for a scalar gluon mass of 150 GeV (350 GeV). Interpreting these results as mass limits on scalar gluons, masses ranging from 150 GeV to 287 GeV are excluded at the 95% confidence level

Search for contact interactions and large extra dimensions in dilepton events from pp collisions at &#8730;<span style="text-decoration:overline">s</span>=7 TeV with the ATLAS detector

A search for nonresonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at &#8730;s=7 TeV, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and 5.0  fb-1 in the e+e- and μ+μ- channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence level lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of ℓℓqq contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combining these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained

Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector

Open Access, Copyright CERN, for the benefit of the ATLAS collaboration. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited

Novel Use of a Bronchial Blocker in a Challenging Case of Congenital Diaphragmatic Hernia-A Case Report.

The diagnosis of congenital diaphragmatic hernia (CDH) is associated with significant morbidity and mortality. Survival of neonates with CDH has improved recently, although the clinical course is complicated by sequelae of hypoplastic pulmonary parenchyma and vasculature, pulmonary hypertension, ventilation/perfusion (V/Q) mismatch, reduced pulmonary function and poor somatic growth. In this case report, we describe an infant with an antenatal diagnosis of CDH with a poor prognosis who underwent initial surgery followed by a tracheostomy but had a worsening clinical course due to a large area of ventilated but poorly perfused lung based on a V/Q nuclear scintigraphy scan. The emphysematous left lung was causing mediastinal shift and compression of the right lung, further compromising gas exchange. The infant had clinical improvement following bronchial blockade of the under-perfused left lung. This paved the way for further management with resection of the under-perfused lung lobe and continued clinical improvement. We present the novel use of selective bronchial blockade in a challenging case of CDH to determine if surgical lung resection may benefit the infant. We also review the physiology of gas exchange during the use of a bronchial occluder and the relevant literature

Search for a supersymmetric partner to the top quark in final states with jets and missing transverse momentum at s\sqrt{s} = 7 TeV with the ATLAS detector

A search for direct pair production of supersymmetric top squarks (stop_1) is presented, assuming the stop_1 decays into a top quark and the lightest supersymmetric particle, neutralino_1, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted Standard Model background of 13.5+3.7-3.6 (4.4+1.7-1.3) events in two signal regions based on int(Ldt) = 4.7 fb^-1 of pp collision data taken at sqrt(s) = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the stop_1 versus neutralino_1 mass plane is evaluated: 370<m(stop_1)<465 GeV is excluded for m(neutralino_1)~0 GeV while m(stop_1)=445 GeV is excluded for m(neutralino_1)<=50 GeV.Comment: 6 pages plus author list (20 pages total), 4 figures, 1 table, submitted to Physical Review Letter

ATLAS search for new phenomena in dijet mass and angular distributions using pp\it{pp} collisions at s=7 \sqrt{s}=7 TeV

Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy sqrt(s)=7 TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8/fb. Dijet masses up to 4.0 TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86 TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario

Measurement of the cross-section for W boson production in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector

This paper reports a measurement of the W+b-jets (W+b+X and W+b (b) over bar +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb(-1), collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with the next-to-leading order QCD prediction, corrected for non-perturbative and double-parton interactions (DPI) contributions, of 4.70 +/- 0.09 (stat) (+0.60)(-0.49) (scale) +/- 0.06 (PDF) +/- 0.16 (non-pert) (+0.52)(-0.38) (DPI) pb

Measurement of the cross-section for W boson production in association with b-jets in pp collisions at s=7 \sqrt{s}=7 TeV with the ATLAS detector

This paper reports a measurement of the W +b-jets (W +b+ X and W + bb¯ +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb−1, collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W +b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W +b-jets is measured to be 7.1 ± 0.5 (stat) ± 1.4 (syst) pb, consistent with the next-to-leading order QCD prediction, corrected for non-perturbative and double-parton interactions (DPI) contributions, of 4.70 ± 0.09 (stat) +0.60−0.49 (scale) ±0.06 (PDF) ±0.16 (non-pert) +0.52−0.38 (DPI) pb