Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at s√=8 TeV with the ATLAS detector

The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fb−1 of proton–proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via t˜→tχ˜01 or t˜→ bχ˜±1 →bW(∗)χ˜01 , where χ˜01 (χ˜±1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of t˜ → tχ˜01 . For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for χ˜01 masses below 30 GeV. For a branching fraction of 50% to either t˜ → tχ˜01 or t˜ → bχ˜±1 , and assuming the χ˜±1 mass to be twice the χ˜01 mass, top squark masses in the range 250–550 GeV are excluded for χ˜01 masses below 60 GeV

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT

Search for R-parity-violating supersymmetry in events with four or more leptons in sqrt(s) =7 TeV pp collisions with the ATLAS detector

A search for new phenomena in final states with four or more leptons (electrons or muons) is presented. The analysis is based on 4.7 fb−1 of $\sqrt{s}=7\;\mathrm{TeV}$ proton-proton collisions delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in two signal regions: one that requires moderate values of missing transverse momentum and another that requires large effective mass. The results are interpreted in a simplified model of R-parity-violating supersymmetry in which a 95% CL exclusion region is set for charged wino masses up to 540 GeV. In an R-parity-violating MSUGRA/CMSSM model, values of m 1/2 up to 820 GeV are excluded for 10 < tan β < 40

Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at √s = 7 TeV with the ATLAS detector

This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of √s = 7 TeV;{\rm Te}{\rm V}$and correspond to an integrated luminosity of$4.6\;{\rm f}{{{\rm b}}^{-1}}$. The measurement is performed by reconstructing the boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet centre-of-mass frame is used to suppress the large multi-jet background. The cross-section for events with a hadronically decaying W or Z boson, with transverse momentum${{p}_{{\rm T}}}\gt 320\;{\rm Ge}{\rm V}$and pseudorapidity$|\eta |\lt 1.9$, is measured to be${{\sigma }_{W+Z}}=8.5\pm 1.7$ pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques

The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs

Half-Time Strategies to Enhance Second-Half Performance in Team-Sports Players: A Review and Recommendations

The competitive demands of numerous intermittent team sports require that two consecutive periods of play are separated by a half-time break. Typically, half-time allows players to: return to the changing rooms, temporarily relax from the cognitive demands of the first half of match-play, rehydrate, re-fuel, attend to injury or equipment concerns, and to receive tactical instruction and coach feedback in preparation for the second half. These passive practices have been associated with physiological changes which impair physical and cognitive performance in the initial stages of the second half. An increased risk of injury has also been observed following half-time. On the day of competition, modification of half-time practices may therefore provide Sports Scientists and Strength and Conditioning Coaches with an opportunity to optimise second half performance. An overview of strategies that may benefit team sports athletes is presented; specifically, the efficacy of: heat maintenance strategies (including passive and active methods), hormonal priming (through video feedback), post-activation potentiation, and modified hydro-nutritional practices are discussed. A theoretical model of applying these strategies in a manner that compliments current practice is also presented

Flavor tagged time-dependent angular analysis of the B0s → J/ψϕ decay and extraction of ΔΓs and the weak phase ϕs in ATLAS

A measurement of the B0s→J/ψϕ decay parameters, updated to include flavor tagging is reported using 4.9  fb−¹ of integrated luminosity collected by the ATLAS detector from √s=7  TeV pp collisions recorded in 2011 at the LHC. The values measured for the physical parameters are ϕs=0.12±0.25(stat)±0.05(syst)  rad ΔΓs=0.053±0.021(stat)±0.010(syst)  ps−¹ Γs=0.677±0.007(stat)±0.004(syst)  ps−¹ |A∥(0)|2=0.220±0.008(stat)±0.009(syst) |A0(0)|2=0.529±0.006(stat)±0.012(syst) δ⊥=3.89±0.47(stat)±0.11(syst)  rad where the parameter ΔΓs is constrained to be positive. The S-wave contribution was measured and found to be compatible with zero. Results for ϕs and ΔΓs are also presented as 68% and 95% likelihood contours, which show agreement with the Standard Model expectations

Measurements of normalized differential cross sections for tt̄ production in pp collisions at √(s)=7 TeV using the ATLAS detector

Measurements of normalized differential cross sections for top-quark pair production are presented as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the t¯t system, in proton–proton collisions at a center-of-mass energy of √s=7  TeV. The data set corresponds to an integrated luminosity of 4.6  fb−1, recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the t¯t system and of the top-quark transverse momentum. The measurements can also discriminate among different sets of parton distribution functions

Search for new phenomena in the dijet mass distribution using pp collision data at √s = 8 TeV with the ATLAS detector

Dijet events produced in LHC proton-proton collisions at a center-of-mass energy √s=8  TeV are studied with the ATLAS detector using the full 2012 data set, with an integrated luminosity of 20.3  fb−1. Dijet masses up to about 4.5 TeV are probed. No resonancelike features are observed in the dijet mass spectrum. Limits on the cross section times acceptance are set at the 95% credibility level for various hypotheses of new phenomena in terms of mass or energy scale, as appropriate. This analysis excludes excited quarks with a mass below 4.06 TeV, color-octet scalars with a mass below 2.70 TeV, heavy W′ bosons with a mass below 2.45 TeV, chiral W∗ bosons with a mass below 1.75 TeV, and quantum black holes with six extra space-time dimensions with threshold mass below 5.66 TeV

Addendum to ‘measurement of the tt̄ production cross-section using eμ events with b-tagged jets in pp collisions at √s= 7 and 8 TeV with the ATLAS detector’

The ATLAS measurement of the inclusive top quark pair (tt̄) cross-section σtt̄ in proton–proton collisions at √s=8 TeV has been updated using the final 2012 luminosity calibration. The updated cross-section result is: σtt¯=242.9±1.7±5.5±5.1±4.2pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity and of the LHC beam energy. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. The measurement of the ratio of tt̄ cross-sections at √s=8 TeV and √s=7 TeV, and the √s=8 TeV fiducial measurement corresponding to the experimental acceptance of the leptons, have also been updated. The most precise measurement of the tt̄ cross-section (σtt̄) in proton–proton collisions at √s=8 TeV from the ATLAS Collaboration was made using events with an opposite-charge electron–muon pair and one or two b-tagged jets [1], and used a preliminary calibration of the integrated luminosity. The luminosity calibration has been finalised since [2] with a total uncertainty of 1.9%, corresponding to a substantial improvement on the previous uncertainty of 2.8%. Since the uncertainty on the integrated luminosity contributed 3.1% of the total 4.3% uncertainty on the σtt¯ measurement reported in [1], a significant improvement in the measurement is possible by using the new luminosity calibration, as documented in this Addendum. The new calibration corresponds to an integrated luminosity of 20.2 fb−¹ for the √s=8 TeV sample, a decrease of 0.2%. The cross-section was recomputed taking into account the effects on both the conversion of the tt¯ event yield to a cross-section, and the background estimates, giving a result of: σtt¯=242.9±1.7±5.5±5.1±4.2pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, knowledge of the integrated luminosity, and of the LHC beam energy, giving a total uncertainty of 8.8 pb (3.6 %). The result is consistent with the theoretical prediction of 252.9−14.5+13.3 pb, calculated at next-to-next-to-leading-order with next-to-next-to-leading-logarithmic soft gluon terms with the top++ 2.0 program [3] as discussed in detail in Ref. [1]. The updated value of the ratio of cross-sections Rtt¯=σtt¯(8 TeV)/σtt¯(7 TeV) is: Rtt¯=1.328±0.024±0.015±0.038±0.001, with uncertainties defined as above, adding in quadrature to a total of 0.047. The largest uncertainty comes from the uncertainties on the integrated luminosities, considered to be uncorrelated between the √s=7 TeV and √s=8 TeV datasets. This result is 2.1σ below the expectation of 1.430±0.013 calculated from top++ 2.0 as discussed in Ref. [1]. The updated fiducial cross-sections, for a tt¯ decay producing an eμ pair within a given fiducial region, are shown in Table 1, updating Table 5 of Ref. [1]. The results are given both for the analysis requirements of pT>25GeV and |η|30GeV and |η|<2.4. They are given separately for the two cases where events with either one or both leptons coming from t→W→τ→ℓ rather than the direct decay t→W→ℓ(ℓ=e or μ) are included, or where the contributions involving τ decays are subtracted. The results shown for the √s=7 TeV data sample are unchanged with respect to those in Ref. [1]. The results for the top quark pole mass and limits on light supersymmetric top squarks presented in Ref. [1] are derived from √s=7 TeV and √s=8 TeV cross-section measurements taken together, and would be only slightly improved by the luminosity update described here