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Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of PLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3.

Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of MINECO and PIC, Spain and EPLANET, ERC and NSRF, European Union. Funded by SCOAP3. ; A search for the production of single-top-quarks in association with missing energy is performed in proton-proton collisions at a centre-of-mass energy of with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of fb. In this search, the boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin- resonance with a mass of GeV, an effective coupling strength above is excluded at 95 confidence level for the top quark and an invisible spin- state with mass between and GeV. In the case of non-resonant production, an effective coupling strength above is excluded at 95 confidence level for the top quark and an invisible spin- state with mass between and GeV.

Ajuts:We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MICINN, Spain. Funded by SCOAP3. ; This paper presents cross sections for the production of a boson in association with jets, measured in proton-proton collisions at with the ATLAS experiment at the large hadron collider. With an integrated luminosity of , this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of and multiplicities up to seven associated jets. The production cross sections for bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators.

Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union, MINECO and PIC, Spain. Funded by SCOAP3. ; A search for a massive gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in collisions at the LHC. The dataset was taken at a centre-of-mass energy of and corresponds to of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass bosons in the range 1.5-3.0 . -tagging is used to identify jets originating from -quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the cross section times branching ratio ranging from to for left-handed bosons, and ranging from to for bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the -boson coupling to as a function of the mass using an effective field theory approach, which is independent of details of particular models predicting a boson.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, Spain. Funded by SCOAP3. ; A measurement of boson production in lead-lead collisions at is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 and 0.15 in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of boson production in multi-nucleon systems.

Ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO and PIC, Spain. Funded by SCOAP3. ; A search is presented for the direct pair production of a chargino and a neutralino , where the chargino decays to the lightest neutralino and the boson, , while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson, . The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3 of proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; The production of a boson in association with a meson in proton-proton collisions probes the production mechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using of data collected with the ATLAS experiment at the LHC in collisions at , the first measurement of associated production is presented for both prompt and non-prompt production, with both signatures having a significance in excess of . The inclusive production cross-sections for boson production (analysed in or decay modes) in association with prompt and non-prompt are measured relative to the inclusive production rate of bosons in the same fiducial volume to be and respectively. Normalised differential production cross-section ratios are also determined as a function of the transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of at confidence level is placed on the effective cross-section regulating double parton interactions.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. ; Studies of the spin and parity quantum numbers of the Higgs boson in the final state are presented, based on proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb at a centre-of-mass energy of TeV. The Standard Model spin-parity hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even () or CP-odd () Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; A search for a new resonance decaying to a W or Z boson and a Higgs boson in the final states is performed using 20.3 fb of pp collision data recorded at 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb of TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between GeV and GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy . The performance of these algorithms is measured in most cases with decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb. An uncertainty on the offline reconstructed tau energy scale of 2-4 %, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5 % for hadronically decaying tau leptons with one associated track, and of 4 % for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 . For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2-8 %, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton-proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC Spain. Funded by SCOAP3. ; Two searches for supersymmetric particles in final states containing a same-flavour opposite-sign lepton pair, jets and large missing transverse momentum are presented. The proton-proton collision data used in these searches were collected at a centre-of-mass energy TeV by the ATLAS detector at the Large Hadron Collider and corresponds to an integrated luminosity of 20.3 fb. Two leptonic production mechanisms are considered: decays of squarks and gluinos with Z bosons in the final state, resulting in a peak in the dilepton invariant mass distribution around the Z -boson mass; and decays of neutralinos (e.g. ), resulting in a kinematic endpoint in the dilepton invariant mass distribution. For the former, an excess of events above the expected Standard Model background is observed, with a significance of three standard deviations. In the latter case, the data are well-described by the expected Standard Model background. The results from each channel are interpreted in the context of several supersymmetric models involving the production of squarks and gluinos.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; Measurements of the ZZ and WW final states in the mass range above the and thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the , and final states. The result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb at a collision energy of TeV. Using the method, the observed 95 confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1-8.6, with an expected range of 6.7-11.0. In each case the range is determined by varying the unknown and background K-factor from higher-order quantum chromodynamics corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs boson production, a combination with the on-shell measurements yields an observed (expected) 95 CL upper limit on in the range 4.5-7.5 (6.5-11.2) using the same variations of the background K-factor. Assuming that the unknown background K-factor is equal to the signal K-factor, this translates into an observed (expected) 95 CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC Spain. Funded by SCOAP3. ; A search for Higgs boson decays to invisible particles is performed using 20.3 of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson ( or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain VH production followed by H decaying to invisible particles for the Higgs boson mass range GeV. The 95 % confidence-level observed upper limit on varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the contribution as signal, the results also lead to an observed upper limit of 78 % at 95 % confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.

Altres ajuts: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of EPLANET, ERC and NSRF, European Union and MINECO, PIC, Spain. Funded by SCOAP3. ; A search for the Standard Model Higgs boson produced in association with a top-quark pair, , is presented. The analysis uses 20.3 fb −1 of pp collision data at , collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the decay mode and uses events containing one or two electrons or muons. In order to improve the sensitivity of the search, events are categorised according to their jet and b -tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by +jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the Standard Model cross section is obtained at 95 % confidence level. The ratio of the measured signal cross section to the Standard Model expectation is found to be assuming a Higgs boson mass of 125.