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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for metastable heavy charged particles with large ionization energy loss in pp collisions at root s=13 TeV using the ATLAS experiment. Phys. Rev. D, 93(11), 112015–25pp.
Abstract: This paper presents a search for massive charged long-lived particles produced in pp collisions at root s = 13 TeV at the LHC using the ATLAS experiment. The data set used corresponds to an integrated luminosity of 3.2 fb(-1). Many extensions of the Standard Model predict the existence of massive charged long-lived particles, such as R-hadrons. These massive particles are expected to be produced with a velocity significantly below the speed of light, and therefore to have a specific ionization higher than any Standard Model particle of unit charge at high momenta. The Pixel subsystem of the ATLAS detector is used to measure the ionization energy loss of reconstructed charged particles and to search for such highly ionizing particles. The search presented here has much greater sensitivity than a similar search performed using the ATLAS detector in the root s = 8 TeV data set, thanks to the increase in expected signal cross section due to the higher center-of-mass energy of collisions, to an upgraded detector with a new silicon layer close to the interaction point, and to analysis improvements. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on R-hadron production cross sections and masses are set. Gluino R-hadrons with lifetimes above 0.4 ns and decaying to q (q) over bar plus a 100 GeV neutralino are excluded at the 95% confidence level, with lower mass limit ranging between 740 and 1590 GeV. In the case of stable R-hadrons the lower mass limit at the 95% confidence level is 1570 GeV.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for squarks and gluinos in final states with jets and missing transverse momentum at root s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 76(7), 392–29pp.
Abstract: A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment in root s = 13 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 fb(-1) of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95 % confidence level on the mass of the gluino is set at 1.51 TeV for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 TeV are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at root s=13 TeV. Phys. Lett. B, 760, 520–537.
Abstract: A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb (1) of proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at root s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for heavy long-lived charged R-hadrons with the ATLAS detector in 3.2 fb(-1) of proton-proton collision data at root s=13 TeV. Phys. Lett. B, 760, 647–665.
Abstract: A search for heavy long-lived charged R-hadronsis reported using a data sample corresponding to 3.2fb(-1)of proton-proton collisions at root s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider at CERN. The search is based on observables related to large ionisation losses and slow propagation velocities, which are signatures of heavy charged particles travelling significantly slower than the speed of light. No significant deviations from the expected background are observed. Upper limits at 95% confidence level are provided on the production cross section of long-lived R-hadronsin the mass range from 600 GeV to 2000 GeV and gluino, bottom and top squark masses are excluded up to 1580 GeV, 805 GeV and 890 GeV, respectively.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for Higgs and Z Boson Decays to phi gamma with the ATLAS Detector. Phys. Rev. Lett., 117(11), 111802–19pp.
Abstract: A search for the decays of the Higgs and Z bosons to a phi meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected at root s = 13 TeV with the ATLAS detector at the LHC. No significant excess of events is observed above the background, and 95% confidence level upper limits on the branching fractions of the Higgs and Z boson decays to phi gamma of 1.4 x 10(-3) and 8.3 x 10(-6), respectively, are obtained.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for new phenomena in different-flavour high-mass dilepton final states in pp collisions at root s=13Tev with the ATLAS detector. Eur. Phys. J. C, 76(10), 541–28pp.
Abstract: A search is performed for a heavy particle decaying into different flavour dilepton pairs (, or ), using 3.2 fb of proton-proton collision data at TeV collected in 2015 by the ATLAS detector at the Large Hadron Collider. No excess over the Standard Model prediction is observed. Limits at the 95 % credibility level are set on the mass of a boson with lepton-flavour-violating couplings at 3.0, 2.7 and 2.6 TeV, and on the mass of a supersymmetric sneutrino with R-parity-violating couplings at 2.3, 2.2 and 1.9 TeV, for , and final states, respectively. The results are also interpreted as limits on the threshold mass for quantum black hole production.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Charged-particle distributions at low transverse momentum in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC. Eur. Phys. J. C, 76(9), 502–22pp.
Abstract: Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 μb(-1). The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector. Phys. Rev. D, 94(5), 052009–32pp.
Abstract: The results of a search for the top squark, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC pp collision data at a center-of-mass energy of root s = 13 TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb(-1). The analysis targets two types of signal models: gluino-mediated pair production of top squarks with a nearly mass-degenerate top squark and neutralino and direct pair production of top squarks, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and top squark masses are set at 95% confidence level. The results extend the LHC run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low top squark mass region and add an excluded top squark mass region from 745 to 780 GeV for the direct top squark model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vectorlike top quarks.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for pair production of gluinos decaying via stop and sbottom in events with b-jets and large missing transverse momentum in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 94(3), 032003–32pp.
Abstract: A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino (chi) over tilde (0)(1) is reported. It uses an LHC proton-proton data set at a center-of-mass energy root s = 13 TeV with an integrated luminosity of 3.2 fb(-1) collected with the ATLAS detector in 2015. The signal is searched for in events containing several energetic jets, of which at least three must be identified as b jets, large missing transverse momentum, and, potentially, isolated electrons or muons. Large-radius jets with a high mass are also used to identify highly boosted top quarks. No excess is found above the predicted background. For (chi) over tilde (0)(1) masses below approximately 700 GeV, gluino masses of less than 1.78 TeVand 1.76 TeV are excluded at the 95% C. L. in simplified models of the pair production of gluinos decaying via sbottom and stop, respectively. These results significantly extend the exclusion limits obtained with the root s = 8 TeV data set.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at root s=13 TeV using the ATLAS detector. Phys. Rev. D, 94(3), 032005–32pp.
Abstract: Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an integrated luminosity of 3.2 fb(-1) at root s = 13 TeV collected in 2015 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons. Several signal regions are considered with increasing missing-transverse-momentum requirements between E-T(miss) > 250 GeV and E-T(miss) > 700 GeV. Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with large extra spatial dimensions, pair production of weakly interacting dark-matter candidates, and the production of supersymmetric particles in several compressed scenarios.
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