Searches for scalar leptoquarks in pp collisions at √s = 8 TeV with the ATLAS detector

Searches for pair-produced scalar leptoquarks are performed using 20 fb$^{-1}$ of proton-proton collision data provided by the LHC and recorded by the ATLAS detector at $\sqrt{s}=8$ TeV. Events with two electrons (muons) and two or more jets in the final state are used to search for first (second)-generation leptoquarks. The results from two previously published ATLAS analyses are interpreted in terms of third-generation leptoquarks decaying to $b\nu_{\tau}\bar{b}\bar{\nu_{\tau}}$ and $t\nu_{\tau}\bar{t}\bar{\nu_{\tau}}$ final states. No statistically significant excess above the Standard Model expectation is observed in any channel and scalar leptoquarks are excluded at 95% CL with masses up to $m_{\mathrm{LQ1}}$ < 1050 GeV for first-generation leptoquarks, $m_{\mathrm{LQ2}}$ < 1000 GeV for second-generation leptoquarks, $m_{\mathrm{LQ3}} <$ 625 GeV for third-generation leptoquarks in the $b\nu_{\tau}\bar{b}\bar{\nu_{\tau}}$ channel, and 200 $< m_{\mathrm{LQ3}} <$ 640 GeV in the $t\nu_{\tau}\bar{t}\bar{\nu_{\tau}}$ channel.Comment: 25 pages plus author list + cover pages (42 pages total), 6 figures, 8 tables, submitted to EPJC, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2014-03

Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at √s=8 TeV using the ATLAS detector

This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton–proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb−1. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: |ηγ | < 1.37 and 1.56 < |ηγ | < 2.37. The measurement covers photon transverse energies 25 < Eγ T < 400 GeV and 25 < Eγ T < 350 GeV respectively for the two |ηγ | regions. For each jet flavour, the ratio of the cross sections in the two |ηγ | regions is also measured. The measurement is corrected for detector effects and compared to leading-order and nextto-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central γ + b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions

Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in√s =13 TeV ppcollisions with the ATLAS detector

aJUTS: s 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, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; MINECO, Spain AND CERCA Programme Generalitat de Catalunya.A search for new phenomena in final states containing an or pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton-proton collision data with an integrated luminosity of , collected during 2015 and 2016 at a centre-of-mass energy with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an or pair and the lightest neutralino () via one of two next-to-lightest neutralino () decay mechanisms: , where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and with no intermediate resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 at 95% confidence level, respectively