Single lepton charge asymmetries in t ¯t and t ¯tγ production at the LHC

We discuss lepton charge asymmetries in tt¯ and tt¯γ production at the LHC, which can be measured in the semileptonic decay channel tt¯→W+bW−b¯→ℓ+νbqq¯′b¯ (or the charge conjugate). Considering several variants of a new physics scenario with a light colour octet, it is seen that for tt¯ these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For tt¯γ the new leptonic asymmetries, as well as the tt¯ charge asymmetry, will reach their full potential with the high luminosity LHC upgrade. These asymmetries can pinpoint deviations at the 3σ−4σ level for new physics scenarios where the charge asymmetries already measured in tt¯ production agree within 1σ.This work has been supported by MINECO Project FPA 2013-47836-C3-2-P (including ERDF)

Mass Unspecific Supervised Tagging (MUST) for boosted jets

Jet identification tools are crucial for new physics searches at the LHC and at future colliders. We introduce the concept of Mass Unspecific Supervised Tagging (MUST) which relies on considering both jet mass and transverse momentum varying over wide ranges as input variables — together with jet substructure observables — of a multivariate tool. This approach not only provides a single efficient tagger for arbitrary ranges of jet mass and transverse momentum, but also an optimal solution for the mass correlation problem inherent to current taggers. By training neural networks, we build MUST-inspired generic and multi-pronged jet taggers which, when tested with various new physics signals, clearly outperform the variables commonly used by experiments to discriminate signal from background. These taggers are also efficient to spot signals for which they have not been trained. Taggers can also be built to determine, with a high degree of confidence, the prongness of a jet, which would be of utmost importance in case a new physics signal is discovered.MICINN project PID2019-110058GB-C21Portuguese Foundation for Science and Technology UIDB/00777/2020 UIDP/00777/2020 CERN/FISPAR/0004/2019 PTDC/FIS-PAR/29436/2017Portuguese Foundation for Science and Technology European Commission SFRH/BD/143891/201

Collider-independent t¯t forward-backward asymmetries

We introduce the forward-backward asymmetries Au, Ad corresponding to u¯u, d ¯ d -> t¯t production, respectively, at hadron colliders. These are collider- and center-of-mass-independent observables, directly related to the forward-backward and charge asymmetries measured at the Tevatron and the LHC, respectively. We discuss how to extract these asymmetries from data. Because these asymmetries are collider-independent, their measurement at these two colliders could elucidate the nature of the anomalous forward-backward asymmetry measured at the Tevatron. Our framework also shows in a model-independent fashion that a positive Tevatron asymmetry exceeding the standard model expectation is compatible with the small asymmetry measured at the LHC.This work has been supported by projects FPA2006-05294 and FPA2010-17915 (MICINN), FQM 101, FQM 03048 and FQM 6552 (Junta de Andalucía)

Correlations between flow and transverse momentum in Xe + Xe and Pb + Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation

The correlations between flow harmonics v(n) for n = 2, 3, and 4 and mean transverse momentum [pT] in Xe-129 + Xe-129 and Pb-208 + Pb-208 collisions at root s = 5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The v(n)-[p(T)] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality -and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v(2)-[p(T)] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb + Pb and Xe + Xe data confirms that the Xe-129 nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the Xe-129 nucleus from high-energy heavy-ion collisions.ANPCyTYerPhI, ArmeniaAustralian Research CouncilBMWFW, AustriaAustrian Science Fund (FWF)Azerbaijan National Academy of Sciences (ANAS)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Foundation for InnovationNational Natural Science Foundation of China (NSFC)MEYS CR, Czech RepublicNational Research Foundation of KoreaDanish Natural Science Research CouncilCentre National de la Recherche Scientifique (CNRS)CEA-DRF/IRFU, FranceFederal Ministry of Education & Research (BMBF)Max Planck SocietyHong Kong SAR, ChinaIsrael Science FoundationIstituto Nazionale di Fisica Nucleare (INFN)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of ScienceMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of ScienceCNRST, MoroccoRCN, NorwayMEiN, PolandFundacao para a Ciencia e a Tecnologia (FCT)MNE/IFA, RomaniaMinistry of Education, Science & Technological Development, SerbiaMSSR, SlovakiaSlovenian Research Agency - SloveniaMIZS, SloveniaSpanish GovernmentWallenberg Foundation, SwedenSERI, SwitzerlandMinistry of Science and Technology, TaiwanUnited States Department of Energy (DOE)National Science Foundation (NSF)BCKDF, CanadaCANARIE, CanadaCompute Canada, CanadaCzech Republic Government PRIMUS 21/SCI/017 UNCE SCI/013COST, European UnionEuropean Union (EU) European Research Council (ERC)European Union (EU) Marie Curie ActionsHorizon 2020, European UnionEuropean Union (EU) Marie Curie ActionsAgence Nationale de la Recherche (ANR)German Research Foundation (DFG)Alexander von Humboldt FoundationHerakleitos programme - EU-ESF, GreeceThales GroupAristeia programme - EU-ESF, GreeceGreek NSRF, GreeceBSF-NSF, IsraelMINERVA, IsraelNorwegian Financial Mechanism 2014-2021, NorwayNCN, PolandPolish National Agency for Academic Exchange (NAWA)La Caixa Banking Foundation, SpainCERCA Programme Generalitat de Catalunya, SpainPROMETEO Programme Generalitat Valenciana, SpainGenT Programme Generalitat Valenciana, SpainGoran Gustafssons Stiftelse, SwedenRoyal SocietyLeverhulme TrustUK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC)TENMAK, TurkiyeCanton of Geneva, SwitzerlandCanton of Bern, SwitzerlandSwiss National Science Foundation (SNSF)SRC, SwedenDSI/NRF, South AfricaNetherlands Organization for Scientific Research (NWO) Netherlands GovernmentBenoziyo Center, IsraelRGC, ChinaGSRI, GreeceHGF, GermanySRNSFG, GeorgiaMinciencias, ColombiaMinistry of Science and Technology, ChinaChinese Academy of SciencesANID, ChileCERNNRC, Canad

Search for a Structure in the B0sπ± Invariant Mass Spectrum with the ATLAS Experiment

A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→Bs0π±, Bs0→J/ψϕ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9  fb-1 of pp collisions at 7 TeV and 19.5  fb-1 at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to Bs0 mesons, ρX, were determined at 95% confidence level. The results are N(X)<382 and ρX<0.015 for Bs0 mesons with transverse momenta above 10 GeV, and N(X)<356 and ρX<0.016 for transverse momenta above 15 GeV. Limits are also set for potential Bs0π± resonances in the mass range 5550 to 5700 MeV.Funded by SCOAP3

Observation of electroweak production of two jets and a Z-boson pair

Electroweak symmetry breaking explains the origin of the masses of elementary particles through their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector bosons with spin 1 allows the nature of electroweak symmetry breaking to be probed. Among all processes related to vector-boson scattering, the electroweak production of two jets and a Z-boson pair is a rare and important one. Here we report the observation of this process from proton–proton collision data corresponding to an integrated luminosity of 139 fb−1 recorded at a centre-of-mass energy of 13 TeV with the ATLAS detector at the Large Hadron Collider. We consider two different final states originating from the decays of the Z-boson pair: one containing four charged leptons and another containing two charged leptons and two neutrinos. The hypothesis of no electroweak production is rejected with a statistical significance of 5.7σ, and the measured cross-section for electroweak production is consistent with the Standard Model prediction. In addition, we report cross-sections for inclusive production of a Z-boson pair and two jets for the two final states.CERNANPCyTYerPhI, ArmeniaAustralian Research CouncilBMWFWAustrian Science Fund (FWF)Azerbaijan National Academy of Sciences (ANAS)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Foundation for InnovationNational Natural Science Foundation of China (NSFC)MEYS CR, Czech RepublicDNRFDanish Natural Science Research CouncilCentre National de la Recherche Scientifique (CNRS)CEA-DRF/IRFU, FranceFederal Ministry of Education & Research (BMBF)Max Planck SocietyRGC and Hong Kong SAR, ChinaIsrael Science FoundationBenoziyo Center, IsraelIstituto Nazionale di Fisica Nucleare (INFN)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of ScienceCNRST, Morocco; NWORCN, NorwayMEiN, PolandFundacao para a Ciencia e a Tecnologia (FCT)MNE/IFA, RomaniaMinistry of Education, Science & Technological Development, SerbiaMSSR, SlovakiaSlovenian Research Agency - SloveniaMIZS, SloveniaSpanish GovernmentWallenberg Foundation, SwedenSwiss National Science Foundation (SNSF)Ministry of Science and Technology, TaiwanUK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC)United States Department of Energy (DOE)National Science Foundation (NSF)BCKDFCANARIECRC, CanadaCOST, ERCEuropean Union (EU)European Union (EU) Marie Curie ActionsAgence Nationale de la Recherche (ANR)German Research Foundation (DFG)Alexander von Humboldt FoundationGreek NSRF, GreeceBSF-NSFGerman-Israeli Foundation for Scientific Research and DevelopmentNorwegian Financial MechanismNCNLa Caixa FoundationCERCA Programme Generalitat de CatalunyaPROMETEOCenter for Forestry Research & Experimentation (CIEF)Goran Gustafssons Stiftelse, SwedenRoyal SocietyLeverhulme TrustNDGF (Denmark, Norway and Sweden) CC-IN2P3KIT/GridKA (Germany)INFN-CNAF (Italy)Netherlands GovernmentASGC (Taiwan)BNL (USA

Measurement of the cross section for isolated-photon plus jet production in pp collisions at √s=13TeV using the ATLAS detector

The dynamics of isolated-photon production in association with a jet in proton–proton collisions at a centre-of-mass energy of 13TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2fb−1. Photons are required to have transverse energies above 125GeV. Jets are identified using the anti-ktalgorithm with radius parameter R =0.4and required to have transverse momenta above 100GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system. Tree-level plus parton-shower predictions fromSherpaandPythiaas well as next-to-leading-order QCD predictions fromJetphoxandSherpaare compared to the measurements.We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS,MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR;MESTD, Serbia; MSSR, Slovakia; ARRS andMIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex and Idex, ANR, Région Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; CERCA Programme Generalitat de Catalunya, Generalitat Valenciana, Spain; the Royal Society and Leverhulme Trust, United Kingdom

Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment

A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ℓ+ℓ-cc¯ is studied. A data set with an integrated luminosity of 36.1  fb-1 of pp collisions at s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→cc¯ signature is identified using charm-tagging algorithms. The observed (expected) upper limit on σ(pp→ZH)×B(H→cc¯) is 2.7 (3.9-1.1+2.1) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.Funded by SCOAP

Search for direct third-generation squark pair production in final states with missing transverse momentum and two b-jets in √s = 8 TeV pp collisions with the ATLAS detector

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MIZ. S, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America.r The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide.The results of a search for pair production of supersymmetric partners of the Standard Model third-generation quarks are reported. This search uses 20.1 fb−1 of pp collisions at √s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The lightest bottom and top squarks (˜b1 and t˜1 respectively) are searched for in a final state with large missing transverse momentum and two jets identified as originating from b-quarks. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the visible cross section for processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of the third-generation squarks are derived in phenomenological supersymmetric R-parityconserving models in which either the bottom or the top squark is the lightest squark. The ˜b 1 is assumed to decay via ˜b1 → bχ˜0 1 and the t˜1 via t˜1 → bχ˜± 1 , with undetectable products of the subsequent decay of the ˜ χ± 1 due to the small mass splitting between the ˜ χ± 1 and the ˜ χ0 1.ANPCyTYerPhI, ArmeniaAustralian Research CouncilBMWF, AustriaAustrian Science Fund (FWF)Azerbaijan National Academy of Sciences (ANAS)SSTC, BelarusNational Council for Scientific and Technological Development (CNPq)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Natural Sciences and Engineering Research Council of CanadaNRC, CanadaCanada Foundation for InnovationCERNComision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)Chinese Academy of SciencesMinistry of Science and Technology, ChinaNational Natural Science Foundation of ChinaDepartamento Administrativo de Ciencia, Tecnologia e Innovacion ColcienciasMinistry of Education, Youth & Sports - Czech Republic Czech Republic GovernmentDNRFDanish Natural Science Research CouncilLundbeckfondenEPLANETEuropean Research Council (ERC)NSRFEuropean Union (EU)Centre National de la Recherche Scientifique (CNRS)CEA-DSM/IRFU, FranceGNSF, GeorgiaFederal Ministry of Education & Research (BMBF)German Research Foundation (DFG)HGFMax Planck SocietyAlexander von Humboldt FoundationScience & Technology Facilities Council (STFC) ST/G006717/1 ST/K501840/1 GRIDPP ST/J004944/1 ST/J500641/1 ST/I000186/1 ST/H001042/2 PP/E003699/2 ST/F00754X/1 ST/K00137X/1 ST/K001361/1 MINOS/MINOS+ ST/H00095X/1 PP/E003087/1 ST/F007337/1 PP/E000487/1 ST/H001093/1 ST/J005576/1 ST/K000659/1 ST/K501840/1 ST/K003496/1 GRIDPP ST/J005460/1 ST/I006080/1 ST/K001248/1 ST/K003437/1 GRIDPP ST/K50208X/1 ST/L001144/1 ST/L00352X/1 ST/K001388/1 ST/K003496/1 ST/K003658/1 GRIDPP ST/L001004/1 ST/M001474/1 ST/K003658/1 ST/I505756/1 ATLAS ST/F007418/1 ST/H001093/2 ST/J004936/1 ST/K001361/1 LHCb ST/K001361/1 ATLAS ST/K001337/1 ST/K00073X/1 PP/E003699/1 ST/J005568/1 ST/K001361/1 ATLAS Upgrades ST/K001361/1 LHCb Upgrades ST/K003437/1 ST/K00140X/1 ST/J002798/1 PP/E000347/1 GRIDPP ST/K001329/1 ATLAS ST/J004928/1 ST/K001337/1 ATLAS ST/M001431/1 ST/M000761/1 ST/L000970/1 ATLAS Upgrade ST/I005803/1 ST/J005541/1 ST/M000664/1 ST/K001264/1 ATLAS ST/I005803/1 GRIDPP PP/E002757/1 ST/J501074/1 ST/H001069/2 ST/G502320/1 ST/L00335X/1 ST/K00140X/1 ATLAS ST/J004804/1 ST/L003325/1 ST/H001042/1 ST/H00095X/2 ST/K000713/1 ST/L001209/1 ATLAS Upgrades ST/I005811/1 ST/J004928/1 ATLAS Upgrade ST/K000195/1 ST/K001361/1 ST/L000970/1ICRE

Study of the hard double-parton scattering contribution to inclusive four-lepton production in pp collisions at s√ = 8 TeV with the ATLAS detector

The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb−1 of data recorded in the ATLAS detector at the LHC at centre-of-mass energy s√ = 8 TeV. In the four-lepton invariant-mass range of 80<m4ℓ<1000 GeV, an artificial neural network is used to enhance the separation between single- and double-parton scattering based on the kinematics of the four leptons in the final state. An upper limit on the fraction of events originating from double-parton scattering is determined at 95% confidence level to be fDPS=0.042, which results in an estimated lower limit on the effective cross section at 95% confidence level of 1.0 mb.We acknowledge the support of ANPCyT, Argentina; YerPhI, Ar-menia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azer-baijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF and Benoziyo Center, Is-rael; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portu-gal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Fed-eration; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallen-berg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, in-dividual groups and members have received support from BCKDF, Canarie, CRC and Compute Canada, Canada; COST, ERC, ERDF, Hori-zon 2020, and Marie Skłodowska-Curie Actions, European Union; Investissements d’ Avenir Labex and Idex, ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia pro-grammes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA Programme Generalitat de Catalunya, Spain; The Royal Society and Leverhulme Trust, United Kingdom