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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Differential cross-section measurements of the production of four charged leptons in association with two jets using the ATLAS detector. J. High Energy Phys., 01(1), 004–51pp.
Abstract: Differential cross-sections are measured for the production of four charged leptons in association with two jets. These measurements are sensitive to final states in which the jets are produced via the strong interaction as well as to the purely-electroweak vector boson scattering process. The analysis is performed using proton-proton collision data collected by ATLAS at root s = 13TeV and with an integrated luminosity of 140 fb(-1). The data are corrected for the effects of detector inefficiency and resolution and are compared to stateof-the-art Monte Carlo event generator predictions. The differential cross-sections are used to search for anomalous weak-boson self-interactions that are induced by dimension-six and dimension-eight operators in Standard Model effective field theory.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Measurement of the inelastic proton-proton cross-section at sqrt(s)=7 TeV with the ATLAS detector. Nat. Commun., 2, 463–14pp.
Abstract: The dependence of the rate of proton-proton interactions on the centre-of-mass collision energy, root s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton-proton interaction cross-section at a centre-of-mass energy, root s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic crosssection of 60.3 +/- 2.1 mb is measured for xi > 5x10(-6), where xi is calculated from the invariant mass, M(X), of hadrons selected using the largest rapidity gap in the event. For diffractive events, this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2020). Measurement of differential cross sections for single diffractive dissociation in root s=8 TeV pp collisions using the ATLAS ALFA spectrometer. J. High Energy Phys., 02(2), 42–37pp.
Abstract: A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s= 8 TeV is used to study inclusive single diffractive dissociation, pp -> X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is -4.0 < log(10)xi < -1.6 and 0.016 < |t| < 0.43 GeV2, where xi is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 +/- 0.13 mb. Cross sections are also measured differentially as functions of xi, t, and increment eta, a variable that characterises the rapidity gap separating the proton and the system X . The data are consistent with an exponential t dependence, d sigma/dt proportional to e(Bt) with slope parameter B = 7.65 +/- 0.34 GeV-2. Interpreted in the framework of triple Regge phenomenology, the xi dependence leads to a pomeron intercept of alpha(0) = 1.07 +/- 0.09.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for squarks and gluinos in final states with jets and missing transverse momentum using 139 fb(-1) of root s=13 TeV pp collision data with the ATLAS detector. J. High Energy Phys., 02(2), 143–64pp.
Abstract: A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Search for dark matter in association with an energetic photon in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 02(2), 226–46pp.
Abstract: A search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at root s = 13 TeV. The data, collected during 2015-2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb(-1). No deviations from the predictions of the Standard Model are observed and 95% confidence-level upper limits between 2.45 fb and 0.5 fb are set on the visible cross section for contributions from physics beyond the Standard Model, in different ranges of the missing transverse momentum. The results are interpreted as 95% confidence-level limits in models where weakly interacting dark-matter candidates are pair-produced via an s-channel axial-vector or vector mediator. Dark-matter candidates with masses up to 415 (580) GeV are excluded for axial-vector (vector) mediators, while the maximum excluded mass of the mediator is 1460 (1470) GeV. In addition, the results are expressed in terms of 95% confidence-level limits on the parameters of a model with an axion-like particle produced in association with a photon, and are used to constrain the coupling g(aZ gamma) of an axion-like particle to the electroweak gauge bosons.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Search for resonant production of dark quarks in the dijet final state with the ATLAS detector. J. High Energy Phys., 02(2), 128–35pp.
Abstract: This paper presents a search for a new Z' resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at root s = 13TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb(-1). After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95% confidence-level upper limits on the production cross-section times branching ratio of the Z' to dark quarks as a function of the Z' mass for various dark-quark scenarios.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the l+l-t(t)over-bar and ν(ν)over-barb(b)over-bar final states using 140 fb-1 of data collected with the ATLAS detector. J. High Energy Phys., 02(2), 197–56pp.
Abstract: A search for a heavy CP-odd Higgs boson, A, decaying into a Z boson and a heavy CP-even Higgs boson, H, is presented. It uses the full LHC Run 2 dataset of pp collisions at root s = 13TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb(-1). The search for A -> ZH is performed in the l(+)l(-)t (t) over bar t and nu(nu) over barb (b) over bar final states and surpasses the reach of previous searches in different final states in the region with m(H) > 350 GeV and m(A) > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed m(t (t) over bar) and m(b (b) over bar) distributions in the l(+)l(-)t (t) over bar and nu(nu) over barb (b) over bar channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models.
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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. (2018). Searches for heavy ZZ and ZW resonances in the llqq and vvqq final states in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 009–53pp.
Abstract: This paper reports searches for heavy resonances decaying into ZZ or ZW using data from proton-proton collisions at a centre-of-mass energy of root s – 13 TeV. The data, corresponding to an integrated luminosity of 36.1 fb(-1), were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The searches are performed in final states in which one Z boson decays into either a pair of light charged leptons (electrons and muons) or a pair of neutrinos, and the associated W boson or the other Z boson decays hadronically. No evidence of the production of heavy resonances is observed. Upper bounds on the production cross sections of heavy resonances times their decay branching ratios to ZZ or ZW are derived in the mass range 300-5000 GeV within the context of Standard Model extensions with additional Higgs bosons, a heavy vector triplet or warped extra dimensions. Production through gluon-gluon fusion, Drell-Yan or vector-boson fusion are considered, depending on the assumed model.
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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. (2018). Search for WW/WZ resonance production in lvqq final states in pp collisions at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 042–45pp.
Abstract: A search is conducted for new resonances decaying into a WW or WZ boson pair, where one W boson decays leptonically and the other W or Z boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb(-1) collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of root s = 13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector-boson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton.
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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. (2018). Measurement of the Higgs boson coupling properties in the H -> ZZ* -> 4l decay channel at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 095–60pp.
Abstract: The coupling properties of the Higgs boson are studied in the four-lepton (e, mu) decay channel using 36.1 fb(-1) of pp collision data from the LHC at a centre-of-mass energy of 13 TeV collected by the ATLAS detector. Cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for H -> ZZ* decay and for a Higgs boson absolute rapidity below 2.5 is measured to be 1.73(-0.23)(+0.24)(stat.)(-0.08)(+0.10)(exp.)+/- 0.04(th.) pb compared to the Standard Model prediction of 1.34 +/- 0.09 pb. In addition, the tensor structure. of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to Z bosons and on the CP-odd coupling to gluons.
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