14 research outputs found

    Search for resonances decaying into photon pairs in 139 fb−1 of pp collisions at √s = 13 TeV with the ATLAS detector

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    Searches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb−1 of √s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass

    System-size dependence of open-heavy-flavor production in nucleus-nucleus collisions at root s(NN)=200 GeV

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    The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open-heavy-flavor production in Cu + Cu collisions at v root s(NN) = 200 GeV through the measurement of electrons at midrapidity that originate from semileptonic decays of charm and bottom hadrons. In peripheral Cu + Cu collisions an enhanced production of electrons is observed relative to p + p collisions scaled by the number of binary collisions. In the transverse momentum range from 1 to 5 GeV/c the nuclear modification factor is R-AA similar to 1.4. As the system size increases to more central Cu + Cu collisions, the enhancement gradually disappears and turns into a suppression. For p(T) > 3 GeV/c, the suppression reaches R-AA similar to 0.8 in the most central collisions. The p(T) and centrality dependence of R-AA in Cu + Cu collisions agree quantitatively with R-AA in d + Au and Au + Au collisions, if compared at a similar number of participating nucleons

    Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in Pb+Pb collisions at √sNN=5.02 TeV with the ATLAS detector

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    Azimuthal anisotropies of muons from charm and bottom hadron decays are measured in Pb+Pb collisions at √sNN=5.02 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2018 with integrated luminosities of  0.5 nb-1 and 1.4 nb-1, respectively. The kinematic selection for heavy-flavor muons requires transverse momentum 4<pT <30GeV and pseudorapidity ŠηŠ <2.0. The dominant sources of muons in this range are semi-leptonic decays of charm and bottom hadrons. These heavy-flavor muons are separated from light-hadron decay muons and punch-through hadrons using the momentum imbalance between the measurements in the tracking detector and in the muon spectrometers. Azimuthal anisotropies, quantified by flow coefficients, are measured via the event-plane method for inclusive heavy-flavor muons as a function of the muon pT  and in intervals of Pb+Pb collision centrality. Heavy-flavor muons are separated into contributions from charm and bottom hadron decays using the muon transverse impact parameter with respect to the event primary vertex. Non-zero elliptic (Îœ2) and triangular  (Îœ3) flow coefficients are extracted for charm and bottom muons, with the charm muon coefficients larger than those for bottom muons for all Pb+Pb collision centralities. The results indicate substantial modification to the charm and bottom quark angular distributions through interactions in the quark-gluon plasma produced in these Pb+Pb collisions, with smaller modifications for the bottom quarks as expected theoretically due to their larger mass

    Test of CP invariance in vector-boson fusion production of the Higgs boson in the H → ττ channel in proton-proton collisions at √<i>s</i>=13TeV with the ATLAS detector

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    A test of CP invariance in Higgs boson production via vector-boson fusion is performed in the H→ττH\rightarrow\tau\tau decay channel. This test uses the Optimal Observable method and is carried out using 36.1 fb−1\mathrm{fb}^{-1} of s\sqrt{s} = 13 TeV proton−-proton collision data collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described by an effective field theory, in which the parameter d~\tilde{d} governs the strength of CP violation. No sign of CP violation is observed in the distributions of the Optimal Observable, and d~\tilde{d} is constrained to the interval [−0.090,0.035][-0.090, 0.035] at the 68% confidence level (CL), compared to an expected interval of d~∈[−0.035,0.033]\tilde{d} \in [-0.035,0.033] based upon the Standard Model prediction. No constraints can be set on d~\tilde{d} at 95% CL, while an expected 95% CL interval of d~∈[−0.21,0.15]\tilde{d} \in [-0.21,0.15] for the Standard Model hypothesis was expected

    Measurements of WH and ZH production in the H→ bb¯ decay channel in pp collisions at 13Te with the ATLAS detector

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    Measurements of the Standard Model Higgs boson decaying into a bbˉb\bar{b} pair and produced in association with a WW or ZZ boson decaying into leptons, using proton-proton collision data collected between 2015 and 2018 by the ATLAS detector, are presented. The measurements use collisions produced by the Large Hadron Collider at a centre-of-mass energy of s=\sqrt{s} = 13 TeV, corresponding to an integrated luminosity of 139 fb−1^{-1}. The production of a Higgs boson in association with a WW or ZZ boson is established with observed (expected) significances of 4.0 (4.1) and 5.3 (5.1) standard deviations, respectively. Cross-sections of associated production of a Higgs boson decaying into bottom quark pairs with an electroweak gauge boson, WW or ZZ, decaying into leptons are measured as a function of the gauge boson transverse momentum in kinematic fiducial volumes. The cross-section measurements are all consistent with the Standard Model expectations, and the total uncertainties vary from 30% in the high gauge boson transverse momentum regions to 85% in the low regions. Limits are subsequently set on the parameters of an effective Lagrangian sensitive to modifications of the WHWH and ZHZH processes as well as the Higgs boson decay into bbˉb\bar{b}

    Search for the Higgs boson decays H -> ee and H -> e mu in pp collisions at root s=13 TeV with the ATLAS detector

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    Searches for the Higgs boson decays and are performed using data corresponding to an integrated luminosity of collected with the ATLAS detector in pp collisions at TeV at the LHC. No significant signals are observed, in agreement with the Standard Model expectation. For a Higgs boson mass of 125 GeV, the observed (expected) upper limit at the 95% confidence level on the branching fraction is ( ) and on is ( ). These results represent improvements by factors of about five and six on the previous best limits on and respectively

    Search for non-resonant Higgs boson pair production in the bbl nu l nu final state with the ATLAS detector in pp collisions at root s=13 TeV

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    A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the channel and the other via one of the ⁎ ⁎ channels. The analysis selection requires events to have at least two b-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb−1 of pp collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 ( ) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 ( ) times the value predicted in the Standard Model
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