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  1. Measurement of prompt charged-particle production in pp collisions at $$\sqrt{s}$$ = 13 TeV

    Aaij, R. ; Abellán Beteta, C. ; Ackernley, T. ; ... - Journal of High Energy Physics (Online)
    The differential cross-section of prompt inclusive production of long-lived charged particles in proton-proton collisions is measured using a data sample recorded by the LHCb experiment at a centre-of-mass energy of $$\sqrt{s}$$ = 13 TeV. The data sample, collected with an unbiased trigger, corresponds to an integrated luminosity of 5.4 nb-1. The differential cross-section is measured as a function of transverse momentum and pseudorapidity in the ranges $$p_T$$ ∋ [80, 10 000) MeV/c and η ∋ [2.0, 4.8) and is determined separately for positively and negatively charged particles. The results are compared with predictions from various hadronic-interaction models.

  2. Search for the radiative $$Ξ_b^{-}$$ → $Ξ^-γ$ decay

    Aaij, R. ; Abdelmotteleb, A. W. ; Abellán Beteta, C. ; ... - Journal of High Energy Physics (Online)
    The first search for the rare radiative decay $$Ξ_b^{-}$$ → $Ξ^-γ$ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb-1. $$Ξ_b^{-}$$ → $Ξ^-J/ψ$ channel is used as normalization. No $$Ξ_b^{-}$$ → $Ξ^-γ$ signal is found and an upper limit of $$\mathcal{B}$$( $$Ξ_b^{-}$$ → $Ξ^-γ$) < 1.3 x 10-4 at 95% confidence level is obtained.

  3. Study of $$\mathrm{B}_{c}^{+}$$ decays to charmonia and three light hadrons

    Aaij, R. ; Abdelmotteleb, A. W. ; Abellán Beteta, C. ; ... - Journal of High Energy Physics (Online)
    Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb-1 collected with the LHCb detector, seven decay modes of the $$B^+_c$$ meson into a $J/ψ$ or $ψ(2S)$ meson and three charged hadrons, kaons or pions, are studied. The decays $$B^+_c$$ → $(ψ(2S)$ →J/$ψπ^+π^-$$)$$π^+$, $$B^+_c$$→$$ψ(2S)π^+π^-π^+, B^+_c$$→ J/$ψK^+π^-π^+$ and $$B^+_c$$ → J/$ψK^+K^-K^+$ are observed for the first time, and evidence for the $$B^+_c$$ →$ψ(2S)K^+K^-π^+$, decay is found, where J/ψ and $(ψ(2S)$ mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $$B^+_c$$ decays are reported as well as the fractions of the decays proceedingmore » via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.« less

  4. Search for exotic decays of the Higgs boson into $$b\bar{b}$$ and missing transverse momentum in $pp$ collisions at $$\sqrt{s}$$ = 13 TeV with the ATLAS detector

    Aad, G ; Abbott, B ; Abbott, DC ; ... - Journal of High Energy Physics
    A search for the exotic decay of the Higgs boson (H) into a $$b\bar{b}$$ resonance plus missing transverse momentum is described. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb-1 of pp collisions at $$\sqrt{s}$$ = 13 TeV. The search targets events from $ZH$ production in an NMSSM scenario where H → $$\tilde{χ}^0_2\tilde{χ}^0_1$$, with $$\tilde{χ}^0_2$$ → a$$\tilde{χ}^0_1$$, where a is a light pseudoscalar Higgs boson and $$\tilde{χ}^0_{1,2}$$ are the two lightest neutralinos. The decay of the a boson into a pair of b-quarks results in a peak in the dijet invariant mass distribution.more » The final-state signature consists of two leptons, two or more jets, at least one of which is identified as originating from a b-quark, and missing transverse momentum. Observations are consistent with Standard Model expectations and upper limits are set on the product of cross section times branching ratio for a three-dimensional scan of the masses of the $$\tilde{χ}^0_2\tilde{χ}^0_1$$ and a boson.« less

  5. Measurement of the W boson mass

    Aaij, R. ; Abdelmotteleb, A. W. ; Abellán Beteta, C. ; ... - Journal of High Energy Physics (Online)
    The W boson mass is measured using proton-proton collision data at $$\sqrt{s}$$ = 13 TeV corresponding to an integrated luminosity of 1.7 fb-1 recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon $$q/ρ_T$$ distribution of a sample of W →$μv$ decays and the $$\phi^*$$ distribution of a sample of Z → $μμ$ decays the W boson mass is determined to be $$m_w$$ =80354±23stat±10 exp±17theory±9PDFMeV, where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. Themore » measurement agrees well with the prediction of the global electroweak fit and with previous measurements.« less

  6. Measurement of b-quark fragmentation properties in jets using the decay $B^±$ → $J/ψK^±$ in pp collisions at $$\sqrt{s}$$ = 13 TeV with the ATLAS detector

    Aad, G. ; Abbott, B. ; Abbott, D. C. ; ... - Journal of High Energy Physics (Online)
    The fragmentation properties of jets containing b-hadrons are studied using charged B mesons in 139 fb-1 of pp collisions at $$\sqrt{s}$$ = 13 TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The B mesons are reconstructed using the decay of B± into J/ψK±, with the J/ψ decaying into a pair of muons. Jets are reconstructed using the anti-kt algorithm with radius parameter R = 0.4. The measurement determines the longitudinal and transverse momentum profiles of the reconstructed B hadrons with respect to the axes of the jets to which they are geometricallymore » associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets.« less

  7. Search for exotic decays of the Higgs boson into long-lived particles in pp collisions at $$\sqrt{s}$$ = 13 TeV using displaced vertices in the ATLAS inner detector

    Aad, G. ; Abbott, B. ; Abbott, D. C. ; ... - Journal of High Energy Physics (Online)
    A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb-1 of $$\sqrt{s}$$ = 13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying Z boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressingmore » Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above 10% are excluded at 95% confidence level for LLP mean proper lifetimes cτ as small as 4 mm and as large as 100 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.« less

  8. Search for dark matter produced in association with a Standard Model Higgs boson decaying into b-quarks using the full Run 2 dataset from the ATLAS detector

    Aad, G. ; Abbott, B. ; Abbott, D. C. ; ... - Journal of High Energy Physics (Online)
    The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and b-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb-1. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. Thesemore » improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson Z' or a pseudoscalar singlet a and which both provide a dark matter candidate χ. In the case of the two-Higgs-doublet model with an additional vector boson Z', the observed limits extend up to a Z' mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar a is excluded for masses of the a up to 520 GeV and 240 GeV for tan β = 1 and tan β = 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and b-quark jet multiplicity requirements.« less

  9. Measurement of $J/ψ$ production cross-sections in $pp$ collisions at $$\sqrt{s}$$ = 5 TeV

    Aaij, R. ; Abdelmotteleb, A. S. W. ; Abellán Beteta, C. ; ... - Journal of High Energy Physics (Online)
    The production cross-sections of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of $$\sqrt{s} = 5 TeV are measured using a data sample corresponding to an integrated luminosity of 9.13 ± 0.18 pb-1, collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum, pT, and rapidity, y, and separately for J/ψ mesons produced promptly and from beauty hadron decays (nonprompt). With the assumption of unpolarised J/ψ mesons, the production cross-sections integrated over the kinematic range 0 < pT < 20 GeV/c and 2.0 < y < 4.5 are σprompt J/Ψ = 8.154 ±more » 0.010 ± 0.283 μb, σnonprompt J/Ψ = 0.820 ± 0.003 ± 0.034 μb, where the first uncertainties are statistical and the second systematic. These cross-sections are compared with those at $$\sqrt{s}$ = 8 TeV and 13 TeV, and are used to update the measurement of the nuclear modification factor in proton-lead collisions for J/ψ mesons at a centre-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ = 5 TeV. The results are compared with theoretical predictions.« less

  10. Measurement of the production cross section of pairs of isolated photons in pp collisions at 13 TeV with the ATLAS detector

    Aad, G. ; Abbott, B. ; Abbott, D. C. ; ... - Journal of High Energy Physics (Online)
    A measurement of prompt photon-pair production in proton-proton collisions at $$\sqrt{s}$$ = 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb-1. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of pT,γ1(2) > 40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictionsmore » from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.« less
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