ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Measurement of the transverse momentum distribution of Drell-Yan lepton pairs in proton-proton collisions at root s=13 TeV with the ATLAS detector. Eur. Phys. J. C, 80(7), 616–28pp.
Abstract: This paper describes precision measurements of the transverse momentum p(T)(ll) (l = e, mu) and of the angular variable phi(eta)*. distributions of Drell-Yan lepton pairs in a mass range of 66-116 GeV. The analysis uses data from 36.1 fb(-1) ovf proton-proton collisions at a centre-of-mass energy of root s = 13 TeV collected by the ATLAS experiment at the LHC in 2015 and 2016. Measurements in electron-pair and muon-pair final states are performed in the same fiducial volumes, corrected for detector effects, and combined. Compared to previous measurements in proton-proton collisions at root s = 7 and 8 TeV, these new measurements probe perturbative QCD at a higher centre-of-mass energy with a different composition of initial states. They reach a precision of 0.2% for the normalized spectra at low values of p(T)(ll). The data are compared with different QCD predictions, where it is found that predictions based on resummation approaches can describe the full spectrum within uncertainties.
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Bernard, V., Descotes-Genon, S., & Vale Silva, L. (2020). Constraining the gauge and scalar sectors of the doublet left-right symmetric model. J. High Energy Phys., 09(9), 088–64pp.
Abstract: We consider a left-right symmetric extension of the Standard Model where the spontaneous breakdown of the left-right symmetry is triggered by doublets. The electroweak rho parameter is protected from large corrections in this Doublet Left-Right Model (DLRM), contrary to the triplet case. This allows in principle for more diverse patterns of symmetry breaking. We consider several constraints on the gauge and scalar sectors of DLRM: the unitarity of scattering processes involving gauge bosons with longitudinal polarisations, the radiative corrections to the muon Delta r parameter and the electroweak precision observables measured at the Z pole and at low energies. Combining these constraints within the frequentist CKMfitter approach, we see that the fit pushes the scale of left-right symmetry breaking up to a few TeV, while favouring an electroweak symmetry breaking triggered not only by the SU (2)(L) x SU (2)(R) bi-doublet, which is the case most commonly considered in the literature, but also by the SU (2)(L) doublet.
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Coppola, M., Gomez Dumm, D., Noguera, S., & Scoccola, N. N. (2020). Magnetic field driven enhancement of the weak decay width of charged pions. J. High Energy Phys., 09(9), 058–19pp.
Abstract: We study the effect of a uniform magnetic field B on the decays pi- > l- nu_l bar, where l(-)=e(-), μ(-), carrying out a general analysis that includes four pi (-) decay constants. Taking the values of these constants from a chiral effective Nambu-Jona-Lasinio (NJL) model, it is seen that the total decay rate gets strongly increased with respect to the B = 0 case, with an enhancement factor ranging from similar to 10 for eB = 0.1 GeV2 up to similar to 10(3) for eB = 1 GeV2. The ratio between electronic and muonic decays gets also enhanced, reaching a value of about 1 : 2 for eB = 1 GeV2. In addition, we find that for large B the angular distribution of outgoing antineutrinos shows a significant suppression in the direction of the magnetic field.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Measurements of inclusive and differential cross-sections of combined t tbar gamma and t W gamma production in the e mu channel at 13 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 049–48pp.
Abstract: Inclusive and differential cross-sections for the production of top quarks in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 139 fb(-1). The data were collected by the ATLAS detector at the LHC during Run 2 between 2015 and 2018 at a centre-of-mass energy of 13 TeV. The measurements are performed in a fiducial volume defined at parton level. Events with exactly one photon, one electron and one muon of opposite sign, and at least two jets, of which at least one is b-tagged, are selected. The fiducial cross-section is measured to be 39.6-2.3+2.7 fb. Differential cross-sections as functions of several observables are compared with state-of-the-art Monte Carlo simulations and next-to-leading-order theoretical calculations. These include cross-sections as functions of photon kinematic variables, angular variables related to the photon and the leptons, and angular separations between the two leptons in the event. All measurements are in agreement with the predictions from the Standard Model.
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Bernal, N., Donini, A., Folgado, M. G., & Rius, N. (2020). Kaluza-Klein FIMP dark matter in warped extra-dimensions. J. High Energy Phys., 09(9), 142–31pp.
Abstract: We study for the first time the case in which Dark Matter (DM) is made of Feebly Interacting Massive Particles (FIMP) interacting just gravitationally with the standard model particles in an extra-dimensional Randall-Sundrum scenario. We assume that both the dark matter and the standard model are localized in the IR-brane and only interact via gravitational mediators, namely the graviton, the Kaluza-Klein gravitons and the radion. We found that in the early Universe DM could be generated via two main processes: the direct freeze-in and the sequential freeze-in. The regions where the observed DM relic abundance is produced are largely compatible with cosmological and collider bounds.
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