ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb(-1) of Pb+Pb data with the ATLAS detector. J. High Energy Phys., 03(3), 243–45pp.
Abstract: This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb(-1) of integrated luminosity collected in 2015 and 2018 at root sNN = 5.02TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy E-T(gamma) > 2.5 GeV, pseudorapidity vertical bar eta(gamma)vertical bar < 2.37, diphoton invariant mass m(gamma gamma) > 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.
|
Escribano, P., & Vicente, A. (2021). Ultralight scalars in leptonic observables. J. High Energy Phys., 03(3), 240–37pp.
Abstract: Many new physics scenarios contain ultralight scalars, states which are either exactly massless or much lighter than any other massive particle in the model. Axions and majorons constitute well-motivated examples of this type of particle. In this work, we explore the phenomenology of these states in low-energy leptonic observables. After adopting a model independent approach that includes both scalar and pseudoscalar interactions, we briefly discuss the current limits on the diagonal couplings to charged leptons and consider processes in which the ultralight scalar phi is directly produced, such as μ-> e phi, or acts as a mediator, as in tau -> μμmu. Contributions to the charged leptons magnetic and electric moments are studied as well.
|
Centelles Chulia, S., Srivastava, R., & Vicente, A. (2021). The inverse seesaw family: Dirac and Majorana. J. High Energy Phys., 03(3), 248–29pp.
Abstract: After developing a general criterion for deciding which neutrino mass models belong to the category of inverse seesaw models, we apply it to obtain the Dirac analogue of the canonical Majorana inverse seesaw model. We then generalize the inverse seesaw model and obtain a class of inverse seesaw mechanisms both for Majorana and Dirac neutrinos. We further show that many of the models have double or multiple suppressions coming from tiny symmetry breaking “mu -parameters”. These models can be tested both in colliders and with the observation of lepton flavour violating processes.
|
Bourguille, B., Nieves, J., & Sanchez, F. (2021). Inclusive and exclusive neutrino-nucleus cross sections and the reconstruction of the interaction kinematics. J. High Energy Phys., 04(4), 004–42pp.
Abstract: We present a full kinematic analysis of neutrino-nucleus charged current quasielastic interactions based on the Local Fermi Gas model and the Random Phase Approximation. The model was implemented in the NEUT Monte Carlo framework, which allows us to investigate potentially measurable observables, including hadron distributions. We compare the predictions simultaneously to the most recent T2K and MINERvA charged current (CC) inclusive, CC0 pi and transverse kinematic-imbalance variable results. We pursuit a microscopic interpretation of the relevant reaction mechanisms, with the aim to achieving in neutrino oscillation experiments a correct reconstruction of the incoming neutrino kinematics, free of conceptual biasses. Such study is of the utmost importance for the ambitious experimental program which is underway to precisely determine neutrino properties, test the three-generation paradigm, establish the order of mass eigenstates and investigate leptonic CP violation.
|
Mandal, S., Srivastava, R., & Valle, J. W. F. (2021). Electroweak symmetry breaking in the inverse seesaw mechanism. J. High Energy Phys., 03(3), 212–28pp.
Abstract: We investigate the stability of Higgs potential in inverse seesaw models. We derive the full two-loop RGEs of the relevant parameters, such as the quartic Higgs self-coupling, taking thresholds into account. We find that for relatively large Yukawa couplings the Higgs quartic self-coupling goes negative well below the Standard Model instability scale similar to 10(10) GeV. We show, however, that the “dynamical” inverse seesaw with spontaneous lepton number violation can lead to a completely consistent and stable Higgs vacuum up to the Planck scale.
|
