|
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.
|
|
|
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.
|
|
|
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.
|
|
|
LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Measurement of the CKM angle gamma and Bs0-Bs0bar mixing frequency with Bs0 -> Ds-/+ h +/ pi+/- pi-/+ decays. J. High Energy Phys., 03(3), 137–46pp.
Abstract: The CKM angle gamma is measured for the first time from mixing-induced CP violation between Bs0 -> Ds -/+ K pi +/- pi -/+ and Bs0bar -> Ds +/- K -/+ pi -/+ pi +/- decays reconstructed in proton-proton collision data corresponding to an integrated luminosity of 9 fb(-1) recorded with the LHCb detector. A time-dependent amplitude analysis is performed to extract the CP-violating weak phase gamma – 2 beta (s) and, subsequently, gamma by taking the Bs0-Bs0bar mixing phase beta (s) as an external input. The measurement yields gamma = (44 +/- 12) degrees modulo 180 degrees, where statistical and systematic uncertainties are combined. An alternative model-independent measurement, integrating over the five-dimensional phase space of the decay, yields gamma = (44 -13+20) degrees modulo 180 degrees. Moreover, the Bs0-Bs0bar oscillation frequency is measured from the flavour-specific control channel Bs0 -> Ds- pi+ pi+ pi- to be m(s) = (17.757 +/- 0.007(stat) +/- 0.008(syst)) ps(-1), consistent with and more precise than the current world-average value.
|
|
|
Barducci, D., Bertuzzo, E., Caputo, A., Hernandez, P., & Mele, B. (2021). The see-saw portal at future Higgs Factories. J. High Energy Phys., 03(3), 117–32pp.
Abstract: We consider an extension of the Standard Model with two right-handed singlet fermions with mass at the electroweak scale that induce neutrino masses, plus a generic new physics sector at a higher scale Lambda. We focus on the effective operators of lowest dimension d = 5, which induce new production and decay modes for the singlet fermions. We assess the sensitivity of future Higgs Factories, such as FCC-ee, CLIC-380, ILC and CEPC, to the coefficients of these operators for various center of mass energies. We show that future lepton colliders can test the cut-off of the theory up to Lambda similar or equal to 500-1000 TeV, surpassing the reach of future indirect measurements of the Higgs and Z boson widths. We also comment on the possibility of determining the underlying model flavor structure should a New Physics signal be observed, and on the impact of higher dimensional d = 6 operators on the experimental signatures.
|
|
|
LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of the Bs0 -> (DD -/+)-D-*+/- decay. J. High Energy Phys., 03(3), 099–19pp.
Abstract: A search for the B-s(0) -> D*(+/-) D--/+ decay is performed using proton-proton collision data at centre-of-mass energies of 7, 8 and 13TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The decay is observed with a high significance and its branching fraction relative to the B-0 -> D*(+/-) D--/+ decay is measured to be B(B-s(0) -> D*D-+/-(-/+))/B(B-0 -> D*D-+/-(-/+)) = 0.137 +/- 0.017 +/- 0.002 +/- 0.006, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the B-s(0) and B-0 hadronisation fractions.
|
|
|
LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of CP violation in two-body B-(s)(0)-meson decays to charged pions and kaons. J. High Energy Phys., 03(3), 075–43pp.
Abstract: The time-dependent CP asymmetries of B-0 -> pi(+)pi(-) and B-s(0) -> K+K- decays are measured using a data sample of pp collisions corresponding to an integrated luminosity of 1.9 fb(-1), collected with the LHCb detector at a centre-of-mass energy of 13TeV. The results are C-pi pi = 0.311 +/- 0.045 +/- 0.015; S-pi pi = 0.706 +/- 0.042 +/- 0.013; C-KK = 0.164 +/- 0.034 +/- 0.014; S-KK = 0.123 +/- 0.034 +/- 0.015; A(KK)(Delta Gamma) = -0.83 +/- 0.05 +/- 0.09; where the first uncertainties are statistical and the second systematic. The same data sample is used to measure the time-integrated CP asymmetries of B-0 -> K + pi(-) and B-s(0) -> K-pi(+) decays and the results are AB(CP)(B0) = -0.0824 +/- 0.0033 +/- 0.0033; A(CP)(Bs0) = 0.236 +/- 0.013 +/- 0.011. All results are consistent with earlier measurements. A combination of LHCb measurements provides the first observation of time-dependent CP violation in B-s(0) decays.
|
|
|
Qin, W., Dai, L. Y., & Portoles, J. (2021). Two and three pseudoscalar production in e(+)e(-) annihilation and their contributions to (g-2)(mu). J. High Energy Phys., 03(3), 092–38pp.
Abstract: A coherent study of e(+)e(-) annihilation into two (pi(+)pi(-), K+K-) and three (pi(+)pi(-)pi(0), pi(+)pi(-)eta) pseudoscalar meson production is carried out within the framework of resonance chiral theory in energy region E less than or similar to 2 GeV. The work of [L.Y. Dai, J. Portoles, and O. Shekhovtsova, Phys. Rev. D88 (2013) 056001] is revisited with the latest experimental data and a joint analysis of two pseudoscalar meson production. Hence, we evaluate the lowest order hadronic vacuum polarization contributions of those two and three pseudoscalar processes to the anomalous magnetic moment of the muon. We also estimate some higher-order additions led by the same hadronic vacuum polarization. Combined with the other contributions from the standard model, the theoretical prediction differs still by (21.6 +/- 7.4) x 10(-10) (2.9 sigma) from the experimental value.
|
|
|
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.
|
|