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Dai, L. R., Yu, Q. X., & Oset, E. (2019). Triangle singularity in tau(-) -> nu(tau)pi(-) f(0)(980) (a(0)(980)) decays. Phys. Rev. D, 99(1), 016021–13pp.
Abstract: We study the triangle mechanism for the decay tau(-) -> nu(tau)pi(-) f(0)(980) with the f(0)(980) decaying into pi(+) pi(-). The mechanism for this process is initiated by tau(-) -> nu K-tau*(0) K- followed by the K*(0) decay into pi K--(+), then the K- K+ produce the f(0)(980) through a triangle loop containing K* K+ K- which develops a singularity around 1420 MeV in the pi f(0)(980) invariant mass. We find a narrow peak in the pi(+) pi(-) invariant mass distribution, which originates from the f(0)(980) amplitude. Similarly, we also study the triangle mechanism for the decay tau -> nu pi(-) a(0)(980), with the a(0)(980) decaying into pi(0)eta.The formalism leads to final branching ratios for pi(-) f(0)(980) and pi(-) a(0)(980) of the order of 4 x 10(-4) and 7 x 10(-5), respectively, which are within present measurable range. Experimental verification of these predictions will shed light on the nature of the scalar mesons and on the origin of the “a(1)(1420)” peak observed in other reactions.
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Molina, R., & Oset, E. (2020). Triangle singularity in B- ->K- X(3872); X ->pi 0 pi+ pi- and the X(3872) mass. Eur. Phys. J. C, 80(5), 451–9pp.
Abstract: We evaluate the contribution to the X(3872) width from a triangle mechanism in which the X decays into D0D<overbar></mml:mover>0-cc, then the D0(D<overbar></mml:mover>0) decays into D0 pi 0 (D<overbar></mml:mover>0 pi 0) and the D0D<overbar></mml:mover>0 fuse to produce pi+pi-. This mechanism produces an asymmetric peak from a triangle singularity in the pi+pi- invariant mass with a shape very sensitive to the X mass. We evaluate the branching ratios for a reaction where this effect can be seen in the B--> K-pi 0 pi+pi- reaction and show that the determination of the peak in the invariant mass distribution of pi <mml:mo>+pi <mml:mo>- is all that is needed to determine the X mass. Given the present uncertainties in the X mass, which do not allow to know whether the D<mml:mo>0<mml:mover accent=“true”>D<mml:mo stretchy=“false”><overbar></mml:mover>0 state is bound or not, measurements like the one suggested here should be most welcome to clarify this issue.
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Beltran, R., Cepedello, R., & Hirsch, M. (2023). Tree-level UV completions for NRSMEFT d=6 and d=7 operators. J. High Energy Phys., 08(8), 31pp.
Abstract: We study ultra-violet completions for operators in standard model effective field theory extended with right-handed neutrinos (NRSMEFT). Using a diagrammatic method, we generate systematically lists of possible tree-level completions involving scalars, fermions or vectors for all operators at d = 6 and d = 7, which contain at least one right-handed neutrino. We compare our lists of possible UV models to the ones found for pure SMEFT. We also discuss how the observation of LNV processes via NRSMEFT operators at the LHC can be related to Majorana neutrino masses of the standard model neutrinos.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector. Eur. Phys. J. C, 80(1), 73–31pp.
Abstract: The azimuthal anisotropy of charged particles produced in sNN=8.16TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb-1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3\, extracted using two-particle correlations with a non-flow template fit procedure, are presented as a function of particle transverse momentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pTintervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9-50 GeV are not explained within current theoretical frameworks. In the pTrange 2-9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.
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Beltran-Palau, P., Navarro-Salas, J., & Pla, S. (2019). Translational anomaly of chiral fermions in two dimensions. Phys. Rev. D, 99(10), 105008–5pp.
Abstract: It is well known that a quantized two-dimensional Weyl fermion coupled to gravity spoils general covariance and breaks the covariant conservation of the energy-momentum tensor. In this brief article, we point out that the quantum conservation of the momentum can also fail in flat spacetime, provided the Weyl fermion is coupled to a time-varying homogeneous electric field. This signals a quantum anomaly of the space-translation symmetry, which has not been highlighted in the literature so far.
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