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Navarro-Salas, J., & Pla, S. (2021). (F, G)-summed form of the QED effective action. Phys. Rev. D, 103(8), L081702–7pp.
Abstract: We conjecture that the proper-time series expansion of the one-loop effective Lagrangian of quantum electrodynamics can be summed in all terms containing the field-strength invariants F = 1/4F F-mu nu(mu nu) (x), G = 1/4 (F) over tilde F-mu nu(mu nu) (x), including those also possessing derivatives of the electromagnetic field strength. This partial resummation is exactly encapsulated in a factor with the same form as the Heisenberg-Euler Lagrangian density, except that now the electric and magnetic fields can depend arbitrarily on spacetime coordinates. We provide strong evidence for this conjecture, which is proved to sixth order in the proper time. Furthermore, and as a byproduct, we generate some solvable electromagnetic backgrounds. We also discuss the implications for a generalization of the Schwinger formula for pair production induced by nonconstant electric fields. Finally, we briefly outline the extension of these results in the presence of gravity.
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Breso-Pla, V., Falkowski, A., & Gonzalez-Alonso, M. (2021). A(FB) in the SMEFT: precision Z physics at the LHC. J. High Energy Phys., 08(8), 021–27pp.
Abstract: We study the forward-backward asymmetry A(FB) in pp -> l(+)l(-) at the Z peak within the Standard Model Effective Field Theory (SMEFT). We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks, which close a flat direction in the electroweak precision SMEFT fit. Moreover, we show that current A(FB) data is precise enough so that its inclusion in the fit improves significantly LEP bounds even in simple New Physics setups. This demonstrates that the LHC can compete with and complement LEP when it comes to precision measurements of the Z boson properties.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2021). Measurement of single top-quark production in association with a W boson in the single-lepton channel at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 81(8), 720–29pp.
Abstract: The production cross-section of a top quark in association with a W boson is measured using proton-proton collisions at root s = 8 TeV. The dataset corresponds to an integrated luminosity of 20.2 fb(-1,) and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant t (t) over bar background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured crosssection is sigma(tW) = 26 +/- 7 pb, in good agreement with the Standard Model expectation.
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Alves, J. M., Botella, F. J., Branco, G. C., Cornet-Gomez, F., & Nebot, M. (2021). The framework for a common origin of delta(CKM) and delta S-PMN. Eur. Phys. J. C, 81(8), 727–11pp.
Abstract: We analyse a possible connection between CP violations in the quark and lepton sectors, parametrised by the CKM and PMNS phases. If one assumes that CP breaking arises from complexYukawa couplings, both in the quark and lepton sectors, the above connection is not possible in general, sinceYukawa couplings in the two sectors have independent flavour structures. We show that both the CKM and PMNS phases can instead be generated by a vacuum phase in a class of two Higgs doublet models, and in this case a connection may be established. This scenario requires the presence of scalar FCNC at tree level, both in the quark and lepton sectors. The appearance of these FCNC is an obstacle and a blessing. An obstacle since one has to analyse which models are able to conform to the strict experimental limits on FCNC, both in the quark and lepton sectors. A blessing, because this class of models is falsifiable since FCNC arise at a level which can be probed experimentally in the near future, specially in the processes h up arrow e(+/-) t +/- and t -> hc. The connection between CP violations in CKM and PMNS is explicitely illustrated in models with Minimal Flavour Violation.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of New Resonances Decaying to J=Psi K plus and J=Psi phi. Phys. Rev. Lett., 127(8), 082001–11pp.
Abstract: The first observation of exotic states with a new quark content ccus decaying to the J/Psi K+ final state is reported with high significance from an amplitude analysis of the B+-> J/ Psi phi K+ decay. The analysis is carried out using proton-proton collision data corresponding to a total integrated luminosity of 9 fb- 1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The most significant state, Z(cs)(4000)+, has a mass of 4003 +/- 6 (-14) (+4) MeV, a width of 131 +/- 15 +/- 26 MeV, and spin parity J(P) = 1(+), where the quoted uncertainties are statistical and systematic, respectively. A new 1(+) X(4685) state decaying to the J/Psi phi final state is also observed with high significance. In addition, the four previously reported J/Psi phi states are confirmed and two more exotic states, Z(cs) (4220) (+) and X(4630), are observed with significance exceeding 5 standard deviations.
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