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Babiano, V., Caballero, L., Calvo, D., Ladarescu, I., Olleros, P., & Domingo-Pardo, C. (2019). gamma-Ray position reconstruction in large monolithic LaCl3(Ce) crystals with SiPM readout. Nucl. Instrum. Methods Phys. Res. A, 931, 1–22.
Abstract: We report on the spatial response characterization of large LaCl3(Ce) monolithic crystals optically coupled to 8 x 8 pixel silicon photomultiplier (SiPM) sensors. A systematic study has been carried out for 511 keV gamma-rays using three different crystal thicknesses of 10 mm, 20 mm and 30 mm, all of them with planar geometry and a base size of 50 x 50 mm(2). In this work we investigate and compare two different approaches for the determination of the main gamma-ray hit location. On one hand, methods based on the fit of an analytical model for the scintillation light distribution provide the best results in terms of linearity and field of view, with spatial resolutions close to similar to 1 mm FWHM. On the other hand, position reconstruction techniques based on neural networks provide similar linearity and field-of-view, becoming the attainable spatial resolution similar to 3 mm FWHM. For the third space coordinate z or depth-of-interaction we have implemented an inverse linear calibration approach based on the cross-section of the measured scintillation-light distribution at a certain height. The detectors characterized in this work are intended for the development of so-called Total Energy Detectors with Compton imaging capability (i-TED), aimed at enhanced sensitivity and selectivity measurements of neutron capture cross sections via the time-of-flight (TOF) technique.
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Gelmini, G. B., Takhistov, V., & Witte, S. J. (2019). Geoneutrinos in large direct detection experiments. Phys. Rev. D, 99(9), 093009–11pp.
Abstract: Geoneutrinos can provide a unique insight into Earth's interior, its central engine, and its formation history. We study the detection of geoneutrinos in large direct detection experiments, which has been considered nonfeasible. We compute the geoneutrino-induced electron and nuclear recoil spectra in different materials, under several optimistic assumptions. We identify germanium as the most promising target element due to the low nuclear recoil energy threshold that could be achieved. The minimum exposure required for detection would be O(10) ton-years. The realistic low thresholds achievable in germanium and silicon permit the detection of K-40 geoneutrinos. These are particularly important to determining Earth's formation history, but they are below the kinematic threshold of inverse beta decay, the detection process used in scintillator-based experiments.
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Beltran Jimenez, J., & Delhom, A. (2019). Ghosts in metric-affine higher order curvature gravity. Eur. Phys. J. C, 79(8), 656–7pp.
Abstract: We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain how these pathologies can be avoided either by imposing a projective symmetry or additional constraints in the gravity sector. Our results put forward that higher order curvature gravity theories generally remain pathological in the metric-affine (and hybrid) formalisms and highlight the key importance of the projective symmetry and/or additional constraints for their physical viability and, by extension, of general metric-affine theories.
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Murgui, C., Peñuelas, A., Jung, M., & Pich, A. (2019). Global fit to b -> c tau nu transitions. J. High Energy Phys., 09(9), 103–45pp.
Abstract: We perform a general model-independent analysis of b -> c tau(nu) over bar (tau) transitions, including measurements of R-D, R-D*, their q(2) differential distributions, the recently measured longitudinal D* polarization F-L(D)*, and constraints from the B-c -> tau(nu) over bar (tau) lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected b -> c tau(nu) over bar (tau) observables, such as the baryonic transition Lambda(b) -> Lambda(c)tau(nu) over bar (tau), the ratio R-J/psi, the forward-backward asymmetries A(FB)(D()*()), the tau polarization asymmetries P-tau(D()*()), and the longitudinal D* polarization fraction F-L(D)*. The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary R-D(*) measurement by the Belle collaboration.
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Chiang, C. W., Cottin, G., & Eberhardt, O. (2019). Global fits in the Georgi-Machacek model. Phys. Rev. D, 99(1), 015001–21pp.
Abstract: Off the beaten track of scalar singlet and doublet extensions of the Standard Model, triplets combine an interesting LHC phenomenology with an explanation for neutrino masses. The Georgi-Machacek model falls into this category, but it has never been fully explored in a global fit. We use the HEPfit package to combine recent experimental Higgs data with theoretical constraints and obtain strong limits on the mixing angles and mass differences between the heavy new scalars as well as their decay widths. We also find that the current signal strength measurements allow for a Higgs to vector boson coupling with an opposite sign to the Standard Model, but this possibility can be ruled out by the lack of direct evidence for heavy Higgs states. For these hypothetical particles, we identify the dominant decay channels and extract bounds on their branching ratios from the global fit, which can be used to single out the decay patterns relevant for the experimental searches.
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Nascimento, J. R., Olmo, G. J., Porfirio, P. J., Petrov, A. Y., & Soares, A. R. (2019). Global monopole in Palatini f(R) gravity. Phys. Rev. D, 99(6), 064053–11pp.
Abstract: We consider the space-time metric generated by a global monopole in an extension of general relativity (GR) of the form f(R) = R – lambda R-2. The theory is formulated in the metric-affine (or Palatini) formalism, and exact analytical solutions are obtained. For lambda < 0, one finds that the solution has the same characteristics as the Schwarzschild black hole with a monopole charge in Einstein's GR. For lambda > 0, instead, the metric is more closely related to the Reissner-Nordstrom metric with a monopole charge and, in addition, it possesses a wormhole-like structure that allows for the geodesic completeness of the spacetime. Our solution recovers the expected limits when lambda = 0 and also at the asymptotic far limit. The angular deflection of light in this space-time in the weak field regime is also calculated.
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Baglio, J., Campanario, F., Glaus, S., Muhlleitner, M., Spira, M., & Streicher, J. (2019). Gluon fusion into Higgs pairs at NLO QCD and the top mass scheme. Eur. Phys. J. C, 79(6), 459–9pp.
Abstract: We present the calculation of the full next-to-leading order (NLO) QCD corrections to Higgs boson pair production via gluon fusion at the LHC, including the exact top-mass dependence in the two-loop virtual and one-loop real corrections. This is the first independent cross-check of the NLO QCD corrections presented in the literature before. Our calculation relies on numerical integrations of Feynman integrals, stabilised with integration-by-parts and a Richardson extrapolation to the narrow width approximation. We present results for the total cross section as well as for the invariant Higgs-pair-mass distribution at the LHC, including for the first time a study of the uncertainty due to the scheme and scale choice for the top mass in the loops.
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Aguilar, A. C., Ferreira, M. N., Figueiredo, C. T., & Papavassiliou, J. (2019). Gluon mass scale through nonlinearities and vertex interplay. Phys. Rev. D, 100(9), 094039–19pp.
Abstract: We present a novel analysis of the gluon gap equation, where its full nonlinear structure is duly taken into account. In particular, while in previous treatments the linearization of this homogeneous integral equation introduced an indeterminacy in the scale of the corresponding mass, the current approach determines it uniquely, once the value of the gauge coupling at a given renormalization point is used as input. A crucial ingredient for this construction is the “kinetic term” of the gluon propagator, whose form is not obtained from the complicated equation governing its evolution, but is rather approximated by suitable initial Ansatze, which are subsequently improved by means of a systematic iterative procedure. The multiplicative renormalization of the central equation is carried out following an approximate method, which is extensively employed in the studies of the standard quark gap equation. This approach amounts to the effective substitution of the vertex renormalization constants by kinematically simplified form factors of the three- and four-gluon vertices. The resulting numerical interplay, exemplified by the infrared suppression of the three-gluon vertex and the mild enhancement of the four-gluon vertex, is instrumental for obtaining positive-definite and monotonically decreasing running gluon masses. The resulting gluon propagators, put together from the gluon masses and kinetic terms obtained with this method, match rather accurately the data obtained from large-volume lattice simulations.
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Cirigliano, V., Falkowski, A., Gonzalez-Alonso, M., & Rodriguez-Sanchez, A. (2019). Hadronic tau Decays as New Physics Probes in the LHC Era. Phys. Rev. Lett., 122(22), 221801–7pp.
Abstract: We analyze the sensitivity of hadronic tau decays to nonstandard interactions within the model-independent framework of the standard model effective field theory. Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the tau -> pi pi nu(tau) channel representing an unexpected powerful new physics probe. We find that the ratios of nonstandard couplings to the Fermi constant are bound at the subpercent level. These bounds are complementary to the ones from electroweak precision observables and pp -> tau nu(tau) measurements at the LHC. The combination of tau decay and LHC data puts tighter constraints on lepton universality violation in the gauge boson-lepton vertex corrections.
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FCC Collaboration(Abada, A. et al), Aguilera-Verdugo, J. J., Hernandez, P., Ramirez-Uribe, N. S., Renteria-Olivo, A. E., Rodrigo, G., et al. (2019). HE-LHC: The High-Energy Large Hadron Collider Future Circular Collider Conceptual Design Report Volume 4. Eur. Phys. J.-Spec. Top., 228(5), 1109–1382.
Abstract: In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.
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