|
ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2019). Search for excited electrons singly produced in proton-proton collisions at root s=13 TeV with the ATLAS experiment at the LHC. Eur. Phys. J. C, 79(9), 803–30pp.
Abstract: A search for excited electrons produced in pp collisions at root s = 13 TeV via a contact interaction q (q) over bar -> ee* is presented. The search uses 36.1 fb(-1) of data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron into an electron and a pair of quarks (eq (q) over bar) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a W boson (nu W) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying W boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the pp -> ee* -> eeq (q) over bar and pp -> ee* -> e nu W production cross sections as a function of the excited electron mass m(e)* at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter Lambda of the model as a function of m(e)*. For m(e)* < 0.5 TeV, the lower bound for Lambda is 11 TeV. In the special case of m(e)* = Lambda, the values of m(e)* < 4.8 TeV are excluded. The presented limits on Lambda are more stringent than those obtained in previous searches.
|
|
|
Centelles Chulia, S., Cepedello, R., Peinado, E., & Srivastava, R. (2019). Systematic classification of two-loop d=4 Dirac neutrino mass models and the Diracness-dark matter stability connection. J. High Energy Phys., 10(10), 093–33pp.
Abstract: We provide a complete systematic classification of all two-loop realizations of the dimension four operator for Dirac neutrino masses. Our classification is multi-layered, starting first with a classification in terms of all possible distinct two loop topologies. Then we discuss the possible diagrams for each topology. Model-diagrams originating from each diagram are then considered. The criterion for genuineness is also defined and discussed at length. Finally, as examples, we construct two explicit models which also serve to highlight the intimate connection between the Dirac nature of neutrinos and the stability of dark matter.
|
|
|
Wang, G. Y., Roca, L., & Oset, E. (2019). Discerning the two K-1 (1270) poles in D-0 -> pi(+) VP decay. Phys. Rev. D, 100(7), 074018–10pp.
Abstract: Within the chiral unitary approach, the axial-vector resonance K-1 (1270) has been predicted to manifest a two-pole nature. The lowest pole has a mass of 1195 MeV and a width of 246 MeV and couples mostly to K*pi, and the highest pole has a mass of 1284 MeV and a width of 146 MeV and couples mostly to rho K. We analyze theoretically how this double-pole structure can show up in D-0 -> pi+VP decays by looking at the vector-pseudoscalar (VP) invariant mass distribution for different VP channels, exploiting the fact that each pole couples differently to different VP pairs. We find that the final (K) over bar*pi and rho(K) over tilde channels are sensible to the different poles of the K-1 (1270) resonance and hence are suitable reactions to analyze experimentally the double-pole nature of this resonance.
|
|
|
NEXT Collaboration(Novella, P. et al), Palmeiro, B., Sorel, M., Uson, A., Alvarez, V., Benlloch-Rodriguez, J. M., et al. (2019). Radiogenic backgrounds in the NEXT double beta decay experiment. J. High Energy Phys., 10(10), 051–26pp.
Abstract: Natural radioactivity represents one of the main backgrounds in the search for neutrinoless double beta decay. Within the NEXT physics program, the radioactivity- induced backgrounds are measured with the NEXT-White detector. Data from 37.9 days of low-background operations at the Laboratorio Subterraneo de Canfranc with xenon depleted in Xe-136 are analyzed to derive a total background rate of (0.84 +/- 0.02) mHz above 1000 keV. The comparison of data samples with and without the use of the radon abatement system demonstrates that the contribution of airborne-Rn is negligible. A radiogenic background model is built upon the extensive radiopurity screening campaign conducted by the NEXT collaboration. A spectral fit to this model yields the specific contributions of Co-60, K-40, Bi-214 and Tl-208 to the total background rate, as well as their location in the detector volumes. The results are used to evaluate the impact of the radiogenic backgrounds in the double beta decay analyses, after the application of topological cuts that reduce the total rate to (0.25 +/- 0.01) mHz. Based on the best-fit background model, the NEXT-White median sensitivity to the two-neutrino double beta decay is found to be 3.5 sigma after 1 year of data taking. The background measurement in a Q(beta beta)+/- 100 keV energy window validates the best-fit background model also for the neutrinoless double beta decay search with NEXT-100. Only one event is found, while the model expectation is (0.75 +/- 0.12) events.
|
|
|
Beltran-Palau, P., Ferreiro, A., Navarro-Salas, J., & Pla, S. (2019). Breaking of adiabatic invariance in the creation of particles by electromagnetic backgrounds. Phys. Rev. D, 100(8), 085014–12pp.
Abstract: Particles are spontaneously created from the vacuum by time-varying gravitational or electromagnetic backgrounds. It has been proven that the particle number operator in an expanding universe is an adiabatic invariant. In this paper we show that, in some special cases, the expected adiabatic invariance of the particle number fails in presence of electromagnetic backgrounds. In order to do this, we consider as a prototype a Sauter-type electric pulse. Furthermore, we also show a close relation between the breaking of the adiabatic invariance and the emergence of the axial anomaly.
|
|
|
Delhom, A., Lobo, I. P., Olmo, G. J., & Romero, C. (2019). A generalized Weyl structure with arbitrary non-metricity. Eur. Phys. J. C, 79(10), 878–9pp.
Abstract: A Weyl structure is usually defined by an equivalence class of pairs (g, omega) related by Weyl transformations, which preserve the relation del g = omega circle times g, where g and omega denote the metric tensor and a 1-form field. An equivalent way of defining such a structure is as an equivalence class of conformally related metrics with a unique affine connection Gamma((omega)), which is invariant under Weyl transformations. In a standard Weyl structure, this unique connection is assumed to be torsion-free and have vectorial non-metricity. This second view allows us to present two different generalizations of standard Weyl structures. The first one relies on conformal symmetry while allowing for a general non-metricity tensor, and the other comes from extending the symmetry to arbitrary (disformal) transformations of the metric.
|
|
|
Hernandez, P., Pena, C., & Romero-Lopez, F. (2019). Large Nc scaling of meson masses and decay constants. Eur. Phys. J. C, 79(10), 865–13pp.
Abstract: We perform an ab initio calculation of the Nc scaling of the low-energy couplings of the chiral Lagrangian of low-energy strong interactions, extracted from the mass dependence of meson masses and decay constants. We compute these observables on the lattice with four degenerate fermions, Nf=4, and varying number of colours, Nc=3-6, at a lattice spacing of a similar or equal to 0.075 fm. We find good agreement with the expected Nc scaling and measure the coefficients of the leading and subleading terms in the large Nc expansion. From the subleading Nc corrections, we can also infer the Nf dependence, that we use to extract the value of the low-energy couplings for different values of Nf. We find agreement with previous determinations at Nc=3 and Nf=2,3 and also, our results support a strong paramagnetic suppression of the chiral condensate in moving from Nf=2 to Nf=3.
|
|
|
Wang, E., Xie, J. J., Geng, L. S., & Oset, E. (2019). The X(4140) and X(4160) resonances in the e(+)e(-) -> gamma J/psi phi reaction. Chin. Phys. C, 43(11), 113101–10pp.
Abstract: We investigate the J/psi phi invariant mass distribution in the e(+)e(-) -> gamma J/psi phi reaction at a center-of-mass energy of root s = 4.6 GeV measured by the BESIII collaboration, which concluded that no significant signals were observed for e(+)e(-) -> gamma J/psi phi because of the low statistics. We show, however, that the J/psi phi invariant mass distribution is compatible with the existence of the X(4140) state, appearing as a peak, and a strong cusp structure at the D-s*(D) over bar (s)* threshold, resulting from the molecular nature of the X(4160) state, which provides a substantial contribution to the reaction. This is consistent with our previous analysis of the B+ -> J psi phi K+ decay measured by the LHCb collaboration. We strongly suggest further measurements of this process with more statistics to clarify the nature of the X(4140) and X(4160) resonances.
|
|
|
NEXT Collaboration(Renner, J. et al), Kekic, M., Martinez-Lema, G., Alvarez, V., Benlloch-Rodriguez, J. M., Carcel, S., et al. (2019). Energy calibration of the NEXT-White detector with 1% resolution near Q(beta beta) of Xe-136. J. High Energy Phys., 10(10), 230–13pp.
Abstract: Excellent energy resolution is one of the primary advantages of electroluminescent high-pressure xenon TPCs. These detectors are promising tools in searching for rare physics events, such as neutrinoless double-beta decay (beta beta 0 nu), which require precise energy measurements. Using the NEXT-White detector, developed by the NEXT (Neutrino Experiment with a Xenon TPC) collaboration, we show for the first time that an energy resolution of 1% FWHM can be achieved at 2.6 MeV, establishing the present technology as the one with the best energy resolution of all xenon detectors for beta beta 0 nu searches.
|
|
|
T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Fernandez, P., Izmaylov, A., & Novella, P. (2019). Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors. Prog. Theor. Exp. Phys., (9), 093C02–30pp.
Abstract: We report a measurement of the flux-integrated v(mu) charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are sigma(H2O)(CC) = (0.840 +/- 0.010(stat.)(0.08)(+0.10)(syst.)) x 10 (38) cm(2)/nucleon, sigma(CH)(CC) = (0.817 +/- 0.007(stat.)(0.08)(+0.11)(syst.)) x 10 (38) cm(2)/nucleon, and sigma(Fe)(CC) = (0.859 +/- 0.003(stat.)(0.10)(+0.12)(syst.)) x 10 (38) cm(2)/nucleon, respectively, for a restricted phase space of induced muons: theta(mu) < 45 degrees and p(mu) >0.4 GeV/c in the laboratory frame. The measured cross section ratios are sigma(H2O)(CC)/sigma(CH)(CC) = 1.028 +/- 0.016(stat.) +/- 0.053(syst.), sigma(Fe)(CC)/sigma(H2O)(CC) = 1.023 +/- 0.012(stat.) +/- 0.058(syst.), and sigma(Fe)(CC)/sigma(CH)(CC) = 1.049 +/- 0.010(stat.) +/- 0.043(syst.). These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.
|
|