LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Isospin Amplitudes in Lambda(0)(b) -> J/psi Lambda (Sigma(0)) and Xi(0)(b)-> J/psi Xi(0) (Lambda) Decays. Phys. Rev. Lett., 124(11), 111802–11pp.
Abstract: Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions and allow searches for physics beyond the standard model. We present the first results on isospin amplitudes in b-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb(-1), collected with the LHCb detector in pp collisions at center of mass energies of 7, 8, and 13 TeV. The isospin amplitude ratio vertical bar A(1) (Delta(0)(b) -> J/psi(Sigma(0)) /A(0) (Delta(0)(b) -> J/psi Lambda)vertical bar, where the subscript on A indicates the final-state isospin, is measured to be less than 1/21.8 at 95% confidence level. The Cabibbo suppressed Xi(0)(b) -> J/psi Lambda decay is observed for the first time, allowing for the measurement vertical bar A(0) (Xi(0)(b) -> J/psi Lambda) / A(1/2 )(Xi(0)(b) -> J/psi Xi(0))vertical bar = 0.37 +/- 0.06 +/- 0.02, where the uncertainties are statistical and systematic, respectively.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Fernandez, P., Izmaylov, A., & Novella, P. (2020). First combined measurement of the muon neutrino and antineutrino charged-current cross section without pions in the final state at T2K. Phys. Rev. D, 101(11), 112001–44pp.
Abstract: This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8 x 10(20) and 6.3 x 10(20) protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference, and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.
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Gisbert, H., & Ruiz Vidal, J. (2020). Improved bounds on heavy quark electric dipole moments. Phys. Rev. D, 101(11), 115010–5pp.
Abstract: New bounds on the electric dipole moment (EDM) of charm and bottom quarks are derived using the stringent limits on their chromo-EDMs. The new limits, vertical bar d(c)vertical bar < 1.5 x 10(-21) e cm and vertical bar d(b)vertical bar < 1.2 x 10(-20) e cm, improve the previous ones by about 3 orders of magnitude. These indirect bounds have implications for different models of new physics, including two-Higgs-doublet, leptoquarks, and supersymmetry models.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2020). Search for lepton-flavor-violating decays D-0 -> X(0)e(+/-)mu(-/+). Phys. Rev. D, 101(11), 112003–11pp.
Abstract: We present a search for seven lepton-flavor-violating neutral charm meson decays of the type D-0 -> X(0)e(+/-)mu(-/+), where X-0 represents a pi(0), K-S(0), (K) over bar*(0), rho(0), phi, omega, or eta meson. The analysis is based on 468 fb(-1) of e(+)e(-) annihilation data collected at or close to the Upsilon(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signals are observed, and we establish 90% confidence level upper limits on the branching fractions in the range (5.0-22.5) x 10(-7). The limits are between 1 and 2 orders of magnitude more stringent than previous measurements.
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Lu, J. N., Liu, X. G., & Ding, G. J. (2020). Modular symmetry origin of texture zeros and quark-lepton unification. Phys. Rev. D, 101(11), 115020–27pp.
Abstract: The even-weight modular forms of level N can be arranged into the common irreducible representations of the inhomogeneous finite modular group Gamma(N) and the homogeneous finite modular group Gamma(N)' which is the double covering of Gamma(N) , and the odd-weight modular forms of level N transform in the new representations of Gamma(N)'. We find that the above structure of modular forms can naturally generate texture zeros of the fermion mass matrices if we properly assign the representations and weights of the matter fields under the modular group. We perform a comprehensive analysis for the Gamma(3)' congruent to T' modular symmetry. The three generations of left-handed quarks are assumed to transform as a doublet and a singlet of T', and we find six possible texture-zero structures of the quark mass matrix up to row and column permutations. We present five benchmark quark models which can produce very good fits to the experimental data. These quark models are further extended to include the lepton sector, and the resulting models can give a unified description of both quark and lepton masses and flavor mixing simultaneously, although they contain a smaller number of free parameters than the observables.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Novella, P. (2020). Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K. Phys. Rev. D, 101(11), 112004–32pp.
Abstract: This paper reports the first simultaneous measurement of the double differential muon neutrino chargedcurrent cross section on oxygen and carbon without pions in the final state as a function of the outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models' ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillation analyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV. The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.
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de Anda, F. J., Nath, N., Valle, J. W. F., & Vaquera-Araujo, C. A. (2020). Probing the predictions of an orbifold theory of flavor. Phys. Rev. D, 101(11), 116012–8pp.
Abstract: We examine the implications of a recently proposed theory of fermion masses and mixings in which an A(4) family symmetry emerges from orbifold compactification. We analyze two variant schemes concerning their predictions for neutrino oscillations, neutrinoless double-beta decay, and the golden quark-lepton unification mass relation. We find that upcoming experiments DUNE as well as LEGEND and nEXO offer good chances of exploring a substantial region of neutrino parameters.
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Mandal, S., Srivastava, R., & Valle, J. W. F. (2020). Consistency of the dynamical high-scale type-I seesaw mechanism. Phys. Rev. D, 101(11), 115030–15pp.
Abstract: We analyze the consistency of electroweak breaking within the simplest high-scale SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) type-I seesaw mechanism. We derive the full two-loop renormalization group equations of the relevant parameters, including the quartic Higgs self-coupling of the Standard Model. For the simplest case of bare “right-handed” neutrino mass terms we find that, with large Yukawa couplings, the Higgs quartic self-coupling becomes negative much below the seesaw scale, so that the model may be inconsistent even as an effective theory. We show, however, that the “dynamical” type-I high-scale seesaw with spontaneous lepton number violation has better stability properties.
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Penalva, N., Hernandez, E., & Nieves, J. (2020). Hadron and lepton tensors in semileptonic decays including new physics. Phys. Rev. D, 101(11), 113004–24pp.
Abstract: We extend our general framework for semileptonic decay, originally introduced in N. Penalva et al. [Phys. Rev. D 100, 113007 (2019)], with the addition of new physics (NP) tensor terms. In this way, all the NP effective Hamiltonians that are considered in lepton flavor universality violation (LFUV) studies have now been included. Those are left and right vector and scalar NP Hamiltonians and the NP tensor one. Besides, we now also give general expressions that allow for complex Wilson coefficients. The scheme developed is totally general and it can be applied to any charged current semileptonic decay, involving any quark flavors or initial and final hadron states. We show that all the hadronic input, including NP effects, can be parametrized in terms of 16 Lorentz scalar structure functions, constructed out of the NP complex Wilson coefficients and the genuine hadronic responses, with the latter determined by the matrix elements of the involved hadron operators. In the second part of this work, we use this formalism to obtain the complete NP effects in the Ab Acr(/ semileptonic decay, where LFUV, if finally confirmed, is also expected to be seen. We- stress the relevance of the center of mass (CM) d2F/ (dwd cos 0i) and laboratory (LAB) d2F/(dwdE,) differential decay widths, with (o the product of the hadron four-velocities, Oe the angle made by the three -momenta of the charged lepton and the final hadron in the 11/- CM frame and the charged lepton energy in the decaying hadron rest frame. While models with very different strengths in the NP terms give the same differential d17 do) and total decay widths for this decay, they predict very different numerical results for some of the cos (.),, and E coefficient -functions that determine the above two distributions. Thus, the combined analysis of the CM d2F1(dcodcos0,,) and LAB d21'/(doidE,.) differential decay widths will help clarifying what kind of NP is a better candidate in order to explain LFUV.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector. J. High Energy Phys., 11(11), 005–41pp.
Abstract: A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton final states at the LHC to use a background estimate from the data. The data, corresponding to an integrated luminosity of 139 fb(-1), were recorded by the ATLAS experiment in proton-proton collisions at a center-of-mass energy of root s= 13 TeV during Run 2 of the Large Hadron Collider. The benchmark signal signature is a two-quark and two-lepton contact interaction, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data in a mass region below the region of interest. It is then extrapolated to a high-mass signal region to obtain the expected background there. No significant deviation from the expected background is observed in the data. Upper limits at 95% CL on the number of events and the visible cross-section times branching fraction for processes involving new physics are provided. Observed (expected) 95% CL lower limits on the contact interaction energy scale reach 35.8 (37.6) TeV.
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