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Aguilar-Saavedra, J. A., & Bernabeu, J. (2016). Breaking down the entire W boson spin observables from its decay. Phys. Rev. D, 93(1), 011301–6pp.
Abstract: We discuss the eight independent spin observables for the W boson in terms of its vector and tensor polarizations and identify the angular distributions and asymmetries able to separate them in collider experiments. The results are applied to the study of polarized top quark decays and diboson resonances. These novel observables are of great value for disentangling new physics mechanisms in W boson production.
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Gonzalez, M., Kovalenko, S. G., & Hirsch, M. (2016). QCD running in neutrinoless double beta decay: Short-range mechanisms. Phys. Rev. D, 93(1), 013017–11pp.
Abstract: The decay rate of neutrinoless double beta (0 nu beta beta) decay contains terms from heavy particle exchange, which lead to dimension-9 (d = 9) six fermion operators at low energies. Limits on the coefficients of these operators have been derived previously neglecting the running of the operators between the high scale, where they are generated, and the energy scale of 0 nu beta beta decay, where they are measured. Here we calculate the leading-order QCD corrections to all possible d = 9 operators contributing to the 0 nu beta beta amplitude and use renormalization group running to calculate 1-loop improved limits. Numerically, QCD running dramatically changes some limits by factors of the order of or larger than typical uncertainties in nuclear matrix element calculations. For some specific cases, operator mixing in the running changes limits even by up to 3 orders of magnitude. Our results can be straightforwardly combined with new experimental limits or improved nuclear matrix element calculations to rederive updated limits on all short-range contributions to 0 nu beta beta decay.
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KM3NeT Collaboration(Adrian-Martinez, S. et al), Barrios-Marti, J., Calvo Diaz-Aldagalan, D., Hernandez-Rey, J. J., Real, D., Zornoza, J. D., et al. (2016). The prototype detection unit of the KM3NeT detector. Eur. Phys. J. C, 76(2), 54–12pp.
Abstract: A prototype detection unit of the KM3NeT deep-sea neutrino telescope has been installed at 3500m depth 80 km offshore the Italian coast. KM3NeT in its final configuration will contain several hundreds of detection units. Each detection unit is a mechanical structure anchored to the sea floor, held vertical by a submerged buoy and supporting optical modules for the detection of Cherenkov light emitted by charged secondary particles emerging from neutrino interactions. This prototype string implements three optical modules with 31 photomultiplier tubes each. These optical modules were developed by the KM3NeT Collaboration to enhance the detection capability of neutrino interactions. The prototype detection unit was operated since its deployment in May 2014 until its decommissioning in July 2015. Reconstruction of the particle trajectories from the data requires a nanosecond accuracy in the time calibration. A procedure for relative time calibration of the photomultiplier tubes contained in each optical module is described. This procedure is based on the measured coincidences produced in the sea by the K background light and can easily be expanded to a detector with several thousands of optical modules. The time offsets between the different optical modules are obtained using LED nanobeacons mounted inside them. A set of data corresponding to 600 h of livetime was analysed. The results show good agreement with Monte Carlo simulations of the expected optical background and the signal from atmospheric muons. An almost background-free sample of muons was selected by filtering the time correlated signals on all the three optical modules. The zenith angle of the selected muons was reconstructed with a precision of about 3 degrees.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Search for an additional, heavy Higgs boson in the H → ZZ decay channel at root s=8 TeV in pp collision data with the ATLAS detector. Eur. Phys. J. C, 76(1), 45–42pp.
Abstract: A search is presented for a high-mass Higgs boson in several decay modes using the ATLAS detector at the CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb. The results of the search are interpreted in the scenario of a heavy Higgs boson with a width that is small compared with the experimental mass resolution. The Higgs boson mass range considered extends up to for all four decay modes and down to as low as 140 , depending on the decay mode. No significant excess of events over the Standard Model prediction is found. A simultaneous fit to the four decay modes yields upper limits on the production cross-section of a heavy Higgs boson times the branching ratio to boson pairs. 95 % confidence level upper limits range from 0.53 pb at GeV to 0.008 pb at GeV for the gluon-fusion production mode and from 0.31 pb at GeV to 0.009 pb at GeV for the vector-boson-fusion production mode. The results are also interpreted in the context of Type-I and Type-II two-Higgs-doublet models.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2016). Upper bound on neutrino mass based on T2K neutrino timing measurements. Phys. Rev. D, 93(1), 012006–15pp.
Abstract: The Tokai to Kamioka (T2K) long-baseline neutrino experiment consists of a muon neutrino beam, produced at the J-PARC accelerator, a near detector complex and a large 295-km-distant far detector. The present work utilizes the T2K event timing measurements at the near and far detectors to study neutrino time of flight as a function of derived neutrino energy. Under the assumption of a relativistic relation between energy and time of flight, constraints on the neutrino rest mass can be derived. The sub-GeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/c(2) range. We study the distribution of relative arrival times of muon and electron neutrino candidate events at the T2K far detector as a function of neutrino energy. The 90% C.L. upper limit on the mixture of neutrino mass eigenstates represented in the data sample is found to be m(v)(2) < 5.6 MeV2/c(4).
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2016). Observation of (B)over-bar -> D-(*()) pi(+)pi(-)l(-)(nu)over-bar Decays in e(+)e(-) Collisions at the Upsilon(4S) Resonance. Phys. Rev. Lett., 116(4), 041801–7pp.
Abstract: We report on measurements of the decays of (B) over bar mesons into the semileptonic final states (B) over bar -> D-(*())pi(+)pi(-)l(-)(nu) over bar, where D-(*()) represents a D or D* meson and l(-) is an electron or a muon. These measurements are based on 471 x 10(6) B (B) over bar pairs recorded with the BABAR detector at the SLAC asymmetric B factory PEP-II. We determine the branching fraction ratios R-pi+pi-(()*()) = B((B) over bar -> D-(*())pi(+)pi(-)l(-)(nu) over bar /B (B) over bar -> D-(*())l(-)(nu) over bar) using events in which the second B meson is fully reconstructed. We find R pi+pi- = 0.067 +/- 0.010 +/- 0.008 and R pi+pi-* = 0.019 +/- 0.005 +/- 0.004, where the first uncertainty is statistical and the second is systematic. Based on these results and assuming isospin invariance, we estimate that (B) over bar -> D-(*())pi pi l (nu) over bar decays, where pi denotes either a pi(+/-) and pi(0) meson, account for up to half the difference between the measured inclusive semileptonic branching fraction to charm hadrons and the corresponding sum of previously measured exclusive branching fractions.
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Song, N. Q., Garcia, R. B., Gomez-Cadenas, J. J., Gonzalez-Garcia, M. C., Conde, A. P., & Taron, J. (2016). Conditions for statistical determination of the neutrino mass spectrum in radiative emission of neutrino pairs in atoms. Phys. Rev. D, 93(1), 013020–10pp.
Abstract: The photon spectrum in macrocoherent atomic deexcitation via radiative emission of neutrino pairs has been proposed as a sensitive probe of the neutrino mass spectrum, capable of competing with conventional neutrino experiments. In this paper we revisit this interesting proposal in order to quantify the requirements for statistical determination of some of the properties of the neutrino spectrum, in particular, the neutrino mass scale and the mass ordering. Our results are shown as the product of the experimental lifetime, the target volume, and the number density of atoms which have to be set in a coherence state with a given electric field in the target, needed for determination of these properties with a given confidence level.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Constraints on non-Standard Model Higgs boson interactions in an effective Lagrangian using differential cross sections measured in the H ->gamma gamma decay channel at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 753, 69–85.
Abstract: The strength and tensor structure of the Higgs boson's interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions that lead to changes in the kinematic properties of the Higgs boson and associated jet spectra with respect to the Standard Model. The parameters of the effective Lagrangian are probed using a fit to five differential cross sections previously measured by the ATLAS experiment in the H ->gamma gamma decay channel with an integrated luminosity of 20.3 fb(-1) at root s= 8 TeV. Inorder to perform a simultaneous fit to the five distributions, the statistical correlations between them are determined by re-analysing the H ->gamma gamma candidate events in the proton-proton collision data. No significant deviations from the Standard Model predictions are observed and limits on the effective Lagrangian parameters are derived. The statistical correlations are made publicly available to allow for future analysis of theories with non-Standard Model interactions.
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Cañas, B. C., Miranda, O. G., Parada, A., Tortola, M., & Valle, J. W. F. (2016). Updating neutrino magnetic moment constraints. Phys. Lett. B, 753, 191–198.
Abstract: In this paper we provide an updated analysis of the neutrino magnetic moments (NMMs), discussing both the constraints on the magnitudes of the three transition moments Lambda(i) and the role of the CP violating phases present both in the mixing matrix and in the NMM matrix. The scattering of solar neutrinos off electrons in Borexino provides the most stringent restrictions, due to its robust statistics and the low energies observed, below 1 MeV. Our new limit on the effective neutrino magnetic moment which follows from the most recent Borexino data is 3.1 x 10(-11) mu(B) at 90% C.L. This corresponds to the individual transition magnetic moment constraints: vertical bar Lambda(1)vertical bar <= 5.6 x10(-11)mu(B), vertical bar Lambda(2)vertical bar <= 4.0 x10(-11)mu(B), and vertical bar Lambda(3)vertical bar <= 3.1 x10(-11)mu B(90% C. L.), irrespective of any complex phase. Indeed, the incoherent admixture of neutrino mass eigenstates present in the solar flux makes Borexino insensitive to the Majorana phases present in the NMM matrix. For this reason we also provide a global analysis including the case of reactor and accelerator neutrino sources, presenting the resulting constraints for different values of the relevant CP phases. Improved reactor and accelerator neutrino experiments will be needed in order to underpin the full profile of the neutrino electromagnetic properties.
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Das, D., Dey, U. K., & Pal, P. B. (2016). S-3 symmetry and the quark mixing matrix. Phys. Lett. B, 753, 315–318.
Abstract: We impose an S-3 symmetry on the quark fields under which two of three quarks transform like a doublet and the remaining one as singlet, and use a scalar sector with the same structure of SU(2) doublets. After gauge symmetry breaking, a Z(2) subgroup of the S-3 remains unbroken. We show that this unbroken subgroup can explain the approximate block structure of the CKM matrix. By allowing soft breaking of the S-3 symmetry in the scalar sector, we show that one can generate the small elements, of quadratic or higher order in the Wolfenstein parametrization of the CKM matrix. We also predict the existence of exotic new scalars, with unconventional decay properties, which can be used to test our model experimentally.
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