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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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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 invisible decays of a Higgs boson using vector-boson fusion in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 01(1), 172–44pp.
Abstract: A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb(-1) of proton-proton collision data at a centre-of-mass energy of 8TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of H -> invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgs-portal dark matter where the branching fraction limit is converted into upper bounds on the dark-matter-nucleon scattering cross section as a function of the dark-matter particle mass, and compared to results from the direct dark-matter detection experiments.
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Double Chooz collaboration(Abe, Y. et al), & Novella, P. (2016). Measurement of theta(13) in Double Chooz using neutron captures on hydrogen with novel background rejection techniques. J. High Energy Phys., 01(1), 163–29pp.
Abstract: The Double Chooz collaboration presents a measurement of the neutrino mixing angle theta(13) using reactor (nu) over bar (e) observed via the inverse beta decay reaction in which the neutron is captured on hydrogen. This measurement is based on 462.72 live days data, approximately twice as much data as in the previous such analysis, collected with a detector positioned at an average distance of 1050m from two reactor cores. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties. Accidental coincidences, the dominant background in this analysis, are suppressed by more than an order of magnitude with respect to our previous publication by a multi-variate analysis. These improvements demonstrate the capability of precise measurement of reactor (nu) over bar (e) without gadolinium loading. Spectral distortions from the (nu) over bar (e) reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin(2) 2 theta(13) = 0.095(0.039)(+0.039)(stat+syst) is obtained from a fit to the observed event rate as a function of the reactor power, a method insensitive to the energy spectrum shape. A simultaneous fit of the hydrogen capture events and of the gadolinium capture events yields a measurement of sin(2) 2 theta(13) = 0.088 +/- 0.033(stat+syst).
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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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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of forward W and Z boson production in pp collisions at root s=8TeV. J. High Energy Phys., 01(1), 155–45pp.
Abstract: Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of root s = 8TeV. The analysis is based on an integrated luminosity of 2.0 fb(-1) recorded with the LHCb detector. The bosons are identified in the W -> μnu and Z -> mu(+)mu(-) decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0 < eta < 4.5, with transverse momenta p(T) > 20 GeV/c and, in the case of the Z boson, a dimuon mass within 60 < M mu+mu- < 120 GeV/c(2). The results are sigma(W+) -> mu(+)nu(-) = 1093.6 +/- 2.1 +/- 7.2 +/- 10.9 +/- 12.7 pb, sigma(W-) -> mu(-)nu(-) = 818.4 +/- 1.9 +/- 5.0 +/- 7.0 +/- 9.5 pb, sigma(Z) -> mu(+)mu(-) = 95.0 +/- 0.3 +/- 0.7 +/- 1.1 +/- 1.1 pb, where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the W and Z boson cross-sections with centre-of-mass energy is studied using previously reported measurements with 1.0 fb(-1) of data at 7 TeV. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
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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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