del Rio, A., Navarro-Salas, J., & Torrenti, F. (2014). Renormalized stress-energy tensor for spin-1/2 fields in expanding universes. Phys. Rev. D, 90(8), 084017–15pp.
Abstract: We provide an explicit expression for the renormalized expectation value of the stress-energy tensor of a spin-1/2 field in a spatially flat Friedmann-Lemaitre-Robertson-Walker universe. Its computation is based on the extension of the adiabatic regularization method to fermion fields introduced recently in the literature. The tensor is given in terms of UV-finite integrals in momentum space, which involve the mode functions that define the quantum state. As illustrative examples of the method efficiency, we see how to compute the renormalized energy density and pressure in two interesting cosmological scenarios: a de Sitter spacetime and a radiation-dominated universe. In the second case, we explicitly show that the late-time renormalized stress-energy tensor behaves as that of classical cold matter. We also check that, if we obtain the adiabatic expansion of the scalar field mode functions with a similar procedure to the one used for fermions, we recover the well-known WKB-type expansion.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Measurement of the Higgs boson mass from the H -> gamma gamma and H -> ZZ* -> 4l channels in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector. Phys. Rev. D, 90(5), 052004–35pp.
Abstract: An improved measurement of the mass of the Higgs boson is derived from a combined fit to the reconstructed invariant mass spectra of the decay channels H -> gamma gamma and H -> ZZ* -> 4l. The analysis uses the pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at center-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 25 fb(-1). The measured value of the Higgs boson mass is m(H) = 125.36 +/- 0.37(stat) +/- 0.18 (syst) GeV. This result is based on improved energy-scale calibrations for photons, electrons, and muons as well as other analysis improvements, and supersedes the previous result from ATLAS. Upper limits on the total width of the Higgs boson are derived from fits to the invariant mass spectra of the H -> gamma gamma and H -> ZZ* -> 4l decay channels.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Measurement of Collins asymmetries in inclusive production of charged pion pairs in e(+)e(-) annihilation at BABAR. Phys. Rev. D, 90(5), 052003–26pp.
Abstract: We present measurements of Collins asymmetries in the inclusive process e(+)e(-) -> pi pi X, where p stands for charged pions, at a center-of-mass energy of 10.6 GeV. We use a data sample of 468 fb(-1) collected by the BABAR experiment at the PEP-II B factory at SLAC, and consider pairs of charged pions produced in opposite hemispheres of hadronic events. We observe clear asymmetries in the distributions of the azimuthal angles in two distinct reference frames. We study the dependence of the asymmetry on several kinematic variables, finding that it increases with increasing pion momentum and momentum transverse to the analysis axis, and with increasing angle between the thrust and beam axis.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation gamma rays. Phys. Rev. D, 90(7), 072012–11pp.
Abstract: We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section gamma It is obtained by observing nuclear deexcitation. rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to 3.01 x 10(20) protons on target. By selecting only events during the T2K beam window and with well-reconstructed vertices in the fiducial volume, the large background rate from natural radioactivity is dramatically reduced. We observe 43 events in the 4-30 MeV reconstructed energy window, compared with an expectation of 51.0, which includes an estimated 16.2 background events. The background is primarily nonquasielastic neutral-current interactions and has only 1.2 events from natural radioactivity. The flux-averaged NCQE cross section we measure is 1.55 x 10(-38) cm(2) with a 68% confidence interval of (1.22, 2.20) x 10(-38) cm(2) at a median neutrino energy of 630 MeV, compared with the theoretical prediction of 2.01 x 10(-38) cm(2).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Dalitz plot analysis of B-s(0) -> (D)over-bar(0)K(-)pi(+) decays. Phys. Rev. D, 90(7), 072003–29pp.
Abstract: The resonant substructure of B-s(0) -> (D) over bar K-0(-)pi(+) decays is studied with the Dalitz plot analysis technique. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb(-1) of pp collision data recorded by LHCb. A structure at m((D) over bar K-0(-)) approximate to 2.86 GeV/c(2) is found to be an admixture of spin-1 and spin-3 resonances. The masses and widths of these states and of the D-s2*(2573)(-) meson are measured, as are the complex amplitudes and fit fractions for all the (D) over bar K-0(-) and K-pi(-) components included in the amplitude model. In addition, the D-s2*(2573)(-) resonance is confirmed to be spin 2.
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Hernandez, P., Kekic, M., & Lopez-Pavon, J. (2014). N_eff in low-scale seesaw models versus the lightest neutrino mass. Phys. Rev. D, 90(6), 065033–12pp.
Abstract: We evaluate the contribution to N_eff of the extra sterile states in low-scale type I seesaw models (with three extra sterile states). We explore the full parameter space and find that at least two of the heavy states always reach thermalization in the early Universe, while the third one might not thermalize provided the lightest neutrino mass is below O(10(-3) eV). Constraints from cosmology therefore severely restrict the spectra of heavy states in the range 1 eV-100 MeV. The implications for neutrinoless double beta decay are also discussed.
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Wendt, A. et al, & Algora, A. (2014). Isospin symmetry in the sd shell: Transition strengths in the neutron-deficient sd shell nucleus Ar-33. Phys. Rev. C, 90(5), 054301–7pp.
Abstract: Reduced transition strengths of the deexciting transitions from the first two excited states in Ar-33 were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary Ar-36 beam on a Be-9 target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The (33A)r beam hit a secondary Au-197 target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for gamma-ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of Ar-33 the reduced transition strengths have been determined. With these first results the T-z = -3/2 nucleus Ar-33 is now, together with Na-21 (T-z = -1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Search for the lepton flavor violating decay Z -> e μin pp collisions at root s=8 TeV with the ATLAS detector. Phys. Rev. D, 90(7), 072010–19pp.
Abstract: The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process Z -> e μin pp collisions using 20.3 fb(-1) of data collected at root s = 8 TeV. An enhancement in the e μinvariant mass spectrum is searched for at the Z-boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, Z -> ee and μmu, significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z-boson mass, resulting in an upper limit on the branching fraction, B(Z -> e mu) < 7.5 x 10(-7) at the 95% confidence level.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Measurement of long-range pseudorapidity correlations and azimuthal harmonics in root s(NN)=5.02 TeV proton-lead collisions with the ATLAS detector. Phys. Rev. C, 90(4), 044906–29pp.
Abstract: Measurements of two-particle correlation functions and the first five azimuthal harmonics, v(1) to v(5), are presented, using 28 nb(-1) of p + Pb collisions at a nucleon-nucleon center-of-mass energy of root s(NN) = 5.02 TeV measured with the ATLAS detector at the LHC. Significant long-range “ridgelike” correlations are observed for pairs with small relative azimuthal angle (|Delta phi| < pi/3) and back-to-back pairs (|Delta phi| > 2 pi/3) over the transverse momentum range 0.4 < p(T) < 12 GeV and in different intervals of event activity. The event activity is defined by either the number of reconstructed tracks or the total transverse energy on the Pb-fragmentation side. The azimuthal structure of such long-range correlations is Fourier decomposed to obtain the harmonics v(n) as a function of p(T) and event activity. The extracted v(n) values for n = 2 to 5 decrease with n. The v(2) and v(3) values are found to be positive in the measured p(T) range. The v(1) is also measured as a function of p(T) and is observed to change sign around p(T) approximate to 1.5-2.0 GeV and then increase to about 0.1 for pT > 4 GeV. The v(2)(p(T)), v(3)(p(T)), and v(4)(p(T)) are compared to the v(n) coefficients in Pb + Pb collisions at root s(NN) = 2.76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average p(T) of particles produced in the two collision systems.
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Forero, D. V., Tortola, M., & Valle, J. W. F. (2014). Neutrino oscillations refitted. Phys. Rev. D, 90(9), 093006–10pp.
Abstract: Here, we update our previous global fit of neutrino oscillations by including the recent results that have appeared since the Neutrino 2012 conference. These include the measurements of reactor antineutrino disappearance reported by Daya Bay and RENO, together with latest T2K and MINOS data including both disappearance and appearance channels. We also include the revised results from the third solar phase of Super-Kamiokande, SK-III, as well as new solar results from the fourth phase of Super-Kamiokande, SK-IV. We find that the preferred global determination of the atmospheric angle theta(23) is consistent with maximal mixing. We also determine the impact of the new data upon all the other neutrino oscillation parameters with an emphasis on the increasing sensitivity to the CP phase, thanks to the interplay between accelerator and reactor data. In the Appendix, we present the updated results obtained after the inclusion of new reactor data presented at the Neutrino 2014 conference. We discuss their impact on the global neutrino analysis.
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