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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2018). Search for the decay mode B-0 -> pp(p)over-bar (p)over-bar. Phys. Rev. D, 98(7), 071102–7pp.
Abstract: A search is presented for the four-body decay B-0 -> pp (p) over bar (p) over bar in a sample of 471 million B (B) over bar pairs collected with the BABAR detector, operated at the SLAC PEP-II asymmetric-energy e(+) e(-) collider. The center-of-mass energy is 10.58 GeV. From a fit to the distribution of the energy-substituted mass m(ES), the branching fraction B(B-0 -> pp (p) over bar (p) over bar) = (1.1 +/- 0.5 +/- 0.2) x 10(-7) is extracted, where the first uncertainty is statistical and the second is systematic. The significance of the signal, including the systematic uncertainty, is 2.9 standard deviations. The upper limit on the branching fraction is determined to be 2.0 x 10(-7) at 90% confidence level.
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Aristizabal Sierra, D., De Romeri, V., & Rojas, N. (2018). COHERENT analysis of neutrino generalized interactions. Phys. Rev. D, 98(7), 075018–14pp.
Abstract: Effective neutrino-quark generalized interactions are entirely determined by Lorentz invariance, so they include all possible four-fermion nonderivative Lorentz structures. They contain neutrino-quark nonstandard interactions as a subset, but span over a larger set that involves effective scalar, pseudoscalar, axial and tensor operators. Using recent COHERENT data, we derive constraints on the corresponding couplings by considering scalar, vector and tensor quark currents and assuming no lepton flavor dependence. We allow for mixed neutrino-quark Lorentz couplings and consider two types of scenarios in which: (i) one interaction at the nuclear level is present at a time, (ii) two interactions are simultaneously present. For scenarios (i) our findings show that scalar interactions are the most severely constrained, in particular for pseudoscalar-scalar neutrino-quark couplings. In contrast, tensor and nonstandard vector interactions still enable for sizable effective parameters. We find as well that an extra vector interaction improves the data fit when compared with the result derived assuming only the standard model contribution. In scenarios (ii) the presence of two interactions relaxes the bounds and opens regions in parameter space that are otherwise closed, with the effect being more pronounced in the scalar-vector and scalar-tensor cases. We point out that barring the vector case, our results represent the most stringent bounds on effective neutrino-quark generalized interactions for mediator masses of order similar to 1 GeV. They hold as well for larger mediator masses, case in which they should be compared with limits from neutrino deep-inelastic scattering data.
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Barenboim, G., Kinney, W. H., & Morse, M. J. P. (2018). Phantom Dirac-Born-Infeld dark energy. Phys. Rev. D, 98(8), 083531–11pp.
Abstract: Motivated by the apparent discrepancy between cosmic microwave background measurements of the Hubble constant and measurements from Type-la supernovae, we construct a model for dark energy with equation of state w = p/rho < -1, violating the null energy condition. Naive canonical models of so-called “phantom” dark energy require a negative scalar kinetic term, resulting in a Hamiltonian unbounded from below and associated vacuum instability. We construct a scalar field model for dark energy with w < -1, which nonetheless has a Hamiltonian bounded from below in the comoving reference frame, i.e., in the rest frame of the fluid. We demonstrate that the solution is a cosmological attractor, and find that early-time cosmological boundary conditions consist of a “frozen” scalar field, which relaxes to the attractor solution once the dark energy component dominates the cosmological energy density. We consider the model in an arbitrary choice of gauge, and find that, unlike the case of comoving gauge, the fluid Hamiltonian is in fact unbounded from below in the reference frame of a highly boosted observer, corresponding to a nonlinear gradient instability. We discuss this in the context of general NEC-violating perfect fluids, for which this instability is a general property.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Observation of B-s(0) -> (D)over-bar*(0)phi and search for B-0 -> (D)over-bar(0)phi decays. Phys. Rev. D, 98(7), 071103–10pp.
Abstract: The first observation of the B-s(0) -> (D) over bar*(0)phi decay is reported, with a significance of more than seven standard deviations, from an analysis of pp collision data corresponding to an integrated luminosity of 3 fb -1 , collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B-0 -> (D) over bar (0)pi(+)pi(-) and is found to be B(B-s(0) -> (D) over bar*(0)phi) = (3.7 +/- 05 +/- 0.3 +/- 0.2) x 10(-5), where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B-0 -> (D) over bar (0)pi(+)pi(-) decay. The fraction of longitudinal polarization in this decay is measured to be f(L) = (73 +/- 15 +/- 4)%. The most precise determination of the branching fraction for the B-s(0) -> (D) over bar (0)phi decay is also obtained, B(B-s(0) -> (D) over bar (0)phi) = (3.0 +/- 0.3 +/- 0.2 +/- 0.2) x 10(-5). An upper limit, B(B-s(0) -> (D) over bar (0)phi) < 2.0 (2.3) x 10(-6) at 90% (95%) confidence level is set. A constraint on the omega – phi mixing angle delta is set at vertical bar delta vertical bar < 5.2 degrees (5.5 degrees) at 90% (95%) confidence level.
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Bonilla, C., Modak, T., Srivastava, R., & Valle, J. W. F. (2018). U(1)(B3-3L2) gauge symmetry as a simple description of b -> s anomalies. Phys. Rev. D, 98(9), 095002–11pp.
Abstract: We present a simple U(1)(B3-3L2) gauge standard model extension that can easily account for the anomalies in R(K) and R(K*) reported by LHCb. The model is economical in its setup and particle content. Among the standard model fermions, only the third generation quark family and the second generation leptons transform nontrivially under the new U(1)(B3-3L2) symmetry. This leads to lepton nonuniversality and flavor changing neutral currents involving the second and third quark families. We discuss the relevant experimental constraints and some implications.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2018). Observation of the decay B-s(0) -> (D)over-bar(0)K (+) K-. Phys. Rev. D, 98(7), 072006–19pp.
Abstract: The first observation of the B-s(0) -> (D) over bar K-0 (+) K- decay is reported, together with the most precise branching fraction measurement of the mode B-0 -> (D) over bar K-0 (+) K- The results are obtained from an analysis of pp collision data corresponding to an integrated luminosity of 3.0 fb(-1). The data were collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, The branching fraction of the B-0 -> (D) over bar K-0 (+) K- decay is measured relative to that of the decay B-0 -> (D) over bar (0)pi (+) pi(-) to be B(B-0 -> (D) over bar K-0 (+) K-)/B(B-0 -> (D) over bar (0)pi (+) pi(-)) =(69 +/- 0.4 +/- 0.3)%, where the first uncertainty is statistical and the second is systematic. The measured branching fraction of the B-s(0) -> (D) over bar K-0 (+) K- decay mode relative to that of the corresponding B-0 decay is B(B-0 -> (D) over bar K-0 (+) K-)/B(B-0 -> (D) over bar K-0 (+) K-) = (93.0 +/- 809 +/- 6.9)%. Using the known branching fraction of B-0 -> (D) over bar (0)pi (+) pi(-), the values of B-0 -> (D) over bar K-0 (+) K- = (6.1 +/- 0.4 +/- 0.3 +/- 0.3) x 10(-5) and B(B-s(0) -> (D) over bar K-0 (+) K- = (5.7 +/- 0.5 +/- 0.4 +/- 0.5) x 10(-5) are obtained, where the third uncertainties arise from the branching fraction of the decay modes B-0 -> (D) over bar (0)pi (+) pi(-) and B-0 -> (D) over bar K-0 (+) K-, respectively.
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Caputo, A., Pena-Garay, C., & Witte, S. J. (2018). Looking for axion dark matter in dwarf spheroidal galaxies. Phys. Rev. D, 98(8), 083024–6pp.
Abstract: We study the extent to which the decay of cold dark matter axions can be probed with forthcoming radio telescopes such as the Square Kilometer Array (SKA). In particular, we focus on signals arising from dwarf spheroidal galaxies, where astrophysical uncertainties are reduced and the expected magnetic field strengths are such that signals arising from axion decay may dominate over axion-photon conversion in a magnetic field. We show that with similar to 100 hr of observing time, SKA could improve current sensitivity by 2-3 orders of magnitude-potentially obtaining sufficient sensitivity to begin probing the decay of cold dark matter axions.
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Harko, T., Koivisto, T. S., Lobo, F. S. N., Olmo, G. J., & Rubiera-Garcia, D. (2018). Coupling matter in modified Q gravity. Phys. Rev. D, 98(8), 084043–13pp.
Abstract: We present a novel theory of gravity by considering an extension of symmetric teleparallel gravity. This is done by introducing, in the framework of the metric-affine formalism, a new class of theories where the nonmetricity Q is nonminimally coupled to the matter Lagrangian. More specifically, we consider a Lagrangian of the form L similar to f(1)(Q) + f(2)(Q)L-M, where f(1) and f(2) are generic functions of Q, and L-M is the matter Lagrangian. This nonminimal coupling entails the nonconservation of the energy-momentum tensor, and consequently the appearance of an extra force. The formulation of the gravity sector in terms of the Q instead of the curvature may result in subtle improvements of the theory. In the context of nonminimal matter couplings, we are therefore motivated to explore whether the new geometrical formulation in terms of the Q, when implemented also in the matter sector, would allow more universally consistent and viable realizations of the nonminimal coupling. Furthermore, we consider several cosmological applications by presenting the evolution equations and imposing specific functional forms of the functions f(1)(Q) and f(2)(Q), such as power-law and exponential dependencies of the nonminimal couplings. Cosmological solutions are considered in two general classes of models, and found to feature accelerating expansion at late times.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Measurement of dijet azimuthal decorrelations in pp collisions at root s=8 TeV with the ATLAS detector and determination of the strong coupling. Phys. Rev. D, 98(9), 092004–31pp.
Abstract: measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity R-Delta phi. The quantity R-Delta phi specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter Delta phi(max). The quantity R-Delta phi is measured in proton-proton collisions at root s = 8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and Delta phi(max). The measurement uses an event sample corresponding to an integrated luminosity of 20.2 fb(-1) collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for nonperturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling alpha(S) and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. Analysis that combines data at all momentum transfers results in alpha(S) (m(Z)) = 0.1127(- 0.0027) (+0.0063).
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Search for pair production of Higgsinos in final states with at least three b-tagged jets in root s=13 TeV pp collisions using the ATLAS detector. Phys. Rev. D, 98(9), 092002–34pp.
Abstract: A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos (H) over tilde) in gaugemediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy root s = 13 TeV, the former with an integrated luminosity of 36.1 fb(-1) and the latter with 24.3 fb(-1), collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No significant excess is found above the predicted background. Limits on the cross section are set as a function of the mass of the <(Hover tilde> in simplified models assuming production via mass-degenerate higgsinos decaying to a Higgs boson and a gravitino. Higgsinos with masses between 130 and 230 GeV and between 290 and 880 GeV are excluded at the 95% confidence level. Interpretations of the limits in terms of the branching ratio of the higgsino to a Z boson or a Higgs boson are also presented, and a 45% branching ratio to a Higgs boson is excluded for m(<(Hover tilde>) approximate to 400 GeV.
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