Hinarejos, M., Di Franco, C., Romanelli, A., & Perez, A. (2014). Chirality asymptotic behavior and non-Markovianity in quantum walks on a line. Phys. Rev. A, 89(5), 052330–7pp.
Abstract: We investigate the time evolution of the chirality reduced density matrix for a discrete-time quantum walk on a one-dimensional lattice. The matrix is obtained by tracing out the spatial degree of freedom. We analyze the standard case, without decoherence, and the situation in which decoherence appears in the form of broken links in the lattice. By examining the trace distance for possible pairs of initial states as a function of time, we conclude that the evolution of the reduced density matrix is non-Markovian, in the sense defined by Breuer, Laine, and Piilo [Phys. Rev. Lett. 103, 210401 (2009)]. As the level of noise increases, the dynamics approaches a Markovian process. The highest non-Markovianity corresponds to the case without decoherence. The reduced density matrix tends always to a well-defined limit that we calculate, but only in the decoherence-free case is this limit nontrivial.
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Andrews, H. L., Taheri, F. B., Barros, J., Bartolini, R., Bharadwaj, V., Clarke, C., et al. (2014). Reconstruction of the time profile of 20.35 GeV, subpicosecond long electron bunches by means of coherent Smith-Purcell radiation. Phys. Rev. Spec. Top.-Accel. Beams, 17(5), 052802–13pp.
Abstract: We have used coherent Smith-Purcell radiation (cSPr) in order to determine the temporal profile of sub-ps long electron bunches at the Facility for Advanced Accelerator Experimental Tests, at SLAC. The measurements reported here were carried out in June 2012 and April 2013. The rms values for the bunch length varied between 356 to 604 fs, depending on the accelerator settings. The resolution of the system was limited by the range of detectable wavelengths which was, in turn, determined by the choice of the grating periods used in these experiments and the achievable beam-grating separation. The paper gives the details of the various steps in the reconstruction of the time profile and discusses possible improvements to the resolution. We also present initial measurements of the polarization properties of cSPr and of the background radiation.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., & Ruiz Valls, P. (2014). Measurement of resonant and CP components in (B)over-bar(s)(0) -> J/psi pi(+)pi(-) decays. Phys. Rev. D, 89(9), 092006–21pp.
Abstract: Structure of the decay B0s. J=.pp- is studied using data corresponding to 3 fb- 1 of integrated luminosity from pp collisions produced by the LHC and collected by the LHCb detector. Five interfering pp- states are required to describe the decay: F-0(980), F-0(1500), F-0(1790), F-2 (1270) and F-2(1525) An alternative model including these states and a nonresonant J=.pp- component also provides a good description of the data. Based on the different transversity components measured for the spin- 2 intermediate states, the final state is found to be compatible with being entirely CP odd. The CP- even part is found to be < 2.3% at a 95% confidence level. The f 0d500 state is not observed, allowing a limit to be set on the absolute value of the mixing angle with the f 0d980 of < 7.7 at a 90% confidence level, consistent with a tetraquark interpretation of the f(0)(980) substructure.
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Lobo, F. S. N., Olmo, G. J., & Rubiera-Garcia, D. (2014). Microscopic wormholes and the geometry of entanglement. Eur. Phys. J. C, 74(6), 2924–5pp.
Abstract: It has recently been suggested that Einstein-Rosen (ER) bridges can be interpreted as maximally entangled states of two black holes that form a complex Einstein-Podolsky-Rosen (EPR) pair. This relationship has been dubbed as the correlation. In this work, we consider the latter conjecture in the context of quadratic Palatini theory. An important result, which stems from the underlying assumptions as regards the geometry on which the theory is constructed, is the fact that all the charged solutions of the quadratic Palatini theory possess a wormhole structure. Our results show that spacetime may have a foam-like microstructure with wormholes generated by fluctuations of the quantum vacuum. This involves the spontaneous creation/annihilation of entangled particle-antiparticle pairs, existing in a maximally entangled state connected by a non-traversable wormhole. Since the particles are produced from the vacuum and therefore exist in a singlet state, they are necessarily entangled with one another. This gives further support to the claim.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Observation of the Resonant Character of the Z(4430)(-) State. Phys. Rev. Lett., 112(22), 222002–9pp.
Abstract: Resonant structures in B-0 -> psi'pi K--(+) decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb(-1) collected with the LHCb detector. The data cannot be described with K+pi(-) resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)(-) -> psi'pi(-) component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)(-) amplitude with the psi'pi(-) mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1(+).
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Deppisch, F. F., Harz, J., & Hirsch, M. (2014). Falsifying High-Scale Leptogenesis at the LHC. Phys. Rev. Lett., 112(22), 221601–5pp.
Abstract: Measuring a nonzero value for the cross section of any lepton number violating (LNV) process would put a strong lower limit on the washout factor for the effective lepton number density in the early Universe at times close to the electroweak phase transition and thus would lead to important constraints on any high-scale model for the generation of the observed baryon asymmetry based on LNV. In particular, for leptogenesis (LG) models with masses of the right-handed neutrinos heavier than the mass scale observed at the LHC, the implied large washout factors would lead to a violation of the out-of-equilibrium condition and exponentially suppress the net lepton number produced in such LG models. We thus demonstrate that the observation of LNV processes at the LHC results in the falsification of high-scale LG models. However, no conclusions about the viability of LG models can be drawn from the nonobservation of LNV processes.
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Orrigo, S. E. A. et al, Rubio, B., Agramunt, J., Algora, A., & Molina, F. (2014). Observation of the beta-Delayed gamma-Proton Decay of Zn-56 and its Impact on the Gamow-Teller Strength Evaluation. Phys. Rev. Lett., 112(22), 222501–5pp.
Abstract: We report the observation of a very exotic decay mode at the proton drip line, the beta-delayed gamma-proton decay, clearly seen in the beta decay of the T-z = -2 nucleus Zn-56. Three gamma-proton sequences have been observed after the beta decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the f p shell. Both. and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurements of Four-Lepton Production at the Z Resonance in pp Collisions at root s=7 and 8 TeV with ATLAS. Phys. Rev. Lett., 112(23), 231806–18pp.
Abstract: Measurements of four-lepton (4l, l = e,mu) production cross sections at the Z resonance in pp collisions at the LHC with the ATLAS detector are presented. For dilepton and four-lepton invariant mass regions m (l+l)- > 5 GeV and 80 < m(4l) < 100 GeV, the measured cross sections are 76 +/- 18(stat) +/- 4(syst) +/- 1.4(lumi) fb and 107 +/- 9(stat) +/- 4(syst) +/- 3.0(lumi) fb at root s=7 and 8 TeV, respectively. By subtracting the nonresonant 4l production contributions and normalizing with Z -> mu(+)mu(-) events, the branching fraction for the Z boson decay to 4l is determined to be (3.20 +/- 0.25(stat) +/- 0.13(syst)) x10(-6), consistent with the standard model prediction.
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Bertolini, S., Maiezza, A., & Nesti, F. (2014). Present and future K and B meson mixing constraints on TeV scale left-right symmetry. Phys. Rev. D, 89(9), 095028–15pp.
Abstract: We revisit the Delta F = 2 transitions in the K and B-d,B-s neutral meson systems in the context of the minimal left-right symmetric model. We take into account, in addition to up-to-date phenomenological data, the contributions related to the renormalization of the flavor-changing neutral Higgs tree-level amplitude. These contributions were neglected in recent discussions, albeit formally needed in order to obtain a gauge-independent result. Their impact on the minimal LR model is crucial and twofold. First, the effects are relevant in B meson oscillations, for both CP conserving and CP violating observables, so that for the first time these imply constraints on the LR scenario which compete with those of the K sector (plagued by long-distance uncertainties). Second, they sizably contribute to the indirect kaon CP violation parameter epsilon. We discuss the bounds from B and K mesons in both cases of LR symmetry: generalized parity (P) and charge conjugation (C). In the case of P, the interplay between the CP-violation parameters epsilon and epsilon' leads us to rule out the regime of very hierarchical bidoublet vacuum expectation values nu(2)/nu(1) < m(b)/m(t) similar or equal to 0.02. In general, by minimizing the scalar field contribution up to the limit of the perturbative regime and by definite values of the relevant CP phases in the charged right-handed currents, we find that a right-handed gauge boson W-R as light as 3 TeV is allowed at the 95% C. L. This is well within the reach of direct detection at the next LHC run. If not discovered, within a decade the upgraded LHCb and Super B factories may reach an indirect sensitivity to a left-right scale of 8 TeV.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of the parity-violating asymmetry parameter ab and the helicity amplitudes for the decay Lambda(0)(b) -> J/psi Lambda(0) with the ATLAS detector. Phys. Rev. D, 89(9), 092009–25pp.
Abstract: A measurement of the parity-violating decay asymmetry parameter, ab, and the helicity amplitudes for the decay.Lambda(0)(b) -> J/psi(mu(+) mu(-)) Lambda(0)(p pi(-)) is reported. The analysis is based on 1400 Lambda(0)(b)and (Lambda) over bar (0)(b) baryons selected in 4.6 fb(-1) of proton-proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the.0 b and. _ 0 b samples under the assumption of CP conservation, the value of ab is measured to be 0.30 +/- 0.16(stat) +/- 0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.
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