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Barenboim, G., Chun, E. J., Jung, S. H., & Park, W. I. (2014). Implications of an axino LSP for naturalness. Phys. Rev. D, 90(3), 035020–12pp.
Abstract: Both the naturalness of the electroweak symmetry breaking and the resolution of the strong CP problem may require a small Higgsino mass μgenerated by a realization of the DFSZ axion model. Assuming the axino is the lightest supersymmetric particle, we study its implications on μand the axion scale. Copiously produced light Higgsinos at collider (effectively only neutral next-to-lightest superparticles pairs) eventually decay to axinos leaving prompt multileptons or displaced vertices which are being looked for at the LHC. We use latest LHC7 + 8 results to derive current limits on μand the axion scale. Various Higgsino-axino phenomenology is illustrated by comparing with a standard case without lightest axinos as well as with a more general case with additional light gauginos in the spectrum.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of CP violation in B-s(0) ->Phi Phi decays. Phys. Rev. D, 90(5), 052011–17pp.
Abstract: A measurement of the decay time-dependent CP-violating asymmetry in B-s(0) -> phi phi decays is presented, along with measurements of the T-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between B-s(0) -(B) over bar (0)(s) mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1) collected with the LHCb detector, a signal yield of approximately 4000 B-s(0) -> phi phi decays is obtained. The CP-violating phase is measured to be phi(s) = -0.17 +/- 0.15(stat) +/- 0.03(syst) rad. The triple-product asymmetries are measured to be A(U) = -0.003 +/- 0.017(stat) +/- 0.006(syst) and A(V) = -0.017 +/- 0.017(stat) +/- 0.006(syst). Results are consistent with the hypothesis of CP conservation.
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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 contact interactions and large extra dimensions in the dilepton channel using proton-proton collisions at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 74(12), 3134–25pp.
Abstract: A search is conducted for non-resonant new phenomena in dielectron and dimuon final states, originating from either contact interactions or large extra spatial dimensions. The LHC 2012 proton-proton collision dataset recorded by the ATLAS detector is used, corresponding to 20 fb(-1) at root s = 8 TeV. The dilepton invariant mass spectrum is a discriminating variable in both searches, with the contact interaction search additionally utilizing the dilepton forward-backward asymmetry. No significant deviations from the Standard Model expectation are observed. Lower limits are set on the llqq contact interaction scale Lambda between 15.4 TeVand 26.3 TeV, at the 95% credibility level. For large extra spatial dimensions, lower limits are set on the string scale MS between 3.2 TeV to 5.0 TeV.
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Maiezza, A., & Nemevsek, M. (2014). Strong P invariance, neutron electric dipole moment, and minimal left-right parity at LHC. Phys. Rev. D, 90(9), 095002–10pp.
Abstract: In the minimal left-right model the choice of left-right symmetry is twofold: either generalized parity P or charge conjugation C. In the minimal model with spontaneously broken strict P, a large tree-level contribution to strong CP violation can be computed in terms of the spontaneous phase alpha. Searches for the neutron electric dipole moments then constrain the size of alpha. Following the latest update on indirect CP violation in the kaon sector, a bound on W-R mass at 20 TeV is set. Possible ways out of this bound require a further hypothesis, either a relaxation mechanism or explicit breaking of P. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is recomputed and provides an estimate of the weak contribution. Combining this constraint with other CP-violating observables in the kaon sector allows for M-WR greater than or similar to 3 TeV. On the other hand, C symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.
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Ledwig, T., Nieves, J., Pich, A., Ruiz Arriola, E., & Ruiz de Elvira, J. (2014). Large-N-c naturalness in coupled-channel meson-meson scattering. Phys. Rev. D, 90(11), 114020–17pp.
Abstract: The analysis of hadronic interactions with effective field theory techniques is complicated by the appearance of a large number of low-energy constants, which are usually fitted to data. On the other hand, the large-N-c limit helps to impose natural short-distance constraints on these low-energy constants, providing a parameter reduction. A Bayesian interpretation of the expected 1/N-c accuracy allows for an easy and efficient implementation of these constraints, using an augmented chi(2). We apply this approach to the analysis of meson-meson scattering, in conjunction with chiral perturbation theory to one loop and coupled-channel unitarity, and show that it helps to largely reduce the many existing ambiguities and simultaneously provide an acceptable description of the available phase shifts.
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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 muon reconstruction performance of the ATLAS detector using 2011 and 2012 LHC proton-proton collision data. Eur. Phys. J. C, 74(11), 3130–34pp.
Abstract: This paper presents the performance of the ATLAS muon reconstruction during the LHC run with pp collisions at root s = 7-8 TeV in 2011-2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of J/psi -> μmu, Z -> μμand gamma -> μμdecays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon |eta| < 2.7 and 5 less than or similar to p(T) less than or similar to 100 GeV) the efficiency is above 99% and is measured with per-mille precision. The momentum resolution ranges from 1.7% at central rapidity and for transverse momentum p(T) similar or equal to 10 GeV, to 4% at large rapidity and p(T) similar or equal to 100 GeV. The momentum scale is known with an uncertainty of 0.05% to 0.2% depending on rapidity. A method for the recovery of final state radiation from the muons is also presented.
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NEXT Collaboration(Lorca, D. et al), Martin-Albo, J., Laing, A., Ferrario, P., Gomez-Cadenas, J. J., Alvarez, V., et al. (2014). Characterisation of NEXT-DEMO using xenon K-alpha X-rays. J. Instrum., 9, P10007–20pp.
Abstract: The NEXT experiment aims to observe the neutrinoless double beta decay of Xe-136 in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. Understanding the response of the detector is imperative in achieving a consistent and well understood energy measurement. The abundance of xenon K-shell X-ray emission during data taking has been identified as a multitool for the characterisation of the fundamental parameters of the gas as well as the equalisation of the response of the detector. The NEXT-DEMO prototype is a similar to 1.5 kg volume TPC filled with natural xenon. It employs an array of 19 PMTs as an energy plane and of 256 SiPMs as a tracking plane with the TPC light tube and SiPM surfaces being coated with tetraphenyl butadiene (TPB) which acts as a wavelength shifter for the VUV scintillation light produced by xenon. This paper presents the measurement of the properties of the drift of electrons in the TPC, the effects of the EL production region, and the extraction of position dependent correction constants using K-alpha X-ray deposits. These constants were used to equalise the response of the detector to deposits left by gammas from Na-22.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2014). Measurement of the inclusive nu(mu) charged current cross section on iron and hydrocarbon in the T2K on-axis neutrino beam. Phys. Rev. D, 90(5), 052010–15pp.
Abstract: We report a measurement of the nu(mu) inclusive charged current cross sections on iron and hydrocarbon in the Tokai-to-Kamioka (T2K) on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux with a mean neutrino energy of 1.51 GeVare (1.444 +/- 0.002(stat)(-0.157)(+0.189)- (syst)) x 10(-38) cm(2)/ nucleon and (1.379 +/- 0.009(stat)(-0.147)(+0.178) (syst)) x 10(-38) 38 cm(2)/ nucleon, respectively, and their cross-section ratio is 1.047 +/- 0.007(stat) +/- 0.035(syst). These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model within the measurement precisions.
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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). Measurements of spin correlation in top-antitop quark events from proton-proton collisions at root s=7 TeV using the ATLAS detector. Phys. Rev. D, 90(11), 112016–32pp.
Abstract: Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb(-1). Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Standard Model prediction at next-to-leading-order accuracy.
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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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