ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for new phenomena in final states with large jet multiplicities and missing transverse momentum with ATLAS using root s=13 TeV proton-proton collisions. Phys. Lett. B, 757, 334–355.
Abstract: Results are reported of a search for new phenomena, such as supersymmetric particle production, that could be observed in high-energy proton-proton collisions. Events with large numbers of jets, together with missing transverse momentum from unobserved particles, are selected. The data analysed were recorded by the ATLAS experiment during 2015 using the 13 TeV centre-of-mass proton-proton collisions at the Large Hadron Collider, and correspond to an integrated luminosity of 3.2 fb(-1). The search selected events with various jet multiplicities from >= 7 to >= 10 jets, and with various b-jet multiplicity requirements to enhance sensitivity. No excess above Standard Model expectations is observed. The results are interpreted within two supersymmetry models, where gluino masses up to 1400 GeV are excluded at 95% confidence level, significantly extending previous limits.
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Albaladejo, M., Nieves, J., Oset, E., Sun, Z. F., & Liu, X. (2016). Can X(5568) be described as a B-s pi, B(K)over-bar resonant state? Phys. Lett. B, 757, 515–519.
Abstract: The DO Collaboration has recently seen a resonant-like peak in the B-s pi invariant mass spectrum, claimed to be a new state called X(5568). Using a B-s pi-B (K) over bar coupled channel analysis, implementing unitarity, and with the interaction derived from Heavy Meson Chiral Perturbation Theory, we are able to reproduce the reported spectrum, with a pole that can be associated to the claimed X(5568) state, and with mass and width in agreement with the ones reported in the experimental analysis. However, if the T-matrix regularization is performed by means of a momentum cutoff, the value for the latter needed to reproduce the spectrum is Lambda = 2.80 +/- 0.04 GeV, which is much larger than a “natural” value Lambda similar or equal to 1 GeV. In view of this, it is difficult to interpret the nature of this new state. This state would not qualify as a resonance dynamically generated by the unitarity loops. Assuming the observed peak to correspond to a physical state, we make predictions for partners in the D, D*, and B* sectors. Their observation (or lack thereof) would shed light into this issue.
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Han, X. F., Wang, L., & Yang, J. M. (2016). An extension of two-Higgs-doublet model and the excesses of 750 GeV diphoton, muon g-2 and h -> μτ. Phys. Lett. B, 757, 537–547.
Abstract: In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and h -> μtau in an extension of the two-Higgs-doublet model (2HDM) with additional vector-like fermions and a CP-odd scalar singlet (P) which is identified as the 750 GeV resonance. This 750 GeV resonance has a mixing with the CP-odd scalar (A) from a second scalar doublet, which leads to a coupling between P and the SM particles as well as a coupling between A and the vector-like fermions. Such mixing and couplings are strongly constrained by tau -> μgamma, muon g-2 and the 750 GeV diphoton data. We scan over the parameter space and find that such an extension can simultaneously account for the observed excesses of 750 GeV diphoton, muon g-2 and h -> μtau. The 750 GeV resonance decays in exotic modes, such as P -> hA, P -> H Z, P -> H A and P -> W-+/- H--/+ and its width can be dozens of GeV and is sensitive to the mixing angle.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First observation of the decay D-0 -> K-pi(+)mu(+)mu(-) in the rho(0)-omega region of the dimuon mass spectrum. Phys. Lett. B, 757, 558–567.
Abstract: A study of the decay D-0 -> K-pi(+)mu(+)mu(-) is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb(-1). Decay candidates with muon pairs that have an invariant mass in the range 675-875 MeV/c(2) are considered. This region is dominated by the rho(0) and omega resonances. The branching fraction in this range is measured to be B(D-0 -> K-pi(+)mu(+)mu(-)) = (4.17 +/- 0.12 (stat) +/- 0.40 (syst)) x 10(-6). This is the first observation of the decay D-0 -> K-pi(+)mu(+)mu(-). Its branching fraction is consistent with the value expected in the Standard Model.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., Costa, M. J., et al. (2016). Combination of searches for WW, WZ, and ZZ resonances in pp collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 755, 285–305.
Abstract: The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb(-1) of pp collision data at root s = 8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the l nu l'l' (l = mu, e), llq (q) over bar, l nu q (q) over bar and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W' boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the llq (q) over bar, l nu q (q) over bar, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall-Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension. (C) 2016 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V.
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Albaladejo, M., Guo, F. K., Hidalgo-Duque, C., & Nieves, J. (2016). Z(c)(3900): What has been really seen? Phys. Lett. B, 755, 337–342.
Abstract: The Z(c)(+/-)(3900)/Z(c)(+/-)(3885) resonant structure has been experimentally observed in the Y(4260) -> J/Psi pi pi and Y(4260) -> (D) over bar* D pi decays. This structure is intriguing since it is a prominent candidate of an exotic hadron. Yet, its nature is unclear so far. In this work, we simultaneously describe the (D) over bar* D and J/Psi pi invariant mass distributions in which the Z(c) peak is seen using amplitudes with exact unitarity. Two different scenarios are statistically acceptable, where the origin of the Z(c) state is different. They correspond to using energy dependent or independent (D) over bar *D S-wave interaction. In the first one, the Z(c) peak is due to a resonance with a mass around the D (D) over bar* threshold. In the second one, the Z(c) peak is produced by a virtual state which must have a hadronic molecular nature. In both cases the two observations, Z(c)(+/-)(3900) and Z(c)(+/-)(3885), are shown to have the same common origin, and a (D) over bar *D bound state solution is not allowed. Precise measurements of the line shapes around the D (D) over bar* threshold are called for in order to understand the nature of this state.
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Valle, J. W. F., & Vaquera-Araujo, C. A. (2016). Dynamical seesaw mechanism for Dirac neutrinos. Phys. Lett. B, 755, 363–366.
Abstract: So far we have not been able to establish that, as theoretically expected, neutrinos are their own anti-particles. Here we propose a dynamical way to account for the Dirac nature of neutrinos and the smallness of their mass in terms of a new variant of the seesaw paradigm in which the energy scale of neutrino mass generation could be accessible to the current LHC experiments.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Charged-particle distributions in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC. Phys. Lett. B, 758, 67–88.
Abstract: Charged-particle distributions are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 μb(-1), recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for single production of a vector-like quark via a heavy gluon in the 4b final state with the ATLAS detector in pp collisions at root s=8 TeV. Phys. Lett. B, 758, 249–268.
Abstract: A search is performed for the process pp -> G* -> B-H(b) over bar/(B) over bar (H)b -> Hb (b) over bar -> b (b) over barb (b) over bar, predicted in composite Higgs scenarios, where G* is a heavy colour octet vector resonance and B-H a vector-like quark of charge -1/3. The data were obtained from pp collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.5 fb(-1), recorded by the ATLAS detector at the LHC. The largest background, multijet production, is estimated using a data-driven method. No significant excess of events with respect to Standard Model predictions is observed, and upper limits on the production cross section times branching ratio are set. Comparisons to the predictions from a specific benchmark model are made, resulting in lower mass limits in the two-dimensional mass plane of m(G*) vs. m(BH).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Measurement of CP observables in B +/- -> DK +/- and B +/- -> D pi +/- with two- and four-body D decays. Phys. Lett. B, 760, 117–131.
Abstract: Measurements of CP observables in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays are presented where the D meson is reconstructed in the final states K-+/-pi(-/+), pi K-+/-(-/+), K+K-, pi(+)pi(-), K-+/-pi(-/+)pi(+)pi(-), pi K-+/-(-/+)pi(+)pi(-) and pi(+)pi(-)pi(+)pi(-). This analysis uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb(-1). Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle gamma. The analysis of the four-pion D decay mode is the first of its kind.
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