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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). Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector. Phys. Rev. D, 97(7), 072003–44pp.
Abstract: A search for the associated production of the Higgs boson with a top quark pair ((tt) over barH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb(-1) of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy root s = 13 TeV at the Large Hadron Collider. Higgs boson decays to WW*, tau tau, and ZZ* are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeVand a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the (tt) over barH production cross section is sot (tt) over barH) = 790(-210)(+230) fb, in agreement with the Standard Model prediction of 507(-50)(+35) fb. The combination of this result with other t <overline> tH searches from the ATLAS experiment using the Higgs boson decay modes to b (b) over bar, gamma gamma and ZZ* -> 4l, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the (tt) over barH production mode.
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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 the standard model Higgs boson produced in association with top quarks and decaying into a b(b)overbar pair in pp collisions at root s=13 TeV with the ATLAS detector. Phys. Rev. D, 97(7), 072016–44pp.
Abstract: A search for the standard model Higgs boson produced in association with a top-quark pair, t(t)overbar H, is presented. The analysis uses 36.1 fb(-1) of pp collision data at root s = 13 TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H -> b(b)overbar decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by ft + jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured t(t)overbarH signal cross-section to the standard model expectation is found to be μ= 0.84(-0.61)(+0.64). A value of μgreater than 2.0 is excluded at 95% confidence level (C.L.) while the expected upper limit is μ< 1.2 in the absence of a t(t)overbar H signal.
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Wang, Y. F., Yao, D. L., & Zheng, H. Q. (2018). New insights on low energy pi N scattering amplitudes. Eur. Phys. J. C, 78(7), 543–18pp.
Abstract: The S- and P- wave phase shifts of low-energy pion-nucleon scatterings are analysed using Peking University representation, in which they are decomposed into various terms contributing either from poles or branch cuts. We estimate the left-hand cut contributions with the help of tree-level perturbative amplitudes derived in relativistic baryon chiral perturbation theory up to O(p(2)). It is found that in S-11 and P-11 channels, contributions from known resonances and cuts are far from enough to saturate experimental phase shift data – strongly indicating contributions from low lying poles undiscovered before, and we fully explore possible physics behind. On the other side, no serious disagreements are observed in the other channels.
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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). Amplitude Analysis of the Decay (B)over-bar(0 )-> K-S(0)pi(+)pi(- )and First Observation of the CP Asymmetry in (B)over-bar(0 )-> K* (892)(-)pi(+). Phys. Rev. Lett., 120(26), 261801–10pp.
Abstract: The time-integrated untagged Dalitz plot of the three-body hadronic charmless decay (B) over bar (0 )-> K-S(0)pi(+)pi(- ) is studied using a pp collision data sample recorded with the LHCb detector, corresponding to an integrated luminosity of 3.0 fb(-1). The decay amplitude is described with an isobar model. Relative contributions of the isobar amplitudes to the (B) over bar (0 )-> K-S(0)pi(+)pi(- ) decay branching fraction and CP asymmetries of the flavor-specific amplitudes are measured. The CP asymmetry between the conjugate (B) over bar (0 )-> K* (892)(-)pi(+) and (B) over bar (0 )-> K* (892)(-)pi(+) decay rates is determined to be -0.308 +/- 0.062.
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MoEDAL Collaboration(Acharya, B. et al), Bernabeu, J., Garcia, C., Mamuzic, J., Mitsou, V. A., Ruiz de Austri, R., et al. (2018). Search for magnetic monopoles with the MoEDAL forward trapping detector in 2.11 fb(-1) of 13 TeV proton-proton collisions at the LHC. Phys. Lett. B, 782, 510–516.
Abstract: We update our previous search for trapped magnetic monopoles in LHC Run 2 using nearly six times more integrated luminosity and including additional models for the interpretation of the data. The MoEDAL forward trapping detector, comprising 222 kg of aluminium samples, was exposed to 2.11 fb(-1) of 13 TeV proton-proton collisions near the LHCb interaction point and analysed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to the Dirac charge or above are excluded in all samples. The results are interpreted in Drell-Yan production models for monopoles with spins 0, 1/2 and 1: in addition to standard point-like couplings, we also consider couplings with momentum-dependent form factors. The search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge.
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