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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Search for Lepton-Flavor Violating Decays B+ -> K+ mu(+/-) e(-/+). Phys. Rev. Lett., 123(24), 241802–11pp.
Abstract: A search for the lepton-flavor violating decays B+ -> K+ mu(+/-)e(-/+) is performed using a sample of proton-proton collision data, collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of 3 fb(-1). No significant signal is observed, and upper limits on the branching fractions are set as B(B+ -> K+ mu(+/-)e(+)) < 7.0(95) x 10(-9) and B(B+ -> K+ mu(+/- )e(-)) < 6.4(8.8) x 10(-9) at 90% (95)% confidence level. The results improve the current best limits on these decays by more than one order of magnitude.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., Fernandez, P., Izmaylov, A., & Novella, P. (2019). Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation gamma rays. Phys. Rev. D, 100(12), 112009–19pp.
Abstract: Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super-Kamiokande using nuclear deexcitation gamma rays to identify signal-like interactions in data from a 14.94(16.35) x 10(20) protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are <sigma(nu-NCQE)> = 1.70 +/- 0.17(stat.)(-0.38)(+0.51) (syst.) x 10(-38) cm(2)/oxygen with a flux-averaged energy of 0.82 GeV and <sigma((nu) over bar -NCQE)> = 0.98 +/- 0.16(stat.)(-0.19)(+0.26)(syst.) x 10(-38)cm(2)/oxygen with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.
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Kogler, R., Nachman, B., Schmidt, A., Asquith, L., Winkels, E., Campanelli, M., et al. (2019). Jet substructure at the Large Hadron Collider. Rev. Mod. Phys., 91(4), 045003–44pp.
Abstract: Jet substructure has emerged to play a central role at the Large Hadron Collider, where it has provided numerous innovative ways to search for new physics and to probe the standard model, particularly in extreme regions of phase space. This review focuses on the development and use of state-of-the-art jet substructure techniques by the ATLAS and CMS experiments.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment. Phys. Rev. D, 101(1), 012002–48pp.
Abstract: Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ*, WW*, tau tau, b (b) over bar, μmu, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8 fb(-1) of proton-proton collision data collected at root S = 13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be μ= 1.11(-0.08)(+0.09). The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5 sigma (5.3 sigma). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersynunetric Standard Model. No significant deviations from Standard Model predictions are observed.
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Sakai, S., Liang, W. H., Toledo, G., & Oset, E. (2020). J/psi -> gamma pi pi, gamma pi(0)eta reactions and the f(0)(980) and a(0)(980) resonances. Phys. Rev. D, 101(1), 014005–9pp.
Abstract: We study the J/psi -> gamma pi(+)pi(-), gamma pi(0)eta reactions from the perspective that they come from the J/psi -> phi(omega)pi(+)pi(-), rho(0)pi(0)eta reactions, where the rho(0), psi, and phi get converted into a photon via vector meson dominance. Using models successfully used previously to study the J/psi -> omega(phi)pi pi reactions, we make determinations of the invariant mass distributions for pi(+)pi(-) in the regions of the f(0)(500), f(0)(980), and for pi(0)eta in the region of the a(0)(980). The integrated differential widths lead to branching ratios below present upper bounds, but they are sufficiently large for future check in updated facilities.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). (U)pdated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays. Phys. Rev. D, 101(1), 012005–12pp.
Abstract: A search for decay-time-dependent charge-parity (CP) asymmetry in D-0 -> K+ K- and D-0 -> pi(+)pi(-) eff decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb(-1). The D-0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D-0 and (D) over bar (0) mesons are determined to be A(Gamma)(K+ K-) = (-4.3 +/- 3.6 +/- 0.5) x 10(-4) and A(Gamma) (K+ K- ) = (2.2 +/- 7.0 +/- 0.8) x 10(-4), where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A(Gamma) (K+ K-) = (-4.4 +/- 2.3 +/- 0.6) x 10(-4) and A(Gamma) (pi(+)pi(-))= (2.5 +/- 4.3 +/- 0.7) x 10(-4).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Observation of Several Sources of CP Violation in B+ -> pi(+)pi(+)pi(-) Decays. Phys. Rev. Lett., 124(3), 031801–11pp.
Abstract: Observations are reported of different sources of CP violation from an amplitude analysis of B+ -> pi(+)pi(+)pi(-) decays, based on a data sample corresponding to an integrated luminosity of 3 fb(-1) of pp collisions recorded with the LHCb detector. A large CP asymmetry is observed in the decay amplitude involving the tensor f(2)(1270) resonance, and in addition significant CP violation is found in the pi(+)pi S- wave at low invariant mass. The presence of CP violation related to interference between the pi(+)pi S- wave and the P wave B+ -> rho(770)(0)pi(+) amplitude is also established; this causes large local asymmetries but cancels when integrated over the phase space of the decay. The results provide both qualitative and quantitative new insights into CP -violation effects in hadronic B decays.
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Casals, M., Fabbri, A., Martinez, C., & Zanelli, J. (2019). Quantum-corrected rotating black holes and naked singularities in (2+1) dimensions. Phys. Rev. D, 99(10), 104023–39pp.
Abstract: We analytically investigate the perturbative effects of a quantum conformally coupled scalar field on rotating (2 + 1)-dimensional black holes and naked singularities. In both cases we obtain the quantum-back-reacted metric analytically. In the black hole case, we explore the quantum corrections on different regions of relevance for a rotating black hole geometry. We find that the quantum effects lead to a growth of both the event horizon and the ergosphere, as well as to a reduction of the angular velocity compared to their corresponding unperturbed values. Quantum corrections also give rise to the formation of a curvature singularity at the Cauchy horizon and show no evidence of the appearance of a superradiant instability. In the naked singularity case, quantum effects lead to the formation of a horizon that hides the conical defect, thus turning it into a black hole. The fact that these effects occur not only for static but also for spinning geometries makes a strong case for the role of quantum mechanics as a cosmic censor in Nature.
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Blanton, T. D., Romero-Lopez, F., & Sharpe, S. R. (2020). I=3 Three-Pion Scattering Amplitude from Lattice QCD. Phys. Rev. Lett., 124(3), 032001–7pp.
Abstract: We analyze the spectrum of two- and three-pion states of maximal isospin obtained recently for isosymmetric QCD with pion mass M approximate to 200 MeV in Horz and Hanlon, [Phys. Rev. Lett. 123, 142002 (2019)]. Using the relativistic three-particle quantization condition, we find similar to 2 sigma evidence for a nonzero value for the contact part of the 3 pi(+) (I = 3) scattering amplitude. We also compare our results to leading-order chiral perturbation theory. We find good agreement at threshold and some tension in the energy dependent part of the 3 pi(+) scattering amplitude. We also find that the 2 pi(+) (I = 2) spectrum is fit well by an s-wave phase shift that incorporates the expected Adler zero.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Amplitude analysis of the B+ -> pi(+)pi(+)pi(-) decay. Phys. Rev. D, 101(1), 012006–46pp.
Abstract: The results of an amplitude analysis of the charmless three-body decay B+ -> pi(+)pi(+)pi(-) , in which CP-violation effects are taken into account, are reported. The analysis is based on a data sample corresponding to an integrated luminosity of 3 fb(-1) of pp collisions recorded with the LHCb detector. The most challenging aspect of the analysis is the description of the behavior of the pi(+)pi(-) S-wave contribution, which is achieved by using three complementary approaches based on the isobar model, the K-matrix formalism, and a quasi-model-independent procedure. Additional resonant contributions for all three methods are described using a common isobar model, and include the rho(770)(0), omega(782)(0) and rho(1450)(0) resonances in the pi(+)pi(-) P-wave, the f(2) (1270) resonance in the pi(+)pi D- -wave, and the rho(3) (1690)(0) resonance in the pi(+)pi(-) F-wave. Significant CP-violation effects are observed in both S- and D-waves, as well as in the interference between the S- and P-waves. The results from all three approaches agree and provide new insight into the dynamics and the origin of CP-violation effects in B+ -> pi(+)pi(+)pi(-) decays.
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