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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Izmaylov, A., Sorel, M., & Stamoulis, P. (2016). Measurement of Muon Antineutrino Oscillations with an Accelerator-Produced Off-Axis Beam. Phys. Rev. Lett., 116(18), 181801–8pp.
Abstract: T2K reports its first measurements of the parameters governing the disappearance of (nu) over bar μin an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic (nu) over bar μbeam, produced with a peak energy of 0.6 GeVat J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the (nu) over bar μsurvival probability is expected to be minimal. Using a data set corresponding to 4.01 x 10(20) protons on target, 34 fully contained mu-like events were observed. The best-fit oscillation parameters are sin(2) ((theta) over bar (23)) = 0.45 and vertical bar Delta(m) over bar (2)(32)vertical bar = 2.51 x 10(-3) eV(2) with 68% confidence intervals of 0.38-0.64 and 2.26-2.80 x 10(-3) eV(2), respectively. These results are in agreement with existing antineutrino parameter measurements and also with the nu(mu) disappearance parameters measured by T2K.
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Cepedello, R., Deppisch, F. F., Gonzalez, L., Hati, C., & Hirsch, M. (2019). Neutrinoless Double-Beta Decay with Nonstandard Majoron Emission. Phys. Rev. Lett., 122(18), 181801–6pp.
Abstract: We present a novel mode of neutrinoless double-beta decay with emission of a light Majoron-like scalar particle phi. We assume it couples via an effective seven-dimensional operator with a (V + A) lepton current and (V +/- A) quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass. We calculate the total double-beta decay rate and determine the fully differential shape for this mode. We find that future double-beta decay searches are sensitive to scales of the order Lambda(NP) approximate to 1 TeV for the effective operator and a light scalar m(phi) < 0.2 MeV, based on ordinary double-beta decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double-beta decay, which is the main background. We point out possible ultraviolet completions where such an effective operator can emerge.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2020). Search for a Dark Leptophilic Scalar in e(+) e(-) Collisions. Phys. Rev. Lett., 125(18), 181801–8pp.
Abstract: Many scenarios of physics beyond the standard model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an e(+) e(-) collider, such a leptophilic scalar (phi(L)) would be produced predominantly through radiation from a tau lepton. We report herein a search for e(+) e(- )-> tau(+) tau(-)phi(L), phi(L)-> l(+) l(-) (l = e, mu) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the phi(L) coupling to leptons in the range 0.04 < m phi(L) < 7.0 GeV. These bounds significantly improve upon the current constraints, excluding almost entirely the parameter space favored by the observed discrepancy in the muon anomalous magnetic moment below 4 GeV at 90% confidence level.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2012). Search for Scalar Bottom Quark Pair Production with the ATLAS Detector in pp Collisions at root s=7 TeV. Phys. Rev. Lett., 108(18), 181802–18pp.
Abstract: The results of a search for pair production of the scalar partners of bottom quarks in 2: 05 fb(-1) of pp collisions at root s = 7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the (b) over tilde (1) – (chi) over tilde (0)(1) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Search for B+ -> K+nu(nu)over-bar Decays Using an Inclusive Tagging Method at Belle H. Phys. Rev. Lett., 127(18), 181802–10pp.
Abstract: A search for the flavor-changing neutral-current decay B+ -> K+nu(nu) over bar is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb(-1) collected at the Upsilon(4S) resonance and a sample of 9 fb(-1) collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B+ -> K+nu(nu) over bar decay, but also the inclusive properties of the other B meson in the Upsilon(4S) -> B (B) over bar event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B+ -> K+nu(nu) over bar of 4.1 x 10(-5) is set at the 90% confidence level.
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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. (2017). Search for Dark Matter Produced in Association with a Higgs Boson Decaying to b(b)over-bar Using 36 fb(-1) of pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 119(18), 181804–21pp.
Abstract: Several extensions of the standard model predict associated production of dark-matter particles with a Higgs boson. Such processes arc searched for in final states with missing transverse momentum and a Higgs boson decaying to a b (b) over bar pair with the ATLAS detector using 36.1 fb(-1) of pp collisions at a center-of mass energy of 13 TeV at the LHC. The observed data are in agreement with the standard model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.
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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. (2017). Observation of D-0 meson decays to pi(+) pi(-) mu(+) mu(-) and K+ K- mu(+) mu(-) final states. Phys. Rev. Lett., 119(18), 181805–10pp.
Abstract: The first observation of the D-0 -> pi(+) pi(-) mu(+) mu(-) and D-0 -> K+ K- mu(+) mu(-) decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2 fb(-1) of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay D-0 -> K- pi(+) [mu(+) mu(-)](rho 0/omega), where the two muons are consistent with coming from the decay of a rho(0) or omega meson. The results are B(D-0 -> pi(+) pi(-) mu(+) mu(-)) = (9.64 +/- 0.48 +/- 0.51 +/- 0.97) x 10(-7) and B(D-0 -> K+ K- mu(+) mu(-)) = (1.54 +/- 0.27 +/- 0.09 +/- 0.16) x 10(-7), where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.
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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. (2017). Search for Baryon-Number Violating Xi(0)(b) Oscillations. Phys. Rev. Lett., 119(18), 181807–9pp.
Abstract: A search for baryon-number violating Xi(0)(b) oscillations is performed with a sample of pp collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb(-1). The baryon number at the moment of production is identified by requiring that the Xi(0)(b) come from the decay of a resonance Xi(b)*(-) -> Xi(0)(b)pi(-) or Xi(b)'(-) -> Xi(0)(b)pi(-) and the baryon number at the moment of decay is identified from the final state using the decays Xi(0)(b) -> Xi(0)(c)pi(-) , Xi(+-)(c) -> pK(-)pi(+). No evidence of baryon-number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of omega < 0.08 ps(-1), where. is the associated angular frequency.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector. Phys. Rev. Lett., 131(18), 181901–22pp.
Abstract: This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb(-1) of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688 +/- 23(stat)(-71)(+75) (syst) fb, to be compared with the standard model prediction of 515(-42)(+36) fb at next-to-leading order in QCD.
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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. (2017). Observation of Five New Narrow Omega(0)(c) States Decaying to Xi K-+(c)-. Phys. Rev. Lett., 118(18), 182001–10pp.
Abstract: The Xi K-+(c)- mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3 fb(-1), collected by the LHCb experiment. The Xi(+)(c) is reconstructed in the decay mode pK(-)pi(vertical bar) . Five new, narrow excited Omega(0)(c) states are observed: the Omega(c)(3000)(0), Omega(c)(3050)(0), Omega(c)(3066)(0), Omega(c) (3090)(0), and Omega(c)(3119)(0). Measurements of their masses and widths are reported.
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