ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Barranco Navarro, L., Cabrera Urban, S., et al. (2020). Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 124(8), 082301–20pp.
Abstract: The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at root s = 13 TeV using a data sample with an integrated luminosity of 150 pb(-1) recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range vertical bar eta vertical bar < 2.4. A significant nonzero elliptic anisotropy coefficient nu(2) is observed for muons from charm decays, while the nu(2) value for muons from bottom decays is consistent with zero within uncertainties.
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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). First Observation of Excited Omega(-)(b) States. Phys. Rev. Lett., 124(8), 082002–12pp.
Abstract: We report four narrow peaks in the Xi K-0(b)- mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb(-1) recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Omega(b)(6316)(-)] = 6315.64 +/- 0.31 +/- 0.07 +/- 0.50 MeV, m[Omega(b)(6330)(-)] = 6330.30 +/- 0.28 +/- 0.07 +/- 0.50 MeV, m[Omega(b)(6340)(-)] = 6339.71 +/- 0.26 +/- 0.05 +/- 0.50 MeV, m[Omega(b)(6350)(-)] = 6349.88 +/- 0.35 +/- 0.05 +/- 0.50 MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Xi(0)(b) mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Gamma[Omega(b)(6316)(-)] < 2.8 MeV, Gamma[Omega(b)(6330)(-)] < 3.1 MeV and Gamma[Omega(b)(6340)-] < 1.5 MeV. The natural width of the Omega(b)(6350)(-) peak is 1.4(-0.8)(+1.0) +/- 0.1 MeV, which is 2.5 sigma from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6 sigma to 7.2 sigma. After accounting for the look-elsewhere effect, the significances of the Omega(b)(6316)(-) and Omega(b)(6330)(-) peaks are reduced to 2.1 sigma and 2.6 sigma, respectively, while the two higher mass peaks exceed 5 sigma. The observed peaks are consistent with expectations for excited Omega(-)(b) resonances.
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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). Search for A ' -> mu(+)mu(-) Decays. Phys. Rev. Lett., 124(4), 041801–12pp.
Abstract: Searches are performed for both promptlike and long-lived dark photons, A ', produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for A '->mu(+)mu(-) decays using a data sample corresponding to an integrated luminosity of 5.5 fb(-1) collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the gamma-A ' kinetic mixing strength. The promptlike A ' search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with 214 < m(A ') less than or similar to 740 MeV and 10.6 < m(A ') less than or similar to 30 GeV. The search for long-lived A '->mu(+)mu(-) decays places world-leading constraints on low-mass dark photons with lifetimes O(1)ps.
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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). Isospin Amplitudes in Lambda(0)(b) -> J/psi Lambda (Sigma(0)) and Xi(0)(b)-> J/psi Xi(0) (Lambda) Decays. Phys. Rev. Lett., 124(11), 111802–11pp.
Abstract: Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions and allow searches for physics beyond the standard model. We present the first results on isospin amplitudes in b-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb(-1), collected with the LHCb detector in pp collisions at center of mass energies of 7, 8, and 13 TeV. The isospin amplitude ratio vertical bar A(1) (Delta(0)(b) -> J/psi(Sigma(0)) /A(0) (Delta(0)(b) -> J/psi Lambda)vertical bar, where the subscript on A indicates the final-state isospin, is measured to be less than 1/21.8 at 95% confidence level. The Cabibbo suppressed Xi(0)(b) -> J/psi Lambda decay is observed for the first time, allowing for the measurement vertical bar A(0) (Xi(0)(b) -> J/psi Lambda) / A(1/2 )(Xi(0)(b) -> J/psi Xi(0))vertical bar = 0.37 +/- 0.06 +/- 0.02, where the uncertainties are statistical and systematic, respectively.
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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). Measurement of f(s)/f(u) Variation with Proton-Proton Collision Energy and B-Meson Kinematics. Phys. Rev. Lett., 124(12), 122002–11pp.
Abstract: The ratio of the B-s(0) and B+ fragmentation fractions f(s) and f(u) is studied with B-s(0) -> J/psi phi and B+ -> J/psi K+ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio f(s)/f(u) is observed to depend on the B-meson transverse momentum with a significance of 6.0 sigma. This dependency is driven by the 13 TeV sample (8.7 sigma), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8 sigma evidence for an increase of f(s)/f(u) as a function of collision energy.
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