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), Jaimes Elles, S. J., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Rebollo De Miguel, M., et al. (2023). Measurement of the Ratios of Branching Fractions R(D*) and R(D0). Phys. Rev. Lett., 131(11), 111802–13pp.
Abstract: The ratios of branching fractions R(D*) = B((B) over bar -> D* tau(-) (v) over bar (tau))/B((B) over bar -> D*.mu(-)(v) over bar mu) and R(D-0) = B(B- -> D(0)t-mu(-)(v) over bar mu) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb(-1) of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode tau(-) -> mu(-)v(tau)(v) over bar mu. The measured values are R(D) = 0.281 +/- 0.018 +/- 0.024 and R(D-0) = 0.441 +/- 0.060 +/- 0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is rho = -0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model.
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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 the Standard Model Higgs Boson in the Diphoton Decay Channel with 4.9 fb(-1) of pp Collision Data at root s=7 TeV with ATLAS. Phys. Rev. Lett., 108(11), 111803–19pp.
Abstract: A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of root s = 7 TeV. In the diphoton mass range 110-150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110-150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113-115 GeV and 134.5-136 GeV.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the Ratio of Branching Fractions B((B)over-bar(0) -> D-*(+)tau(-)(nu)over-bar(tau))/B((B)over-bar(0) -> D-*(+)mu(-)(nu)over-bar(mu)). Phys. Rev. Lett., 115(11), 111803–10pp.
Abstract: The branching fraction ratio R(D-*) = B((B) over bar (0) -> D-*(+)tau(-)(nu) over bar (tau))/B((B) over bar (0) -> D-*(+)mu(-)(nu) over bar (mu)) is measured using a sample of proton-proton collision data corresponding to 3.0 fb(-1) of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode tau(-) -> mu(-)(nu) over bar (mu)nu(tau). The semitauonic decay is sensitive to contributions from non-standard-model particles that preferentially couple to the third generation of fermions, in particular, Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate (B) over bar (0) decays gives R(D-*) = 0.336 +/- 0.027(stat) +/- 0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the standard model.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Observation of B-c(+) -> (DK+)-K-0 Decays. Phys. Rev. Lett., 118(11), 111803–9pp.
Abstract: Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb(-1), recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the B-c(+) -> (DK+)-K-0 decay is observed with a statistical significance of 5.1 standard deviations. By normalizing to B-c(+) -> (D) over bar (0)pi(+) decays, a measurement of the branching fraction multiplied by the production rates for B-c(+) relative to B+ mesons in the LHCb acceptance is obtained, R-D0K = (f(c)/f(u)) x B(B-c(+) -> (DK+)-K-0) = (9.3(-2.5)(+2.8) +/- 0.6) x 10(-7), where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first B-c(+) decay of this nature to be observed.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). First Observation of Top Quark Production in the Forward Region. Phys. Rev. Lett., 115(11), 112001–10pp.
Abstract: Top quark production in the forward region in proton-proton collisions is observed for the first time. The W + b final state with W -> μnu is reconstructed using muons with a transverse momentum, p(T), larger than 25 GeV in the pseudorapidity range 2.0 < eta < 4.5. The b jets are required to have 50 < p(T) < 100 GeV and 2.2 < eta < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p(T) > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb(-1) collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are sigma(top)[7 TeV] = 239 +/- 53(stat) +/- 33(syst) +/- 24(theory) fb; sigma(top)[8 TeV ] = 289 +/- 43(stat) +/- 40(syst) +/- 29(theory) fb: These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.
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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 the Doubly Charmed Baryon Xi(++)(cc). Phys. Rev. Lett., 119(11), 112001–10pp.
Abstract: A highly significant structure is observed in the Lambda K-+(c)-pi(+)pi(+) mass spectrum, where the Lambda(+)(c) baryon is reconstructed in the decay mode pK(-)pi(+). The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon Xi(++)(cc). The difference between the masses of the Xi(++)(cc) and Lambda(+)(c) states is measured to be 1334.94 +/- 0.72(stat.) +/- 0.27(syst.) MeV/c(2), and the Xi(++)(cc) mass is then determined to be 3621.40 +/- 0.72(stat.) +/- 0.27(syst.) +/- 0.14(Lambda(+)(c)) MeV/c(2), where the last uncertainty is due to the limited knowledge of the Lambda(+)(c) mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb(-1), and confirmed in an additional sample of data collected at 8 TeV.
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Perez-Vidal, R. M. et al, Gadea, A., Jurado, M., Domingo-Pardo, C., & Huyuk, T. (2022). Evidence of Partial Seniority Conservation in the pi g9/2 Shell for the N=50 Isotones. Phys. Rev. Lett., 129(11), 112501–7pp.
Abstract: The reduced transition probabilities for the 4+1 -2+1 and 2+1 -0+1 transitions in 92Mo and 94Ru and for the 4+1 -2+1 and 6+1 -4+1 transitions in 90Zr have been determined in this experiment making use of a multinucleon transfer reaction. These results have been interpreted on the basis of realistic shell-model calculations in the f5=2, p3=2, p1=2, and g9=2 proton valence space. Only the combination of extensive lifetime information and large scale shell-model calculations allowed the extent of the seniority conservation in the N = 50 g9=2 orbital to be understood. The conclusion is that seniority is largely conserved in the first 71g9=2 orbital.
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Fujita, Y. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2014). Observation of Low- and High-Energy Gamow-Teller Phonon Excitations in Nuclei. Phys. Rev. Lett., 112(11), 112502–5pp.
Abstract: Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A = 42, 46, 50, and 54 “f-shell” nuclei in (He-3, t) charge-exchange reactions. In the Ca-42 -> Sc-42 reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the Fe-54 -> Co-54 reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.
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BABAR and Belle Collaborations(Abdesselam, A. et al), Martinez-Vidal, F., & Oyanguren, A. (2015). First Observation of CP Violation in (B)over-bar(0) -> D(CP)((*))h(0) Decays by a Combined Time-Dependent Analysis of BABAR and Belle Data. Phys. Rev. Lett., 115(12), 121604–10pp.
Abstract: We report a measurement of the time-dependent CP asymmetry of (B) over bar (0) -> D(CP)((*))h(0) decays, where the light neutral hadron h(0) is a pi(0), eta , or omega meson, and the neutral D meson is reconstructed in the CP eigenstates K+K-, K-S(0)pi(0) or K-S(0)omega. The measurement is performed combining the final data samples collected at the Upsilon(4S) resonance by the BABAR and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471 +/- 3) x 10(6) B (B) over bar pairs recorded by the BABAR detector and (772 +/- 11) x 10(6) B (B) over bar pairs recorded by the Belle detector. We measure the CP asymmetry parameters -eta S-f = +0.66 +/- 0.10(stat) +/- 0.06(syst) and C = -0.02 +/- 0.07(stat) +/- 0.03(syst). These results correspond to the first observation of CP violation in (B) over bar (0) -> D(CP)((*))h(0) decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.
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