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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Evidence for the Strangeness-Changing Weak Decay Xi(-)(b) -> Lambda(0)(b)pi(-). Phys. Rev. Lett., 115(24), 241801–10pp.
Abstract: Using a pp collision data sample corresponding to an integrated luminosity of 3.0 fb(-1), collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Xi(-)(b) -> Delta(0)(b)pi(-). No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be f Xi(-)(b)/f Lambda B-0(b)(Xi(-)(b) -> Lambda(0)(b)pi(-)) = (5.7 +/- 1.8(-0.9)(+0.8)) x 10(-4) where f Xi(-)(b) and f Lambda(0)(b) are the b -> Xi(-)(b) and b -> Lambda(0)(b) fragmentation fractions, and B(Xi(-)(b) -> Lambda(0)(b)pi(-)) is the branching fraction. Assuming f Xi(-)(b)/f Lambda(0)(b) is bounded between 0.1 and 0.3, the branching fraction B(Xi(-)(b) -> Lambda(0)(b)pi(-)) would lie in the range from (0.57 +/- 0.21)% to (0.19 +/- 0.07)%.
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Caballero-Folch, R. et al, Domingo-Pardo, C., Agramunt, J., Algora, A., Rubio, B., & Tain, J. L. (2016). First Measurement of Several beta-Delayed Neutron Emitting Isotopes Beyond N=126. Phys. Rev. Lett., 117(1), 012501–6pp.
Abstract: The beta-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with beta-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N greater than or similar to 126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the beta-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.
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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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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). First Observation of D-0 – (D)over-bar(0) Oscillations in D-0 -> K+pi(-)pi(+)pi(-) Decays and Measurement of the Associated Coherence Parameters. Phys. Rev. Lett., 116(24), 241801–10pp.
Abstract: Charm meson oscillations are observed in a time-dependent analysis of the ratio of D-0 -> K+pi(-)pi(+)pi(-) to D-0 -> K-pi(+)pi(-)pi(+) decay rates, using data corresponding to an integrated luminosity of 3.0 fb(-1) recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes r(D)(K3 pi) and the product of the coherence factor R-D(K3 pi) and a charm mixing parameter y'(K3 pi). The constraints measured are r(D)(K3 pi) = (5.67 +/- 0.12) x 10(-2), which is the most precise determination to date, and R-D(K3 pi) y'(K3 pi) = (0.3 +/- 1.8) x 10(-3), which provides useful input for determinations of the CP-violating phase gamma in B-+/- -> DK +/-, D -> K--/+pi(+/-)pi(-/+)pi(+/-) decays. The analysis also gives the most precise measurement of the D-0 -> K+pi(-)pi(+)pi(-) branching fraction, and the first observation of D-0-(D) over bar (0) oscillations in this decay mode, with a significance of 8.2 standard deviations.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Observation of B-s(0) -> (D)over-bar(0)K(S)(0) and Evidence for B-s(0) -> (D)over-bar*K-0(S)0 Decays. Phys. Rev. Lett., 116(16), 161802–9pp.
Abstract: The first observation of the B-s(0) -> (D) over bar K-0(S)0 decay mode and evidence for the B-s(0) -> (D) over bar*K-0(S)0 decay mode are reported. The data sample corresponds to an integrated luminosity of 3.0 fb-1 collected in pp collisions by LHCb at center-of-mass energies of 7 and 8 TeV. The branching fractions are measured to be B(B-s(0) -> (D) over bar (0)(K) over bar (0)) = [4.3 +/- 0.5(stat) +/- 0.3 (syst) +/- 0.3(frag) +/- 0.6(norm)] x 10(-4), B(B-s(0) -> (D) over bar*(0)(K) over bar (0)) = [2.8 +/- 1.0(stat) +/- 0.3 (syst) +/- 0.2(frag) +/- 0.4(norm)] x 10(-4), where the uncertainties are due to contributions coming from statistical precision, systematic effects, and the precision of two external inputs, the ratio f(s)/f(d) and the branching fraction of B-0 (D) over bar K-0(S)0, which is used as a calibration channel.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Search for violations of Lorentz invariance and CPT symmetry in B-(s)(0) mixing. Phys. Rev. Lett., 116(24), 241601–10pp.
Abstract: Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B-0 mixing and in B-s(0) mixing. Samples of B-0 -> J/psi K-S(0) and B-0(s) -> J/psi K+K- decays are recorded by the LHCb detector in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb(-1). No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and CPT symmetry. Results are expressed in terms of the standard model extension parameter Delta a(mu) with precisions of O(10(-15)) and O(10(-14)) GeV for the B-0 and B-s(0) systems, respectively. With no assumption on Lorentz (non) invariance, the CPT-violating parameter z in the B-s(0) system is measured for the first time and found to be Re(z) = -0.022 +/- 0.033 +/- 0.005 and Im(z) = 0.004 +/- 0.011 +/- 0.002, where the first uncertainties are statistical and the second systematic.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Novella, P., Izmaylov, A., Sorel, M., & Stamoulis, P. (2016). Measurement of Coherent pi(+) Production in Low Energy Neutrino-Carbon Scattering. Phys. Rev. Lett., 117(9), 192501–7pp.
Abstract: We report the first measurement of the flux-averaged cross section for charged current coherent pi(+) production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The measured flux-averaged cross sections are below those predicted by both the Rein-Sehgal and Alvarez-Ruso et al. models.
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Miranda, O. G., Tortola, M., & Valle, J. W. F. (2016). New Ambiguity in Probing CP Violation in Neutrino Oscillations. Phys. Rev. Lett., 117(6), 061804–5pp.
Abstract: If neutrinos get mass via the seesaw mechanism the mixing matrix describing neutrino oscillations can be effectively nonunitary. We show that in this case the neutrino appearance probabilities involve a new CP phase phi associated with nonunitarity. This leads to an ambiguity in extracting the “standard” three-neutrino phase delta(CP), which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of delta(CP).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2016). Model-Independent Evidence for J/psi p Contributions to Lambda(0)(b) -> J/psi pK(-) Decays. Phys. Rev. Lett., 117(8), 082002–9pp.
Abstract: The data sample of Lambda(0)(b) -> J/psi pK(-) decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb(-1), is inspected for the presence of J/psi p or J/psi K- contributions with minimal assumptions about K(-)p contributions. It is demonstrated at more than nine standard deviations that Lambda(0)(b) -> J/psi pK(-) decays cannot be described with K- p contributions alone, and that J/psi K- contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P-c(+)-> J/psi p charmonium-pentaquark states in the same data sample.
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IceCube Collaboration(Aartsen, M. G. et al), & Salvado, J. (2016). Searches for Sterile Neutrinos with the IceCube Detector. Phys. Rev. Lett., 117(7), 071801–9pp.
Abstract: The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous nu(mu) or (nu) over bar (mu) disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3 + 1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin(2)2 theta(24) <= 0.02 at Delta m(2) similar to 0.3 eV(2) at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of vertical bar U-e4 vertical bar(2).
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