LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of the (B)over-bar(s)(0) Meson Lifetime in D-s(+)pi(-) Decays. Phys. Rev. Lett., 113(17), 172001–9pp.
Abstract: We present a measurement of the ratio of the (B) over bar (0)(s) meson lifetime, in the flavor-specific decay to D-s(+)pi(-), to that of the (B) over bar (0) meson. The pp collision data used correspond to an integrated luminosity of 1 fb(-1), collected with the LHCb detector, at a center-of-mass energy of 7 TeV. Combining our measured value of 1.010 +/- 0.010 +/- 0.008 for this ratio with the known (B) over bar (0) lifetime, we determine the flavor-specific (B) over bar (0)(s) lifetime to be tau((B) over bar (0)(s) ) = 1.535 +/- 0.015 +/- 0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.
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Marchi, T. et al, & Gadea, A. (2014). Quadrupole Transition Strength in the Ni-74 Nucleus and Core Polarization Effects in the Neutron-Rich Ni Isotopes. Phys. Rev. Lett., 113(18), 182501–5pp.
Abstract: The reduced transition probability B(E2;0(+) -> 2(+)) has been measured for the neutron-rich nucleus Ni-74 in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained B(E2;0(+) -> 2(+)) = 642(-226)(+216) e(2) fm(4) value defines a trend which is unexpectedly small if referred to Ni-70 and to a previous indirect determination of the transition strength in Ni-74. This indicates a reduced polarization of the Z = 28 core by the valence neutrons. Calculations in the pfgd model space reproduce well the experimental result indicating that the B(E2) strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation gamma rays. Phys. Rev. D, 90(7), 072012–11pp.
Abstract: We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section gamma It is obtained by observing nuclear deexcitation. rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to 3.01 x 10(20) protons on target. By selecting only events during the T2K beam window and with well-reconstructed vertices in the fiducial volume, the large background rate from natural radioactivity is dramatically reduced. We observe 43 events in the 4-30 MeV reconstructed energy window, compared with an expectation of 51.0, which includes an estimated 16.2 background events. The background is primarily nonquasielastic neutral-current interactions and has only 1.2 events from natural radioactivity. The flux-averaged NCQE cross section we measure is 1.55 x 10(-38) cm(2) with a 68% confidence interval of (1.22, 2.20) x 10(-38) cm(2) at a median neutrino energy of 630 MeV, compared with the theoretical prediction of 2.01 x 10(-38) cm(2).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Observation of charmonium pairs produced exclusively in pp collisions. J. Phys. G, 41(11), 115002–17pp.
Abstract: A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of 3 fb(-1) collected at centre-of-mass energies of 7 and 8 TeV, J/psi J/psi and J/psi psi (2S) pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges (-3.5,-1.5) and (1.5, 5.0). Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be sigma (J/psi J/psi) = 58 +/- 10(stat) +/- 6(syst) pb, sigma(J/psi psi(2S)) = 63(-18)(+27)(stat) +/- 10(syst) pb, sigma(psi(2S)psi(2S)) < 237 pb, sigma(chi)(chi)(C0)(C0) < 69 nb, sigma(chi)(chi)(C1)(C1) < 45 pb, sigma(chi)(chi)(C2)(C2) < 141 pb, where the upper limits are set at the 90% confidence level. The measured J/psi J/psi and J/psi psi (2S) cross-sections are consistent with theoretical expectations.
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Langer, C. et al, & Domingo-Pardo, C. (2014). Determining the rp-Process Flow through Ni-56: Resonances in Cu-57(p,gamma)Zn-58 Identified with GRETINA. Phys. Rev. Lett., 113(3), 032502–5pp.
Abstract: An approach is presented to experimentally constrain previously unreachable (p,gamma) reaction rates on nuclei far from stability in the astrophysical rp process. Energies of all critical resonances in the Cu-57(p,gamma)Zn-58 reaction are deduced by populating states in Zn-58 with a (d, n) reaction in inverse kinematics at 75 MeV/u, and detecting.-ray-recoil coincidences with the state-of-the-art gamma-ray tracking array GRETINA and the S800 spectrograph at the National Superconducting Cyclotron Laboratory. The results reduce the uncertainty in the Cu-57(p,gamma) reaction rate by several orders of magnitude. The effective lifetime of Ni-56, an important waiting point in the rp process in x-ray bursts, can now be determined entirely from experimentally constrained reaction rates.
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