ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of the low-mass Drell-Yan differential cross section at root s=7 TeV using the ATLAS detector. J. High Energy Phys., 06(6), 112–46pp.
Abstract: The differential cross section for the process Z/gamma* -> ll (l = e, mu) as a function of dilepton invariant mass is measured in pp collisions at root s = 7 TeV at the LHC using the ATLAS detector. The measurement is performed in the e and μchannels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb(-1) collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb(-1) of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.
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Karakoc, M. et al, & Molina, F. (2014). Gamow-Teller transitions in the A=40 isoquintet of relevance for neutrino captures in Ar-40. Phys. Rev. C, 89(6), 064313–7pp.
Abstract: Background: The Gamow-Teller response of Ar-40 is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of 1(+) states at 2290 and 2730 keV in K-40 results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from Ar-40(p, n) charge-exchange data and the transition strengths for the analog transitions studied in the beta decay of Ti-40. Purpose: This study was aimed at resolving the ambiguity between the results from the Ar-40(p, n) charge-exchange and Ti-40 beta-decay data. Method: Shell-model calculations in the sd-pf shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from Ar-40 and Ti-40. Distorted-wave Born approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the Ar-40(p, n) data. New high-resolution data for the Ar-40(He-3,t) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations. Results: The shell-model calculations showed that interference between amplitudes associated with pf and sd components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for Ar-40 and Ti-40, can produce the differences on the scale of those observed between the Ar-40 charge-exchange and Ti-40 beta-decay data. In combination with the difference in nuclear penetrability of the (p, n) and (He-3,t) probes, the different contributions from amplitudes associated with transitions in the pf and sd shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying 1(+) states in the Ar-40(p, n) and Ar-40(He-3,t) data. Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the Ar-40(p, n) data, not the Ti-40 beta-decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying 1(+) states in K-40 and Sc-40 and the experimentally observed Gamow-Teller strengths.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Antideuteron production in Upsilon(nS) decays and in e(+)e(-) -> q(q) over bar at root s approximate to 10.58 GeV. Phys. Rev. D, 89(11), 111102–8pp.
Abstract: We present measurements of the inclusive production of antideuterons in e(+)e(-) annihilation into hadrons at approximate to 10.58 GeV center-of-mass energy and in Upsilon(1S, 2S, 3S) decays. The results are obtained using data collected by the BABAR detector at the PEP-II electron-positron collider. Assuming a fireball spectral shape for the emitted antideuteron momentum, we find B(Upsilon(1S) -> (d) over barX) = (2.81 +/- 0.49(stat)-(+0.20)(0.24)(syst)) x 10(-5), B(Upsilon(2S) -> (d) over barX) = (2.64 +/- 0.11(stat)(-0.21)(+0.26)(syst)) x 10(-5), B(Upsilon(3S) -> (d) over barX) = (2.33 +/- 0.15(stat)(-0.28)(+0.31)(syst)) x 10(-5), and sigma(e(+)e(-) -> (d) over barX) = (9.63 +/- 0.41(stat)(-1.01)(+1.17)(syst) fb.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2014). Study of the reaction e(+)e(-) -> psi(2S)pi(+)pi(-) via initial-state radiation at BABAR. Phys. Rev. D, 89(11), 111103–8pp.
Abstract: We study the process e(+)e(-) -> psi(2S)pi(+)pi(-) with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BABAR detector at center-of-mass energies at and near the (nS) (n = 2, 3, 4) resonances and correspond to an integrated luminosity of 520 fb(-1). We investigate the psi(2S)pi(+)pi(-) mass distribution from 3.95 to 5.95 GeV/c(2), and measure the center-of-mass energy dependence of the associated e(+)e(-) -> psi(2S)pi(+)pi(-) cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the psi(2S)pi(+)pi(-) mass distribution corresponding to the decay mode psi(2S) -> J/psi pi(+)pi(-) yields a mass value of 4340 +/- 16 (stat) +/- 9 (syst) MeV/c(2) and a width of 94 +/- 32 (stat) +/- 13 (syst) MeV for the first resonance, and for the second a mass value of 4669 +/- 21 (stat) +/- 3 (syst) MeV/c(2) and a width of 104 +/- 48 (stat) +/- 10 (syst) MeV. In addition, we show the pi(+)pi(-) mass distributions for these resonant regions.
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Borexino Collaboration(Bellini, G. et al), & Pena-Garay, C. (2014). Final results of Borexino Phase-I on low-energy solar neutrino spectroscopy. Phys. Rev. D, 89(11), 112007–68pp.
Abstract: Borexino has been running since May 2007 at the Laboratori Nazionali del Gran Sasso laboratory in Italy with the primary goal of detecting solar neutrinos. The detector a large unsegmented liquid scintillator calorimeter characterized by unprecedented low levels of intrinsic radioactivity is optimized for the study of the lower energy part of the spectrum. During Phase-I (2007-2010) Borexino first detected and then precisely measured the flux of the Be-7 solar neutrinos ruled out any significant day-night asymmetry of their interaction rate made the first direct observation of the pep neutrinos and set the tightest upper limit on the flux of solar neutrinos produced in the CNO cycle (carbon nitrogen oxigen) where carbon nitrogen and oxygen serve as catalysts in the fusion process. In this paper we discuss the signal signature and provide a comprehensive description of the backgrounds quantify their event rates describe the methods for their identification selection or subtraction and describe data analysis. Key features are an extensive in situ calibration program using radioactive sources the detailed modeling of the detector response the ability to define an innermost fiducial volume with extremely low background via software cuts and the excellent pulse-shape discrimination capability of the scintillator that allows particle identification. We report a measurement of the annual modulation of the Be-7 neutrino interaction rate. The period the amplitude and the phase of the observed modulation are consistent with the solar origin of these events and the absence of their annual modulation is rejected with higher than 99% C.L. The physics implications of Phase-I results in the context of the neutrino oscillation physics and solar models are presented.
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