Department of Physics and Astronomy

Permanent link for this collectionhttps://hdl.handle.net/2022/22354

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Browsing Department of Physics and Astronomy by Author "Aharmin, Bassam"

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    Constraints on Neutrino Lifetime from the Sudbury Neutrino Observatory
    (American Physical Society, 2019-02) Aharmin, Bassam; Levine, Ilan
    The long baseline between Earth and the Sun makes solar neutrinos an excellent test beam for exploring possible neutrino decay. The signature of such decay would be an energy-dependent distortion of the traditional survival probability which can be fit for using well-developed and high-precision analysis methods. Here a model including neutrino decay is fit to all three phases of 8B solar neutrino data taken by the Sudbury Neutrino Observatory (SNO). This fit constrains the lifetime of neutrino mass state ν2 to be >8.08×10−5  s/eV at 90% confidence. An analysis combining this SNO result with those from other solar neutrino experiments results in a combined limit for the lifetime of mass state ν2 of >1.92×10−3  s/eV at 90% confidence.
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    Cosmogenic Neutron Production at the Sudbury Neutrino Observatory
    (American Physical Society, 2019-12) Aharmin, Bassam; Levine, Ilan
    Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10−4  cm2/(g⋅μ), is measured to be 7.28±0.09(stat)+1.59−1.12(syst) in pure heavy water and 7.30±0.07(stat)+1.40−1.02(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB
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    Electron Antineutrino Search at the Sudbury Neutrino Observatory
    (American Physical Society, 2004) Aharmin, Bassam; Levine, Ilan
    Upper limits on the v¯e flux at the Sudbury Neutrino Observatory have been set based on the v¯e charged-current reaction on deuterium. The reaction produces a positron and two neutrons in coincidence. This distinctive signature allows a search with very low background for v¯e’s from the Sun and other potential sources. Both differential and integral limits on the v¯e flux have been placed in the energy range from 4 – 14.8 MeV. For an energy-independent ve -> v¯e conversion mechanism, the integral limit on the flux of solar v¯e’s in the energy range from 4 – 14.8 MeV is found to be Φv¯e ≤ 3.4 × 104cm−2s−1 (90% C.L.), which corresponds to 0.81% of the standard solar model 8B e flux of 5.05 × 106cm−2s−1, and is consistent with the more sensitive limit from KamLAND in the 8.3 – 14.8 MeV range of 3.7×102cm−2s−1 (90% C.L.). In the energy range from 4 – 8 MeV, a search for v¯e’s is conducted using coincidences in which only the two neutrons are detected. Assuming a v¯e spectrum for the neutron induced fission of naturally occurring elements, a flux limit of Φv¯e 2.0 × 106cm−2s−1 (90% C.L.) is obtained.
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    Low Energy Threshold Analysis of the Phase I and Phase II Data Sets of the Sudbury Neutrino Observatory
    (American Physical Society, 2010-06) Aharmin, Bassam; Levine, Ilan
    Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is Teff = 3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 106 cm−2 s−1, the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8B neutrino energy spectrum, is found to be (NC) = 5.140 +0.160 −0.158(stat) +0.132 −0.117(syst). These uncertainties are more than a factor of two smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the SNO data in which the free parameters directly describe the total 8B neutrino flux and the energy-dependent ve survival probability provides a measure of the total 8B neutrino flux Φ8B = 5.046 +0.159 −0.152(stat) +0.107 −0.123(syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of Θ12 = 34.06 +1.16 −0.84 degrees and Δm2 21 = 7.59 +0.20 −0.21 × 10^−5 eV2. The global value of Φ8B is extracted to a precision of +2.38 −2.95%. In a three-flavor analysis the best fit value of sin^2Θ13 is 2.00+2.09 −1.63 × 10−2. This implies an upper bound of sin^2Θ13 < 0.057 (95% C.L.).
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    Measurement of Neutron Production in Atmospheric Neutrino Interactions at the Sudbury Neutrino Observatory
    (American Physical Society, 2019-06) Aharmin, Bassam; Levine, Ilan
    Neutron production in giga electron volt–scale neutrino interactions is a poorly studied process. We have measured the neutron multiplicities in atmospheric neutrino interactions in the Sudbury Neutrino Observatory experiment and compared them to the prediction of a Monte Carlo simulation using genie and a minimally modified version of geant4. We analyzed 837 days of exposure corresponding to Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy water. Neutrons produced in atmospheric neutrino interactions were identified with an efficiency of 15.3% and 44.3%, for Phases I and II respectively. The neutron production is measured as a function of the visible energy of the neutrino interaction and, for charged current quasielastic interaction candidates, also as a function of the neutrino energy. This study is also performed by classifying the complete sample into two pairs of event categories: charged current quasielastic and non charged current quasielastic, and νμ and νe. Results show good overall agreement between data and Monte Carlo for both phases, with some small tension with a statistical significance below 2σ for some intermediate energies.
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    Measurement of the Cosmic Ray and Neutrino-Induced Muon Flux at the Sudbury Neutrino Observatory
    (American Physical Society, 2009-02) Aharmin, Bassam; Levine, Ilan
    Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth's surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and un-oscillated portion of the neutrino flux. A total of 514 muon-like events are measured between -1 ≤ cos Θ zenith ≤ 0:4 in a total exposure of 2.30 x 1014 cm^2 s. The measured flux normalization is 1.22±0.09 times the Bartol three-dimensional flux prediction. This is the fi rst measurement of the neutrino-induced flux where neutrino oscillations are minimized. The zenith distribution is consistent with previously measured atmospheric neutrino oscillation parameters. The cosmic ray muon flux at SNO with zenith angle cos Θ zenith > 0:4 is measured to be (3.31±0.01 (stat:) 0:09 (sys:)) x 10^-10 μ/s/cm^2.