Department of Physics and Astronomy

Permanent link for this collection


Recent Submissions

Now showing 1 - 20 of 44
  • Item
    Improved Limits on Spin-Dependent WIMP-Proton Interactions from a Two Liter CF3I Bubble Chamber
    (American Physical Society, 2011-03) Behnke, Ed; Behnke, J.; Hinnefeld, Jerry; Levine, Ilan; Shepherd, T.
    Data from the operation of a bubble chamber filled with 3.5 kg of CF3I in a shallow underground site are reported. An analysis of ultrasound signals accompanying bubble nucleations confirms that alpha decays generate a significantly louder acoustic emission than single nuclear recoils, leading to an efficient background discrimination. Three dark matter candidate events were observed during an effective exposure of 28.1 kg-day, consistent with a neutron background. This observation provides strong direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses > 20 GeV/c2.
  • Item
    Multifield Reheating after Modular j-Inflation
    (Elsevier, 2018-03-22) Schimmrigk, Rolf
    In the inflationary framework of cosmology the initial phase of rapid expansion has to be followed by a reheating stage, which is envisioned to end in a radiation dominated big bang. Key parameters that characterize this big bang state are the temperature at the end of the reheating stage and the baryon asymmetry. For general interacting theories these parameters are difficult to obtain analytically because of the involved structure of the potential. In this paper multifield reheating is considered for interacting theories in which the inflaton trajectory is weakly curved. This scenario is realized in the model of j-inflation, a particular example of modular inflation, allowing an estimate of the reheat temperature.
  • Item
    On Flux Vacua and Modularity
    (Springer, 2020-09) Schimmrigk, Rolf
    Geometric modularity has recently been conjectured to be a characteristic feature for flux vacua with W = 0. This paper provides support for the conjecture by computing motivic modular forms in a direct way for several string compactifications for which such vacua are known to exist. The analysis of some Calabi-Yau mani-folds which do not admit supersymmetric flux vacua shows that the reverse of the conjecture does not hold.
  • Item
    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
  • Item
    Fabrication of a Nodular Neutron Array: A Collaborative Approach to Undergraduate Research
    (American Association of Physics Teachers, 2005-02) Howes, R. H.; Hinnefeld, J.
    The construction of the modular neutron array, a highly efficient time-of-flight detector, for use with the recently upgraded coupled cyclotron facility at the National Superconducting Cyclotron Laboratory has been accomplished by a collaboration of undergraduate physics departments. The collaboration presents an opportunity for involving faculty and students from undergraduate physics programs in state-of-the-art physics experiments at large user facilities.
  • Item
    New Insights into Particle Detection with Superheated Liquids
    (IOP Publishing, 2010-11) Archambault, Simon; Behnke, Ed; Behnke, Joshua; Hinnefeld, Jerry; Levine, Ilan; Vander Werf, Nathan P.
    We report new results obtained in calibrations of superheated liquid droplet detectors used in dark matter searches with different radiation sources (n,α,γ). In particular, detectors were spiked with alpha-emitters located inside and outside the droplets. It is shown that the responses are different, depending on whether alpha particles or recoil nuclei create the signals. The energy thresholds for α-emitters are compared with test beam measurements using mono-energetic neutrons, as well as with theoretical predictions. Finally a model is presented which describes how the observed intensities of particle induced acoustic signals can be related to the dynamics of bubble growth in superheated liquids. An improved understanding of the bubble dynamics is an important first step in obtaining better discrimination between particle types interacting in detectors of this kind.
  • Item
    New developments and recent results in nuclear astrophysics at Louvain-la-Neuve
    (American Physical Society, 2002-04) Cherubini, S.; Hinnefeld, Jerry
    Nuclear astrophysics using radioactive nuclear beams is one of the major research topics in Louvain-la-Neuve. Recently, experiment aiming at the measurement of (α,γ), and (α, p) reactions have been performed. The 15O(α,γ)19Ne reaction was studied using an indirect method based on the study of the 18Ne(d, p)19Ne*. Preliminary results of a new analysis of this experiment are presented here. The new mass recoil separator ARES, coupled to the new cyclotron CYCLONE-44, is now operational. The ARES project status and results of performance tests are reported here.
  • Item
    Neutron-unbound states in 25,26F
    (American Physical Society, 2011) Frank, Nathan H.; Hinnefeld, Jerry
    Neutron-unbound states in 25F and 26F were populated via the reactions 9Be(26Ne,24F+n) and 9Be(26Ne,25F+n), respectively. A resonance close to the neutron separation energy in 25F was identified with a decay energy of 28 ± 4 keV. This resonance corresponds to an excited state in 25F at 4249 ± 116 keV assuming it decays to the ground state of 24F. Guided by shell-model calculations, a spin and parity of 1/2− can be assigned to this state. In the spectrum of 26F, which was produced in a nucleon-exchange reaction, there are indications for an excited state with a decay energy of ∼270 keV.
  • Item
    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.).
  • Item
    First Dark Matter Search Results from a 4-kg CF3I Bubble Chamber Operated in a Deep Underground Site
    (American Physical Society, 2012-09) Behnke, Ed; Behnke, Joshua; Conner, A.; Grace, Emily A.; Levine, Ilan; Moan, T.; Nania, T.
    New data are reported from the operation of a 4.0 kg CF3I bubble chamber in the 6800 foot deep SNOLAB underground laboratory. The effectiveness of ultrasound analysis in discriminating alpha decay background events from single nuclear recoils has been confirmed, with a lower bound of >99.3% rejection of alpha decay events. Twenty single nuclear recoil event candidates and three multiple bubble events were observed during a total exposure of 553 kg-days distributed over three different bubble nucleation thresholds. The effective exposure for single bubble recoil-like events was 437.4 kg-days. A neutron background internal to the apparatus, of known origin, is estimated to account for five single nuclear recoil events and is consistent with the observed rate of multiple bubble events. The remaining excess of single bubble events exhibits characteristics indicating the presence of an additional background. These data provide new direct detection constraints on WIMP-proton spin-dependent scattering for WIMP masses >20 GeV/c2 and demonstrate significant sensitivity for spin-independent interactions.
  • Item
    Final state interaction or a 3H excited state?
    (American Physical Society, 2003) Rogachev, Grigoriy V.; Hinnefeld, Jerry
    An inclusive a-particle spectrum from the 1H(6He,a) reaction has been measured at a 6He laboratory energy of 23.9 MeV. A resonancelike structure is observed at an a-particle lab energy of about 20 MeV, which corresponds to an energy of End50.6 MeV in the n-d channel. An analysis of the spectrum shows that it cannot be explained by the effect of binary final-state interactions. The hypotheses that this structure represents ~a! a new excited state of tritium or ~b! a three-body final-state interaction are discussed.
  • Item
    Exploring the Low-Z Shore of the Island of Inversion at N=19
    (American Physical Society, 2012-01) Christian, Gregory A.; Hinnefeld, Jerry
    The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound 28F, determined to be a resonance in the 27F+n continuum at 220(50) keV. States in 28F were populated by the reactions of a 62MeV/u 29Ne beam impinging on a 288 mg/cm2 beryllium target. The measured 28F ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that p f shell intruder configurations play only a small role in the ground state structure of 28F and establishing a low-Z boundary of the island of inversion for N = 19 isotones. Keywords: Binding energies and masses; Single-particle levels and strength functions
  • Item
    Evolution of Li, Be and B in the Galaxy
    (American Astronomical Society, 2001-10) Valle, Giada; Ferrini, Federico; Galli, Daniele; Shore, Steven N.
    In this paper we study the production of Li, Be and B nuclei by Galactic cosmic ray spallation processes. We include three kinds of processes: (i ) spallation by light cosmic rays impinging on interstellar CNO nuclei (direct processes); (ii ) spallation by CNO cosmic ray nuclei impinging on interstellar p and 4He (inverse processes); and (iii ) α–α fusion reactions. The latter dominate the production of 6,7Li. We calculate production rates for a closed-box Galactic model, verifying the quadratic dependence of the Be and B abundances for low values of Z. These are quite general results and are known to disagree with observations. We then show that the multi-zone multi-population model we used previously for other aspects of Galactic evolution produces quite good agreement with the linear trend observed at low metallicities without fine tuning. We argue that reported discrepancies between theory and observations do not represent a nucleosynthetic problem, but instead are the consequences of inaccurate treatments of Galactic evolution.
  • Item
    Evidence for nonequilibrium proton emission in a low-energy heavy-ion reaction
    (American Physical Society, 1999) DeYoung, Paul A.; Hinnefeld, Jerry
    Correlation functions for p-p, p-d, p-α, d-α, and α-α were measured for the 16O+27Al system at a beam energy of 72 MeV. The detector array was centered at laboratory angle of 20°. Compared to published data obtained at larger scattering angles, an unexpected dependence on angle is seen for the p-p channel. The observed anticorrelation is stronger at more forward angles, which suggests that correlation functions are sensitive to the specific reaction mechanisms producing the light-charged particles.
  • Item
    Emergent Spacetime from Modular Motives
    (Springer, 2008-12) Schimmrigk, Rolf
    The program of constructing spacetime geometry from string theoretic modular forms is extended to Calabi-Yau varieties of dimensions two, three, and four, as well as higher rank motives. Modular forms on the worldsheet can be constructed from the geometry of spacetime by computing the L-functions associated to omega motives of Calabi-Yau varieties, generated by their holomorphic n−forms via Galois representations. The modular forms that emerge from the Ω−motive and other motives of the intermediate cohomology are related to characters of the underlying rational conformal field theory. The converse problem of constructing space from string theory proceeds in the class of diagonal theories by determining the motives associated to modular forms in the category of pure motives with complex multiplication. The emerging picture indicates that the L-function can be interpreted as a map from the geometric category of motives to the category of conformal field theories on the worldsheet.
  • Item
    Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory
    (American Physical Society, 2002-07) Ahmad, Q. R.; Levine, Ilan
    Observations of neutral-current n interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the ne component of the 8B solar flux is Φe = 1.76 +0.05 -0.05 (stat)+0.09 -0.09(syst) x 10^6 cm^-2 s^-1 for a kinetic energy threshold of 5 MeV. The non-ve component is Φe = 3.41 +0.45 -0.45(stat) +0.48 -0.45(syst) x 10^6 cm^-2 s^-1, 5.3o greater than zero, providing strong evidence for solar ve flavor transformation. The total flux measured with the NC reaction is ΦNC = 5.09 +0.44 -0.43(stat) =0.46 -0.43(syst) x 10^6 cm^-2 s^-1, consistent with solar models.
  • Item
    Constraints on low-mass WIMP interactions on 19F from PICASSO
    (Elsevier, 2012) Archambault, Simon; Behnke, Ed; Grace, Emily A.; Levine, Ilan
    Recent results from the PICASSO dark matter search experiment at SNOLAB are reported. These results were obtained using a subset of 10 detectors with a total target mass of 0.72 kg of 19F and an exposure of 114 kgd. The low backgrounds in PICASSO allow recoil energy thresholds as low as 1.7 keV to be obtained which results in an increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below 10 GeV/c2. No dark matter signal was found. Best exclusion limits in the spin dependent sector were obtained for WIMP masses of 20 GeV/c2 with a cross section on protons of σ SD p = 0.032 pb (90% C.L.). In the spin independent sector close to the low mass region of 7 GeV/c2 favoured by CoGeNT and DAMA/LIBRA, cross sections larger than σ S I p = 1.41 × 10−4 pb (90% C.L.) are excluded. Keywords: Dark matter, WIMPs, Superheated droplets, SNOLAB
  • Item
    Complex Multiplication Symmetry of Black Hole Attractors
    (Elsevier, 2003) Lynker, Monika; Periwal, Vipul; Schimmrigk, Rolf
    We show how Moore’s observation, in the context of toroidal compactifications in type IIB string theory, concerning the complex multiplication structure of black hole attractor varieties, can be generalized to Calabi-Yau compactifications with finite fundamental groups. This generalization leads to an alternative general framework in terms of motives associated to a Calabi-Yau variety in which it is possible to address the arithmetic nature of the attractor varieties in a universal way via Deligne’s period conjecture.
  • Item
    General Framework of Automorphic Inflation
    (Springer Verlag, 2016) Schimmrigk, Rolf
    Automorphic inflation is an application of the framework of automorphic scalar field theory, based on the theory of automorphic forms and representations. In this paper the general framework of automorphic and modular inflation is described in some detail, with emphasis on the resulting stratification of the space of scalar field theories in terms of the group theoretic data associated to the shift symmetry, as well as the automorphic data that specifies the potential. The class of theories based on Eisenstein series provides a natural generalization of the model of j-inflation considered previously. Keywords: Cosmology of Theories beyond the SM, Differential and Algebraic Geometry, Discrete Symmetries
  • Item
    A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium
    (IOP Publishing, 1998-09) LaRosa, Theodore N.; Shore, Steven N.; Magnani, Loris Alberto
    We present the results of a velocity correlation study of the high latitude cloud MBM16 using a fully sampled 12CO map, supplemented by new 13CO data. We find a correlation length of 0.4 pc. This is similar in size to the formaldehyde clumps described in our previous study. We associate this correlated motion with coherent structures within the turbulent flow. Such structures are generated by free shear flows. Their presence in this non-star forming cloud indicates that kinetic energy is being supplied to the internal turbulence by an external shear flow. Such large scale driving over long times is a possible solution to the dissipation problem for molecular cloud turbulence.