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Search Results: 1 - 10 of 368799 matches for " G. C. McLaughlin "
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Neutrino-Nucleus Cross Section Measurements using Stopped Pions and Low Energy Beta Beams
G. C. McLaughlin
Physics , 2004, DOI: 10.1103/PhysRevC.70.045804
Abstract: Two new facilities have recently been proposed to measure low energy neutrino-nucleus cross sections, the nu-SNS (Spallation Neutron Source) and low energy beta beams. The former produces neutrinos by pion decay at rest, while the latter produces neutrinos from the beta decays of accelerated ions. One of the uses of neutrino-nucleus cross section measurements is for supernova studies, where typical neutrino energies are 10s of MeV. In this energy range there are many different components to the nuclear response and this makes the theoretical interpretation of the results of such an experiment complex. Although even one measurement on a heavy nucleus such as lead is much anticipated, more than one data set would be still better. We suggest that this can be done by breaking the electron spectrum down into the parts produced in coincidence with one or two neutrons, running a beta beam at more than one energy, comparing the spectra produced with pions and a beta beam or any combination of these.
Active-Sterile Neutrino Transformation and r-Process Nucleosynthesis
G. C. McLaughlin
Physics , 2000, DOI: 10.1063/1.1345369
Abstract: The type II supernova is considered as a candidate site for the production of heavy elements. Since the supernova produces an intense neutrino flux, neutrino scattering processes will impact element formation. We examine active-sterile neutrino conversion in this environment and find that it may help to produce the requisite neutron-to-seed ratio for synthesis of the r-process elements.
Neutrinos and Nucleosynthesis in Gamma-Ray Burst Accretion Disks
R. Surman,G. C. McLaughlin
Physics , 2003, DOI: 10.1086/381672
Abstract: We calculate the nuclear composition of matter in accretion disks surrounding stellar mass black holes as are thought to accompany gamma-ray bursts (GRBs). We follow a mass element in the accretion disk starting at the point of nuclear dissociation and calculate the evolution of the electron fraction due to electron, positron, electron neutrino and electron antineutrino captures. We find that the neutronization of the disk material by electron capture can be reversed by neutrino interactions in the inner regions of disks with accretion rates of 1 M_solar/s and higher. For these cases the inner disk regions are optically thick to neutrinos, and so to estimate the emitted neutrino fluxes we find the surface of last scattering for the neutrinos (the equivalent of the proto-neutron star neutrinosphere) for each optically thick disk model. We also estimate the influence of neutrino interactions on the neutron-to-proton ratio in outflows from GRB accretion disks, and find it can be significant even when the disk is optically thin to neutrinos.
Reconstructing supernova-neutrino spectra using low-energy beta-beams
N. Jachowicz,G. C. McLaughlin
Physics , 2006, DOI: 10.1103/PhysRevLett.96.172301
Abstract: Only weakly interacting, neutrinos are the principal messengers reaching us from the center of a supernova. Terrestrial neutrino telescopes, such as SNO and SuperKamiokande, can provide precious information about the processes in the core of a collapsing and exploding star. But the information about the supernova that a neutrino detector can supply, is restricted by the fact that little experimental data on the neutrino-nucleus cross sections exists and by the uncertainties in theoretical calculations. In this letter, we propose a novel procedure that determines the response of a target nucleus in a supernova-neutrino detector directly, by using low-energy beta-beams. We show that fitting 'synthetic' spectra, constructed by taking linear combinations of beta-beam spectra, to the original supernova-neutrino spectra reproduces the folded differential cross sections very accurately. Comparing the response in a terrestrial detector to these synthetic responses provides a direct way to determine the main parameters of the supernova-neutrino energy-distribution.
Neutrino Interactions in the Outflow from Gamma-Ray Burst Accretion Disks
R. Surman,G. C. McLaughlin
Physics , 2004, DOI: 10.1086/425901
Abstract: We examine the composition of matter as it flows away from gamma ray burst accretion disks, in order to determine what sort of nucleosynthesis may occur. Since there is a large flux of neutrinos leaving the surface of the disk, the electron fraction of the outflowing material will change due to charged current neutrino interactions. We calculate the electron fraction in the wind using detailed neutrino fluxes from every point on the disk and study a range of trajectories and outflow conditions for several different accretion disk models. We find that low electron fractions, conducive to making r-process elements, only appear in outflows from disks with high accretion rates that have a significant region both of trapped neutrinos and antineutrinos. Disks with lower accretion rates that have only a significant region of trapped neutrinos can have outflows with very high electron fractions, whereas the lowest accretion rate disks with little trapping have outflow electrons fractions of closer to one half.
Prospects for obtaining an r-process from Gamma Ray Burst Disk Winds
G. C. McLaughlin,R. Surman
Physics , 2004, DOI: 10.1016/j.nuclphysa.2005.05.036
Abstract: We discuss the possibility that r-process nucleosynthesis may occur in the winds from gamma ray burst accretion disks. This can happen if the temperature of the disk is sufficiently high that electron antineutrinos are trapped as well as neutrinos. This implies accretion disks with greater than a solar mass per second accretion rate, although lower accretion rates with higher black hole spin parameters may provide viable environments as well. Additionally, the outflow from the disk must either have relatively low entropy, e.g. around s = 10, or the initial acceleration of the wind must be slow enough that it is neutrino and antineutrino capture as opposed to electron and positron capture that sets the electron fraction.
Understanding Supernova Neutrino Physics using Low-Energy Beta-Beams
N. Jachowicz,G. C. McLaughlin
Physics , 2005, DOI: 10.1016/j.ppnp.2005.11.013
Abstract: We show that fitting linear combinations of low-energy beta-beam spectra to supernova-neutrino energy-distributions reconstructs the response of a nuclear target to a supernova flux in a very accurate way. This allows one to make direct predictions about the supernova-neutrino signal in a terrestrial neutrino detector.
Supernova Neutrinos: The Accretion Disk Scenario
G. C. McLaughlin,R. Surman
Physics , 2006, DOI: 10.1103/PhysRevD.75.023005
Abstract: Neutrinos from core collapse supernovae can be emitted from a rapidly accreting disk surrounding a black hole, instead of the canonical proto-neutron star. For Galactic events, detector count rates are considerable and in fact can be in the thousands for Super-Kamiokande. The rate of occurrence of these accreting disks in the Galaxy is predicted to be on the order of 10^-5 yr^-1, yet there is little observational evidence to provide an upper limit on their formation rate. It would therefore be useful to discriminate between neutrinos which have been produced in a proto-neutron star and those which have been produced accretion disks. In order to distinguish between the two scenarios, either the time profile of the neutrino luminosity or the relative fluxes of different neutrino flavors may be considered. There are some signals that would clearly point to one scenario or the other.
Uncovering the Matter-Neutrino Resonance
D. Vaananen,G. C. McLaughlin
Physics , 2015,
Abstract: Matter Neutrino Resonances (MNRs) can drastically modify neutrino flavor evolution in astrophysical environments and may significantly impact nucleosynthesis. Here we further investigate the underlying physics of MNR type flavor transitions. We provide generalized resonance conditions and make analytical predictions for the behavior of the system. We discuss the adiabatic evolution of these transitions, considering both Symmetric and Standard scenarios. Symmetric MNR transitions differ from Standard MNR transitions in that both neutrinos and antineutrinos can completely transform to other flavors simultaneously. We provide an example of the simplest system in which such transitions can occur with a neutrino and an antineutrino having a single energy and emission angle. We further apply linearized stability analysis to predict the location of self-induced nutation type (or bipolar) oscillations due to neutrino-neutrino interactions in the regions where MNR is ineffective. In all cases, we compare our analytical predictions to numerical calculations.
Weak Charge-Changing Flow in Expanding r-Process Environments
G. C. McLaughlin,G. M. Fuller
Physics , 1997, DOI: 10.1086/304801
Abstract: We assess the prospects for attaining steady nuclear flow equilibrium in expanding r-process environments where beta decay and/or neutrino capture determine the nuclear charge-changing rates. For very rapid expansions, we find that weak steady flow equilibrium normally cannot be attained. However, even when neutron capture processes freeze out in such nonequilibrium conditions, abundance ratios of nuclear species in the r-process peaks might still mimic those attained in weak steady flow. This result suggests that the r-process yield in a regime of rapid expansion can be calculated reliably only when all neutron capture, photodisintegration, and weak interaction processes are fully coupled in a dynamical calculation. We discuss the implications of these results for models of the r-process sited in rapidly expanding neutrino-heated ejecta.
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