49 research outputs found
Edge states on graphene ribbon in magnetic field: interplay between Dirac and ferromagnetic-like gaps
By combining analytic and numerical methods, edge states on a finite width
graphene ribbon in a magnetic field are studied in the framework of low-energy
effective theory that takes into account the possibility of quantum Hall
ferromagnetism (QHF) gaps and dynamically generated Dirac-like masses. The
analysis is done for graphene ribbons with both zigzag and armchair edges. The
characteristic features of the spectrum of the edge states in both these cases
are described. In particular, the conditions for the existence of the gapless
edge states are established. Implications of these results for the
interpretation of recent experiments are discussed.Comment: 13 pages, 7 figures. v2: analysis for ribbons with armchair edges
added, to appear in Phys. Rev.
Modelling of the multi-transition periodic flaring in G9.62+0.20E
We present detailed modeling of periodic flaring events in the 6.7 GHz and
12.2 GHz methanol lines as well as the OH 1665 MHz and 1667 MHz transitions
observed in the G9.62+0.20E star-forming region. Our analysis is performed
within the framework of the one-dimensional Maxwell-Bloch equations, which
intrinsically cover the complementary quasi-steady state maser and transient
superradiance regimes. We find that the variations in flaring time-scales
measured for the different species/transitions, and sometimes even for a single
spectral line, are manifestations of and are best modeled with Dicke's
superradiance, which naturally accounts for a modulation in the duration of
flares through corresponding changes in the inversion pump. In particular, it
can explain the peculiar behaviour observed for some features, such as the
previously published result for the OH 1667 MHz transition at
km s as well as the methanol 6.7 GHz line at
km s, through a partial quenching of the
population inversion during flaring events.Comment: 13 pages, 13 figures, accepted MNRA
The Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND)
The observation of neutrinoless double-beta decay (0)
would show that lepton number is violated, reveal that neutrinos are Majorana
particles, and provide information on neutrino mass. A discovery-capable
experiment covering the inverted ordering region, with effective Majorana
neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with
excellent energy resolution and extremely low backgrounds, at the level of
0.1 count /(FWHMtyr) in the region of the signal. The
current generation Ge experiments GERDA and the MAJORANA DEMONSTRATOR
utilizing high purity Germanium detectors with an intrinsic energy resolution
of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in
the 0 signal region of all 0
experiments. Building on this success, the LEGEND collaboration has been formed
to pursue a tonne-scale Ge experiment. The collaboration aims to develop
a phased 0 experimental program with discovery potential
at a half-life approaching or at years, using existing resources as
appropriate to expedite physics results.Comment: Proceedings of the MEDEX'17 meeting (Prague, May 29 - June 2, 2017
Impact of cross-section uncertainties on supernova neutrino spectral parameter fitting in the Deep Underground Neutrino Experiment
A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is
to measure the MeV neutrinos produced by a Galactic
core-collapse supernova if one should occur during the lifetime of the
experiment. The liquid-argon-based detectors planned for DUNE are expected to
be uniquely sensitive to the component of the supernova flux, enabling
a wide variety of physics and astrophysics measurements. A key requirement for
a correct interpretation of these measurements is a good understanding of the
energy-dependent total cross section for charged-current
absorption on argon. In the context of a simulated extraction of
supernova spectral parameters from a toy analysis, we investigate the
impact of modeling uncertainties on DUNE's supernova neutrino
physics sensitivity for the first time. We find that the currently large
theoretical uncertainties on must be substantially reduced
before the flux parameters can be extracted reliably: in the absence of
external constraints, a measurement of the integrated neutrino luminosity with
less than 10\% bias with DUNE requires to be known to about 5%.
The neutrino spectral shape parameters can be known to better than 10% for a
20% uncertainty on the cross-section scale, although they will be sensitive to
uncertainties on the shape of . A direct measurement of
low-energy -argon scattering would be invaluable for improving the
theoretical precision to the needed level.Comment: 25 pages, 21 figure
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
The DUNE far detector vertical drift technology. Technical design report
DUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including the mystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on a near and a far detector as it aims to determine the neutrino mass hierarchy and to make high-precision measurements of the PMNS matrix parameters, including the CP-violating phase. It will also stand ready to observe supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines the many tens-of-kiloton fiducial mass necessary for rare event searches with the sub-centimeter spatial resolution required to image those events with high precision. The addition of a photon detection system enhances physics capabilities for all DUNE physics drivers and opens prospects for further physics explorations. Given its size, the far detector will be implemented as a set of modules, with LArTPC designs that differ from one another as newer technologies arise. In the vertical drift LArTPC design, a horizontal cathode bisects the detector, creating two stacked drift volumes in which ionization charges drift towards anodes at either the top or bottom. The anodes are composed of perforated PCB layers with conductive strips, enabling reconstruction in 3D. Light-trap-style photon detection modules are placed both on the cryostat's side walls and on the central cathode where they are optically powered. This Technical Design Report describes in detail the technical implementations of each subsystem of this LArTPC that, together with the other far detector modules and the near detector, will enable DUNE to achieve its physics goals
Super-radiance from a relativistic source
Cooperative super-radiant emission from a highly relativistic multi-particle source is modeled and solved for the simple case of two particles. An existing model of a single relativistic two-level particle is used to construct a Hamiltonian describing relativistic velocity dependent multi-particle super-radiance. The standard diagrammatic framework is applied to the calculation of time evolution and density operators from this Hamiltonian, demonstrating during the process a departure from standard results and calculation methods. In particular, the so-called vertical photon result of the literature is shown to be modified by the relativistic Lorentz factor of the sample; additionally, a set of coupled differential equations describing certain propagators in the velocity-dependent small sample framework are introduced and solved numerically via a hybrid fourth order RungeâKutta and convolution approach. The model is applied to the simple case of two highly relativistic particles travelling with slightly differing velocities simulated at varying relativistic mean sample ÎČ factors, and velocity coherence requirements for a sample to demonstrate enhanced super-radiant emission in the observer frame are evaluated. These coherence requirements are found to become increasingly restrictive at higher ÎČ factors, even in the context of standard results of relativistic velocity differential transformations
Generalization of the Menegozzi and Lamb maser algorithm to the transient superradiance regime
We investigate the application of the conventional quasi-steady state maser modelling algorithm of Menegozzi & Lamb (ML) to the high field transient regime of the one-dimensional Maxwell-Bloch (MB) equations for a velocity distribution of atoms or molecules. We quantify the performance of a first order perturbation approximation available within the ML framework when modelling regions of increasing electric field strength, and we show that the ML algorithm is unable to accurately describe the key transient features of R. H. Dicke\u27s superradiance (SR). We extend the existing approximation to one of variable fidelity, and we derive a generalization of the ML algorithm convergent in the transient SR regime by performing an integration on the MB equations prior to their Fourier representation. We obtain a manifestly unique integral Fourier representation of the MB equations which is complex in the number of velocity channels N and which is capable of simulating transient SR processes at varying degrees of fidelity. As a proof of operation, we demonstrate our algorithm\u27s accuracy against reference time domain simulations of the MB equations for transient SR responses to the sudden inversion of a sample possessing a velocity distribution of moderate width. We investigate the performance of our algorithm at varying degrees of approximation fidelity, and we prescribe fidelity requirements for future work simulating SR processes across wider velocity distributions
Variability, flaring and coherence -- the complementarity of the maser and superradiance regimes
We discuss the role that coherence phenomena can have on the intensity
variability of spectral lines associated with maser radiation. We do so by
introducing the fundamental cooperative radiation phenomenon of (Dicke's)
superradiance and discuss its complementary nature to the maser action, as well
as its role in the flaring behaviour of some maser sources. We will consider
examples of observational diagnostics that can help discriminate between the
two, and identify superradiance as the source of the latter. More precisely, we
show how superradiance readily accounts for the different time-scales observed
in the multi-wavelength monitoring of the periodic flaring in G9.62+0.20E.Comment: 15 pages, 11 figure