143 research outputs found
Investigation of the Chaotic Dynamics of an Electron Beam with a Virtual Cathode in an External Magnetic Field
The effect of the strength of the focusing magnetic field on chaotic dynamic
processes occurring inan electron beam with a virtual cathode, as well as on
the processes whereby the structures form in the beamand interact with each
other, is studied by means of two-dimensional numerical simulations based on
solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as
the focusing magnetic field is decreased,the dynamics of an electron beam with
a virtual cathode becomes more complicated due to the formation andinteraction
of spatio-temporal longitudinal and transverse structures in the interaction
region of a vircator. The optimum efficiency of the interaction of an electron
beam with the electromagnetic field of the vircator isachieved at a
comparatively weak external magnetic field and is determined by the
fundamentally two-dimensional nature of the motion of the beam electrons near
the virtual cathode.Comment: 12 pages, 8 figure
Transverse-momentum-dependent Multiplicities of Charged Hadrons in Muon-Deuteron Deep Inelastic Scattering
A semi-inclusive measurement of charged hadron multiplicities in deep
inelastic muon scattering off an isoscalar target was performed using data
collected by the COMPASS Collaboration at CERN. The following kinematic domain
is covered by the data: photon virtuality (GeV/), invariant
mass of the hadronic system GeV/, Bjorken scaling variable in the
range , fraction of the virtual photon energy carried by the
hadron in the range , square of the hadron transverse momentum
with respect to the virtual photon direction in the range 0.02 (GeV/ (GeV/). The multiplicities are presented as a
function of in three-dimensional bins of , , and
compared to previous semi-inclusive measurements. We explore the
small- region, i.e. (GeV/), where
hadron transverse momenta are expected to arise from non-perturbative effects,
and also the domain of larger , where contributions from
higher-order perturbative QCD are expected to dominate. The multiplicities are
fitted using a single-exponential function at small to study
the dependence of the average transverse momentum on , and . The power-law behaviour of the
multiplicities at large is investigated using various
functional forms. The fits describe the data reasonably well over the full
measured range.Comment: 28 pages, 20 figure
Corrigendum to "Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section" [Phys. Lett. B 793 (2019) 188]
n/
Measurement of P T -weighted Sivers asymmetries in leptoproduction of hadrons
The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted
with the hadron transverse momentum PT , allow for the extraction of important transverse-momentumdependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information
on the Sivers function, which is a leading-twist distribution that arises from a correlation between the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the spin of the nucleon.
Using the high-statistics data collected by the COMPASS Collaboration in 2010 with a transversely polarised proton target, we have evaluated two types of PT -weighted Sivers asymmetries, which are both
proportional to the product of the first transverse moment of the Sivers function and of the fragmentation
function. The results are compared to the standard unweighted Sivers asymmetries and used to extract the
first transverse moments of the Sivers distributions for u and d quark
Triangle Singularity as the Origin of the a1(1420)
The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a(1)(1420), decaying to f(0)(980)(pi). With a mass too close to and a width smaller than the axial-vector ground state a(1)(1260), it was immediately interpreted as a new light exotic meson, similar to the X, Y, Z states in the hidden-charm sector. We show that a resonancelike signal fully matching the experimental data is produced by the decay of the a(1) (1260) resonance into K* (-> K pi) (K) over bar and subsequent rescattering through a triangle singularity into the coupled f(0)(980)p channel. The amplitude for this process is calculated using a new approach based on dispersion relations. The triangle-singularity model is fitted to the partial-wave data of the COMPASS experiment. Despite having fewer parameters, this fit shows a slightly better quality than the one using a resonance hypothesis and thus eliminates the need for an additional resonance in order to describe the data. We thereby demonstrate for the first time in the lightmeson sector that a resonancelike structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect
Seasonal Variation of Multiple-Muon Cosmic Ray Air Showers Observed in the NOvA Detector on the Surface
We report the rate of cosmic ray air showers with multiplicities exceeding 15
muon tracks recorded in the NOvA Far Detector between May 2016 and May 2018.
The detector is located on the surface under an overburden of 3.6 meters water
equivalent. We observe a seasonal dependence in the rate of multiple-muon
showers, which varies in magnitude with multiplicity and zenith angle. During
this period, the effective atmospheric temperature and surface pressure ranged
between 210 K to 230 K and 940mbar to 990mbar, respectively; the shower rates
are anti-correlated with the variation in the effective temperature. The
variations are about 30% larger for the highest multiplicities than the lowest
multiplicities and 20% larger for showers near the horizon than vertical
showers
Search for multimessenger signals in NOvA coincident with LIGO/Virgo detections
Using the NOvA neutrino detectors, a broad search has been performed for any signal coincident with 28 gravitational wave events detected by the LIGO/Virgo Collaboration between September 2015 and July 2019. For all of these events, NOvA is sensitive to possible arrival of neutrinos and cosmic rays of GeV and higher energies. For five (seven) events in the NOvA Far (Near) Detector, timely public alerts from the LIGO/Virgo Collaboration allowed recording of MeV-scale events. No signal candidates were found
Search for multimessenger signals in NOvA coincident with LIGO/Virgo detections
Using the NOvA neutrino detectors, a broad search has been performed for any signal coincident with 28 gravitational wave events detected by the LIGO/Virgo Collaboration between September 2015 and July 2019. For all of these events, NOvA is sensitive to possible arrival of neutrinos and cosmic rays of GeV and higher energies. For five (seven) events in the NOvA Far (Near) Detector, timely public alerts from the LIGO/Virgo Collaboration allowed recording of MeV-scale events. No signal candidates were found
Measurement of the Double-Differential Muon-neutrino Charged-Current Inclusive Cross Section in the NOvA Near Detector
We report cross-section measurements of the final-state muon kinematics for
\numu charged-current interactions in the NOvA near detector using an
accumulated 8.09 protons-on-target (POT) in the NuMI beam. We
present the results as a double-differential cross section in the observed
outgoing muon energy and angle, as well as single-differential cross sections
in the derived neutrino energy, , and square of the four-momentum
transfer, . We compare the results to inclusive cross-section predictions
from various neutrino event generators via calculations using a
covariance matrix that accounts for bin-to-bin correlations of systematic
uncertainties. These comparisons show a clear discrepancy between the data and
each of the tested predictions at forward muon angle and low , indicating
a missing suppression of the cross section in current neutrino-nucleus
scattering models
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