610 research outputs found
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
Training Auto-encoder-based Optimizers for Terahertz Image Reconstruction
Terahertz (THz) sensing is a promising imaging technology for a wide variety
of different applications. Extracting the interpretable and physically
meaningful parameters for such applications, however, requires solving an
inverse problem in which a model function determined by these parameters needs
to be fitted to the measured data. Since the underlying optimization problem is
nonconvex and very costly to solve, we propose learning the prediction of
suitable parameters from the measured data directly. More precisely, we develop
a model-based autoencoder in which the encoder network predicts suitable
parameters and the decoder is fixed to a physically meaningful model function,
such that we can train the encoding network in an unsupervised way. We
illustrate numerically that the resulting network is more than 140 times faster
than classical optimization techniques while making predictions with only
slightly higher objective values. Using such predictions as starting points of
local optimization techniques allows us to converge to better local minima
about twice as fast as optimization without the network-based initialization.Comment: This is a pre-print of a conference paper published in German
Conference on Pattern Recognition (GCPR) 201
Measurement of higher cumulants of net-charge multiplicity distributions in AuAu collisions at GeV
We report the measurement of cumulants () of the net-charge
distributions measured within pseudorapidity () in AuAu
collisions at GeV with the PHENIX experiment at the
Relativistic Heavy Ion Collider. The ratios of cumulants (e.g. ,
) of the net-charge distributions, which can be related to volume
independent susceptibility ratios, are studied as a function of centrality and
energy. These quantities are important to understand the quantum-chromodynamics
phase diagram and possible existence of a critical end point. The measured
values are very well described by expectation from negative binomial
distributions. We do not observe any nonmonotonic behavior in the ratios of the
cumulants as a function of collision energy. The measured values of and can be directly compared to lattice
quantum-chromodynamics calculations and thus allow extraction of both the
chemical freeze-out temperature and the baryon chemical potential at each
center-of-mass energy.Comment: 512 authors, 8 pages, 4 figures, 1 table. v2 is version accepted for
publication in Phys. Rev. C as a Rapid Communication. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm
Nuclear matter effects on production in asymmetric Cu+Au collisions at = 200 GeV
We report on production from asymmetric Cu+Au heavy-ion collisions
at =200 GeV at the Relativistic Heavy Ion Collider at both
forward (Cu-going direction) and backward (Au-going direction) rapidities. The
nuclear modification of yields in CuAu collisions in the Au-going
direction is found to be comparable to that in AuAu collisions when plotted
as a function of the number of participating nucleons. In the Cu-going
direction, production shows a stronger suppression. This difference is
comparable in magnitude and has the same sign as the difference expected from
shadowing effects due to stronger low- gluon suppression in the larger Au
nucleus. The relative suppression is opposite to that expected from hot nuclear
matter dissociation, since a higher energy density is expected in the Au-going
direction.Comment: 349 authors, 10 pages, 4 figures, and 4 tables. Submitted to Phys.
Rev. C. For v2, fixed LaTeX error in 3rd-to-last sentence. Plain text data
tables for the points plotted in figures for this and previous PHENIX
publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Inclusive cross section and double-helicity asymmetry for production at midrapidity in collisions at GeV
PHENIX measurements are presented for the cross section and double-helicity
asymmetry () in inclusive production at midrapidity from
collisions at ~GeV from data taken in 2012 and 2013 at
the Relativistic Heavy Ion Collider. The next-to-leading-order
perturbative-quantum-chromodynamics theory calculation is in excellent
agreement with the presented cross section results. The calculation utilized
parton-to-pion fragmentation functions from the recent DSS14 global analysis,
which prefer a smaller gluon-to-pion fragmentation function. The
results follow an increasingly positive asymmetry trend with
and with respect to the predictions and are in excellent
agreement with the latest global analysis results. This analysis incorporated
earlier results on and jet , and suggested a positive
contribution of gluon polarization to the spin of the proton for the
gluon momentum fraction range . The data presented here extend to a
currently unexplored region, down to , and thus provide additional
constraints on the value of . The results confirm the evidence for
nonzero using a different production channel in a complementary
kinematic region.Comment: 413 authors, 8 pages, 4 figures. v2 is version accepted as PRD Rapid
Communication. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Single electron yields from semileptonic charm and bottom hadron decays in AuAu collisions at GeV
The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured
open heavy-flavor production in minimum bias AuAu collisions at
GeV via the yields of electrons from semileptonic decays
of charm and bottom hadrons. Previous heavy-flavor electron measurements
indicated substantial modification in the momentum distribution of the parent
heavy quarks due to the quark-gluon plasma created in these collisions. For the
first time, using the PHENIX silicon vertex detector to measure precision
displaced tracking, the relative contributions from charm and bottom hadrons to
these electrons as a function of transverse momentum are measured in AuAu
collisions. We compare the fraction of electrons from bottom hadrons to
previously published results extracted from electron-hadron correlations in
collisions at GeV and find the fractions to be
similar within the large uncertainties on both measurements for
GeV/. We use the bottom electron fractions in AuAu and along
with the previously measured heavy flavor electron to calculate the
for electrons from charm and bottom hadron decays separately. We find
that electrons from bottom hadron decays are less suppressed than those from
charm for the region GeV/.Comment: 432 authors, 33 pages, 23 figures, 2 tables, 2011 data. v2 is version
accepted for publication by Phys. Rev. C. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
- …