4,776 research outputs found
Design, Construction, Operation and Performance of a Hadron Blind Detector for the PHENIX Experiment
A Hadron Blind Detector (HBD) has been developed, constructed and
successfully operated within the PHENIX detector at RHIC. The HBD is a
Cherenkov detector operated with pure CF4. It has a 50 cm long radiator
directly coupled in a window- less configuration to a readout element
consisting of a triple GEM stack, with a CsI photocathode evaporated on the top
surface of the top GEM and pad readout at the bottom of the stack. This paper
gives a comprehensive account of the construction, operation and in-beam
performance of the detector.Comment: 51 pages, 39 Figures, submitted to Nuclear Instruments and Method
Strong extinction of a far-field laser beam by a single quantum dot
Through the utilization of index-matched GaAs immersion lens techniques we
demonstrate a record extinction (12%) of a far-field focused laser by a single
InAs/GaAs quantum dot. This contrast level enables us to report for the first
time resonant laser transmission spectroscopy on a single InAs/GaAs quantum dot
without the need for phase-sensitive lock-in detection
European spaces and the Roma: Denaturalizing the naturalized in online reader comments
With the entry of several Eastern European nations into the European Union (EU), a âthirdâ space has developed in the discourse for nations perceived as not fully integrated âinsideâ the EU system. This article investigates the construction of this âthird spaceâ in the resultant âmoral panicâ about undesired immigration from other EU countries and its potential drain on the social services of the United Kingdom and links it to Euroskeptic discourse in British media. The article uses construal operations from cognitive linguistics combined with critical discourse studies as a way of denaturalizing the discourse in online comments that focus on the Bulgarian/Romanian immigration issue which we then connect to anti-Roma discourse. Results reveal a view of the United Kingdom as contaminated by Roma and underscore the need for novel metaphors to be countered before they become entrenched and used as tools for political propaganda
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Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions.
The PHENIX collaboration presents first measurements of low-momentum (0.41ââGeV/c) direct-photon yield dN_{Îł}^{dir}/dη is a smooth function of dN_{ch}/dη and can be well described as proportional to (dN_{ch}/dη)^{α} with αâ1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A+A collision systems. At a given beam energy, the scaling also holds for high p_{T} (>5ââGeV/c), but when results from different collision energies are compared, an additional sqrt[s_{NN}]-dependent multiplicative factor is needed to describe the integrated-direct-photon yield
Measurements of Sub-degree B-mode Polarization in the Cosmic Microwave Background from 100 Square Degrees of SPTpol Data
We present a measurement of the -mode polarization power spectrum (the
spectrum) from 100 of sky observed with SPTpol, a
polarization-sensitive receiver currently installed on the South Pole
Telescope. The observations used in this work were taken during 2012 and early
2013 and include data in spectral bands centered at 95 and 150 GHz. We report
the spectrum in five bins in multipole space, spanning the range , and for three spectral combinations: 95 GHz 95 GHz, 95
GHz 150 GHz, and 150 GHz 150 GHz. We subtract small ( in units of statistical uncertainty) biases from these spectra and
account for the uncertainty in those biases. The resulting power spectra are
inconsistent with zero power but consistent with predictions for the
spectrum arising from the gravitational lensing of -mode polarization. If we
assume no other source of power besides lensed modes, we determine a
preference for lensed modes of . After marginalizing over
tensor power and foregrounds, namely polarized emission from galactic dust and
extragalactic sources, this significance is . Fitting for a single
parameter, , that multiplies the predicted lensed -mode
spectrum, and marginalizing over tensor power and foregrounds, we find
, indicating that our measured spectra are
consistent with the signal expected from gravitational lensing. The data
presented here provide the best measurement to date of the -mode power
spectrum on these angular scales.Comment: 21 pages, 4 figure
CMB Polarization B-mode Delensing with SPTpol and Herschel
We present a demonstration of delensing the observed cosmic microwave
background (CMB) B-mode polarization anisotropy. This process of reducing the
gravitational-lensing generated B-mode component will become increasingly
important for improving searches for the B modes produced by primordial
gravitational waves. In this work, we delens B-mode maps constructed from
multi-frequency SPTpol observations of a 90 deg patch of sky by subtracting
a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing
potential map estimated from the map of the
CIB. We find that our delensing procedure reduces the measured B-mode power
spectrum by 28% in the multipole range ; this is shown to be
consistent with expectations from theory and simulations and to be robust
against systematics. The null hypothesis of no delensing is rejected at . Furthermore, we build and use a suite of realistic simulations to
study the general properties of the delensing process and find that the
delensing efficiency achieved in this work is limited primarily by the noise in
the lensing potential map. We demonstrate the importance of including realistic
experimental non-idealities in the delensing forecasts used to inform
instrument and survey-strategy planning of upcoming lower-noise experiments,
such as CMB-S4.Comment: 17 pages, 10 figures. Comments are welcome
Measurements of the Temperature and E-Mode Polarization of the CMB from 500 Square Degrees of SPTpol Data
We present measurements of the -mode polarization angular auto-power
spectrum () and temperature--mode cross-power spectrum () of the
cosmic microwave background (CMB) using 150 GHz data from three seasons of
SPTpol observations. We report the power spectra over the spherical harmonic
multipole range , and detect nine acoustic peaks in the
spectrum with high signal-to-noise ratio. These measurements are the most
sensitive to date of the and power spectra at and , respectively. The observations cover 500 deg, a fivefold increase
in area compared to previous SPTpol analyses, which increases our sensitivity
to the photon diffusion damping tail of the CMB power spectra enabling tighter
constraints on \LCDM model extensions. After masking all sources with
unpolarized flux mJy we place a 95% confidence upper limit on residual
polarized point-source power of at , suggesting that the damping tail
dominates foregrounds to at least with modest source masking. We
find that the SPTpol dataset is in mild tension with the model
(), and different data splits prefer parameter values that differ
at the level. When fitting SPTpol data at we
find cosmological parameter constraints consistent with those for
temperature. Including SPTpol data at results in a preference for
a higher value of the expansion rate (H_0 = 71.3 \pm
2.1\,\mbox{km}\,s^{-1}\mbox{Mpc}^{-1} ) and a lower value for present-day
density fluctuations ().Comment: Updated to match version accepted to ApJ. 34 pages, 17 figures, 6
table
A Measurement of the Cosmic Microwave Background Gravitational Lensing Potential from 100 Square Degrees of SPTpol Data
We present a measurement of the cosmic microwave background (CMB)
gravitational lensing potential using data from the first two seasons of
observations with SPTpol, the polarization-sensitive receiver currently
installed on the South Pole Telescope (SPT). The observations used in this work
cover 100 deg of sky with arcminute resolution at 150 GHz. Using a
quadratic estimator, we make maps of the CMB lensing potential from
combinations of CMB temperature and polarization maps. We combine these lensing
potential maps to form a minimum-variance (MV) map. The lensing potential is
measured with a signal-to-noise ratio of greater than one for angular
multipoles between . This is the highest signal-to-noise mass map
made from the CMB to date and will be powerful in cross-correlation with other
tracers of large-scale structure. We calculate the power spectrum of the
lensing potential for each estimator, and we report the value of the MV power
spectrum between as our primary result. We constrain the ratio
of the spectrum to a fiducial CDM model to be . Restricting ourselves to
polarized data only, we find . This measurement rejects the hypothesis of no lensing at
using polarization data alone, and at using both
temperature and polarization data.Comment: 16 pages, 8 figure
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Multiparticle azimuthal correlations for extracting event-by-event elliptic and triangular flow in Au + Au collisions at sNN =200 GeV
We present measurements of elliptic and triangular azimuthal anisotropy of charged particles detected at forward rapidity 1<|η|<3 in Au + Au collisions at sNN=200 GeV, as a function of centrality. The multiparticle cumulant technique is used to obtain the elliptic flow coefficients v2{2},v2{4},v2{6}, and v2{8}, and triangular flow coefficients v3{2} and v3{4}. Using the small-variance limit, we estimate the mean and variance of the event-by-event v2 distribution from v2{2} and v2{4}. In a complementary analysis, we also use a folding procedure to study the distributions of v2 and v3 directly, extracting both the mean and variance. Implications for initial geometrical fluctuations and their translation into the final-state momentum distributions are discussed
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