709 research outputs found
High-Efficiency Ge-on-Si SPADs for Short-Wave Infrared
High efficiency, Ge-on-Si single-photon avalanche diode (SPAD) detectors operating in the short-wave infrared region (1310 nm - 1550 nm) at near room temperature have the potential to be used for numerous emerging applications, including quantum communications, quantum imaging and eye-safe LIDAR applications. In this work, planar geometry Ge-on-Si SPAD designs demonstrate a significant decrease in the dark count rate compared to previous generations of Ge-on-Si detectors. 100 μm diameter microfabricated SPADs demonstrate record low NEPs of 2.2×10-16 WHz-1/2, and single-photon detection efficiencies of 18% for 1310 nm at 78 K. The devices demonstrate single-photon detection at temperatures up to 175 K
High performance planar germanium-on-silicon single-photon avalanche diode detectors
Single-photon detection has emerged as a method of choice for ultra-sensitive measurements of picosecond optical transients. In the short-wave infrared, semiconductor-based single-photon detectors typically exhibit relatively poor performance compared with all-silicon devices operating at shorter wavelengths. Here we show a new generation of planar germanium-on-silicon (Ge-on-Si) single-photon avalanche diode (SPAD) detectors for short-wave infrared operation. This planar geometry has enabled a significant step-change in performance, demonstrating single-photon detection efficiency of 38% at 125 K at a wavelength of 1310 nm, and a fifty-fold improvement in noise equivalent power compared with optimised mesa geometry SPADs. In comparison with InGaAs/InP devices, Ge-on-Si SPADs exhibit considerably reduced afterpulsing effects. These results, utilising the inexpensive Ge-on-Si platform, provide a route towards large arrays of efficient, high data rate Ge-on-Si SPADs for use in eye-safe automotive LIDAR and future quantum technology applications
Measuring Black Hole Spin using X-ray Reflection Spectroscopy
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The
Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds
a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the
referencing of the discovery of soft lags in 1H0707-495 (which were in fact
first reported in Fabian et al. 2009
Geiger Mode Ge-on-Si Single-Photon Avalanche Diode Detectors
High efficiency single photon avalanche detectors (SPADs) based on the Ge-on-Si material system are a promising emerging technology for high sensitivity optical detection in the short-wave infrared region. Here we demonstrate record single photon detection efficiencies of 38% at 1310nm with an operating temperature of 125K. This was achieved using a novel planar geometry which allowed us to achieve an NEPs of 3×10 −16 WHz −1/2 and reduced afterpulsing when compared to InGaAs/InP based SPADs operated in nominally identical conditions
Signals of neutralinos and charginos from gauge boson fusion at the CERN Large Hadron Collider
We point out that interesting signals of the non-strongly interacting sector
of the supersymmetric standard model arise from the production of charginos and
neutralinos via vector boson fusion (VBF) at the Large Hadron Collider (LHC).
In particular, if R-parity is violated, the hadronically quiet signals of
charginos and neutralinos through direct production get considerably
suppressed. We show that in such cases, the VBF channel can be useful in
identifying this sector through clean and background-free final states.Comment: 10 pages Latex, 8 figures, minor changes in text and few references
added, to be published in Phys. Rev.
Like Sign Dilepton Signature for R-Parity Violating SUSY Search at the Tevatron Collider
The like sign dileptons provide the most promising signature for
superparticle search in a large category of -parity violating SUSY models.
We estimate the like sign dilepton signals at the Tevatron collider, predicted
by these models, over a wide region of the MSSM parameter space. One expects an
unambiguous signal upto a gluino mass of GeV ( GeV) with
the present (proposed) accumulated luminosity of .Comment: 12 page LaTeX file; 5 figures available upon request from the autho
R-parity violation effect on the top-quark pair production at linear colliders
We investigate in detail the effects of the R-parity lepton number violation
in the minimal supersymmetric standard model (MSSM) on the top-quark pair
production via both and collision modes at the linear
colliders. We find that with the present experimental constrained
parameters, the effect from interactions on the processes
and could be
significant and may reach -30% and several percent, respectively. Our results
show that the effects are sensitive to the c.m.s. energy and the
relevant parameters. However, they are not sensitive to squark and
slepton masses when (or ) and are almost independent on the Comment: Accepted by Phys.Rev.
NMR and Mossbauer study of spin dynamics and electronic structure of Fe{2+x}V{1-x}Al and Fe2VGa
In order to assess the magnetic ordering process in Fe2VAl and the related
material Fe2VGa, we have carried out nuclear magnetic resonance (NMR) and
Mossbauer studies. 27Al NMR relaxation measurements covered the temperature
range 4 -- 500 K in Fe(2+x)V(1-x)Al samples. We found a peak in the NMR
spin-lattice relaxation rate, 27T1^-1, corresponding to the magnetic
transitions in each of these samples. These peaks appear at 125 K, 17 K, and
165 K for x = 0.10, 0, and - 0.05 respectively, and we connect these features
with critical slowing down of the localized antisite defects. Mossbauer
measurements for Fe2VAl and Fe2VGa showed lines with no hyperfine splitting,
and isomer shifts nearly identical to those of the corresponding sites in Fe3Al
and Fe3Ga, respectively. We show that a model in which local band filling leads
to magnetic regions in the samples, in addition to the localized antisite
defects, can account for the observed magnetic ordering behavior.Comment: 5 pages, 3 figure
T-odd Gluon-Top-Quark Effective Couplings at the CERN Large Hadron Collider
The T-odd top-quark chromoelectric dipole moment (tCEDM) is probed through
top-quark-pair production via gluon fusion at the CERN Large Hadron Collider
(LHC) by considering the possibility of having polarized protons. The complete
analytic expressions for the tree-level helicity amplitudes of gg-> ttbar is
also presented. For the derived analytic results we determine the 1-sigma
statistical sensitivities to the tCEDM form factor for (i) typical CP-odd
observables composed of lepton and anti-lepton momenta from t and tbar
semileptonic decays for unpolarized protons, and (ii) a CP-odd event asymmetry
for polarized protons by using the so-called Berger-Qiu (BQ) parametrization of
polarized gluon distribution functions. We find that at the CERN LHC, the
CP-odd energy and angular correlations can put a limit of 10^{-18} to 10^{-17}
g_scm on the real and imaginary parts of the tCEDM, while the simple CP-odd
event asymmetry with polarized protons could put a very strong limit of
10^{-20} g_scm on the imaginary part of the tCEDM.Comment: 14 pages(LaTeX), 1 Postscript figure(use epsfig.sty
Effects of new physics in neutrino oscillations in matter
A new flavor changing electron neutrino interaction with matter would always
dominate the nu_e oscillation probability at sufficiently high neutrino
energies. Being suppressed by theta_{13}, the energy scale at which the new
effect starts to be relevant may be within the reach of realistic experiments,
where the peculiar dependence of the signal with energy could give rise to a
clear signature in the nu_e --> nu_tau channel. The latter could be observed by
means of a coarse large magnetized detector by exploiting tau --> mu decays. We
discuss the possibility of identifying or constraining such effects with a high
energy neutrino factory. We also comment on the model independent limits on
them.Comment: 11 pages, 5 figure
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