241 research outputs found
Angle-resolved photoemission spectroscopy of Co-based boride superconductor LaCo1.73Fe0.27B2
We have performed angle-resolved photoemission spectroscopy of Co-based
boride superconductor LaCo1.73Fe0.27B2 (Tc = 4.1 K), which is isostructural to
the 122-type Fe-pnictide superconductor with the pnictogen atom being replaced
with boron. We found that the Fermi level is located at a dip in the density of
states (DOS) in contrast to Co-pnictide ferromagnets. This reduction in DOS
together with the strong Co 3d-B 2p covalent bonding removes the ferromagnetic
order and may cause the superconductivity. The energy bands near the Fermi
level show higher three dimensionality and a weaker electron-correlation effect
than those of Fe pnictides. The Fermi surface topology is considerably
different from that of Fe pnictides, suggesting the difference in the
superconducting mechanism between boride and pnictide superconductors.Comment: 5 pages, 4 figure
Possible nodal superconducting gap emerging at the Lifshitz transition in heavily hole-doped Ba0.1K0.9Fe2As2
We performed a high energy resolution ARPES investigation of over-doped
Ba0.1K0.9Fe2As2 with T_c= 9 K. The Fermi surface topology of this material is
similar to that of KFe2As2 and differs from that of slightly less doped
Ba0.3K0.7Fe2As2, implying that a Lifshitz transition occurred between x=0.7 and
x=0.9. Albeit for a vertical node found at the tip of the emerging
off-M-centered Fermi surface pocket lobes, the superconducting gap structure is
similar to that of Ba0.3K0.7Fe2As2, suggesting that the paring interaction is
not driven by the Fermi surface topology.Comment: 5 pages, 4 figure
ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(FeRu)As
We used high-energy resolution angle-resolved photoemission spectroscopy to
extract the momentum dependence of the superconducting gap of Ru-substituted
Ba(FeRu)As ( K). Despite a strong
out-of-plane warping of the Fermi surface, the magnitude of the superconducting
gap observed experimentally is nearly isotropic and independent of the
out-of-plane momentum. More precisely, we respectively observed 5.7 meV and 4.5
meV superconducting gaps on the inner and outer -centered hole Fermi
surface pockets, whereas a 4.8 meV gap is recorded on the M-centered electron
Fermi surface pockets. Our results are consistent with the model with
a dominant antiferromagnetic exchange interaction between the next-nearest Fe
neighbors.Comment: 5 pages, 4 figure
A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics
In a previous paper, we calculated the fully quantum-mechanical cross section
for electromagnetic excitation during peripheral heavy-ion collisions. Here, we
examine the sensitivity of that cross section to the detailed structure of the
projectile and target nuclei. At the transition energies relevant to nuclear
physics, we find the cross section to be weakly dependent on the projectile
charge radius, and to be sensitive to only the leading momentum-transfer
dependence of the target transition form factors. We exploit these facts to
derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the
long-wavelength limit. This improved spectrum includes the effects of
projectile size, the finite longitudinal momentum transfer required by
kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure
Different mechanism of two-proton emission from proton-rich nuclei Al and Mg
Two-proton relative momentum () and opening angle ()
distributions from the three-body decay of two excited proton-rich nuclei,
namely Al p + p + Na and Mg p
+ p + Ne, have been measured with the projectile fragment separator
(RIPS) at the RIKEN RI Beam Factory. An evident peak at MeV/c as
well as a peak in around 30 are seen in the two-proton
break-up channel from a highly-excited Mg. In contrast, such peaks are
absent for the Al case. It is concluded that the two-proton emission
mechanism of excited Mg is quite different from the Al case, with
the former having a favorable diproton emission component at a highly excited
state and the latter dominated by the sequential decay process
Measurement of the radiative decay of polarized muons in the MEG experiment
We studied the radiative muon decay by
using for the first time an almost fully polarized muon source. We identified a
large sample (~13000) of these decays in a total sample of 1.8x10^14 positive
muon decays collected in the MEG experiment in the years 2009--2010 and
measured the branching ratio B() =
(6.03+-0.14(stat.)+-0.53(sys.))x10^-8 for E_e > 45 MeV and E_{\gamma} > 40 MeV,
consistent with the Standard Model prediction. The precise measurement of this
decay mode provides a basic tool for the timing calibration, a normalization
channel, and a strong quality check of the complete MEG experiment in the
search for process.Comment: 8 pages, 7 figures. Added an introduction to NLO calculation which
was recently calculated. Published versio
Hadron shower decomposition in the highly granular CALICE analogue hadron calorimeter
The spatial development of hadronic showers in the CALICE scintillator-steel
analogue hadron calorimeter is studied using test beam data collected at CERN
and FNAL for single positive pions and protons with initial momenta in the
range from 10 to 80 GeV/c. Both longitudinal and radial development of hadron
showers are parametrised with two-component functions. The parametrisation is
fit to test beam data and simulations using the QGSP_BERT and FTFP_BERT physics
lists from Geant4 version 9.6. The parameters extracted from data and simulated
samples are compared for the two types of hadrons. The response to pions and
the ratio of the non-electromagnetic to the electromagnetic calorimeter
response, h/e, are estimated using the extrapolation and decomposition of the
longitudinal profiles.Comment: 38 pages, 19 figures, 5 tables; author list changed; submitted to
JINS
Shower development of particles with momenta from 15 GeV to 150 GeV in the CALICE scintillator-tungsten hadronic calorimeter
We present a study of showers initiated by electrons, pions, kaons, and
protons with momenta from 15 GeV to 150 GeV in the highly granular CALICE
scintillator-tungsten analogue hadronic calorimeter. The data were recorded at
the CERN Super Proton Synchrotron in 2011. The analysis includes measurements
of the calorimeter response to each particle type as well as measurements of
the energy resolution and studies of the longitudinal and radial shower
development for selected particles. The results are compared to Geant4
simulations (version 9.6.p02). In the study of the energy resolution we include
previously published data with beam momenta from 1 GeV to 10 GeV recorded at
the CERN Proton Synchrotron in 2010.Comment: 35 pages, 21 figures, 8 table
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