4,285 research outputs found
Interesting magnetic properties of FeCoSi alloys
Solid solution between nonmagnetic narrow gap semiconductor FeSi and
diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with
long-range helical magnetic ordering, for a wide range of intermediate
concentration. We report various interesting magnetic properties of these
alloys, including low temperature re-entrant spin-glass like behaviour and a
novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya
interaction in the magnetic response of these non-centrosymmetric alloys is
discussed.Comment: 11 pages and 3 figure
On handling urban informality in southern Africa
In this article I reconsider the handling of urban informality by urban planning and management systems in southern Africa. I argue that authorities have a fetish about formality and that this is fuelled by an obsession with urban modernity. I stress that the desired city, largely inspired by Western notions of modernity, has not been and cannot be realized. Using illustrative cases of top–down interventions, I highlight and interrogate three strategies that authorities have deployed to handle informality in an effort to create or defend the modern city. I suggest that the fetish is built upon a desire for an urban modernity based on a concept of formal order that the authorities believe cannot coexist with the “disorder” and spatial “unruliness” of informality. I question the authorities' conviction that informality is an abomination that needs to be “converted”, dislocated or annihilated. I conclude that the very configuration of urban governance and socio-economic systems in the region, like the rest of sub-Saharan Africa, renders informality inevitable and its eradication impossible
Higgs-Boson Production Induced by Bottom Quarks
Bottom quark-induced processes are responsible for a large fraction of the
LHC discovery potential, in particular for supersymmetric Higgs bosons.
Recently, the discrepancy between exclusive and inclusive Higgs boson
production rates has been linked to the choice of an appropriate bottom
factorization scale. We investigate the process kinematics at hadron colliders
and show that it leads to a considerable decrease in the bottom factorization
scale. This effect is the missing piece needed to understand the corresponding
higher order results. Our results hold generally for charged and for neutral
Higgs boson production at the LHC as well as at the Tevatron. The situation is
different for single top quark production, where we find no sizeable
suppression of the factorization scale. Turning the argument around, we can
specify how large the collinear logarithms are, which can be resummed using the
bottom parton picture.Comment: 18 page
Centrality and transverse momentum dependence of elliptic flow of multi-strange hadrons and meson in Au+Au collisions at = 200 GeV
We present high precision measurements of elliptic flow near midrapidity
() for multi-strange hadrons and meson as a function of
centrality and transverse momentum in Au+Au collisions at center of mass energy
200 GeV. We observe that the transverse momentum dependence of
and is similar to that of and , respectively,
which may indicate that the heavier strange quark flows as strongly as the
lighter up and down quarks. This observation constitutes a clear piece of
evidence for the development of partonic collectivity in heavy-ion collisions
at the top RHIC energy. Number of constituent quark scaling is found to hold
within statistical uncertainty for both 0-30 and 30-80 collision
centrality. There is an indication of the breakdown of previously observed mass
ordering between and proton at low transverse momentum in the
0-30 centrality range, possibly indicating late hadronic interactions
affecting the proton .Comment: 7 pages and 4 figures, Accepted for publication in Physical Review
Letter
Observation of charge asymmetry dependence of pion elliptic flow and the possible chiral magnetic wave in heavy-ion collisions
We present measurements of and elliptic flow, , at
midrapidity in Au+Au collisions at 200, 62.4, 39, 27,
19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry,
, based on data from the STAR experiment at RHIC. We find that
() elliptic flow linearly increases (decreases) with charge asymmetry
for most centrality bins at and higher.
At , the slope of the difference of
between and as a function of exhibits a
centrality dependence, which is qualitatively similar to calculations that
incorporate a chiral magnetic wave effect. Similar centrality dependence is
also observed at lower energies.Comment: 6 pages, 4 figure
Azimuthal anisotropy in U+U and Au+Au collisions at RHIC
Collisions between prolate uranium nuclei are used to study how particle
production and azimuthal anisotropies depend on initial geometry in heavy-ion
collisions. We report the two- and four-particle cumulants, and
, for charged hadrons from U+U collisions at =
193 GeV and Au+Au collisions at = 200 GeV. Nearly fully
overlapping collisions are selected based on the amount of energy deposited by
spectators in the STAR Zero Degree Calorimeters (ZDCs). Within this sample, the
observed dependence of on multiplicity demonstrates that ZDC
information combined with multiplicity can preferentially select different
overlap configurations in U+U collisions. An initial-state model with gluon
saturation describes the slope of as a function of multiplicity in
central collisions better than one based on Glauber with a two-component
multiplicity model.Comment: Final paper version accepted for publication in Phys. Rev. Lett. New
version includes comparisons to a constituent quark glauber mode
Observation of Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in at GeV
We report the observation of transverse polarization-dependent azimuthal
correlations in charged pion pair production with the STAR experiment in
collisions at RHIC. These correlations directly probe quark
transversity distributions. We measure signals in excess of five standard
deviations at high transverse momenta, at high pseudorapidities eta>0.5, and
for pair masses around the mass of the rho-meson. This is the first direct
transversity measurement in p+p collisions. Comparing the results to data from
lepton-nucleon scattering will test the universality of these spin-dependent
quantities.Comment: 11 pages, 5 figures, 15 tables. Submitted to PR
Isolation of Flow and Nonflow Correlations by Two- and Four-Particle Cumulant Measurements of Azimuthal Harmonics in 200 GeV Au+Au Collisions
A data-driven method was applied to measurements of Au+Au collisions at
200 GeV made with the STAR detector at RHIC to isolate
pseudorapidity distance -dependent and -independent
correlations by using two- and four-particle azimuthal cumulant measurements.
We identified a component of the correlation that is -independent,
which is likely dominated by anisotropic flow and flow fluctuations. It was
also found to be independent of within the measured range of
pseudorapidity . The relative flow fluctuation was found to be for particles of transverse momentum
less than GeV/. The -dependent part may be attributed to
nonflow correlations, and is found to be relative to the
flow of the measured second harmonic cumulant at
Centrality dependence of identified particle elliptic flow in relativistic heavy ion collisions at sqrt(s)= 7.7--62.4 GeV
Elliptic flow (v_2) values for identified particles at midrapidity in Au + Au
collisions measured by the STAR experiment in the Beam Energy Scan at the
Relativistic Heavy Ion Collider at sqrt{s_{NN}}= 7.7--62.4 GeV are presented
for three centrality classes. The centrality dependence and the data at
sqrt{s_{NN}}= 14.5 GeV are new. Except at the lowest beam energies we observe a
similar relative v_2 baryon-meson splitting for all centrality classes which is
in agreement within 15% with the number-of-constituent quark scaling. The
larger v_2 for most particles relative to antiparticles, already observed for
minimum bias collisions, shows a clear centrality dependence, with the largest
difference for the most central collisions. Also, the results are compared with
A Multiphase Transport Model and fit with a Blast Wave model.Comment: 14 pages, 12 figures, Phys. Rev. C, to be published. Data tables
available at
https://drupal.star.bnl.gov/STAR/publications/centrality-dependence-identified-particle-elliptic-flow-relativistic-heavy-ion-collisi
Charged-to-neutral correlation at forward rapidity in Au+Au collisions at =200 GeV
Event-by-event fluctuations of the ratio of inclusive charged to photon
multiplicities at forward rapidity in Au+Au collision at =200
GeV have been studied. Dominant contribution to such fluctuations is expected
to come from correlated production of charged and neutral pions. We search for
evidences of dynamical fluctuations of different physical origins. Observables
constructed out of moments of multiplicities are used as measures of
fluctuations. Mixed events and model calculations are used as baselines.
Results are compared to the dynamical net-charge fluctuations measured in the
same acceptance. A non-zero statistically significant signal of dynamical
fluctuations is observed in excess to the model prediction when charged
particles and photons are measured in the same acceptance. We find that, unlike
dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated
by correlation due to particle decay. Results are compared to the expectations
based on the generic production mechanism of pions due to isospin symmetry, for
which no significant (<1%) deviation is observed.Comment: 14 pages, 6 figure
- …