968 research outputs found
The ATLAS discovery potential for a heavy charged Higgs boson in gg->tbH^{+-} with H^{+-}->tb
The feasibility of detecting a heavy charged Higgs boson,
m(H^{+-})>m(t)+m(b), decaying in the H^{+-}->tb channel is studied with the
fast simulation of the ATLAS detector. We study the gg->H^{+-}tb production
process at the LHC which together with the aforementioned decay channel leads
to four b-quarks in the final state. The whole production and decay chain reads
gg->H^{+-}tb->t\bar{t}b\bar{b}->b\bar{b}b\bar{b}l\nu\bar{q}q'. Combinatorial
background is a major difficulty in this multi-jet environment but can be
overcome by employing multivariate techniques in the event reconstruction.
Requiring four b-tagged jets in the event helps to effectively suppress the
Standard Model backgrounds but leads to no significant improvement in the
discovery potential compared to analyses requiring only three b-tagged jets.
This study indicates that charged Higgs bosons can be discovered at the LHC up
to high masses (m(H^{+-})>400 GeV) in the case of large tan(beta)
Dynamical heterogeneity in soft particle suspensions under shear
We present experimental measurements of dynamical heterogeneities in a dense
system of microgel spheres, sheared at different rates and at different packing
fractions in a microfluidic channel, and visualized with high speed digital
video microscopy. A four-point dynamic susceptibility is deduced from video
correlations, and is found to exhibit a peak that grows in height and shifts to
longer times as the jamming transition is approached from two different
directions. In particular, the time for particle-size root-mean square relative
displacements is found to scale as where is the strain rate and
is the distance from the random close packing volume
fraction. The typical number of particles in a dynamical heterogeneity is
deduced from the susceptibility peak height and found to scale as . Exponent uncertainties are less than ten
percent. We emphasize that the same power-law behavior is found at packing
fractions above and below . Thus, our results considerably extend a
previous observation of for granular heap flow at
fixed packing below . Furthermore, the implied result compares well with expectation from mode-coupling theory and
with prior observations for driven granular systems
Generating Information-Diverse Microwave Speckle Patterns Inside a Room at a Single Frequency With a Dynamic Metasurface Aperture
We demonstrate that dynamic metasurface apertures (DMAs) are capable of generating a multitude of highly uncorrelated speckle patterns in a typical residential environment at a single frequency. We use a DMA implemented as an electrically-large cavity excited by a single port and loaded with many individually-addressable tunable metamaterial radiators. We placed such a DMA in one corner of a plywood-walled L-shape room transmitting microwave signals at 19 GHz as we changed the tuning states of the metamaterial radiators. In another corner, in the non-line-of-sight of the DMA, we conducted a scan of the field generated by the DMA. For comparison, we also performed a similar test where the DMA was replaced by a simple dipole antenna with fixed pattern but generating a signal that spanned 19-24 GHz. Using singular value decomposition of the scanned data, we demonstrate that the DMA can generate a multitude of highly uncorrelated speckle patterns at a single frequency. In contrast, a dipole antenna with a fixed pattern can only generate such a highly uncorrelated set of patterns when operating over a large bandwidth. The experimental results of this paper suggest that DMAs can be used to capture a diversity of information at a single frequency which can be used for single frequency computational imaging systems, NLOS motion detection, gesture recognition systems, and more
Discovery potential for a charged Higgs boson decaying in the chargino-neutralino channel of the ATLAS detector at the LHC
We have investigated charged Higgs boson production via the gluon-bottom
quark mode, gb -> tH+, followed by its decay into a chargino and a neutralino.
The calculations are based on masses and couplings given by the Minimal
Supersymmetric Standard Model (MSSM) for a specific choice of MSSM parameters.
The signature of the signal is characterized by three hard leptons, a
substantial missing transverse energy due to the decay of the neutralino and
the chargino and three hard jets from the hadronic decay of the top quark. The
possibility of detecting the signal over the Standard Model (SM) and non-SM
backgrounds was studied for a set of tanBeta and mA. The existence of 5-sigma
confidence level regions for H+ discovery at integrated luminosities of 100
fb-1 and 300 fb-1 is demonstrated, which cover also the intermediate region 4 <
tanBeta < 10 where H+ decays to SM particles cannot be used for H+ discovery
Microfluidic rheology of soft colloids above and below jamming
The rheology near jamming of a suspension of soft colloidal spheres is
studied using a custom microfluidic rheometer that provides stress versus
strain rate over many decades. We find non-Newtonian behavior below the jamming
concentration and yield stress behavior above it. The data may be collapsed
onto two branches with critical scaling exponents that agree with expectations
based on Hertzian contacts and viscous drag. These results support the
conclusion that jamming is similar to a critical phase transition, but with
interaction-dependent exponents.Comment: 4 pages, experimen
Comparing Flow Thresholds and Dynamics for Oscillating and Inclined Granular Layers
The onset and dynamics of flow in shallow horizontally oscillating granular layers are studied as a function of the depth of the layer and imposed acceleration. Measurements of the flow velocity made from the top and side are presented in the frame of reference of the container. As is also found for avalanches of inclined layers, the thresholds for starting and stopping of flow are slightly different. The variation with depth of the starting acceleration Γstart for the oscillating layer is similar to the corresponding variation of the tangent of the starting angle tan(Θstart) for avalanches in the same container at low frequencies, but deviates as the frequency is increased. However, the threshold behavior depends significantly on the measurement protocol. Just above Γstart, the motion decays with time as the material reorganizes over a minute or so, causing the apparent threshold to increase. Furthermore, the rms velocity as a function of acceleration rises more sharply above the starting threshold if the first minute or so of excitation is discarded. Once excited, the rheology of the material is found to vary in time during the cycle in surprising ways. If the maximum inertial force (proportional to the container acceleration amplitude) is slightly higher than that required to produce flow, the flow velocity grows as soon as the inertial force exceeds zero in each cycle, but jamming occurs long before the inertial force returns to zero. At higher Γ, the motion is fluidlike over the entire cycle. However, the fraction of the cycle during which the layer is mobile is typically far higher than what one would predict from static considerations or the behavior of the inclined layer. Finally, we consider the flow profiles as a function of both the transverse distance across the cell at the free surface and also as a function of the vertical coordinate in the boundary layer near the sidewall. These profiles have time-dependent shapes and are therefore significantly different from profiles previously measured for avalanche flows
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