Ultrafast optical control using the Kerr nonlinearity in hydrogenated amorphous silicon microcylindrical resonators

Microresonators are ideal systems for probing nonlinear phenomena at low thresholds due to their small mode volumes and high quality (Q) factors. As such, they have found use both for fundamental studies of light-matter interactions as well as for applications in areas ranging from telecommunications to medicine. In particular, semiconductor-based resonators with large Kerr nonlinearities have great potential for high speed, low power all-optical processing. Here we present experiments to characterize the size of the Kerr induced resonance wavelength shifting in a hydrogenated amorphous silicon resonator and demonstrate its potential for ultrafast all-optical modulation and switching. Large wavelength shifts are observed for low pump powers due to the high nonlinearity of the amorphous silicon material and the strong mode confinement in the microcylindrical resonator. The threshold energy for switching is less than a picojoule, representing a significant step towards advantageous low power silicon-based photonic technologies.

Inclusive search for supersymmetry using razor variables in pp collisions at √s=7 TeV

An inclusive search is presented for new heavy particle pairs produced in √s=7 TeV proton-proton collisions at the LHC using 4.7±0.1 fb(-1) of integrated luminosity. The selected events are analyzed in the 2D razor space of M(R), an event-by-event indicator of the heavy particle mass scale, and R, a dimensionless variable related to the missing transverse energy. The third-generation sector is probed using the event heavy-flavor content. The search is sensitive to generic supersymmetry models with minimal assumptions about the superpartner decay chains. No excess is observed in the number of events beyond that predicted by the standard model. Exclusion limits are derived in the CMSSM framework as well as for simplified models. Within the CMSSM parameter space considered, gluino masses up to 800 GeV and squark masses up to 1.35 TeV are excluded at 95% confidence level depending on the model parameters. The direct production of pairs of top or bottom squarks is excluded for masses as high as 400 GeV.

Search for physics beyond the standard model in events with τ leptons, jets, and large transverse momentum imbalance in pp collisions at [Formula: see text]

A search for physics beyond the standard model is performed with events having one or more hadronically decaying τ leptons, highly energetic jets, and large transverse momentum imbalance. The data sample corresponds to an integrated luminosity of 4.98 fb-1 of proton-proton collisions at [Formula: see text] collected with the CMS detector at the LHC in 2011. The number of observed events is consistent with predictions for standard model processes. Lower limits on the mass of the gluino in supersymmetric models are determined.

Nonlinear transmission properties of hydrogenated amorphous silicon core fibers towards the mid-infrared regime

The nonlinear transmission properties of hydrogenated amorphous silicon (a-Si:H) core fibers are characterized from the near-infrared up to the edge of the mid-infrared regime. The results show that this material exhibits linear losses on the order of a few dB/cm, or less, over the entire wavelength range, decreasing down to a value of 0.29 dB/cm at 2.7μm, and negligible nonlinear losses beyond the two-photon absorption (TPA) edge ~ 1.7μm. By measuring the dispersion of the nonlinear Kerr and TPA parameters we have found that the nonlinear figure of merit (FOM(NL)) increases dramatically over this region, with FOM(NL) > 20 around 2μm and above. This characterization demonstrates the potential for a-Si:H fibers and waveguides to find use in nonlinear applications extending beyond telecoms and into the mid-infrared regime.

Search for supersymmetry in pp collisions at [Formula: see text] TeV in events with a single lepton, jets, and missing transverse momentum

Results are reported from a search for new physics processes in events containing a single isolated high-transverse-momentum lepton (electron or muon), energetic jets, and large missing transverse momentum. The analysis is based on a 4.98 fb-1 sample of proton-proton collisions at a center-of-mass energy of 7 TeV, obtained with the CMS detector at the LHC. Three separate background estimation methods, each relying primarily on control samples in the data, are applied to a range of signal regions, providing complementary approaches for estimating the background yields. The observed yields are consistent with the predicted standard model backgrounds. The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model, as well as on cross sections for simplified models, which provide a generic description of the production and decay of new particles in specific, topology based final states.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1140/epjc/s10052-013-2404-z) contains supplementary material, which is available to authorized users.

Search for pair production of third-generation leptoquarks and top squarks in pp collisions at sqrt[s] = 7 TeV

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a τ lepton and a b quark. The search is based on a data sample of pp collisions at sqrt[s] = 7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4.8 fb(-1). The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a τ lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, τ lepton, and b quark, λ(333)(') are obtained. These results are the most stringent for these scenarios to date.

Microbial electrolysis cell scale-up for combined wastewater treatment and hydrogen production

This study demonstrates microbial electrolysis cell (MEC) scale-up from a 50mL to a 10L cell. Initially, a 50mL membraneless MEC with a gas diffusion cathode was operated on synthetic wastewater at different organic loads. It was concluded that process scale-up might be best accomplished using a "reactor-in-series" concept. Consequently, 855mL and 10L MECs were built and operated. By optimizing the hydraulic retention time (HRT) of the 855mL MEC and individually controlling the applied voltages of three anodic compartments with a real-time optimization algorithm, a COD removal of 5.7g L(R)(-1)d(-1) and a hydrogen production of 1.0-2.6L L(R)(-1)d(-1) was achieved. Furthermore, a two MECs in series 10L setup was constructed and operated on municipal wastewater. This test showed a COD removal rate of 0.5g L(R)(-1)d(-1), a removal efficiency of 60-76%, and an energy consumption of 0.9Whperg of COD removed.

Measurement of the azimuthal anisotropy of neutral pions in Pb-Pb collisions at sqrt[s](NN)] = 2.76 TeV

First measurements of the azimuthal anisotropy of neutral pions produced in Pb-Pb collisions at a center-of-mass energy of sqrt[s(NN)] = 2.76 TeV are presented. The amplitudes of the second Fourier component (v(2)) of the π(0) azimuthal distributions are extracted using an event-plane technique. The values of v(2) are studied as a function of the neutral pion transverse momentum (p(T)) for different classes of collision centrality in the kinematic range 1.6<p(T) <8.0 GeV/c, within the pseudorapidity interval |η|<0.8. The CMS measurements of v(2) (p(T)) are similar to previously reported π(0) azimuthal anisotropy results from sqrt[s(NN)] = 200 GeV Au-Au collisions at RHIC, despite a factor of ∼ 14 increase in the center-of-mass energy. In the momentum range 2.5<p(T)<5.0 GeV/c, the neutral pion anisotropies are found to be smaller than those observed by CMS for inclusive charged particles.

Evidence for associated production of a single top quark and W boson in pp collisions at sqrt[s]=7 TeV

Evidence is presented for the associated production of a single top quark and W boson in pp collisions at sqrt[s]=7  TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4.9  fb(-1). The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the tt background from the signal. The observed signal has a significance of 4.0σ and corresponds to a cross section of 16(-4)(+5)  pb, in agreement with the standard model expectation of 15.6±0.4(-1.2)(+1.0)  pb.

Intravenous versus oral outpatient antibiotic therapy for pediatric acute osteomyelitis

The optimal route (oral versus intravenous) of antibiotic administration for pediatric acute osteomyelitis is not well established. Seventy-eight children from our university hospital and 17 children at our county hospital were treated for acute osteomyelitis. The rates of intravenous antibiotics upon discharge were 95% versus 65% (P=0.002), respectively. The recurrence rate and line complication rates were 10% and 24% at the university hospital, compared to 0% (P=0.34) and 6% (P=0.29) at the county hospital. Based on this data, a prospective comparison between intravenous and early oral antibiotic therapy for pediatric acute osteomyelitis is recommended.

Study of the Dijet mass spectrum in pp → W+jets events at sqrt[s] = 7 TeV

We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in pp → W+2-jet and W+3-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of 5.0 fb(-1) collected with the CMS detector at sqrt[s] = 7 TeV. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.

Measurement of the relative prompt production rate of χc2 and χc1 in pp collisions at [Formula: see text]

A measurement is presented of the relative prompt production rate of χc2 and χc1 with 4.6 fb-1 of data collected by the CMS experiment at the LHC in pp collisions at [Formula: see text]. The two states are measured via their radiative decays χc→J/ψ+γ, with the photon converting into an e+e- pair for J/ψ rapidity |y(J/ψ)|<1.0 and photon transverse momentum pT(γ)>0.5 GeV/c. The measurement is given for six intervals of pT(J/ψ) between 7 and 25 GeV/c. The results are compared to theoretical predictions.

Observation of sequential Υ suppression in PbPb collisions

The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 μb(-1) and 230 nb(-1), respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, R(AA), is measured as a function of the collision centrality. Integrated over centrality, the R(AA) values are 0.56±0.08(stat)±0.07(syst), 0.12±0.04(stat)±0.02(syst), and lower than 0.10 (at 95% confidence level), for the Υ(1S), Υ(2S), and Υ(3S) states, respectively. The results demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.

Search for new physics in the multijet and missing transverse momentum final state in proton-proton collisions at √s = 7 TeV

A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of √s=7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 fb(-1) of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches.