Prospect studies for Higgs Boson pair production to bbyy final state at the HL-LHC with the ATLAS detector

By the end of the HL-LHC era, before 2040, the ATLAS experiment aims to increase the size of the dataset from $\sim$300fb$^{-1}$, acquired at the end of LHC running, up to $\sim$3000fb$^{-1}$. The large dataset expected after HL-LHC operation increases the likelihood of seeing rare processes such as the $H \rightarrow HH \rightarrow b\bar{b}\gamma\gamma$ decay channel. This channel is one of the most promising for measuring the Higgs boson self-coupling. To mimic the expected ATLAS detector response to various physics objects at the HL-LHC, upgrade performance functions are constantly developed and updated. A recent update to these functions included the addition of a considerably more realistic estimate of the expected material budget of the ITk, as well as dedicated functions for both the 50$\times$50$\mu$m$^2$ and 25$\times$100$\mu$m$^2$ pixel sensor geometries. A Boosted Decision Tree method was applied to the $H \rightarrow HH \rightarrow b\bar{b}\gamma\gamma$ channel to determine the effects of these changes. It was shown that the more realistic material budget and dedicated 50$\times$50$\mu$m$^2$ functions result in a significance for observing this channel of 3.10$\pm$0.13. Comparable results are obtained when using either a pixel sensor geometry of 25$\times$100$\mu$m$^2$ or reducing the radius of the innermost pixel layer

Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at √s = 8 TeV

The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Prospect studies for Higgs boson pair production to bbbˉ\bar{b}γγ\gamma\gamma final state at the HL-LHC with the ATLAS detector

By the end of the HL-LHC era, before 2040, the ATLAS experiment aims to increase the size of the dataset from ∼300fb$^{−1}$, acquired at the end of LHC running, up to ∼3000fb$^{−1}$. The large dataset expected after HL-LHC operation increases the likelihood of seeing rare processes such as the $H$ → $HH$ → $b$$\bar{b}$$\gamma\gamma$ decay channel. This channel is one of the most promising for measuring the Higgs boson self-coupling. To mimic the expected ATLAS detector response to various physics objects at the HL-LHC, upgrade performance functions are constantly developed and updated. A recent update to these functions included the addition of a considerably more realistic estimate of the expected material budget of the ITk, as well as dedicated functions for both the 50×50$\mu$m$^{2}$ and 25×100$\mu$m$^{2}$ pixel sensor geometries. A Boosted Decision Tree method was applied to the $H$ → $HH$ → $b$$\bar{b}$$\gamma\gamma$ channel to determine the effects of these changes. It was shown that the more realistic material budget and dedicated 50×50$\mu$m$^{2}$ functions result in a significance for observing this channel of 3.10±0.13. Comparable results are obtained when using either a pixel sensor geometry of 25×100$\mu$m$^{2}$ or reducing the radius of the innermost pixel layer

Mechanism for enhanced wavelength tuning in gain-levered InP quantum dot lasers

Peak gain wavelength tuning via the gain-lever effect is demonstrated in segmented contact InP quantum dot Fabry–Perot lasers. A tuning range of 6.5 ± 0.1 nm was recorded in the lasing spectra of a 1.9 mm long broad area device operating at 22°C. The authors clarify the nature of the tuning mechanism and identify the critical material and device parameters that determine the limits of the wavelength tuning range

Chemiresistive sensing with chemically modified metal and alloy nanoparticles

  This review describes the use of chemically-modified pure and alloy metal nanoparticles for chemiresistive sensing applications. Chemiresistors are materials that change their resistance in the presence of a particular analyte of interest. Chemically-modified metal nanoparticles consist of a pure or alloy metallic core that has some type of chemical coating, which could be an organic monolayer, polymer, surfactant, biomolecules, inorganic material, or organometallic molecules. Researchers have studied the electronic properties of one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) assemblies of chemically-modified metal nanoparticles and even single individual nanoparticles. These assemblies are well-suited for chemiresistive sensing applications as the metallic core provides a conductive path and the nanoparticle coating provides a means for controlling interactions with an analyte of interest. The interaction with the analyte alters the conductivity of the material, providing a signal to measure the analyte concentration. Much of this review focuses on the use of metal monolayer-protected clusters (MPCs) for chemiresistive sensing applications. This particular class of nanoparticles consists of a pure or alloy metallic core surrounded by a self-assembled monolayer coating, usually an organomercaptan or amine-based ligand. The versatile and well-understood synthesis of MPCs has allowed researchers to tailor the size and composition of the metallic core and coating for chemiresistive sensing of a wide variety of gas- and liquid-phase analytes. This review also describes chemiresistive sensing applications of other types of metal nanoparticles synthesized with different coatings (or stabilizers), such as ions, polymers, surfactants, and biomolecules. Chemiresistive sensing can be performed with these materials assembled as large scale films, micro/nano-patterned films, or as individual nanoparticles. The nanoparticles may be chemically-linked or assembled through weak intermolecular forces. Here we review different strategies used to incorporate chemically-modified nanoparticles into chemiresistive sensing devices, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, analytes (vapors, gases, liquid phase, biological), and other various factors, such as particle size, stability, conditioning steps, and practical considerations. This review also includes a summary and future directions of the field.Fil: Ibañez, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Zamborini, Francis P.. The University Of Louisville; Estados Unido