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Search for b-hadron decays to long-lived particles in the CMS endcap muon detectors
No full textA search for long-lived particles originating from the decay of b hadrons produced in proton-proton collisions with a center-of-mass energy of 13 TeV at the LHC is presented. The analysis is performed on a dataset recorded in 2018, corresponding to an integrated luminosity of 41.6 fb-1. Interactions of the long-lived particles in the CMS endcap muon system would create hadronic or electromagnetic showers, producing clusters of detector hits. Selected events contain at least one such high-multiplicity cluster in the muon endcaps and require the presence of a displaced muon. The most stringent upper limits to date on the branching fraction B(B→KΦ), where the long-lived particle Φ decays to a pair of hadrons, are obtained for Φ masses of 0.3–3.0 GeV and Φ mean proper decay lengths in the range of 1–500 cm
Cavity Controls Core-to-Core Resonant Inelastic X-Ray Scattering
No full textX-ray cavity quantum optics with inner-shell transitions has been limited by the spectral overlap between resonant and continuum states. Here, we report the first experimental demonstration of cavity-controlled core-to-core resonant inelastic x-ray scattering (RIXS). We suppress the absorption-edge effects by monitoring the RIXS profile, thereby resolving the resonant state from the overlapping continuum. We observe distinct cavity-induced energy shifts and cavity-enhanced decay rates in the 23RIXS spectra of WSi. These effects, manifesting as stretched or shifted profiles in the RIXS planes, enable novel spectroscopic applications via cavity-controlled core-hole states. Our results establish core-to-core RIXS as a powerful tool to manipulate inner-shell dynamics in x-ray cavities, offering new avenues for integrating quantum optical effects with x-ray spectroscopy
Femtosecond concerted rotation of molecules on a 2D material interface
No full textInterfaces between molecules and 2D materials exhibit energy-driven functionalities, wherein charge transfer directs molecular motion. Unlike equilibrium systems, where molecular assemblies settle into static configurations, continuous energy input can drive transient, collective molecular rearrangements. Here, we reveal ultrafast spectroscopic fingerprints of a collective rotational response of molecules on a 2D material following photoexcitation. Our results suggest that photoinduced charge transfer reshapes the interfacial energy potential, giving rise to macroscopic, unidirectional molecular rotation and the formation of a homochiral molecular arrangement. Using a multiplexed ultrafast photoemission spectroscopy approach, we simultaneously track, electronic states, atomic positions, and orbital wavefunctions with femtosecond and sub-Ångström resolution. Multimodal valence and core electron emission analysis disentangles the intertwined electronic-structural dynamics of the molecule and the 2D material, revealing the dynamic modulation of charge distribution and intermolecular forces that drive collective molecular motion. Our findings open a pathway for designing energy-driven molecular systems with tunable interfacial dynamics, with potential applications in chiral engineering and active matter systems
Assembling Xanthan Gum at the Air–Water Interface and Disentangling It with Ionic Liquids
No full textXanthan gum is a biopolymer used in a wide range of products in the foodand cosmetic industries. As ionic liquids (ILs) have emerged as antimicrobial molecules,they can be used as preservatives for this polymer. Hence, it is important to understand theinteraction of ionic liquids with Xanthan gum. In this investigation, polymer self-assemblyat the air−water interface has been studied in the presence of ionic liquids floating at theair−water interface. From the surface pressure−area isotherm, it is shown that theelectrostatic interaction drives the polymer to the interface, resulting in a viscoelastic film.In-plane dilation rheology has determined the storage and loss moduli of the film, whichare found to depend on the concentration of the polymer dissolved in the water subphase.Additionally, a synchrotron-based X-ray reflectivity study has produced the electrondensity profile across the interface, depicting the structure of the film and suggesting thatthe negatively charged side groups of Xanthan gum attach to the positively chargedheadgroup of ionic liquids. This assembly drives the polymer to disentangle, which has been further verified in an aqueous solutionof the polymer showing a non-newtonian shear-thinning behavior. The storage and loss moduli curves show two crossoverfrequencies, manifesting an elastic plateau width that decreases in the presence of IL in the solution. This, in turn, is a signature ofthe disentangling effect of the IL
Cholesterol modulated assembly of graphene oxide nano-flakes at a phospholipid interface
No full textCholesterol, a key structural component of mammalian cell membranes, is crucial in stabilizing the membraneand regulating its biophysical properties. Herein, the self-assembly of graphene oxide (GO) around differentlycharged lipid monolayers modulated by cholesterol has been investigated using surface pressure-area isothermsand synchrotron-based X-ray reflectivity. In pristine lipid monolayers, electrostatic interactions control the selfassemblyof GO nano-flakes around the lipid molecules. However, upon the addition of cholesterol, theadsorption and penetration kinetics of GO nano-flakes into the lipid monolayers are drastically amplified, irrespectiveof the ionic nature of lipids. The experimental observations are discussed in terms of interactionsoccurring among GO nano-flakes, phospholipids, and cholesterol molecules
Crystal structure controlled energy transfer to Tb in KTb(MoO) and KTb(MoO) crystals
No full textLuminescent properties of KTb(MoO) and K5Tb(MoO) crystals, possessing the same elemental composition but different crystal structures, were studied. The structural arrangement of Tb ions, ordered in KTb(MoO) and disordered in KTb(MoO), determines their luminescence properties. Partial lattice disorder of KTb(MoO) results in broadened bands of Tb emission and excitation spectra, but also in more efficient energy transfer from electron-hole excitations to Tb due to the disorder-induced limitation of charge carriers’ mean path. It is shown that interband excitation of the Tb D terms responsible for the green emission is realized via the intermediate stage of self-trapped exciton creation, while that of the D terms responsible for the blue emission is realized through the impact interaction. Crystal structure determining the position of Tb states in the electronic energy band structure and the distance between neighboring Tb sites was found to strongly influence thermal stability and decay characteristics of the Tb emission
Room Temperature Gas-Phase Detection and Formation Gibbs Energy of the Water Dimethylether Bimolecular Complex
No full textHydrated complexes are of general interest for understanding nucleation processes in the atmosphere, where water is abundant, especially as the role of whether water enhances or inhibits nucleation is still uncertain. We have recorded the Fourier transform infrared absorption spectrum of the water dimethyl ether bimolecular complex in the gas phase at room temperature. Four distinct bands are observed and assigned. The equilibrium constant of complex formation is determined from the experimental integrated absorbance of the bands and the corresponding calculated intensities. The calculated band intensities are obtained with a 9D reduced-dimensional variational local mode model with the CCSD(T)-F12a/cc-pVDZ-F12 potential energy and dipole moment surfaces. A similar equilibrium constant for a majority of the observed bands is obtained, with an average value of 0.042 ± 0.003 at T = 298 K. The water dimethyl ether complex studied here is similar to the water dimer, and our determined equilibrium constant may serve as a reasonable estimate for that of water dimer, which is especially relevant in atmospheric chemistry
Dispersion-compensated Rowland spectrometer: implications for uranium VB-RIXS
No full textThe total energy resolution (ΔE) of a valence-band resonant inelastic X-ray scattering (VB-RIXS) instrument serves as an important point of reference in an otherwise complex field. Since VB-RIXS is a flux-limited technique, a pragmatic approach to reducing ΔE is often required—the specifications of a spectrometer should be matched with a comparable incident bandwidth (ΔE) and the source size contribution (focal point) should be negligible. Although it advocates for a good efficiency, this approach is in many places already limited by count-rates. Here we follow a recent trend emerging in soft X-ray VB-RIXS and look at the performance of our tender X-ray Rowland spectrometer (Gretarsson et al., 2020) when being exposed to a source with a large linear dispersion (higher flux). Detailed ray tracing work, performed at the U M5-edge (3551 eV), finds that the intrinsic resolution of the Rowland spectrometer (ΔE) can be obtained if the linear dispersion of the source matches the spectrometer's, but opposite in sign—here ΔE does not matter. This finding is supported by experimental data where ΔE = 48 meV (ΔE = 44 meV) was recently achieved. Furthermore, we demonstrate that the dispersion rate can be tuned, ensuring the method's applicability to other atomic edges
Polarization-dependent formation of side channels during percussion drilling with ultrafast lasers observed by means of high-speed X-ray imaging
No full textThe side channels that occur during percussion drilling in stainless steel with ultrafast lasers with linear or circular polarization were observed using high-speed X-ray imaging, capturing the dynamic process in real-time and thus providing primary insights into their formation dynamics. We identified two distinct phenomena directly linked to the formation of side channels: (1) deflection of the borehole tip and (2) melt-induced obstructions that alter the propagation of the laser radiation. These phenomena can occur independently of each other and strongly depend on the state of polarization. With linear polarization, the side channels consistently form in the plane perpendicular to the direction of polarization, while the side channels occur without any preferred orientation when drilling with circular polarization. Additionally, the first side channels form at greater depths when higher pulse energies are applied. This study improves our understanding of the complex interplay between the state of polarization, melt dynamics, and side channel formation. The findings provide valuable information for optimizing laser drilling processes, particularly for high-aspect-ratio hole drilling with high pulse energies, and have promising applications in precision micromachining and industrial laser processing
Improved protein binder design using β-pairing targeted RFdiffusion
No full textDesigning proteins that bind with high affinity to hydrophilic protein target sites remains a challenging problem. Here we show that RFdiffusion can be conditioned to generate protein scaffolds that form geometrically matched extended β-sheets with target protein edge β-strands in which polar groups on the target are complemented with hydrogen bonding groups on the design. We use this approach to design binders against edge-strand target sites on KIT, PDGFRɑ, ALK-2, ALK-3, FCRL5, NRP1, and α-CTX, and obtain higher (pM to mid nM) affinities and success rates than unconditioned RFdiffusion. Despite sharing β-strand interactions, designs have high specificity, reflecting the precise customization of interacting β-strand geometry and additional designed binder-target interactions. A binder-KIT co-crystal structure is nearly identical to the design model, confirming the accuracy of the design approach. The ability to robustly generate binders to the hydrophilic interaction surfaces of exposed β-strands considerably increases the range of computational binder design