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Search for the pair production of long-lived supersymmetric partners of the tau lepton in proton-proton collisions at = 13 TeV
No full textGauge-mediated supersymmetry-breaking models provide a strong motivation to search for a supersymmetric partner of the tau lepton (stau) with a macroscopic lifetime. Long-lived stau decays produce tau leptons that are displaced from the primary proton-proton interaction vertex, leading to an unconventional signature. This paper presents a search for the direct production of long-lived staus decaying within the CMS tracker volume in proton-proton collisions at = 13 TeV, performed for the first time with an identification algorithm based on a graph neural network dedicated to displaced tau leptons. The data sample, corresponding to an integrated luminosity of 138 fb, was recorded with the CMS experiment at the CERN LHC between 2016 and 2018. This search excludes, at 95% confidence level, stau masses, m_\tildeτ, in the 126260 (906425) GeV range for a proper decay length of 50 mm in the maximally mixed (mass-degenerate) scenario, while for m_\tildeτ = 200 GeV, stau proper decay lengths are excluded in the range 2194 (6333) mm. These results improve the exclusion limits compared to previous searches, and extend the parameter space explored in the context of supersymmetry
Structure matters: A synchrotron study reveals how crystallite structure influences the deposition mechanism for the powder aerosol deposition method
No full textPowder aerosol deposition (PAD or ADM) is a coating technique to produce ceramic films at room temperature. Although the deposition mechanism has been clarified in some respects, unanswered questions remain. The present work reports films of titanium oxide, which forms a typical PAD microstructure, and films of incommensurate misfit-layered calcium cobalt oxide (CaCoO, CCO-349), which forms a atypical film. For this work, films made of these two materials were examined using X-ray diffraction with synchrotron radiation and a scanning electron microscopy. It turned out that due to its aperiodic crystal structure, CCO-349 can be deformed more easily than conventional technical ceramics like TiO. The deformation occurs when the layers in the crystal slide in the direction of the misfit. As a result, it is unnecessary to break the crystals, and a larger crystallite size remains in the film. Therefore, PAD films of CCO-349 have a different microstructure
Hexagonal and Lamellar Superstructure in DSPE-PEG1000 Monolayers at the Air/Water Interface
No full textInspired by diblock copolymer self-assembly, we study lipopolymer monolayers at the air/water interface. We investigated DSPE-PEG1000 (DSPE-EO22) monolayers with alkyl chains in the liquid-condensed phase in dependence of the molecular area. Due to its conformational entropy, the moderately hydrophilic PEG has a larger area requirement than the alkyl chains in all-trans conformation. Small-angle grazing incidence X-ray diffraction (GID) measurements identified a hexagonal superstructure. The ordered alkyl chains form hydrophobic domains that are embedded in dissolved PEG. These domains consist of the alkyl chains of ≈200 PEGylated lipid molecules. During monolayer compression, the number of alkyl chains in a domain remains constant, while their area fraction increases. At an area fraction of 50%, a transition to a lamellar superstructure occurs. During this transition, the alkyl chain domains merge. This transition is attributed to the entropy loss of the laterally compressed PEG chains. Wide-angle GID reveals that the alkyl chains in the liquid-condensed phase possess the same small cross-sectional area (19.75 Å2) as those in DSPE monolayers, indicating that PEG has little influence on the liquid-condensed phase. The hexagonal superstructure was confirmed with AFM images
Unification of Gravities with GUTs
No full textWithin the gauge-theoretic approach of gravity, the gauging of an enlarged symmetry of the tangent space in four dimensions allows gravity to be unified with internal interactions. We study the unification of the conformal and noncommutative (fuzzy) gravities with internal interactions based on the GUT
Light‐Triggered Reversible Assembly of Halide Perovskite Nanoplatelets
No full textAdvancements in stimuli-driven nanoactuators necessitate the discovery of photo-switchable, self-contained semiconductor nanostructures capable of precise mechanical responses. The reversible assembly of 0D Cs3Bi2I9 halide perovskite nanoplatelets (NPLs) between stacked and scattered configurations are demonstrated under light and dark, respectively. This sunlight-triggered perpetual flipping of the NPLs, occurring in less than a minute, is associated with a color change between brown and red. The photomechanical response is driven by the formation and cleavage of sulfide linkages at the NPL surface. In the stacked configuration, various stacking modes create moiré superstructures, enhancing the interlayer charge distribution, and increasing the electronic conductivity and optical absorbance. This leads to a decrease in exciton binding energy from 247 meV for scattered NPLs to 162 meV for stacked NPLs, resulting in a 3.5-fold enhancement in dark current for the stacked NPL films. The switchable control over color and electric current is continuously reversible and retraceable, exhibiting a minor memory effect observed during extended cycling. The self-flipping NPL nanoactuators demonstrate reversible mechanical responses, with topographical oscillations ranging from 14 nm in scattered NPLs to 50 nm in the vertically stacked configuration. This seamless reversible nano-assembly with color interchangeability offers numerous possibilities for nanorobotics, nanoscale switches, and sensors
Magnetic circular dichroism in core-level x-ray photoelectron spectroscopy of altermagnetic RuO films
No full textWhile ferromagnetism and antiferromagnetism are well-established classes of magnetic order, a third class of collinear magnetic order, termed altermagnetism, has recently attracted scientific interest. We measured magnetic circular dichroism (MCD) in core-level photoemission (XPS) at the Ru 2 and 2 core levels in epitaxial RuO(110)/TiO(110)films using circularly polarized x rays at 6 keV, as well as x-ray magnetic circular dichroism (XMCD) in resonant x-ray absorption at the Ru M(3 and 3 ) edges. Charge transfer multiplet calculations show that the MCD-XPS and the XMCD can be explained by an altermagnetic locking of Ru magnetic moments and a distorted crystal field orientation. The distortion is caused by the epitaxial strain. The collinear magnetic moments in RuOoccupy sublattice sites with distorted octahedral crystal fields that are rotated by 90∘with respect to each other. A change in the sign of the MCD-XPS at different sample positions indicates the presence of altermagnetic domains with the size of around hundreds of micrometers
Stretcher and Amplifier design for the LPA Drive Lasers ANGUS and KALDERA
No full textLaser-plasma accelerators (LPAs) are a promising technology to build compact andcost-efficient accelerators for a variety of applications. To realize this promise, thereliability and long-term stability of the accelerated electrons have to be improved.Much of this improvement relates to the stability of the drive laser. Apart fromimproving passive stability, increasing the repetition rate of the laser from a few Hzto >100 Hz, enables the use of active stabilizations, that can account for many lowerfrequency contributions from e.g. mechanical vibrations and air-fluctuations. Theoverarching goal of the thesis is to develop setups for the Ti:Sa CPA TW-class lasersystems ANGUS and KALDERA, that allow for a stable laser performance andacceleration of high-quality electrons.To improve the long-term stability of the ANGUS laser, a new, more stable front-end,based on optical-parametric chirped-pulse amplification (OPCPA) was built. Thisthesis reports on the design, alignment and characterization of the stretcher, that wasrequired to integrate the OPCPA front-end into the laser system. The design goalwas to achieve a stable and tunable stretcher and to minimize the angular chirp ofthe output beam by alignment with a three-color-laser. The characterization of thestretcher and its implementation into the laser system, which led to the compressionof pulses to 31 fs with sub-percent pulse duration stability will be presented.With KALDERA a >100Hz repetition rate LPA drive laser is currently being developedon DESY campus. To withstand the >100W average power in the final pulsecompressor, multi-layer dielectric (MLD) gratings need to be used. This thesis reportson the development, setup and characterization of a two-transmission grating, two-passOeffner stretcher, that matches such a MLD compressor. Using this stretcher, compressionto sub-30 fs pulse lengths at Ti:Sa wavelength in an out-of-plane compressorwith MLD gratings could be demonstrated for the first time. The characterization ofthe output pulses showed the viability of the stretcher and compressor concept for theKALDERA laser and other future high-average power, TW, fs laser systems.To efficiently seed the final amplifiers, a Booster amplifier is required for the KALDERAlaser. The designed three-pass Ti:Sa amplifier provides 0.5-1mJ output energy andsub-percent energy stability. The stretcher and the Booster amplifier successfully seedthe KALDERA multi-pass amplifiers to saturation, enabling sub-0.5% energy stabilityin the final amplifier stage
Automated Optimization of an ATLAS Search for Higgs Boson Pair Production at the LHC
No full textParticle physics analyses are inherently complex and need to process large datasets through a chain of many interdependent steps. These analyses typically aim to optimize their sensitivity to potential signals. However, due to the stepwise nature, optimizations at several stages often need to rely on approximations to the final analysis sensitivity. This approach leads to extensive re-optimizations that require a careful balance between optimizing selection criteria, accounting for uncertainties, and maintaining a meaningful statistical analysis. This work explores neural end-to-end-optimized summary statistics (NEOS) as a novel, automated alternative to this procedure. For the first time, it is applied to a full-featured analysis in a search for boosted Higgs boson pair production via vector boson fusion, decaying into a four b-quark final state. A dedicated optimization framework, auTOMATed Optimization of Sensitivity (TOMATOS), is introduced, enabling a unified analysis optimization that targets the analysis sensitivity directly. Its performance is benchmarked against traditional methods, demonstrating comparable results. This thesis presents the latest expected ATLAS constraints on the coupling using Run 2 data:
