Fingerprints of slingshot non-sequential double ionization on two-electron probability distributions

We study double ionization of He driven by a near-single-cycle laser pulse at low intensities at 400 nm. Using a three-dimensional semiclassical model, we identify the pathways that prevail non-sequential double ionization (NSDI). We focus mostly on the delayed pathway, where one electron ionizes with a time-delay after recollision. We have recently shown that the mechanism that prevails the delayed pathway depends on intensity. For low intensities slingshot-NSDI is the mechanism that prevails. Here, we identify the differences in two-electron probability distributions of the prevailing NSDI pathways. This allows us to identify properties of the two-electron escape and thus gain significant insight into slingshot-NSDI. Interestingly, we find that an observable fingerprint of slingshot-NSDI is the two electrons escaping with large and roughly equal energies.Comment: 9 pages, 5 figure

Attosecond phenomena in atoms and molecules driven by intense and ultra-fast laser pulses

In this thesis, we study theoretically the physical mechanisms underlying ionisation processes in strongly driven atoms and molecules. We start by investigating double ionisation in atomic systems, in particular, in Helium and Argon. For Helium, we present a new mechanism for double ionisation, called Slingshot Nonsequential Double Ionisation. This mechanism offers an alternative explanation to the anticorrelated two-electron escape found in this work and in previous studies at low intensities of the laser pulses. For Argon, we take the first step towards time-resolving double ionisation triggered by an ultra-short visible laser pulse, using a perpendicularly aligned mid-infrared long laser pulse. Next, we focus on two-electron molecules. We demonstrate that one can significantly increase frustrated double ionisation in the triatomic molecule D₃⁺ by using counter-rotating two-colour circular laser pulses. This enhancement of the frustrated double ionisation probability is achieved by tuning the ratio of the field strengths of the two pulses. We explain the basic features of the system that we study by employing a simplified model of the system. Finally, we investigate nondipole effects in the nonsequential double ionisation of strongly driven two-electron diatomic molecules. We formulate a three-dimensional semiclassical model that fully accounts for magnetic field effects while treating all Coulomb forces. Using this model, we show that the recolliding electron backscatters along the direction of light propagation. This is in striking contrast to the atomic case, where the recolliding electron scatters forward

Enhancing frustrated double ionisation with no electronic correlation in triatomic molecules using counter-rotating two-color circular laser fields

We demonstrate significant enhancement of frustrated double ionization (FDI) in the two-electron triatomic molecule D$_{3}^{+}$ when driven by counter-rotating two-color circular (CRTC) laser fields. We employ a three-dimensional semiclassical model that fully accounts for electron and nuclear motion in strong fields. For different pairs of wavelengths, we compute the probabilities of the FDI pathways as a function of the ratio of the two field-strengths. We identify a pathway of frustrated double ionization that is not present in strongly-driven molecules with linear fields. In this pathway the first ionization step is "frustrated" and electronic correlation is essentially absent. This pathway is responsible for enhancing frustrated double ionization with CRTC fields. We also employ a simple model that predicts many of the main features of the probabilities of the FDI pathways as a function of the ratio of the two field-strengths.Comment: 8 pages, 3 figure

A general model and toolkit for the ionization of three or more electrons in strongly driven molecules using an effective Coulomb potential for the interaction between bound electrons

We formulate a general three-dimensional semiclassical model for the study of correlated multielectron escape during fragmentation of molecules driven by intense infrared laser pulses, while fully accounting for the magnetic field of the laser pulse. We do so in the context of triple ionization of strongly driven HeH$_{2}^{+}$. Our model fully accounts for the singularity in the Coulomb potentials of a recolliding electron with the core and a bound electron with the core as well as for the interaction of a recolliding with a bound electron. To avoid artificial autoionization, our model employs effective potentials to treat the interaction between bound electrons. We focus on triple and double ionization as well as frustrated triple and frustrated double ionization. In these processes, we identify and explain the main features of the sum of the kinetic energies of the final ion fragments. We find that frustrated double ionization is a major ionization process, and we identify the different channels and hence different final fragments that are obtained through frustrated double ionization. Also, we discuss the differences between frustrated double and triple ionization.Comment: 20 pages, 9 figure

A “Net-Centric” conduct of navigation and ship management

Following the so-called “Industrial Revolution”, the shipping industry has benefitted from a very extended number of technology innovations. Over time, shipbuilding practices and the equipment of ships have been significantly improved. Furthermore, during the last couple of decades, the continuous improvement and integration- interconnection of electronics systems (the “network-centric” approach), have created a new operating environment for shipping. It is therefore not a coincidence that recent discussions on digitalization and autonomous ships provide a disruptive picture of how this industry may be transformed in the near future. Contemporary sea-going vessels are equipped with various technologically advanced systems and are highly automated. Today, all systems supporting the conduct of navigation and the various information technology (IT) applications related to ship management activities are heavily reliant upon real-time information to safely/effectively fulfil their allocated tasks. The issues of connectivity and interconnection clearly stand out. It is important to assess how navigation will be conducted in the near future. This analysis is based on a qualitative methodology, and its starting point, which also serves as the necessary “literature review”, is to identify and briefly discuss a certain number of technological developments that follow the network-centric architecture and have been recently introduced as equipment appropriate for ships. Next, it will examine how interactive processes and applications, both on the shore side and onboard vessels, can facilitate a safer working environment for seafarers and allow personnel based ashore to have a better understanding of what is happening at sea, as part of explaining the so-called “net-centric” framework of operations. Another important aim is to evaluate these promising technological trends according to their capacity of adoption in order to promote efficient and safe operations within the extended maritime transport domain. An important conclusion is that a net-centric philosophy and associated software applications can truly break down any existing limitations and create a collaborative environment for people and “machines”, including remotely controlled unmanned vessels

Streaking strong-field double ionization

Double ionization in intense laser fields can comprise electron correlations, which manifest in the non-independent emission of two electrons from an atom or molecule. However, experimental methods that directly access the electron emission times have been scarce. Here, we explore the application of an all-optical streaking technique to strong-field double ionization both theoretically and experimentally. We show that both sequential and non-sequential double ionization processes lead to streaking delays that are distinct from each other and single ionization. Moreover, coincidence detection of ions and electrons provides access to the emission time difference, which is encoded in the two-electron momentum distributions. The experimental data agree very well with simulations of sequential double ionization. We further test and discuss the application of this method to non-sequential double ionization, which is strongly affected by the presence of the streaking field

Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at √s = 13 TeV

Abstract The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d̂ t) and chromomagnetic (μ̂ t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable AFB(1) is used to approximate the asymmetry. Candidate t t ¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t t ¯ final states. The values found for the parameters are AFB(1)=0.048−0.087+0.095(stat)−0.029+0.020(syst),μ̂t=−0.024−0.009+0.013(stat)−0.011+0.016(syst), and a limit is placed on the magnitude of | d̂ t| < 0.03 at 95% confidence level. [Figure not available: see fulltext.

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

Peer reviewe

An embedding technique to determine ττ backgrounds in proton-proton collision data

An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).Peer reviewe