In this paper, we give a detailed description of an electrospray ion source test bench and a single-pass setup for ion fragmentation studies at the Double ElectroStatic Ion Ring ExpEriment infrastructure at Stockholm University. This arrangement allows for collision-induced dissociation experiments at the center-of-mass energies between 10 eV and 1 keV. Charged fragments are analyzed with respect to their kinetic energies (masses) by means of an electrostatic energy analyzer with a wide angular acceptance and adjustable energy resolution.

Collisions between molecules and gas phase targets often lead to various intriguing processes. Such collisions may induce fragmentation of molecules that can be divided into different subsets depending on the projectile, target, and collision energy. One major part of the present research is the exploration of astrophysical relevant collision mechanisms. In collisions between polycyclic aromatic hydrocarbon (PAH) molecules or fullerenes with, for example, helium, nuclear stopping can lead to the prompt knockout of a carbon atom from the molecule. Such a vacancy in the molecular carbon backbone can be highly reactive, and lead to the formation of larger molecules. The energy dependencies of such processes are important for the understanding of astrochemical molecular growth processes, which in turn may lead to the formation of larger and more complex molecules in space. In addition, hydrogenation of PAHs changes their structures and internal properties, including their resistance against fragmentation. To better understand the effects of hydrogenation on the fragmentation of PAHs, low energy photofragmentation experiments are presented along with the collision experiments, and a detailed comparison is made between the effects of these different types of energy transfer processes.

Besides astrophysically relevant research, studies on the response of biomolecules to collisions with gas phase targets are presented. Here, the energy dependence for formation of the protonated n-butyl β-ionone Schiff base through electrocyclization of the protonated n-butylamine Schiff base of all-trans-retinal in collisions is presented. The latter is a model compound for all-trans-retinal, the chromophore of the light sensitive opsin proteins, and such studies are essential for the understanding of the operation of mammal vision.

While our collision studies are very successful, they are sometimes also limited by the experimental timescale. Therefore, we have constructed an experimental setup for ion storage and fragmentation analysis. The goal of this new experiment is to store internally hot fragments to investigate their behavior on extended timescales and as functions of internal excitation energies.

Since the recent detection of an astrophysical flux of high-energy neutrinos, the question of its origin has not yet fully been answered. Much of what is known about this flux comes from a small event sample of high neutrino purity, good energy resolution, but large angular uncertainties. In searches for point-like sources, on the other hand, the best performance is given by using large statistics and good angular reconstructions. Track-like muon events produced in neutrino interactions satisfy these requirements. We present here the results of searches for point-like sources with neutrinos using data acquired by the IceCube detector over 7 yr from 2008 to 2015. The discovery potential of the analysis in the northern sky is now significantly below E(nu)(2)d phi/dE(nu) = 10(-12) TeV cm(-2) s(-1), on average 38% lower than the sensitivity of the previously published analysis of 4 yr exposure. No significant clustering of neutrinos above background expectation was observed, and implications for prominent neutrino source candidates are discussed.

We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules.

The Precision IceCube Next Generation Upgrade (PINGU) is a proposed low-energy in-fill extension to the IceCube Neutrino Observatory. With detection technology modeled closely on the successful IceCube example, PINGU will provide a 6 Mton effective mass for neutrino detection with an energy threshold of a few GeV. With an unprecedented sample of over 60 000 atmospheric neutrinos per year in this energy range, PINGU will make highly competitive measurements of neutrino oscillation parameters in an energy range over an order of magnitude higher than long-baseline neutrino beam experiments. PINGU will measure the mixing parameters theta(23) and Delta m(32)(2), including the octant of theta(23) for a wide range of values, and determine the neutrino mass ordering at 3 sigma median significance within five years of operation. PINGU's high precision measurement of the rate of nu(T) appearance will provide essential tests of the unitarity of the 3 x 3 PMNS neutrino mixing matrix. PINGU will also improve the sensitivity of searches for low mass dark matter in the Sun, use neutrino tomography to directly probe the composition of the Earth's core, and improve IceCube's sensitivity to neutrinos from Galactic supernovae. Reoptimization of the PINGU design has permitted substantial reduction in both cost and logistical requirements while delivering performance nearly identical to configurations previously studied.

The Advanced LIGO observatories detected gravitational waves from two binary black hole mergers during their first observation run (O1). We present a high-energy neutrino follow-up search for the second gravitational wave event, GW151226, as well as for gravitational wave candidate LVT151012. We find two and four neutrino candidates detected by IceCube, and one and zero detected by ANTARES, within +/- 500 s around the respective gravitational wave signals, consistent with the expected background rate. None of these neutrino candidates are found to be directionally coincident with GW151226 or LVT151012. We use nondetection to constrain isotropic-equivalent high-energy neutrino emission from GW151226, adopting the GW event's 3D localization, to less than 2 x 10(51)-2 x 10(54) erg.

An ongoing discussion revolves around the question of what effect hydrogenation has oncarbon backbone fragmentation in polycyclic aromatic hydrocarbons (PAHs). In order to shedmore light on this issue, we have measured absolute single carbon loss cross sections incollisions between native or hydrogenated pyrene cations (C16H+ 10+m , m = 0, 6, 16) and He as functions of center-of-massenergies down to 20 eV. Classical molecular dynamics (MD) simulations give further insightinto energy transfer processes and also yield m-dependent threshold energies for prompt(femtoseconds) carbon knockout. Such fast, non-statistical fragmentation processesdominate CH x -loss for native pyrene (m = 0), while much slowerstatistical fragmentation processes contribute significantly to single-carbon loss for thehydrogenated molecules (m =6 and m =16). The latter is shown by measurements of large CH x -loss crosssections far below the MD knockout thresholds for C16H+ 16 and C16H+ 26.

We have investigated the photo-stability of pristine and super-hydrogenated pyrene cations (C16H10+m+, m = 0, 6, or 16) by means of gas-phase action spectroscopy. Optical absorption spectra and photoinduced dissociation mass spectra are presented. By measuring the yield of mass-selected photo-fragment ions as a function of laser pulse intensity, the number of photons (and hence the energy) needed for fragmentation of the carbon backbone was determined. Backbone fragmentation of pristine pyrene ions (C16H10+) requires absorption of three photons of energy just below 3 eV, whereas super-hydrogenated hexahydropyrene (C16H16+) must absorb two such photons and fully hydrogenated hexadecahydropyrene (C16H26+) only a single photon. These results are consistent with previously reported dissociation energies for these ions. Our experiments clearly demonstrate that the increased heat capacity from the additional hydrogen atoms does not compensate for the weakening of the carbon backbone when pyrene is hydrogenated. In photodissociation regions, super-hydrogenated Polycyclic Aromatic Hydrocarbons (PAHs) have been proposed to serve as catalysts for H-2 formation. Our results indicate that carbon backbone fragmentation may be a serious competitor to H-2 formation at least for small hydrogenated PAHs like pyrene.

We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e. g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015.

A recent study of soft x-ray absorption in native and hydrogenated coronene cations, C24H12+m + m = 0-7, led to the conclusion that additional hydrogen atoms protect (interstellar) polycyclic aromatic hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C16H10+m +, m = 0, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules.