Upgraded Cherenkov time-of-flight detector for the AFP project.

We present the results of our performance studies of the upgraded Cherenkov time-of-flight (ToF) detector for the AFP (ATLAS Forward Proton) project. The latest version consists of solid L-shaped fused silica bars, new customized ALD-coated micro-channel plate photomultipliers (MCP-PMTs) miniPlanacon XPM85112-S-R2D2 with an extended lifetime which operate at low gains (order of 103), and an updated construction. The improvements were aimed to increase the efficiency, the lifetime as well as the radiation hardness of the detector which has been designed to operate in high radiation areas (above 400 kGy/year). The detector was finally tested at the CERN-SPS test-beam facility (120 GeV π+ particles) in August 2021 prior to its installation at the Large Hadron Collider (LHC) at CERN. Measurements proved the detector kept its inner timing resolution of 20 ps despite the rather low gain of its photodetector and reduced optical throughput caused by inevitable changes in the detector geometry.

Quantum-state-selective electron recombination studies suggest enhanced abundance of primordial HeH.

The epoch of first star formation in the early Universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires a thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a pronounced decrease of the electron recombination rates for the lowest rotational states of the helium hydride ion (HeH+), compared with previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.

Fragmentation channels in dissociative electron recombination with hydronium and other astrophysically important species.

We report on our recent studies of dissociative recombination (DR) employing two different fragment imaging detection techniques at the TSR storage ring in Heidelberg, Germany. Principles of an upgraded 3D optical system and the new energy-sensitive multistrip detector (EMU) are explained together with possible applications in reaction dynamics studies. With the EMU imaging detector we succeeded to observe the branching ratios after DR of deuterated hydronium ions D(3)O(+) at energies of 0-0.5 and 4-21 eV. The branching ratios are almost constant at low energies while above 6 eV both oxygen-producing channels O + D + D + D and O + D(2) + D strongly increase and dominate by about 85% at 11 eV. To demonstrate further capabilities of our fragment imaging detectors, we also summarize some of our additional recent studies on DR of molecular ions important for astrophysics as well as for fundamental unimolecular dynamics.