Time, Place:

09:30 ,Central Seminar Room, library building

Speaker:

Dr. Tobias Heldt; Highly charged ion dynamics

Title:

Ultrashort Kapitza-Dirac effect in a femtosecond enhancement cavity

Time, Place:

15:00 ,Hybrid seminar: central seminar room, library building + Zoom: Meeting-ID: 915 1204 2752 Passcode: 758933

Speaker:

Carlos Fajardo Zambrano, CERN/KU Leuven

Title:

Molecular laser spectroscopy for beyond the standard model

Time, Place:

15:30 ,Glaskasten, Bothe lab

Speaker:

Gorachand Das; Tata Institute of Fundamental Research (TIFR), Mumbai

Title:

Low-Energy Electron Scattering in Molecules with Large Dipole Moments

The study of electron-molecule interactions encompasses various topics, from gaseous plasmas tocomplex molecular structures [1]. One of the most intriguing and significant processes in this contextis dissociative electron attachment (DEA), which occurs at low electron energies (0–20 eV). A low-energy free electron attaches to a target molecule, forming a temporary negative ion (TNI). Thisunstable ion decays by autodetachment, i.e., ejection of the excess electron, bringing the target moleculeto its ground or excited state. On surviving against autodetachment, the TNI may undergo dissociation,also known as DEA, forming one negatively charged fragment (anion) and one or more neutralfragments.Theoretical and experimental studies have shown that molecules with a sufficiently large permanentelectric dipole moment (greater than ~2.5 D [2,3]) can bind an electron through dipolar interactions(~1/𝑟²). The strong dipole moment extends the range of attraction, making electron capture moreefficient along the dipole moment axis. This results in the formation of a diffused electron-capturingorbital, known as a dipole-stabilized orbital. Such an orbital has a diffuse nature, with a strong entrance-channel amplitude along the dipole-moment axis. This may result in a high electron capture cross-section. If the TNI has a high survival probability against autodetachment, such an electron captureprocess can lead to a high DEA cross-section. Additionally, when dissociation occurs rapidly ascompared to any other energy redistribution timescale for the molecule, the angular distribution of theresulting negative ion fragments would reflect the entrance channel amplitude responsible for electroncapture. Here, we present a case of DEA to nitromethane, a molecule with a high electric dipole moment of3.46 D [4]. The NO₂⁻ fragment formation via DEA peaks at 0.7 eV electron energy with a cross-sectionof 1.4 × 10!"# cm². The momentum image of the NO₂⁻ fragment at the resonance peak shows a stronganisotropy about the electron beam direction. This reflects the nature of the electron-capturing dipolestabilized orbital obtained using the Equation of Motion Coupled Cluster (EOMCC-EA) [5], as shownin Figure 1.In other polar molecules, such as 2-methyl-2-nitropropane, 2-nitrothiophene, and nitrobenzene, theDEA peak is in the 0.6–0.8 eV energy range due to electron capture into a dipole-supported orbital.Notably, this mechanism is largely independent of the detailed internal molecular structure, in contrastto the conventional DEA mechanism, which strongly depends on the specific valence orbital frameworkof each molecule.References:[1] Fabrikant I et al. 2017 Adv. At. Mol. Opt. Phys. 66 545 [2] Turner et al. 1977 Am. J. Phys. 45 758[3] Zhang et al. 2023 J. Phys Chem. Lett. 14 7368 [4] Compton et al. 1996 J. Chem. Phys. 105 3472[5] Jeffrey R. et al. 2006 J. Chem. Phys. 125 234107

Time, Place:

09:30 ,Central seminar room, library building

Speaker:

Magdalena Winkelvoß; Search for new physics with highly charged ions

Title:

tba

Time, Place:

11:15 ,Central seminar room, library building

Speaker:

Dr. Andrea Serafini (INFN / Università di Padova)

Title:

First Results from the JUNO Experiment

Neutrinos are elusive particles with unique properties that offer key insights into the fundamental structure of matter and the cosmic sources that produce them. To study these particles, the Jiangmen Underground Neutrino Observatory (JUNO), the largest of its kind in the world, officially began physics data taking in August 2025 in China, after more than a decade of preparation. In this seminar, I will outline the experimental path from JUNO's construction and commissioning phases to its initial operations, highlighting the early performance milestones achieved. Furthermore, I will present the fi rst physics results from the experiment, based on our initial 59.1 days of data. These early measurements provide the fi rst simultaneous high-precision determination of the solar neutrino oscillation parameters (𝜃𝜃12 and Δ𝑚𝑚212 ), improving upon existing global precision after less than two months of data taking. Finally, I will outline the broader physics program enabled by JUNO, demonstrating how these early milestones validate the detector's design and confi rm the experiment’s readiness to tackle the determination of the neutrino mass ordering and beyond.

Time, Place:

11:15 ,Grosser Hoersaal/Big Lecture Hall (library)

Speaker:

Louis DiMauro

Title:

What can we learn from attosecond pulses?

The genesis of light pulses with attosecond (10-18 seconds) durations signifies a new frontier in time-domain physics. This achievement was recognized by the 2023 Nobel prize in Physics for Agostini, Krausz and L'Huillier. The scientific impact is obvious: the time-scale necessary for probing the motion of an electron(s) in the ground state is attoseconds (atomic unit of time -- 24 as). In the first part of the talk, I will describe the underlying attosecond dynamics that emerges when an atom interacts with an intense optical field. Next, I will show how the physics can be applied to engineer a tabletop extreme ultraviolet attosecond light source and associated metrology.The second part of the talk will focus on two measurements that emphasize how these pulses can be applied to access novel physics. First, attosecond pulse trains are used in a reversed engineering scheme to study strong field physics with exquisite control of the initial conditions beyond conventional experiments thus allowing direct timing of recollision processes, both elastic and inelastic, with attosecond resolution [1]. Second, recent studies on thin liquid phase targets have introduced a new wrinkle to strong field physics defined by the local short range order [2-4]. I will show that mixtures composed of a methanol solvent manifest an interference effect in the harmonic emission indicative of local solvation dynamics in a binary solution and correlate with radial distribution functions derived from classical molecular dynamics simulations [5].1 Piper, A. J. et al., Phys. Rev. Lett. 2025, 134, 0732012 Luu, Tran Trung et al., Nat. Commun. 2018, 9, 37233 Neufeld, O. et al., J. Chem. Theory Comput. 2022, 18, 4117-41264 Annunziata, A. et al., APL Photonics 2024, 9, 0608015 Moore, Eric et al., Proc. Natl. Acad. Sci. 2025, 122, e251425122