[ NIKHEF theory group ]


To meet, discuss, collaborate, generate ideas, share expertise, in the context of the FOM programme "Higgs as Probe and Portal"

We hope to see you here!

Agenda 18 May

Time: 10.00 - 17.00
  • 10.25 - 10.55, H320:

    Mikko Laine (University of Bern)
    On the quantum statistical physics of dark matter freeze-out

    Abstract: The non-observation of dark matter at the LHC and other searches poses a challenge both for model building and for the theoretical tools with which any given model is addressed. In this talk issues related to the latter challenge are discussed, within the context of the classic WIMP paradigm. As a concrete example, we illustrate the recently fashionable idea that bound states could appear in the dark sector and significantly affect the freeze-out dynamics.

  • 11.00 - 12.00, H331, Nikhef Colloquium

    Chris Rasmussen (Alpha Collaboration)
    Spectroscopy of Antihydrogen in the ALPHA Experiment

    Abstract: Precision measurements of magnetically trapped antihydrogen provides a unique and powerful way to test matter-antimatter symmetries. A cornerstone of the standard model, CPT symmetry demands that the spectrum of antihydrogen be identical to that of its ordinary matter counterpart. Of particular interest is the 1S-2S transition which has been measured in hydrogen[1] with the remarkable relative precision of a few parts in 1015, and promises a particularly elegant and high precision test of CPT symmetry by comparis onto antihydrogen. In 2016, the ALPHA collaboration made the first observation[2] of the 1S-2S transition in antihydrogen, and very recently this measurement was drastically improved[3] to reach a fractional precision of  2x 10-12. The observed frequency in antihydrogen is consistent with CPT symmetry at the current level of precision. In this talk, I will present this latest measurement of the 1S-2S transition and introduce the methods of anti-atom spectroscopy developed by ALPHA. Finally, I will touch on future improvements needed to take this milestone measurement to the same precision as its hydrogen counterpart.

  • 13.00 - 13.30, H320
    Plot of the Month/Pie of the Month

  • 13.30 - 14.00, H320

    António Morais (University of Aveiro)
    Multi-peaked signatures of primordial gravitational waves from multi-step electroweak phase transition

    Abstract: The first-order electroweak phase transition in the early universe could occur in multiple steps leading to specific multi-peaked signatures in the primordial gravitational wave (GW) spectrum. In this talk we argue that these signatures are generic phenomena in multi-scalar extensions of the Standard Model. In a simple example of such an extension, we study the emergence of reoccurring and nested vacuum bubble configurations and their role in the formation of multiple peaks in the GW spectrum. The conditions for potential detectability of these features by the forthcoming generation of interferometers are discussed.

  • 14.30 - 15.30, H320
    Student meeting/discussion:

    Rabah Abdul Khalek (VU)
    Sophisticated particle identification by means of Machine Learning

    Abstract: Astronomy, astrophysics, and particle physics all have made rapid progress as observational sciences in recent years. Much of this progress is due to the development of detector technology, coupled with a parallel development of analysis methods. Confronted with a daunting challenge of extracting a small number of interesting events from an overwhelming sea of background, physicists have become familiar with quite sophisticated multi-variate techniques. I will give a brief introduction on Machine Learning techniques focusing on Artificial Neural Networks and how they work. I will further discuss how they are used in high energy physics to efficiently discriminate between different types of particles (Primary gammas versus hadronic showers initiated by cosmic ray) that are almost undistinguishable from the perspective of classical analysis, taking the MAGIC (Major Atmospheric Gamma Imaging Cherenkov Telescope) as a case study.

  • 16.00 Science Cafe (Jan-Willem van Holten), followed by borrel/reception.