Deutsches Elektronen-Synchrotron DESY
Notkestraße 85
22607 Hamburg


Particle Physics and
Detector Development
Institute of Experimental Physics
University of Hamburg
Luruper Chaussee
22761 Hamburg

Of the fundamental laws of physics, the laws of gravity are among the best tested. In the last decades, however, increasing evidence for deviations from these laws have arisen in various different astrophysical observables at the largest scales. The most striking of these
observables is arguably the collision of galaxy clusters, where the measured distribution of mass after the collisions does not coincide with the distribution of all visible matter. A mysterious new type of matter, so called Dark Matter, is needed to explain this and several other discrepancies. Dark Matter is named after the fact that it does not interact via the electromagnetic force. The other extreme in physics is at the smallest scale, were the theory of particle physics describes the fundamental particles. This theory is tested to very high precision at laboratories around the world. However, this theory does not have a candidate for Dark Matter, nor has any experiment to date seen a new particle that the theory doesn’t predict. While there is evidence for the existence of Dark Matter, its nature is completely unknown.

The proposed Young Investigators Group (YIG) will search for light Dark Matter particles, and particles that can mediate a very weak interaction between Dark Matter and ordinary matter, at the Belle II experiment in Japan. The proposed YIG will be part of the DESY Hamburg Belle II group and cooperate with the University of Hamburg. The Belle II experiment is currently being built and commissioned at the high intensity electron-positron collider SuperKEKB. SuperKEKB will operate at a center of mass energy of about 10.6 GeV with a very high instantaneous luminosity. Belle II will start data taking early 2018, and accumulate a dataset that is more than 50 times larger than that of the predecessor experiment Belle by 2025.

The proposed YIG will make use of optimized triggers to analyze the earliest dataset acquired by Belle II in 2018. These triggers will select events that contain a single high energetic photon only. In combination with a precise knowledge of the complete initial state at an electron-positron collider and the hermetic Belle II particle detector, it will allow to search for Dark Matter via a missing energy signature. These light Dark Matter particles are out of reach for the Large Hadron Collider or direct detection experiments underground. In addition, the proposed YIG will search for so-called Dark Photons that decay into pairs of ordinary matter. This Dark Photon search is expected to improve existing limits by at least a factor of five due to the huge number of particle collisions and the improvements to the detector itself. Another set of particles that could mediate interactions between Dark Matter and ordinary matter are Axion-Like Particles (ALPs), a generalization of hypothetical particles
originally postulated to solve the so-called “strong CP problem” in Quantum Chromodynamics. The proposed YIG will search for ALPs in events with one and three photons in the final state. These searches will be sensitive to ALP masses up to 10 GeV and small couplings to photons in a previously unexplored region of ALP parameter space if the full Belle II dataset is analyzed.

The aforementioned analyses require an excellent electromagnetic calorimeter (ECL) performance and reconstruction. The proposed YIG will lead the ECL reconstruction software improvements with a focus on machine learning methods. The very high beam backgrounds at Belle II will require constant work to keep up an excellent neutral particle reconstruction. In addition to the reconstruction, the proposed YIG will contribute to photon efficiency and photon energy calibration. In conclusion, the proposed YIG will contribute significantly to the electromagnetic calorimeter reconstruction and calibration at Belle II. It will add unique insights to the worldwide efforts in the search for Dark Matter.

Leader of the Helmholtz Young Investigators Group:

Dr. Torben Ferber
Deutsches Elektronen-Synchrotron DESY
Notkestr. 85
22607 Hamburg

Phone: +49 40 8998-0
Email: torben.ferber@desy.de

Partner university:

Prof. Dr. Johannes Haller
Particle Physics and
Detector Development
Institute of Experimental Physics
University of Hamburg
Luruper Chaussee
22761 Hamburg

Weiterführende Links:

Sachbericht 2018 (101KB)

 

Sachbericht 2019 (1.8 MB)