Bjoern Penning
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Research Interest
Dark matter (DM) accounts for about one quarter of the Universe’s energy budget, five times as much as regular matter. Yet, its particle nature remains unknown. The direct detection of DM interacting with a detector target will revolutionise our understanding of astrophysics, cosmology, and fundamental physics. The UZH Dark Matter Group of Prof.~Penning is among the world’s leading teams in the search for DM. Contributions from the group are central to some of the most sensitive experiments currently operating, utilising both noble-liquid detectors and quantum-sensor technologies. In addition, the team is developing new technologies for future searches and has abundant experience in the construction and operation of underground detectors. The Bedretto physics programme builds on this expertise in tight collaboration with other Swiss research groups.
The group is a leading member of two international direct detection experiments, LUX-Zeplin (LZ) and TESSERACT. In addition, the Penning group, in close collaboration with Prof. Laura Baudis's group at UZH has pioneered the use of superconductive nanowire single-photon detectors (SNSPDs) to search for dark matter in the QROCODILE experiment, and is laying the foundation for the next generation of liquid xenon experiments as part of XLZD.
The group has very large has experience designing, building, and operating large large underground detectors. Penning co-led the design, manufacturing, fabrication, installation, operation, and analysis of the Outer Detector (OD) of LZ, shown in Fig.~\ref{fig:outer_detector}. The OD is LZ's active neutron shield and approximately doubles the experiment's sensitivity to DM. The OD was built by only two groups: UCSB, focusing on the Gd-LS, and the Penning group, which operated and calibrated the detector after data taking started for several years. Postdoc Birch took extensive responsibility for the ongoing monitoring of the OD. The group further contributes to reconstructing events in the LXe, underground operations, TPC calibration and detector stability, and science exploitation.
Locally, the group, assumed a co-leadership role in the XENOSCOPE R\&D LXe experiment developed by Prof. Laura Baudis, contributing substantially to the XENOSCOPE demonstrator at UZH which contains 360 kg of liquid xenon. In addition, the Penning group designs and operates small-scale LXe TPCs and performs LXe microphysics measurements. This proven expertise in instrumentation and underground operations is a critical asset for planning the needs of the Bedretto physics lab.
Building on the experience in building the LZ outer detector, Penning is the TESSERACT manager of shielding, and the cryostat vacuum vessel. The shielding concept chosen is based on well-established radiation shielding principles to suppress external neutron and gamma-ray backgrounds and radioactive decay in the detector and shielding material itself. The experiment's underground location suppresses cosmic rays. Penning developed the shielding and cryostat vessel, focusing on low background rates and the ability to change the detector payloads quickly. The group contirbutd strongly to the authoring of TESSERACT's fridge selection documents, and and operates a dilution refrigerator with a second one to be delivered soon.
The group further performs sensor and cryogenic characterisations in Zurich, including major contributions to the setup, calibration, characterisation and data taking of superconducting sensors (`quantum sensors') using Transition Edge Sensors (TES) and Superconducting Nanowire Single-Photon Detectors (SNDPDs), this includes commissioning of the dil firdges, sensor characteriation an dcalibration, and installation of cryogenic readout electronics such as SQUIDS.
Further, the group contributes strongly the reconstruction, modelling and understanding of rare event search data. The most recent contributions include the first direct observation of a rare nuclear decay of 125Xe enabled by detailed modelling of multiple-scatter events, measurement of the muon flux underground and contributions in analysis and operations to the leading dark matter results. We also work with theorists on expanding the science reach of our work by considering new interpenetrations and new models when analysing our data.
In addition to specialised searches, the group contributes to all levels of the main LZ analyses which provide the best sensitivity to weakly interacting DM at weak-scale masses. For example we extended LZ's physics program by establishing the high nuclear recoil search group and studying the required performance of the planned XLZD detector.
The group has led the effort to characterise the suitability of the Bedretto tunnel for particle physics, with postdocs Angelides and Kavner performing measurements of radon as well as the muon and neutron flux. In the process, the group also gained a close working relationship with the currently operating BedrettoLab scientists, and have conceptualised several of the science cases for the Bedretto physics lab.
