Astroparticle physics 2021

Neutrino Programme

Programme Leader

Paul de Jong, Dorothea Samtleben (deputy)

Main points: scientific

ANTARES

  • Search for point-sources of neutrinos using astrophysical catalogs and likelihood stacking.
  • Search for neutrino flares from the direction of radio-bright blazars.
  • Search for correlations between high-energy gamma rays and neutrinos with the HAWC and ANTARES detectors.
  • Measurement of the atmospheric electron-neutrino and muon-neutrino energy spectra.
  • Search for non-standard neutrino interactions with 10 years of ANTARES data.

KM3NeT

  • First measurement of neutrino oscillations in KM3NeT/ORCA.
  • First selection of neutrinos in KM3NeT/ARCA.
  • Sensitivity study of the neutrino mass ordering determination through combined analysis with JUNO and KM3NeT/ORCA.
  • Sensitivity estimates for diffuse, point-like and extended neutrino sources with KM3NeT/ARCA.
  • Tuning of atmospheric muon simulations with KM3NeT data.

DUNE

  • Physics performance studies, e.g. on supernova neutrino detection, and sensitivity to physics beyond the Standard Model.

Main points: technical

KM3NeT

  • Deployment of 4 ORCA Detection Units (DUs) and continuous data taking with 10 ORCA DUs.
  • Deployment of ARCA DUs and data taking with up to 8 ARCA DUs.
  • Mass production of Digital Optical Modules and DUs.
  • Refurbishment of ARCA sea floor network and junction boxes.
  • Reconstruction and event classification software, general software, oscillation and cosmic neutrino analysis software frameworks. Event reconstruction for KM3NeT using convolutional neural networks.

DUNE

  • Further advances in the design of DUNE: completion of near-detector conceptual design report, advances in photon detection system and the introduction of vertical-drift detector concept.
  • Construction of infrastructure for the excavation of the DUNE Far Detector cavities.

Awards/Fellowships

  • Winner of the Young Speakers Contest at FYSICA 2021: Thijs van Eeden
  • AAAS Newcomb Cleveland Prize for a team of scientists of the ASKAP collaboration, including Mieke Bouwhuis
  • Winner Best Poster Prize at ICRC 2021: Thijs van Eeden and Jordan Seneca

Key positions in collaborations

KM3NeT

  • Physics and software manager: Aart Heijboer
  • Software/computing co-coordinator: Mieke Bouwhuis
  • Detection Unit integration coordinator: Daan van Eijk
  • Optical systems coordinator: Antonio D’Amico
  • Mechanics coordinator: Edward Berbee
  • Cosmic ray physics group convener: Ronald Bruijn
  • Calibration group co-convener: Dorothea Samtleben
  • EU Liaison officer: Maarten de Jong
  • System Engineer: Ernst-Jan Buis (TNO)

ANTARES

  • Point sources group co-convener: Dorothea Samtleben
  • Conference committee chair: Mieke Bouwhuis

Main papers in 2021

ANTARES

  • ANTARES Search for Point Sources of Neutrinos Using Astrophysical Catalogs: A Likelihood Analysis, Astrophys.J. 911 (2021) 1, 48

KM3NeT

  • First neutrino oscillations measurement in KM3NeT/ORCA, PoS ICRC2021 (2021) 1123

DUNE

  • Prospects for beyond the Standard Model physics searches at the Deep Underground Neutrino Experiment, Eur. Phys..J.C 81 (2021) 4, 322

Cosmic Rays (Pierre Auger Observatory & GRAND)

Programme Leader

Sijbrand de Jong

Main points: scientific

  • Auger Radio Detector Upgrade prototypes performance as expected; air showers seen in the new Radio Detector combined with the Surface Detector
  • A complete spectrum of cosmic rays from 0.1 EeV to beyond 100 EeV

Main points: technical

  • All AugerPrime upgrade SSD modules are assembled, close to 100 % installed in the field
  • GRANDProto300 mechanical and electronics design completed, production 100 units completed; installation imminent
  • Array Auger Radio mechanical and electronics design completed, production ongoing

Awards, fellowships, grants, etc.

  • Prof. David Nitz was awarded a Radboud Excellence Initiative (REI) professorship, will be effective in 2022
  • Teresa Bister obtained an REI excellence fellowship.
  • SURFsara Grid resource grant

Key positions in collaborations

  • Auger radio group leader: Jörg Hörandel
  • Auger outreach convenor: Charles Timmermans
  • Auger Conference Committee chair: Charles Timmermans
  • GRAND technical coordinator: Charles Timmermans

Main paper in 2021

  • The Energy Spectrum of Cosmic Rays beyond the Turn-Down at 10^17 eV as Measured with the Surface Detector of the Pierre Auger Observatory, The Pierre Auger Collaboration, Eur. Phys. J. C 81 (2021) 966

Dark Matter

Programme Leader

Patrick Decowski

Main points: scientific

  • Construction of the XENONnT detector was completed in 2020 and the detector was filled with 8.4 tons of liquid xenon. The detector was then commissioned until spring 2021 and started taking scientific data in May 2021.
  • The commissioning period revealed a possible short between the cathode and the bottom PMT-screening mesh limiting the electric drift field to ~23 V/cm. Various detector parameters were subsequently tuned to optimize the readout at this low drift field. An extensive calibration campaign demonstrated that the detector performance was acceptable for a dark matter run. More than three months of dark matter data was recorded in 2021.
  • The XENONnT experiment includes several innovative new subsystems, such as a liquid xenon purification system, an online radon (Rn) distillation column, a neutron veto system and a triggerless data-acquisition system. The liquid xenon purification system worked extraordinarily well, allowing an electron lifetime of more than 20ms (for comparison, XENON1T achieved ~700 \mus). The neutron veto system, still without gadolinium-loading the water volume around the xenon TPC, was fully functional and the online Rn distillation column was also exercised, albeit not yet in the final configuration. The collaboration is confident that XENONnT will achieve its Rn background target of 1 \muBq/kg.
  • The Nikhef-designed triggerless data-acquisition system worked extremely well. The flexibility of this system allowed the readout to be adapted to the unexpected low-field situation.  The rapid raw data processing also allowed a first pass towards reconstructed data, simplifying offline data processing at remote sites.
  • XENON1T data analysis is continuing. An analysis published in PRL lowered the nuclear recoil energy threshold, allowing the search for coherent elastic neutrino-nucleus scattering (CEvNS) of solar B-8 neutrinos with xenon nuclei. Although no events compatible with CEvNS were found, XENON1T reported new limits on low-mass WIMP interactions. Another analysis examined single and few electron signals in XENON1T to derive first direct limits on the electric dipole, magnetic dipole, and anapole interactions, and bosonic dark matter models, to exclude new parameter space for dark photons and solar dark photons.
  • The LZ and DARWIN/XENON collaborations signed a Memorandum of Understanding to work together towards the next-generation liquid xenon observatory. Detailed physics sensitivity studies for this observatory are ongoing.

Main points: technical

  • Many ongoing R&D activities in the Nikhef XAMS lab. The XAMS TPC was modified to investigate a single-phase liquid xenon configuration.

Grants

  • NWO Computing Grant “Computing for the XENONnT Rare Event Search Experiment”

Key positions in collaborations

  • XENON Editorial Board: Patrick Decowski (chair)
  • XENONnT Technical Coordinator: Auke-Pieter Colijn
  • DARWIN Executive Board: Patrick Decowski

Main paper in 2021

Search for Coherent Elastic Scattering of Solar B-8 Neutrinos in the XENON1T Dark Matter Experiment, XENON collaboration, Phys. Rev. Lett. 126, 091301 (2021); arXiv:2012.02846.

 

Gravitational Waves

Programme leaders   

Frank Linde

Chris Van Den Broeck, Andreas Freise (deputies)

Main scientific points

O3, the third LIGO-Virgo observing run, has brought the total number of detections to 90. Nikhef researchers made significant contributions to a number of flagship analyses on this data set, in terms of detection, strong-field tests of general relativity, searches for lensed gravitational waves, and searches for primordial black holes. Highlights include:

  • For the first time, coalescences of neutron star-black hole systems were observed: GW200105 and GW200115. These were detected by (among others) the GstLAL pipeline in which Nikhef plays a major role, and a number of tests of general relativity were performed on the signals.
  • Just like light, gravitational waves can undergo gravitational lensing due to a massive object (e.g. a galaxy) on their path. The multiple “images” would manifest themselves as repeated signals in the detectors, though with different overall amplitudes. For the first time, the LIGO-Virgo Collaboration searched for lensed events, for now not finding compelling evidence. The analyses, and the writing of the results paper, were led by postdoc Hannuksela.
  • A search was performed for binary black holes with component masses lower than one solar mass. Such objects can not result from the collapse of a star, so if they exist, they would most likely be primordial, having originated a fraction of a second after the Big Bang. Upper limits were placed, in some mass bins reaching an improvement of almost an order of magnitude over more traditional methods.

Meanwhile, Nikhef researchers have been continuing the development of new data analysis methodology:

  • With colleagues in Liege, Belgium, machine learning algorithms were developed to enable early detection and sky localization of binary neutron star inspirals, with a view on genuinely real-time multimessenger astronomy.
  • In the context of multi-messenger observations of neutron stars geared towards measuring their equation of state, recently also information from (for now, low-energy) heavy-ion collision experiments was included in a joint analysis framework.
  • A new way of searching for lensed gravitational waves was devised which is computationally much less expensive than previous algorithms, and methodology was developed that can in principle enable identification of a lensed event even if only a single image is detected, thanks to a distinctive phase shift that gets added by lensing.

Main other points

The ETpathfinder cleanroom was completed and the first vacuum vessels were delivered and installed in Maastricht. On 8 November 2021, the ETpathfinder facility was opened by the Dutch Minister of Education, Culture and Science in the presence of a large international audience.

The Dutch science tv show ATLAS devoted two episodes to gravitational waves: one focussed on the ETpathfinder R&D laboratory in Maastricht and one focussed on the geology studies in the Euregio Meuse-Rhine in view of the ambition to host the future Einstein Telescope there.

Funding-wise, the NWA “Dutch Black Hole Consortium, DBHC” project –a science-wide collaboration between e.g. theorists, experimentalists, geologists and science educators and including two science museums– as well as the “Einstein Telescope Technologies” (ETT-OPZuid) project –a collaboration with several Dutch industrial partners on key technologies (including vacuum, cryogenics, algorithms, specialized sensors) for the Einstein Telescope– were approved. Stefan Hild received the prestigious ERC Advanced Grant and in October, the Dutch Ministry of Education, Culture and Science submitted a funding proposal to the Nationaal Groeifonds aimed at hosting –together with our co-hosts Belgium and Germany– the Einstein Telescope in the Euregio Meuse-Rhine.

Key positions in the collaboration

  • Matteo Tacca: Virgo commissioning coordinator 2020-2022.
  • Alessandro Bertolini: AdV+ project, Filter Cavity subsystem manager since 2018.
  • Bas Swinkels: AdV+ project, Electronics, Software and Controls system manager since 2019.
  • Sebastian Steinlechner: AdV+ project, Optical System Design subsystem manager since 2020.
  • Henk-Jan Bulten: AdV+ project, SBE subsystem manager since 2020.
  • Otto Hannuksela (postdoc): head of the LIGO-Virgo group on Gravitational Wave Lensing since 2020.
  • Peter Pang (PhD student): coordinator of parameterized tests of GR for the dynamics of binary black hole mergers.
  • Andreas Freise: Einstein Telescope Instrumentation Science Board co-chair 2019-2022.
  • Chris Van Den Broeck: Einstein Telescope Observational Science Board co-chair for Division 1 (Fundamental Physics) and Division 10 (Data Analysis Platform) since 2021.

Main papers in 2021

  • LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration, GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run, arXiv:2111.03606
  • LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration, Tests of General Relativity with GWTC-3, arXiv:2112.06861
  • LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration, Search for Sub-Solar-Mass Binaries in the First Half of Advanced LIGO and Virgo’s Observing Run, arXiv:2109.12197
  • LIGO Scientific and Virgo Collaborations, Search for Lensing Signatures in the Gravitational-Wave Observations from the First Half of LIGO-Virgo’s Third Observing Run, Astrophys. J. 923, 14 (2021)
  • LIGO Scientific Collaboration, Virgo Collaboration, and KAGRA Collaboration, Observation of Gravitational Waves from Two Neutron Star-Black Hole Coalescences, Astrophys. J. Lett. 915, L5 (2021)