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Particle Physics 2021

ATLAS  

Programme Leaders

Wouter Verkerke, Frank Filthaut, Ivo van Vulpen (deputy)

Main points: scientific

  • A new framework for the interpretation of differential distributions of abundant Higgs decays, based on SM Effective Field Theory (SMEFT) is being rolled out. Highlights of this new approach include new public results on constraints of the strength of 5 SMEFT operators in highly boosted H → bb decays, followed by a public result on combined analysis of these decays with H → ZZ* and H → γγ decays constraining a total of 10 operators.
  • Four new results on the search for rare SM Higgs boson decays (h→μμ, h→Zγ) and rare BSM Higgs boson decays (H→ ZZ, A→ Zh) have been published, with their sensitivity boosted by the availability of the full LHC Run-2 dataset of 139 fb-1. Each of these rare Higgs decays has a different sensitivity to specific types of BSM physics and complements the constraints derived from precision analyses of abundant Higgs decays.
  • In the area of direct new physics searches with signatures involving one or more leptons, two new results have been published: the search for weakly produced supersymmetric particles resulting in 3-lepton final states, and the search for lepton-flavor violating tau lepton decays originating from Z boson decays.
  • In the area of top quark physics, besides the ongoing program of SMEFT interpretations of measurements of polarized single top quark production, a first constraint was published on the rate of the simultaneous production of 4 top quarks (tttt). This process, with a tiny SM cross-section, is highly sensitive to the effects of a broad array of new physics theories.

Main points: technical

  • The FELIX Trigger and readout system, co-developed at Nikhef, is in production: all Phase-1 cards have been delivered to ATLAS, and FELIX is being used for the commissioning efforts of the new detectors, notably the muon New Small Wheel and the upgraded Level-1 calorimeter trigger.
  • The revised RASNIK hardware, which will monitor the alignment of the new muon detector components (New Small Wheel, BIS chambers) has been produced and successfully commissioned.
  • The upgrade of the ATLAS Inner Tracker (ITk) focuses currently on global mechanical structures. Following the ITk Global Mechanics project’s production readiness review in 2019, fire-safe epoxies for use in the ITk have been identified. The carbon fiber rings needed for the construction of the endcaps have been produced, while the production of the stiffener disks is in preparation.
  • Nikhef has joined the ATLAS High-Granularity Timing Detector (HGTD) consortium, which will construct a detector subsystem consisting of layers of Low-Gain Avalanche Diodes (LGADs) aiming to provide a per-track time resolution of about 50 ps. The HGTD is planned to be installed in the next LHC shutdown, before 2027.

Awards, fellowships etc.

  • NWO VIDI (Flavia Dias)
  • CERN Fellowship (Brian Moser)
  • CERN Fellowship (Carlo Gottardo)
  • eScience small-scale initiatives grant

Key positions in collaborations

  • Deputy physics coordinator: Pamela Ferrari
  • Publication committee chair: Pamela Ferrari
  • Authorship committee chair: Frank Filthaut
  • Member publication committee: Frank Filthaut
  • Collaboration Board Chairperson Advisory Group member: Wouter Verkerke
  • Statistics committee: Wouter Verkerke
  • Exotics group convener: Flavia Dias
  • Early Career Scientist Board: Flavia Dias
  • Outreach Coordinator: Clara Nellist
  • Diversity and Inclusion contact: Clara Nellist
  • Convener H→bb/cc subgroup: Hannah Arnold
  • ITK system engineer & global structures coordinator: Marcel Vreeswijk
  • FELIX firmware coordinator: Frans Schreuder
  • FELIX software coordinator: Mark Dönszelmann
  • HGTD DAQ/Luminosity/DCS coordinator: Mengqing Wu

Main papers in 2021

  • “Combination of searches for resonant and non-resonant Higgs boson pair production in the bbbb,  bbττ and bbγγ decay channels using pp collisions at √s = 13 TeV with the ATLAS detector”, ATLAS Collaboration, ATLAS-CONF-2021-052
  • “Constraints on Higgs boson production with large transverse momentum using H→bb decays in the ATLAS detector”, arXiv:2111.08340
  • “Combination of measurements of Higgs boson production in association with a W or Z boson in the H→bb decay channel with the ATLAS experiment”, ATLAS Collaboration, ATLAS-CONF-2021-051
  • “Direct constraint on the Higgs-charm coupling using Higgs boson decays to charm quarks with the ATLAS detector”, ATLAS Collaboration, arXiv:2201.11428
  • “Measurement of the polarisation of single top quarks and antiquarks produced in the t-channel collected with the ATLAS detector at √s= 13 TeV and bounds on the tWb dipole operator”, ATLAS Collaboration, arXiv:2202.11382
  • “Search for chargino-neutralino pair production in final states with three leptons and missing transverse momentum in √s = 13 TeV pp collisions with the ATLAS detector”, ATLAS Collaboration, Eur. Phys. J. C 81 (2021) 1118
  • “Search for new phenomena in three- or four-lepton events in pp collisions at √s=13 TeV with the ATLAS detector”, ATLAS Collaboration, Phys. Lett. B 824 (2022) 136832

LHCb

Programme Leader

Marcel Merk, Mara Soares (deputy)

Main points: scientific

  • High precision measurement of the Bs – anti-Bs meson oscillation frequency using decays of the type Bs → Ds pi.
  • Decay-time dependent CP violation studies: the study of the mixing phase φs of Bs0 oscillations using Bs→ J/ψ φ decays and the decay phase γ using Bs → DsK decays.
  • Precise measurement of very rare decays of B0s→μ+μ– including the effective lifetime of this decay. Subsequently, the search for B0→μμ and the relative branching ratio of B0 over Bs for these decays. Furthermore, the search for the even stronger suppressed decays involving electrons and tau leptons: B0(s)→ e+e–, Bc → τν, and of the Lepton Flavor violating decays B0(s)→ e μ.
  • Lepton universality tests in semileptonic b-quark to s-quark decays probing physics beyond the standard model, in particular using the angular distribution variables.
  • Searches for long-lived massive particles through signals of displaced as well as emerging jets

Main points: technical

  • Production of Velo upgrade detector modules and the installation of two sets of vacuum encapsulation boxes for the detector.
  • Installation of Scintillating Fiber detector modules, the Coldboxes and the cooling infrastructure.
  • Commissioning of SciFi modules in the C-frames at CERN.
  • Development and commissioning of the real-time reconstruction framework and implementation of reconstruction algorithms.

Awards, fellowships etc.

  • Vici: Niels Tuning and Wouter Hulsbergen,
  • Swiss SNF mobility grant, Maxime Schgubiger, Andrea Mauri,
  • Marie Curie Fellowship: Suzanne Klaver,
  • Veni: Andrii Usachov, Jacco de Vries, Suzanne Klaver
  • CERN scientific associate: Gerhard Raven

Key positions in collaborations

  • Physics Coordinator: Niels Tuning
  • Outer Tracker project leader: Niels Tuning,
  • Velo Deputy project leader: Kazu Akiba,
  • SciFi deputy project leader: Antonio Pellegrino,
  • Data Processing and Analysis deputy project leader: Patrick Koppenburg
  • Membership Committee chair: Marcel Merk,
  • Working group convenor of B to CC decays: Miriam Lucio Martinez
  • Working group convenor B to Open Charm Time Dependent: Emmy Gabriel
  • Working group convenor Very rare decays: Mick Mulder
  • Real Time Analysis deputy project leader: Gerhard Raven
  • Speakers Bureau deputy chair: Keri Vos
  • SciFi controls and monitor convenor: Kazu Akiba

Main papers in 2021

  • Test of lepton universality in beauty-quark decays, arXiv:2103.11769 (Nature Physics)
  • Precise determination of the Bs-anti Bs  oscillation frequency, arXiv:2104.04421, Nature Physics volume 18, pages 1–5 (2022)
  • Measurement of the  Bs →μμ decay properties and search for the B0→μμ and Bs→mumu\gamma decays, arXiv:2108.09283 (PRD)
  • Temporal characterisation of silicon sensors on Timepix3 ASICs, E.Dall’Occo et al., 2021 JINST 16, P07035

ALICE

Programme Leader

Raimond Snellings, Marta Verweij (deputy)

Main points: scientific

  • Measurements of transport properties of Quark Gluon Plasma
  • Constraints on magnitude chiral magnetic effect
  • Charm baryon and meson cross-sections as function of multiplicity in proton-proton collisions

Main points: technical

  • Installation of the upgrade of inner-tracking system at CERN, commissioning and first data taking.
  • Research and development for 4D tracking technology for ITS3 (run 3+4) and ALICE3 (run 5)

Key positions in collaborations

  • Upgrade coordinator : M. van Leeuwen
  • Physics Working Group Convenor: M. Verweij
  • System Run Coordinator: I. Ravasenga
  • Conference Committee: A. Grelli
  • Editorial Board: P. Christakoglou, T. Peitzmann

Main papers in 2021

  • Multiharmonic Correlations of Different Flow Amplitudes in Pb-Pb Collisions at √sNN = 2.76 TeV
    Phys. Rev. Lett. 127 (2021) 092302
  • Transverse Momentum Differential Global Analysis of Heavy-Ion Collisions
    Phys. Rev. Lett. 126 (2021) 202301
  • Event shapes and jets in $e^+e^-$ and pp collisions
    Nucl. Phys. A 1011 (2021) 122195
  • First measurements of N-subjettiness in central Pb-Pb collisions at √sNN = 2.76 TeV
    JHEP 10 (2021) 003

eEDM

Programme Leader

Steven Hoekstra

Main points: scientific

  • First Stark deceleration of BaF molecules
  • All-optical creation of the superposition eEDM measurement state
  • Accurate analysis of the hyperfine structure in the X2Sigma and A2Pi state of BaF
  • Completed the uncertainty analysis of molecular properties for BaF molecules

Main points: technical

  • Optimization of a BaF cryogenic source
  • Characterisation of a hexapole guide for SrF and BaF
  • Completion of the magnetically shielded interaction zone
  • Laser system and frequency stabilisation upgraded

Main papers in 2021

  • P. Aggarwal, Y. Yin, K. Esajas, H. L. Bethlem, A. Boeschoten, A. Borschevsky, S. Hoekstra (et al.), Deceleration and Trapping of SrF Molecules, Phys. Rev. Lett. 127 (2021) 173201
  • P. A. B. Haase, D. J. Doeglas, A. Boeschoten, E. Eliav, M. Ilias, P. Aggarwal, H. L. Bethlem, A. Borschevsky (et al.), Systematic study and uncertainty evaluation of P, T-odd molecular enhancement factors in BaF, J. Chem. Phys. 155 (2021) 34309
  • P. Aggarwal, H. L. Bethlem, A. Boeschoten, A. Borschevsky, K. Esajas, Y. Hao, S. Hoekstra, K. Jungmann (et al.). A supersonic laser ablation beam source with narrow velocity spreads, Rev. Sci. Instrum. 92 (2021) 33202