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Particle Physics 2020

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 VENI grant (Hannah Arnold)
  • NWO ENW-GROOT grant “At the heart of the Higgs” (W. Verkerke, I. van Vulpen, H. Snoek, P. Kluit, B. van Eijk, T. du Pree, N. de Groot, P. Ferrari & F. Filthaut)
  • NWO ENW-KLEIN-II grant “Fingerprinting the Higgs” (W. Verkerke & J. Rojo)
  • DESY Fellowship (Carsten Burgard)
  • Swiss NF mobility grant (Marko Stamenkovic)

Key positions in collaborations

  • Publications committee chair: Pamela Ferrari
  • Authorship committee and Publications committee member: Frank Filthaut
  • Convener H→bb/cc subgroup: Hannah Arnold
  • Early Career Scientist Board: Flavia Dias
  • Outreach Coordinator: Clara Nellist
  • ITK system engineer & global structures coordinator: Marcel Vreeswijk
  • FELIX firmware coordinator: Frans Schreuder
  • FELIX software coordinator: Mark Dönszelmann
  • FELIX user support coordinator: Nikolina Ilić
  • Statistics committee: Wouter Verkerke

Main papers in 2020

  • ATLAS Collaboration, G. Aad et al, ”Evidence for tttt production in the multilepton final state in proton-proton collisions at √s = 13 TeV with the Atlas detector”, Eur.Phys.J.C 80 (2020) 11
  • ATLAS Collaboration, G. Aad et al., ”Search for heavy resonances decaying into a pair of Z bosons in the l+l–l’+l’- and l+l– νvbar final states using 139 fb-1 of proton–proton collisions at √s  = 13 TeV with the ATLAS detector”, submitted to Eur. Phys. J.
  • ATLAS Collaboration, G. Aad et al., “A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector”, Phys. Lett. B 812 (2021) 135980
  • ATLAS Collaboration, G. Aad et al., “A search for the Zγ decay mode of the Higgs boson in pp collisions in √s = 13 TeV with the ATLAS detector”, Phys.Lett.B 809 (2020)
  • ATLAS Collaboration, G. Aad et al. “Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb and ℓℓWW final states in pp collisions at √s= 13 TeV with the ATLAS detector”, submitted to EPJC
  • ATLAS Collaboration, G. Aad et al., “Charged-lepton-flavour violation at the LHC: a search for Z→eτ/μτ decays with the ATLAS detector”, submitted to Nature Physics
  • ATLAS Collaboration, G. Aad et al., “Measurement of the associated production of a Higgs boson decaying into b-quarks with a vector boson at high transverse momentum in pp collisions at √s = 13 TeV with the ATLAS detector”, submitted to PLB

LHCb

Programme Leader

Marcel Merk, Antonio Pellegrino (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 B0(s)→ e+e– 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,
  • LHCb Thesis prize: Jacco de Vries, Daniel Campora,
  • LHCb industry award for 3D systems company through collaboration with Antonio Pellegrino,
  • Welcome of Maastricht University in the LHCb collaboration.

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

Main papers in 2020

  • LHCb, Observation of CP-violation in two-body Bs0 meson decays to charged pions and kaons, arXiv:2012.05319.
  • LHCb, Measurement of CP violation in the decay B^+ -> K^+ \pi^0, arXiv:2012.12789.
  • LHCb, Measurement of the CKM angle \gamma and Bs – Busbar mixing frequency, arXiv:2011.12041
  • LHCb, Measurement of the CP averaged observables in the B0 -> K* mu^+ mu^- decay, Phys. Rev. Lett. 125 (2020) 011802
  • LHCb, Measurement of the branching fraction of the B0 -> Ds^+ pi^- decay, arXiv:2010.11986
  • LHCb, Search for long-lived particles decaying to e^\pk \mu^\mp \nu, arXiv:2012.02696.

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

  • Upgrade of inner-tracking system at CERN and tested.

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

Awards, fellowships etc.

  • Veni: H. J. Correia Zanoli
  • Veni: N. Mohammadi
  • Stuart Jay Freedman Award: M. Verweij

Main papers in 2020

  • Probing the effects of strong electromagnetic fields with charge-dependent directed flow in Pb-Pb collisions at the LHC (Oct 31, 2019) Phys.Rev.Lett. 125 (2020) 2, 022301
  • Unveiling the strong interaction among hadrons at the LHC: ALICE Collaboration  (May 23, 2020) Published in: Nature 588 (2020) 232-238
  • Constraining the chiral magnetic effect with charge-dependent azimuthal correlations in Pb-Pb at 2.76 and 5.02 TeV (0.1007/JHEP09(2020)160)

eEDM

Programme Leader

Steven Hoekstra

Main points: scientific

  • Deceleration to standstill of SrF molecules
  • Determination of the lifetime of electronically excited SrF molecules
  • Optical pumping of BaF molecules between rotational and hyperfine states
  • Measurement of the hyperfine structure in the X2Sigma and A2Pi state of BaF
  • Accurate calculation of the effective electric field in BaF molecules

Main points: technical

  • Development of a BaF cryogenic source
  • Design, construction and implementation of a hexapole guide for SrF and BaF

Main papers in 2020

  • R. J. Marshman, A. Mazumdar, G. W. Morley, P. F. Barker, S. Hoekstra, S. Bose
    Mesoscopic Interference for Metric and Curvature (MIMAC) & Gravitational Wave Detection, New J. Phys. 22 (2020) 083012
  • Enhanced 𝒫,𝒯-violating nuclear magnetic quadrupole moment effects in laser-coolable molecules, Denis, M., Hao, Y., Eliav, E., Hutzler, N. R., Nayak, M. K., Timmermans, R. G. E., & Borschevsky, A. (2020)., J. Chem. Phys. 152, 084303 (2020)