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Abstract The CODEX-βapparatus is a demonstrator for the proposed future CODEX-b experiment, a long-lived-particle detector foreseen for operation at IP8 during HL-LHC data-taking. The demonstrator project, intended to collect data in 2025, is described, with a particular focus on the design, construction, and installation of the new apparatus. 

Radiocarbon (¹⁴C) is a critical tool for understanding the global carbon cycle. During the Anthropocene, two new processes influenced¹⁴C in atmospheric, land and ocean carbon reservoirs. First,¹⁴C-free carbon derived from fossil fuel burning has diluted¹⁴C, at rates that have accelerated with time. Second, ‘bomb’¹⁴C produced by atmospheric nuclear weapon tests in the mid-twentieth century provided a global isotope tracer that is used to constrain rates of air–sea gas exchange, carbon turnover, large-scale atmospheric and ocean transport, and other key C cycle processes. As we write, the¹⁴C/¹²C ratio of atmospheric CO₂is dropping below pre-industrial levels, and the rate of decline in the future will depend on global fossil fuel use and net exchange of bomb¹⁴C between the atmosphere, ocean and land. This milestone coincides with a rapid increase in¹⁴C measurement capacity worldwide. Leveraging future¹⁴C measurements to understand processes and test models requires coordinated international effort—a ‘decade of radiocarbon’ with multiple goals: (i) filling observational gaps using archives, (ii) building and sustaining observation networks to increase measurement density across carbon reservoirs, (iii) developing databases, synthesis and modelling tools and (iv) establishing metrics for identifying and verifying changes in carbon sources and sinks. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'. 

Long-lived particles (LLPs) show up in many extensions of the Standard Model, but they are challenging to search for with current detectors, due to their very displaced vertices. This study evaluated the ability of the trigger algorithms used in the Large Hadron Collider beauty (LHCb) experiment to detect long-lived particles and attempted to adapt them to enhance the sensitivity of this experiment to undiscovered long-lived particles. A model with a Higgs portal to a dark sector is tested, and the sensitivity reach is discussed. In the LHCb tracking system, the farthest tracking station from the collision point is the scintillating fiber tracker, the SciFi detector. One of the challenges in the track reconstruction is to deal with the large amount of and combinatorics of hits in the LHCb detector. A dedicated algorithm has been developed to cope with the large data output. When fully implemented, this algorithm would greatly increase the available statistics for any long-lived particle search in the forward region and would additionally improve the sensitivity of analyses dealing with Standard Model particles of large lifetime, such as K S 0 or Λ 0 hadrons. 

Abstract In this work, we consider the case of a strongly coupled dark/hidden sector, which extends the Standard Model (SM) by adding an additional non-Abelian gauge group. These extensions generally contain matter fields, much like the SM quarks, and gauge fields similar to the SM gluons. We focus on the exploration of such sectors where the dark particles are produced at the LHC through a portal and undergo rapid hadronization within the dark sector before decaying back, at least in part and potentially with sizeable lifetimes, to SM particles, giving a range of possibly spectacular signatures such as emerging or semi-visible jets. Other, non-QCD-like scenarios leading to soft unclustered energy patterns or glueballs are also discussed. After a review of the theory, existing benchmarks and constraints, this work addresses how to build consistent benchmarks from the underlying physical parameters and present new developments for the pythia Hidden Valley module, along with jet substructure studies. Finally, a series of improved search strategies is presented in order to pave the way for a better exploration of the dark showers at the LHC. 

Abstract We present cosmological constraints from a gravitational lensing mass map covering 9400 deg²reconstructed from measurements of the cosmic microwave background (CMB) made by the Atacama Cosmology Telescope (ACT) from 2017 to 2021. In combination with measurements of baryon acoustic oscillations and big bang nucleosynthesis, we obtain the clustering amplitudeσ₈= 0.819 ± 0.015 at 1.8% precision, $S_8\equiv {\sigma }_8{\left({\mathrm{\Omega }}_{\mathrm{m}}/0.3\right)}^{0.5}=0.840\pm 0.028$, and the Hubble constantH₀= (68.3 ± 1.1) km s⁻¹Mpc⁻¹at 1.6% precision. A joint constraint with Planck CMB lensing yieldsσ₈= 0.812 ± 0.013, $S_8\equiv {\sigma }_8{\left({\mathrm{\Omega }}_{\mathrm{m}}/0.3\right)}^{0.5}=0.831\pm 0.023$, andH₀= (68.1 ± 1.0) km s⁻¹Mpc⁻¹. These measurements agree with ΛCDM extrapolations from the CMB anisotropies measured by Planck. We revisit constraints from the KiDS, DES, and HSC galaxy surveys with a uniform set of assumptions and find thatS₈from all three are lower than that from ACT+Planck lensing by levels ranging from 1.7σto 2.1σ. This motivates further measurements and comparison, not just between the CMB anisotropies and galaxy lensing but also between CMB lensing probingz∼ 0.5–5 on mostly linear scales and galaxy lensing atz∼ 0.5 on smaller scales. We combine with CMB anisotropies to constrain extensions of ΛCDM, limiting neutrino masses to ∑m_ν< 0.13 eV (95% c.l.), for example. We describe the mass map and related data products that will enable a wide array of cross-correlation science. Our results provide independent confirmation that the universe is spatially flat, conforms with general relativity, and is described remarkably well by the ΛCDM model, while paving a promising path for neutrino physics with lensing from upcoming ground-based CMB surveys. 

Abstract We present new measurements of cosmic microwave background (CMB) lensing over 9400 deg²of the sky. These lensing measurements are derived from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB data set, which consists of five seasons of ACT CMB temperature and polarization observations. We determine the amplitude of the CMB lensing power spectrum at 2.3% precision (43σsignificance) using a novel pipeline that minimizes sensitivity to foregrounds and to noise properties. To ensure that our results are robust, we analyze an extensive set of null tests, consistency tests, and systematic error estimates and employ a blinded analysis framework. Our CMB lensing power spectrum measurement provides constraints on the amplitude of cosmic structure that do not depend on Planck or galaxy survey data, thus giving independent information about large-scale structure growth and potential tensions in structure measurements. The baseline spectrum is well fit by a lensing amplitude ofA_lens= 1.013 ± 0.023 relative to the Planck 2018 CMB power spectra best-fit ΛCDM model andA_lens= 1.005 ± 0.023 relative to the ACT DR4 + WMAP best-fit model. From our lensing power spectrum measurement, we derive constraints on the parameter combination $S_8^{\mathrm{CMBL}}\equiv {\sigma }_8{\left({\mathrm{\Omega }}_m/0.3\right)}^{0.25}$of $S_8^{\mathrm{CMBL}}=0.818\pm 0.022$from ACT DR6 CMB lensing alone and $S_8^{\mathrm{CMBL}}=0.813\pm 0.018$when combining ACT DR6 and PlanckNPIPECMB lensing power spectra. These results are in excellent agreement with ΛCDM model constraints from Planck or ACT DR4 + WMAP CMB power spectrum measurements. Our lensing measurements from redshiftsz∼ 0.5–5 are thus fully consistent with ΛCDM structure growth predictions based on CMB anisotropies probing primarilyz∼ 1100. We find no evidence for a suppression of the amplitude of cosmic structure at low redshifts.