ATLAS

Abstract:

The MALTA family of Depleted Monolithic Active Pixel Sensors (DMAPS) is produced using Tower 180 nm CMOS technology, specifically targeting radiation-hard applications in the HL-LHC and beyond. Several process modifications have resulted in radiation hardness up to 3 × 1015 1 MeV neq/cm2 and time resolution below 2 ns, with uniform charge collection efficiency across the chip formed of 512 × 224 pixels with a size of 36.4 × 36.4 μm2. This is achieved when adopting high-resistivity Czochralski substrates with backside metallisation to obtain a good propagation of the bias voltage. This contribution will show the most recent results obtained on MALTA2 chip demonstrators, including signal efficiency, noise occupancy and time resolution, at different levels of irradiation as well as the performance of the MALTA telescope permanently installed at the SPS at CERN and used in the test beam campaign in 2021-2023.

Abstract:

The ATLAS trigger system is a crucial component of the ATLAS experiment at the LHC. It is responsible for selecting events in line with the ATLAS physics programme. This paper presents an overview of the changes to the trigger and data acquisition system during the second long shutdown of the LHC, and shows the performance of the trigger system and its components in the proton-proton collisions during the 2022 commissioning period as well as its expected performance in proton-proton and heavy-ion collisions for the remainder of the third LHC data-taking period (2022–2025).

Abstract:

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behavior differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. We present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN’s Super Proton Synchrotron (SPS) accelerator. Monte Carlo simulations agree well with the experimental data and show that the characteristic scales necessary for collective plasma behavior, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations.