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Precision Tests in () at FCC-ee
No full textThe rare semi-leptonic decays , with , are highly sensitive to new physics (NP) due to their suppression in the Standard Model (SM). Current LHCb measurements in the muon channel exhibit a significant tension with state-of-the-art SM theory predictions. The proposed tera- run at FCC-ee provides a unique opportunity to untangle the origin of this tension by producing a very large sample of -mesons in a clean environment. We explore the expected precision of () measurements at FCC-ee, complementing existing studies with in the final state, and compare with HL-LHC projections. For the case of muons in the final state, we show that HL-LHC and FCC-ee are expected to deliver a similar number of events, while the latter performs much better in the case of final state electrons. Regardless of the lepton flavour, we expect the FCC-ee environment to be much cleaner than at HL-LHC, with subleading systematics. We also find that a significant reduction in theory uncertainties on the SM predictions is required to capitalize on the advantage going from HL-LHC to FCC-ee. We demonstrate the power of such measurements at FCC-ee to extract information on the long-distance contribution to these decays, and to reveal evidence for new physics even if no deviations are seen in electroweak precision tests
The Higgs boson’s lifetime measurement via off-shell decays to W-bosons
No full textThe discovery of the Higgs boson just over 10 years ago motivated many new questions as to the precise nature of this elusive particle. One such question pertains to the lifetime of the Higgs boson, which is a particularly interesting quantity as it holds information on the particle content in our universe. Measuring a deviation from the standard model might indicate that there exist different types of particles in our universe, beyond the ones we currently know to exist through experimental evidence. Measuring the lifetime of the Higgs boson is however complicated by the fact that the Standard Model predicts it to be extremely short, so short that it was long thought to not be within experimental reach of the particle detectors at the LHC in CERN. However, using a technique which relies on its off-shell decays the lifetime of the Higgs boson can experimentally be determined with great precision. In this presentation I will show this technique applied to Higgs bosons when they decay via two W-bosons. I will introduce how this technique is applied in practice to experimental data collected by the ATLAS detector at CERN, leading to the most sensitive measurement of the Higgs boson lifetime in the WW-channel to date. The results reveal that we can indeed experimentally constrain the Higgs width to within a couple Mega-electronVolt (MeV) in this channel, reaching a precision that is of the same order of magnitude as the width itself. The results are moreover compatible with predictions from the standard model, proving once again that the standard model has excellent predictive power within the current range of energies explored at the LHC
The ATLAS Trigger System
No full textThe ATLAS experiment in the LHC Run 3 uses a two-level trigger system to select events of interest to reduce the 40 MHz bunch crossing rate to a recorded rate of up to 3 kHz of fully-built physics events. The trigger system is composed of a hardware based Level-1 trigger and a software based High Level Trigger. The selection of events by the High Level Trigger is based on a wide variety of reconstructed objects, including leptons, photons, jets, b-jets, missing transverse energy, and B-hadrons in order to cover the full range of the ATLAS physics programme. We will present an overview of improvements in the reconstruction, calibration, and performance of the different trigger objects, as well as computational performance of the High Level Trigger system
Metal Foil Detectors assembly for the beam and background monitoring in the LHCb experiment
No full textAfter an upgrade in 2019--2021, the LHCb experiment is taking data in Run 3 (2022--2026) with an instantaneous luminosity of proton-proton collisions of cms. This article presents the Radiation Monitoring System (RMS-R3) for controlling the beam and background conditions at LHCb. It runs continuously during the detector's operation, and independently of the main LHCb data acquisition. Its design is based on robust and radiation-hard Metal Foil Detector technology. The RMS-R3 monitors the instantaneous luminosity and its evolution. The analysis of the RMS-R3 Run 3 data demonstrates its linear response with a high reproducibility in a five-decade dynamic range of luminosity over a long period of operation
U(1) Gauging, Continuous TQFTs, and Higher Symmetry Structures
No full textQuantum field theories can exhibit various generalized symmetry structures, among which higher-group symmetries and non-invertible symmetry defects are particularly prominent. In this work, we explore a new general scenario in which these two structures are intertwined. This phenomenon arises in four dimensions when gauging one of multiple 0-form symmetries in the presence of mixed 't Hooft anomalies. We illustrate this with two distinct models that flow to an IR gapless phase and a gapped phase, respectively, and examine how this symmetry structure manifests in each case. Additionally, we investigate a five-dimensional model where a similar structure exists intrinsically. Our main tool is a symmetry TQFT in one higher dimension, formulated using non-compact gauge fields and having infinitely many topological operators. We carefully determine its boundary conditions and provide a detailed discussion on various dressing choices for its bulk topological operators
Recent results on strangeness enhancement in small collision systems with ALICE
No full textQuantum Chromodynamics (QCD) predicts that, at sufficiently high temperature and energy density, nuclear matter undergoes a phase transition from confined hadrons to a deconfined state of quarks and gluons known as the quark-gluon plasma (QGP). One of the historically proposed signatures of QGP formation is strangeness enhancement (SE), characterized by an increased production of strange hadrons in heavy-ion collisions relative to proton--proton (pp) interactions. At the LHC, the ALICE experiment has measured a continuous increase in the strange-to-non-strange hadron yield ratios as a function of midrapidity charged-particle multiplicity, not only in large systems like Pb--Pb but also in small systems such as pp and p--Pb. The origin of SE in small systems is still under debate, motivating further experimental investigations. This article presents recent ALICE analyses that offer complementary insights into the phenomenon. These include (i) multi-differential studies using event-shape observables such as transverse spherocity and the concept of effective energy, and (ii) the first measurement of multiplicity distributions of strange and multi-strange hadrons, P(), in pp collisions