We present a study of the energy resolution of transition-edge sensors (TESs) for the detection of electrons in the 100 eV kinetic energy range. The TES is a Ti-Au bilayer with an active area of (60 × 60) μm^2 and a critical temperature of ∼ 80 mK. The electron source is based on vertically-aligned multiwall carbon nanotubes located inside the cryostat, with electrons generated via field emission. For electrons in the (92 - 99) eV kinetic energy range, we obtain a Gaussian energy resolution for fully-absorbed electrons of (0.479 ± 0.041 ± 0.055) eV. When considering the full-width at half-maximum of the peak, the corresponding resolution is of (1.44 ± 0.17 ± 0.27) eV. The former represents an improvement of (46 - 60)

The PTOLEMY project is prototyping a novel electromagnetic filter for high-precision /3 spectroscopy, with the ultimate and ambitious long-term goal of detecting the cosmic neutrino background through electron capture on tritium bound to graphene. Intermediate small-scale prototypes can achieve competitive sensitivity to the effective neutrino mass, even with reduced energy resolution. To reach an energy resolution better than 500 meV at the tritium /3-spectrum endpoint of 18.6 keV, and accounting for all uncertainties in the filtering chain, the electrode voltage must be controlled at the level of a few parts per million and monitored in real time. In this work, we present the first results obtained in this effort, using a chain of commercial ultra-high-precision voltage references, read out by precision multimeters and afield mill device. The currently available precision on high voltage is, in the conservative case, as low as 0.2 ppm per 1 kV single board and less than or similar to 50 mV over the 10 kV series, presently limited by field mill read-out noise. However, assuming uncor related Gaussian noise extrapolation, the real precision could in principle be as low as 0.05 ppm over 20 kV.

This paper reports the measurement of Higgs boson production in association with a t (t) over bar pair in the H -> b (b) over bar decay channel. The analysis uses 140 fb(-1) of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The final states with one or two electrons or muons are employed. An excess of events over the expected background is found with an observed (expected) significance of 4.6 (5.4) standard deviations. The t (t) over barH cross-section is sigma(t (t) over barH)=411(-92)(+101)fb=411 +/- 54(stat.)(-75)(+85)(syst.)fb for a Higgs boson mass of 125.09 GeV, consistent with the prediction of the Standard Model of 507(-50)(+35) fb. The cross-section is also measured differentially in bins of the Higgs boson transverse momentum within the simplified template cross-section framework.

To resolve the effective neutrino mass $m_\beta$ with an energy resolution of 50 meV, the PTOLEMY experiment has proposed a novel transverse electromagnetic filtering process. Perniciously reducing the kinetic energy of tritium $\beta$-decay electrons by counteracting motion from ${\bf E}$ $\times$ ${\bf B}$ and $\nabla{\rm B}$ drift, the PTOLEMY filter requires an input of emitted electron kinematic information to generate a tailored, suitable electric field for each endpoint candidate. The collaboration proposes to extract these quantities by using antennae to observe the relativistic frequency shift of emitted cyclotron radiation as an electron transits by ${\bf E}$ $\times$ ${\bf B}$ drift through a uniform magnetic field region preceding the filter. Electrons must be contained within this region long enough such that an adequate integrated radiated power signal is received to accurately estimate kinematics. This necessitates a controlled, slowed drift speed. However, a demonstration of slowing ${\bf E}$ $\times$ ${\bf B}$ drift for the purpose of increasing containment time has yet to be shown in a physical setup. Actualizing such a system is a crucial milestone in developing the detector, enabling future cyclotron radiation measurements, filter implementation, and source injection. This paper presents the experimental design to vary ${\bf E} \times {\bf B}$ drift speed of carbon-14 $\beta$-decay electrons using a custom electrode field cage situated between the pole faces of an electromagnet. Matching our results with high-fidelity simulation, we deduce a capacity to increase particle time of flight by a factor of 5 in the field cage's slow drift region. Limited only by the dimensions of our system, we assert drift speed can be arbitrarily slowed to meet the needs of PTOLEMY's future detector.

A search for neutral long-lived particles (LLPs) decaying in the ATLAS hadronic calorimeter using 140 fb−1 of proton-proton collisions at √(s) = 13 TeV delivered by the LHC is presented. The analysis is composed of three channels. The first targets pair-produced LLPs, where at least one LLP is produced with sufficiently low boost that its decay products can be resolved as separate jets. The second and third channels target LLPs respectively produced in association with a W or Z boson that decays leptonically. In each channel, different search regions target different kinematic regimes, to cover a broad range of LLP mass hypotheses and models. No excesses of events relative to the background predictions are observed. Higgs boson branching fractions to pairs of hadronically decaying neutral LLPs larger than 1

To resolve the effective neutrino mass m(beta) with an energy resolution of 50 meV, the PTOLEMY experiment has proposed a novel transverse electromagnetic filtering process. Substantially reducing the kinetic energy of tritium beta-decay electrons by counteracting motion from E x B and del B drift, the PTOLEMY filter requires an input of emitted electron kinematic information to generate a tailored, suitable electric field for each candidate. The collaboration proposes to extract these quantities by using antennae to observe the relativistic frequency shift of emitted cyclotron radiation as an electron transits by E x B drift through a uniform magnetic field region preceding the filter. Electrons must be contained within this region long enough such that an adequate integrated radiated power signal is received to accurately estimate these kinematics. This necessitates a controlled, slowed drift speed. This paper presents the experimental design to vary E x B drift speed of 14C beta-decay electrons using a custom electrode field cage situated between the pole faces of an electromagnet. Matching our results with high-fidelity simulation, we deduce a capacity to increase particle time of flight by a factor of 5 in the field cage's slow drift region. Limited only by the dimensions of our system, we assert drift speed can be arbitrarily slowed to meet the needs of PTOLEMY's future detector. Actualizing such a system is a crucial milestone in developing the detector, enabling future cyclotron radiation measurements, filter implementation, and source injection.

A search is presented for the pair production of higgsinos χ˜ in gauge-mediated supersymmetry models, where the lightest neutralinos χ˜10 decay into a light gravitino G˜ in association with either a Higgs h or a Z boson. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb−1 of proton–proton collisions at a centre-of-mass energy of s=13TeV. It targets final states in which a Higgs boson decays into a photon pair, while the other Higgs or Z boson decays into a bb¯ pair, with missing transverse momentum associated with the two gravitinos. Search regions dependent on the amount of missing transverse momentum are defined by the requirements that the diphoton mass should be consistent with the mass of the Higgs boson, and the bb¯ mass with the mass of the Higgs or Z boson. The main backgrounds are estimated with data-driven methods using the sidebands of the diphoton mass distribution. No excesses beyond Standard Model expectations are observed and higgsinos with masses up to 320GeV are excluded, assuming a branching fraction of 100% for χ˜10→hG˜. This analysis excludes higgsinos with masses of 130GeV for branching fractions to hG˜ as low as 36%, thus providing complementarity to previous ATLAS searches in final states with multiple leptons or multiple b-jets, targeting different decays of the electroweak bosons.

Abstract Precision measurements of electron reconstruction, identification, and isolation efficiencies and photon identification efficiencies are presented. They use the full Run 2 data sample collected by the ATLAS experiment in pp collisions at a centre-of-mass energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb −1. The measured electron identification efficiencies have uncertainties that are around 30%–50% smaller than the previous Run 2 results due to an improved methodology and the inclusion of more data. A better pile-up subtraction method leads to electron isolation efficiencies that are more independent of the amount of pile-up activity. Updated photon identification efficiencies are also presented, using the full Run 2 data. When compared to the previous measurement, a 30%–40% smaller uncertainty is observed on the photon identification efficiencies, thanks to the increased amount of available data.

This paper reports cross-section measurements of ZZ production in pp collisions at s=13.6TeV at the Large Hadron Collider. The data were collected by the ATLAS detector in 2022, and correspond to an integrated luminosity of 29 fb−1. Events in the ZZ→4ℓ (ℓ=e, μ) final states are selected and used to measure the inclusive and differential cross-sections in a fiducial region defined close to the analysis selections. The inclusive cross-section is further extrapolated to the total phase space with a requirement of 66

Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of 140 fb^-1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the (g-2)_μ discrepancy. This analysis covers an ALP mass range from 100 to 62 GeV and ALP-photon couplings in the range 10^-7 TeV^-1

The energy and mass measurements of jets are crucial tasks for the Large Hadron Collider experiments. This paper presents a new calibration method to simultaneously calibrate these quantities for large-radius jets measured with the ATLAS detector using a deep neural network (DNN). To address the specificities of the calibration problem, special loss functions and training procedures are employed, and a complex network architecture, which includes feature annotation and residual connection layers, is used. The DNN-based calibration is compared to the standard numerical approach in an extensive series of tests. The DNN approach is found to perform significantly better in almost all of the tests and over most of the relevant kinematic phase space. In particular, it consistently improves the energy and mass resolutions, with a 30% better energy resolution obtained for transverse momenta $p_{\text{T}}>500$ GeV.

A search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair ( bb ) and the other decays to WW*, ZZ*, or τ+τ−, with in each case a final state with ℓ+ℓ−+ neutrinos (ℓ = e, μ). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1, are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95

This paper presents for the first time a precise measurement of the production properties of the Z boson in the full phase space of the decay leptons. This is in contrast to the many previous precise unfolded measurements performed in the fiducial phase space of the decay leptons. The measurement is obtained from proton–proton collision data collected by the ATLAS experiment in 2012 at √(s) = 8 TeV at the LHC and corresponding to an integrated luminosity of 20.2 fb ^-1 . The results, based on a total of 15.3 million Z-boson decays to electron and muon pairs, extend and improve a previous measurement of the full set of angular coefficients describing Z-boson decay. The double-differential cross-section distributions in Z-boson transverse momentum p_T and rapidity y are measured in the pole region, defined as 80< m^ℓℓ< 100 GeV, over the range |y| < 3.6 . The total uncertainty of the normalised cross-section measurements in the peak region of the p_T distribution is dominated by statistical uncertainties over the full range and increases as a function of rapidity from 0.5–1.0 |y| < 2.0 to 2-7% at higher rapidities. The results for the rapidity-dependent transverse momentum distributions are compared to state-of-the-art QCD predictions, which combine in the best cases approximate N ^4 LL resummation with N ^3 LO fixed-order perturbative calculations. The differential rapidity distributions integrated over p_T are even more precise, with accuracies from 0.2–0.3 |y| < 2.0 to 0.4–0.9

AbstractA search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark ($$q=u,c$$ q = u , c ) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two $$W$$ W bosons, two $$Z$$ Z bosons or a $$\tau ^{+}\tau ^{-}$$ τ + τ - pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are $$t\bar{t}$$ t t ¯ and Ht production. For the $$t\bar{t}$$ t t ¯ production, one top quark decays via $$t\rightarrow Hq$$ t → H q . The proton–proton collision data set analysed amounts to $$({140}\,{\hbox {fb}^{-1}})$$ ( 140 fb - 1 ) at $$(\sqrt{s}={13}\,\hbox {TeV})$$ ( s = 13 TeV ) . No significant excess beyond Standard Model expectations is observed and upper limits are set on the $$t\rightarrow Hq$$ t → H q branching ratios at 95 % confidence level, amounting to observed (expected) limits of $$\mathcal {B}(t\rightarrow Hu)<2.8\,(3.0) \times 10^{-4}$$ B ( t → H u ) < 2.8 ( 3.0 ) × 10 - 4 and $$\mathcal {B}(t\rightarrow Hc)<3.3\,(3.8) \times 10^{-4}$$ B ( t → H c ) < 3.3 ( 3.8 ) × 10 - 4 . Combining this search with other searches for $$tHq$$ tHq flavour-changing neutral-current interactions previously conducted by ATLAS, considering $$H\rightarrow b\bar{b}$$ H → b b ¯ and $$H\rightarrow \gamma \gamma $$ H → γ γ decays, as well as $$H\rightarrow \tau ^{+}\tau ^{-}$$ H → τ + τ - decays with one or two hadronically decaying $$\tau $$ τ -leptons, yields observed (expected) upper limits on the branching ratios of $$\mathcal {B}(t\rightarrow Hu)<2.6\,(1.8) \times 10^{-4}$$ B ( t → H u ) < 2.6 ( 1.8 ) × 10 - 4 and $$\mathcal {B}(t\rightarrow Hc)<3.4\,(2.3) \times 10^{-4}$$ B ( t → H c ) < 3.4 ( 2.3 ) × 10 - 4 .

Higgs boson production via gluon–gluon fusion is measured in the WW^*→ eνμν decay channel. The dataset utilized corresponds to an integrated luminosity of 139 fb ^-1 collected by the ATLAS detector from √(s)=13 TeV proton–proton collisions delivered by the Large Hadron Collider between 2015 and 2018. Differential cross sections are measured in a fiducial phase space restricted to the production of at most one additional jet. The results are consistent with Standard Model expectations, derived using different Monte Carlo generators.

A search for a new massive charged gauge boson, $W'$, is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected from proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =13$ TeV, and corresponds to an integrated luminosity of 139 fb$^{-1}$. The reconstructed $tb$ invariant mass is used to search for a $W'$ boson decaying into a top quark and a bottom quark. The result is interpreted in terms of a $W'$ boson with purely right-handed or left-handed chirality in a mass range of 0.5-6 TeV. Different values for the coupling of the $W'$ boson to the top and bottom quarks are considered, taking into account interference with single-top-quark production in the $s$-channel. No significant deviation from the background prediction is observed. The results are expressed as upper limits on the $W' \rightarrow tb$ production cross-section times branching ratio as a function of the $W'$-boson mass and in the plane of the coupling vs the $W'$-boson mass.

A bstract A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb − 1 of pp collision data collected at $$ \sqrt{s} $$ s = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small R -parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $$ m\left(\overset{\sim }{g}\right) $$ m g ~ = 2 . 4 TeV gluinos, electroweakinos with $$ m\left({\overset{\sim }{\chi}}_1^0\right) $$ m χ ~ 1 0 = 1 . 5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.

A search for the charged-lepton-flavor-violating process Z -> e mu is presented, using 139 fb(-1) of root s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. An excess in the e mu invariant mass spectrum near the Z boson mass would be a striking signature of new physics. No excess is observed, and an upper limit B(Z -> e mu) < 2.62 x 10(-7) is placed on the branching fraction at 95% confidence level, which is the most stringent limit to date.

Abstract A search for vector-like leptons in multilepton (two, three, or four-or-more electrons plus muons) final states with zero or more hadronic τ-lepton decays is presented. The search is performed using a dataset corresponding to an integrated luminosity of 139 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. To maximize the separation of signal and background, a machine-learning classifier is used. No excess of events is observed beyond the Standard Model expectation. Using a doublet vector-like lepton model, vector-like leptons coupling to third-generation Standard Model leptons are excluded in the mass range from 130 GeV to 900 GeV at the 95% confidence level, while the highest excluded mass is expected to be 970 GeV.