Rubin-LSST

Abstract:

A search for pair production of vector-like leptons coupling to first- and second-generation Standard Model leptons is presented. The search is based on a dataset of proton-proton collisions at s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. Events are categorised depending on the flavour and multiplicity of leptons (electrons or muons), as well as on the scores of a deep neural network targeting particular signal topologies according to the decay modes of the vector-like leptons. In each of the signal regions, the scalar sum of the transverse momentum of the leptons and the missing transverse momentum is analysed. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No significant excess above the Standard Model background expectation is observed and limits are set at 95% confidence level on the production cross-sections of vector-like electrons and muons as a function of the vector-like lepton mass, separately for SU(2) doublet and singlet scenarios. The resulting mass lower limits are 1220 GeV (1270 GeV) and 320 GeV (400 GeV) for vector-like electrons (muons) in the doublet and singlet scenarios, respectively.

Abstract:

A measurement of the ratio of the branching fractions, Rτ/e = B(W → τν)/B(W → eν), is performed using a sample of W bosons originating from top-quark decays to final states containing τ-leptons or electrons. This measurement uses pp collisions at s = 13 TeV, collected by the ATLAS experiment at the Large Hadron Collider during Run 2, corresponding to an integrated luminosity of 140 fb−1. The W → τντ (with τ → eνeντ) and W → eνe decays are distinguished using the differences in the impact parameter distributions and transverse momentum spectra of the electrons. The measured ratio of branching fractions Rτ/e = 0.975 ± 0.012 (stat.) ± 0.020 (syst.), is consistent with the Standard Model assumption of lepton flavour universality in W-boson decays.

Abstract:

High angular resolution radio observations of relativistic jets are necessary to understand the causal connection between accretion and jet ejection in low-mass X-ray binaries. Images from these observations can be difficult to reconstruct due to the rapid intra-observational motion and variability of transient jets. We have developed a time-dependent visibility model fitting and self-calibration procedure and applied it to a single 4 hr VLBA observation of the low-mass X-ray binary Swift J1727.8−1613 during the bright flaring period of its 2023 outburst. This allowed us to detect and model a slightly resolved self-absorbed compact core, as well as three downstream transient jet knots. We were able to precisely measure the proper motion and flux density variability of these three jet knots, as well as (for the first time) their intra-observational expansion. Using simultaneous multifrequency data, we were also able to measure the spectral index of the furthest downstream jet knot, and the core, as well as the frequency-dependent core shift between 2.3 and 8.3 GHz. Using these measurements, we inferred the ejection dates of the three jet knots, including one to within ±40 minutes, which is one of the most precise ever measured. The ejection of the transient jet knots coincided with a bright X-ray flare and a drastic change in the X-ray spectral and timing properties as seen by HXMT, which is the clearest association ever seen between the launching of transient relativistic jets in an X-ray binary and a sudden change in the X-ray properties of the accretion inflow.

Abstract:

<jats:p>We present a generalisation of the standard pseudo- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>C</mml:mi><mml:mo>ℓ</mml:mo></mml:msub></mml:math> approach for power spectrum estimation to the case of spin- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>s</mml:mi></mml:math> fields weighted by a general positive-definite weight matrix that couples the different spin components of the field (e.g.  <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Q</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>U</mml:mi></mml:math> maps in CMB polarisation analyses, or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>γ</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>γ</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> shear components in weak lensing). Relevant use cases are, for example, data with significantly anisotropic noise properties, or situations in which different masks must be applied to the different field components. The weight matrix map is separated into a spin-0 part, which corresponds to the “mask” in the standard pseudo- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>C</mml:mi><mml:mo>ℓ</mml:mo></mml:msub></mml:math> approach, and a spin- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mi>s</mml:mi></mml:mrow></mml:math> part sourced solely by the anisotropic elements of the matrix, leading to additional coupling between angular scales and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>E</mml:mi><mml:mi>/</mml:mi><mml:mi>B</mml:mi></mml:mrow></mml:math> modes. The general expressions for the mode-coupling coefficients involving the power spectra of these anisotropic weight components are derived and validated. The generalised algorithm is as computationally efficient as the standard approach. We implement the method in the public code NaMaster.</jats:p>