Rubin-LSST

Abstract:

This article reports on a search for dijet resonances using $132{\mathrm{fb}}^{-1}$ of $pp$ collision data recorded at $\sqrt{s}=13\mathrm{TeV}$ by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of $p_{\mathrm{T}}\ge 85\mathrm{GeV}$ and jet rapidity separation of $|y^{*}|<0.6$ are analysed for dijet resonances with invariant masses from 375 to $1800\mathrm{GeV}$ . A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at 95% confidence level on coupling values for a benchmark leptophobic axial-vector $Z^{\prime }$ model and on the production cross section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution.

Abstract:

A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using $140{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than $\mathcal{O}(10)\mathrm{cm}$ .

Abstract:

Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions. This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of R = 1.0 and its dependence on the jet substructure. The measurement uses 1.72 nb − 1 of Pb+Pb data and 255 pb − 1 of p p data, both at s NN = 5.02 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering R = 0.2 calorimetric jets and are measured for transverse momentum above 200 GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor ( R AA ). The jet R AA is measured as a function of jet p T , the charged k t splitting scale ( d 12 ), and the angular separation ( Δ R 12 ) of two leading sub-jets. The jet R AA gradually decreases with increasing d 12 , implying significantly stronger suppression of large-radius jets with larger k t splitting scale. The jet R AA gradually decreases for Δ R 12 in the range 0.01 − 0.2 and then remains consistent with a constant for Δ R 12 ≳ 0.2 . The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.

Abstract:

Abstract The relationship between the already formed stellar mass in a galaxy and the gas reservoir of neutral atomic hydrogen, is a key element in our understanding of how gas is turned into stars in galaxy haloes. In this paper, we measure the $M_{\rm H\, \small {\rm i}}-M_{\star }$ relation based on a stellar-mass selected sample at 0.25 &lt; z &lt; 0.5 and the MIGHTEE-H i DR1 spectral data. Using a powerful Bayesian stacking technique, for the first time we are also able to measure the underlying bivariate distribution of H i mass and stellar mass of galaxies with M⋆ &gt; 109.5 M⊙, finding that an asymmetric underlying H i distribution is strongly preferred by our complete samples. We define the concepts of the average of the logarithmic H i mass, $\langle \log _{10}(M_{\rm H\, \small {\rm i}})\rangle$, and the logarithmic average of the H i mass, $\log _{10}(\langle M_{\rm H\, \small {\rm i}}\rangle )$, and find that the difference between $\langle \log _{10}(M_{\rm H\, \small {\rm i}})\rangle$ and $\log _{10}(\langle M_{\rm H\, \small {\rm i}}\rangle )$ can be as large as ∼0.5 dex for the preferred asymmetric H i distribution. We observe shallow slopes in the underlying $M_{\rm H\, \small {\rm i}}-M_{\star }$ scaling relations, suggesting the presence of an upper H i mass limit beyond which a galaxy can no longer retain further H i gas. From our bivariate distribution we also infer the H i mass function at this redshift and find tentative evidence for a decrease of 2-10 times in the co-moving space density of the most H i massive galaxies up to z ∼ 0.5.

Abstract:

ABSTRACT Atomic hydrogen constitutes the gas reservoir from which molecular gas and star formation in galaxies emerges. However, the weakness of the line means it has been difficult to directly detect in all but the very local Universe. Here, we present results from the first search using the MeerKAT International Tiered Extragalactic Exploration (MIGHTEE) Survey for high-redshift ($z&gt;0.25$) H i emission from individual galaxies. By searching for 21-cm emission centred on the position and redshift of optically selected emission-line galaxies we overcome difficulties that hinder untargeted searches. We detect 11 galaxies at $z&gt;0.25$, forming the first sample of $z&gt;0.25$ detections with an interferometer, with the highest redshift detection at $z = 0.3841$. We find they have much larger H i masses than their low-redshift H i-selected counterparts for a given stellar mass. This can be explained by the much larger cosmological volume probed at these high redshifts, and does not require any evolution of the H i mass function. We make the first-ever measurement of the baryonic Tully–Fisher relation (bTFr) with H  i at $z&gt;0.25$ and find consistency with the local bTFr, but with tentative evidence of a flattening in the relation at these redshifts for higher-mass objects. This may signify evolution, in line with predictions from hydrodynamic simulations, or that the molecular gas mass in these high-mass galaxies could be significant. This study paves the way for future studies of H i beyond the local Universe, using both searches targeted at known objects and via pure H i selection.