Archivio istituzionale della Ricerca - Scuola Normale Superiore
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Search for dark matter produced in association with one or two top quarks in proton-proton collisions at = 13 TeV
No full textA search is performed for dark matter (DM) produced in association with a single top quark or a pair of top quarks using the data collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to 138 fb−1 of integrated luminosity. An excess of events with a large imbalance of transverse momentum is searched for across 0, 1 and 2 lepton final states. Novel multivariate techniques are used to take advantage of the differences in kinematic properties between the two DM production mechanisms. No significant deviations with respect to the standard model predictions are observed. The results are interpreted considering a simplified model in which the mediator is either a scalar or pseudoscalar particle and couples to top quarks and to DM fermions. Axion-like particles that are coupled to top quarks and DM fermions are also considered. Expected exclusion limits of 410 and 380 GeV for scalar and pseudoscalar mediator masses, respectively, are set at the 95% confidence level. A DM particle mass of 1 GeV is assumed, with mediator couplings to fermions and DM particles set to unity. A small signal-like excess is observed in data, with the largest local significance observed to be 1.9 standard deviations for the 150 GeV pseudoscalar mediator hypothesis. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% confidence level upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb
The EDGES measurement disfavors an excess radio background during the cosmic dawn
Full text linkIn 2018 the EDGES experiment claimed the first detection of the global cosmic 21 cm signal, which featured an absorption trough centered around za 17 with a depth of approximately 500 mK. This amplitude is deeper than the standard prediction (in which the radio background is determined by the cosmic microwave background) by a factor of two and potentially hints at the existence of a radio background excess. While this result was obtained by fitting the data with a phenomenological flattened-Gaussian shape for the cosmological signal, here we develop a physical model for the inhomogeneous radio background sourced by the first galaxies hosting population III stars. Star formation in these galaxies is quenched at lower redshifts due to various feedback mechanisms, so they serve as a natural candidate for the excess radio background indicated by EDGES without violating present-day measurements by ARCADE2. We forward-model the EDGES sky temperature data, jointly sampling our physical model for the cosmic signal, a foreground model, and residual calibration errors. We compared the Bayesian evidence obtained by varying the complexity and prior ranges for the systematics. We find that the data are best explained by a model with seven log-polynomial foreground terms and a component accounting for calibration residuals. Interestingly, the presence of a cosmic 21 cm signal with a non-standard depth is decisively disfavored. This result is contrary to previous EDGES analyses in the context of extra radio background models, thus serving as a caution against using a a pseudo-likelihooda built on a model (flattened Gaussian) that is different from the one being used for inference. We make our simulation code and associated emulator publicly available
Search for rare decays of the Z and Higgs bosons to a J/ψ or ψ(2S) meson and a photon in proton-proton collisions at s=13TeV
Full text linkA search is presented for rare decays of the [Figure presented] and Higgs bosons to a photon and a [Figure presented] or a [Figure presented] meson, with the charmonium state subsequentially decaying to a pair of muons. The data set corresponds to an integrated luminosity of 123fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the LHC. No evidence for branching fractions of these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set: [Figure presented], [Figure presented], [Figure presented], and [Figure presented]. The ratio of the Higgs boson coupling modifiers [Figure presented] is constrained to be in the interval (−157,+199) at 95% confidence level. Assuming [Figure presented], this interval becomes (−166,+208)
Multiplicity dependence of charm baryon and charm meson production in pPb collisions at sNN=8.16TeV
Full text linkMeasurements of the production yields of charm baryons (Λc+) and charm mesons (D0) in proton-lead collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV are presented. The data were collected in 2016 with the CMS experiment and correspond to an integrated luminosity of 186 nb−1. The Λc+ baryon is reconstructed from the decay channel Λc+→KS0p, while the D0 meson is reconstructed via D0→K−π+. The Λc+ baryon and D0 meson yields are extracted in several charged-particle multiplicity classes. No strong multiplicity dependence of the Λc+-to-D0 yield ratio is observed, unlike the observed strange baryon to strange meson yield ratio of Λ/Λ ̅ to KS0, which shows a strong multiplicity dependence. This observation indicates different mechanisms for the multiplicity evolution of hadronization processes for charm and strange quarks and provides new constraints to the understanding of heavy flavor production and collectivity in small collision systems
5 Ways Cooperatives Can Shape the Future of AI
No full textAI development is dominated by a handful of powerful firms, raising concerns about equity, accountability, and social harm. AI cooperatives-democratically governed and community-owned-offer a promising alternative through five key interventions: 1) Democratizing data governance by giving individuals control over how their data is used; 2) Bridging research and civil society by grounding AI debates in public needs, not elite institutions; 3) Advancing education to equip members with the knowledge to influence AI systems; 4) Building alternative ownership models to keep AI value creation in stakeholder hands; and 5) Adapting AI for cooperative ends, ensuring systems support solidarity and worker power. Though cooperatives face barriers in scale and resources, these strategies point to a viable, inclusive path for AI aligned with public interest
Modeling Raman Spectra in Complex Environments : from Solutions to Surface-Enhanced Raman Scattering
Full text linkThis perspective highlights the essential physicochemical factors required for accurate computational modeling of Raman and Resonance Raman signals in complex environments. It highlights the theoretical challenges for obtaining a balanced quantum mechanical description of the molecular target, integration of target-environment interactions into the Hamiltonian, and explicit treatment of strong interactions such as hydrogen bonding. The dynamical sampling of solute-solvent phase space and the incorporation of plasmonic effects for Surface-Enhanced Raman Scattering (SERS) are also addressed. Through selected applications, we illustrate how these factors influence Raman signals and propose a framework to tackle these challenges effectively, advancing the reliability of theoretical Raman spectroscopy in real-world scenarios
Constructive theories through a modal lens
Full text linkWe present a uniform proof-theoretic proof of the Gödel–McKinsey–Tarski embedding for a class of first-order intuitionistic theories. This is achieved by adapting to the case of modal logic the methods of proof analysis in order to convert axioms into rules of inference of a suitable sequent calculus. The soundness and the faithfulness of the embedding are proved by induction on the height of the derivations in the augmented calculi. Finally, we define an extension of the modal system for which the result holds with respect to geometric intuitionistic
Unprecedented “Off‐Pathway” [2+2] Cycloaddition‐Retroelectrocyclization Reaction between an Unsymmetric Alkyne and Tetracyanoquinodimethane
Full text linkIn recent years, the [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction between electron-rich alkynes and electron-deficient alkenes has emerged as one of the most effective synthetic routes to prepare a large variety of molecular and polymeric electron donor-acceptor systems. Besides its simplicity, fast rate, and high yield, this reaction may also display complete and predictable regioselectivity, as for the case when tetracyanoquinodimethane (TCNQ) is used in combination with unsymmetric, activated alkynes. Here, we report the first example of a [2+2] CA-RE reaction between TCNQ and an aniline-activated alkyne following an "inverted" regiochemistry, thus leading to the exclusive formation of an unexpected regioisomer in contrast to the expected one. A combined experimental and theoretical study helped us to unravel the peculiar reaction mechanism underlying the regioselectivity switching
