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Federico Betti

Publications and source records attributed to Federico Betti.

12 recordsLinked to original sources

Hallucination Early Detection in Diffusion Models

Text-to-Image generation has seen significant advancements in output realism with the advent of diffusion models. However, diffusion models encounter difficulties when tasked with generating multiple objects, frequently resulting in hallucinations where certain entities are omitted. While existing solutions typically focus on optimizing latent representations within diffusion models, the relevance of the initial generation seed is typically underestimated. While using various seeds in multiple iterations can improve results, this method also significantly increases time and energy costs. To address this challenge, we introduce HEaD+ (Hallucination Early Detection +), a novel approach designed to identify incorrect generations early in the diffusion process. The HEaD+ framework integrates cross-attention maps and textual information with a novel input, the Predicted Final Image. The objective is to assess whether to proceed with the current generation or restart it with a different seed, thereby exploring multiple-generation seeds while conserving time. HEaD+ is trained on the newly created InsideGen dataset of 45,000 generated images, each containing prompts with up to seven objects. Our findings demonstrate a 6-8% increase in the likelihood of achieving a complete generation (i.e., an image accurately representing all specified subjects) with four objects when applying HEaD+ alongside existing models. Additionally, HEaD+ reduces generation times by up to 32% when aiming for a complete image, enhancing the efficiency of generating complete and accurate object representations relative to leading models. Moreover, we propose an integrated localization module that predicts object centroid positions and verifies pairwise spatial relations (if requested by the users) at an intermediate timestep, gating generation together with object presence to further improve relation-consistent outcomes.

cs.CV

What Changed? Detecting and Evaluating Instruction-Guided Image Edits with Multimodal Large Language Models

Instruction-based image editing models offer increased personalization opportunities in generative tasks. However, properly evaluating their results is challenging, and most of the existing metrics lag in terms of alignment with human judgment and explainability. To tackle these issues, we introduce DICE (DIfference Coherence Estimator), a model designed to detect localized differences between the original and the edited image and to assess their relevance to the given modification request. DICE consists of two key components: a difference detector and a coherence estimator, both built on an autoregressive Multimodal Large Language Model (MLLM) and trained using a strategy that leverages self-supervision, distillation from inpainting networks, and full supervision. Through extensive experiments, we evaluate each stage of our pipeline, comparing different MLLMs within the proposed framework. We demonstrate that DICE effectively identifies coherent edits, effectively evaluating images generated by different editing models with a strong correlation with human judgment. We publicly release our source code, models, and data.

cs.CV

Luminosity measurement with the LHCb RICH detectors in Run 3

The LHCb Ring-Imaging Cherenkov detectors are built to provide charged hadron identification over a large range of momentum. The upgraded detectors are also capable of providing an independent measurement of the luminosity for the LHCb experiment during LHC Run 3. The modelling of the opto-electronics chain, the application of the powering strategy during operations, the calibration procedures and the proof of principle of a novel technique for luminosity determination are presented. In addition, the preliminary precision achieved during the 2023 data-taking year for real-time and offline luminosity measurements is reported.

hep-ex

Optimizing Resource Consumption in Diffusion Models through Hallucination Early Detection

Diffusion models have significantly advanced generative AI, but they encounter difficulties when generating complex combinations of multiple objects. As the final result heavily depends on the initial seed, accurately ensuring the desired output can require multiple iterations of the generation process. This repetition not only leads to a waste of time but also increases energy consumption, echoing the challenges of efficiency and accuracy in complex generative tasks. To tackle this issue, we introduce HEaD (Hallucination Early Detection), a new paradigm designed to swiftly detect incorrect generations at the beginning of the diffusion process. The HEaD pipeline combines cross-attention maps with a new indicator, the Predicted Final Image, to forecast the final outcome by leveraging the information available at early stages of the generation process. We demonstrate that using HEaD saves computational resources and accelerates the generation process to get a complete image, i.e. an image where all requested objects are accurately depicted. Our findings reveal that HEaD can save up to 12% of the generation time on a two objects scenario and underscore the importance of early detection mechanisms in generative models.

cs.CV

Let's ViCE! Mimicking Human Cognitive Behavior in Image Generation Evaluation

Research in Image Generation has recently made significant progress, particularly boosted by the introduction of Vision-Language models which are able to produce high-quality visual content based on textual inputs. Despite ongoing advancements in terms of generation quality and realism, no methodical frameworks have been defined yet to quantitatively measure the quality of the generated content and the adherence with the prompted requests: so far, only human-based evaluations have been adopted for quality satisfaction and for comparing different generative methods. We introduce a novel automated method for Visual Concept Evaluation (ViCE), i.e. to assess consistency between a generated/edited image and the corresponding prompt/instructions, with a process inspired by the human cognitive behaviour. ViCE combines the strengths of Large Language Models (LLMs) and Visual Question Answering (VQA) into a unified pipeline, aiming to replicate the human cognitive process in quality assessment. This method outlines visual concepts, formulates image-specific verification questions, utilizes the Q&A system to investigate the image, and scores the combined outcome. Although this brave new hypothesis of mimicking humans in the image evaluation process is in its preliminary assessment stage, results are promising and open the door to a new form of automatic evaluation which could have significant impact as the image generation or the image target editing tasks become more and more sophisticated.

cs.CV

CKM and $C\!P$ violation in beauty and charm decays in LHCb

Measurements of $C\!P$ violation and Cabibbo-Kobayashi-Maskawa matrix in beauty and charm hadron decays are the core business of the LHCb physics programme. In this contribution, the most recent measurements performed by the LHCb collaboration on this topic are reported. The most precise measurement of time-dependent $C\!P$ asymmetry parameters in $B_s^0 \to \phi \phi$ decays has been done, providing results fully compatible with Standard Model expectations. The polarisation-dependent $C\!P$-violation parameters of the same decay are measured for the first time. The combination of beauty and charm results gives $\gamma = \left( 63.8^{+3.5}_{-3.7} \right)^\circ$. The first search for local $C\!P$ violation in $D_{(s)}^+ \to K^- K^+ K^+$ has been performed, resulting in no local $C\!P$ violation observed. The measurement of time-integrated $C\!P$ violation in $D^0 \to K^- K^+$ decays, combined with previous measurements performed by LHCb, provides evidence of direct $C\!P$ violation in charm in a single decay channel at the level of $3.8$ standard deviations.

hep-ex

Performance of a spaghetti calorimeter prototype with tungsten absorber and garnet crystal fibres

A spaghetti calorimeter (SPACAL) prototype with scintillating crystal fibres was assembled and tested with electron beams of energy from 1 to 5 GeV. The prototype comprised radiation-hard Cerium-doped Gd$_3$Al$_2$Ga$_3$O$_{12}$ (GAGG:Ce) and Y$_3$Al$_5$O$_{12}$ (YAG:Ce) embedded in a pure tungsten absorber. The energy resolution was studied as a function of the incidence angle of the beam and found to be of the order of $10\% / \sqrt{E} \oplus1\%$, in line with the LHCb Shashlik technology. The time resolution was measured with metal channel dynodes photomultipliers placed in contact with the fibres or coupled via a light guide, additionally testing an optical tape to glue the components. Time resolution of a few tens of picosecond was achieved for all the energies reaching down to (18.5 $\pm$ 0.2) ps at 5 GeV.

physics.ins-det

Mixing and $C\!P$ violation in charm decays at LHCb

The LHCb experiment has collected the world's largest sample of charmed hadrons. This sample is used to measure observables related to $D^0 -\overline{D}^0$ mixing, direct $C\!P$ violation and $C\!P$ violation in mixing and interference in the charm sector. In this document, the most recent results from LHCb on the search of direct $C\!P$ violation in $D^0$ and $D_{(s)}^+$ decays are summarised, as well as the first observation of mass difference between neutral charm-meson eigenstates and the most precise measurement of time-dependent $C\!P$ asymmetry in $D^0 \to K^+ K^-$ and $D^0 \to π^+ π^-$ decays.

hep-ex

A Review of $C\!P$ Violation Measurements in Charm at LHCb

The LHCb experiment has been able to collect the largest sample ever produced of charm-hadron decays, performing a number of measurements of observables related to $C\!P$ violation in the charm sector. In this document, the most recent results from LHCb on the search of direct $C\!P$ violation in $D^0 \to K_s^0 K_s^0$, $D_{(s)}^+ \to h^+ π^0$ and $D_{(s)}^+ \to h^+ η$ decays are summarised, in addition to the most precise measurement of time-dependent $C\!P$ asymmetry in $D^0 \to h^+ h^-$ decays and the first observation of mass difference between neutral charm-meson eigenstates.

hep-ex

Observation of CP violation in charm decays at LHCb

A search for charge-parity (CP) violation in $D^0 \to K^- K^+$ and $D^0 \to π^-π^+$ decays is reported, using $pp$ collision data corresponding to an integrated luminosity of 5.9 $\mathrm{fb}^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the $D^0$ meson is determined from the charge of the pion in $D^*(2010)^+ \to D^0 π^+$ decays or from the charge of the muon in $\kern 0.18em\overline{\kern -0.18em B}{} \to D^0 μ^- \barν_μX$ decays. The difference between the CP asymmetries in $D^0 \to K^- K^+$ and $D^0 \to π^-π^+$ decays is measured to be $ΔA_{\rm CP} = [ -18.2 \pm 3.2\,(\rm stat.) \pm 0.9\,(\rm syst.) ] \times 10^{-4}$ for $π$-tagged and $ΔA_{\rm CP} = [ -9 \pm 8\,(\rm stat.) \pm 5\,(\rm syst.) ] \times 10^{-4} $ for $μ$-tagged $D^0$ mesons. The combination with previous LHCb results leads to $$ΔA_{\rm CP} = ( -15.4 \pm 2.9) \times 10^{-4},$$ where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than five standard deviations. This is the first observation of CP violation in the decay of charm hadrons.

hep-ex

Tests of Lepton Flavour Universality with Semileptonic Decays at LHCb

The observable $\mathcal{R} \left( D^{(*)} \right) = \mathcal{B}\left( B^{0}\to D^{(*)-} τ^{+} ν_τ \right) / \mathcal{B}\left( B^{0}\to D^{(*)-} μ^{+} ν_μ \right)$ is a probe for Lepton Universality violation, so it is sensitive to New Physics processes. The current combination of the measurements of $\mathcal{R} \left( D^{(*)} \right)$ differs from Standard Model predictions with a $4σ$ significance. A measurement of $\mathcal{R} ( D^* )$ using three-prong $τ$ decays has been performed at LHCb, resulting in $\mathcal{R}(D^*) = 0.285 \pm 0.019 (\text{stat}) \pm 0.025(\text{syst}) \pm 0.014 (\text{ext})$. This value, combined with the LHCb result obtained with $τ\to μν_τ\barν_μ$ decays, gives ${\mathcal{R}}(D^*) = 0.306 \pm 0.016 (\text{stat}) \pm 0.022 (\text{syst})$, consistent with the world average and 2.1 standard deviations above the SM prediction.

hep-ex

Measurement of $\mathcal{R}(D^*)$ with Three-Prong $τ$ Decays at LHCb

The observable $\mathcal{R} ( D^{(*)} ) = \mathcal{B}\left( B^{0}\to D^{(*)-} τ^{+} ν_τ \right) / \mathcal{B}\left( B^{0}\to D^{(*)-} μ^{+} ν_μ \right)$ is a probe for Lepton Universality violation, so it is sensitive to New Physics processes. The current combination of the measurements of $\mathcal{R} ( D^{(*)} )$ differs from Standard Model predictions with a $4σ$ significance. A measurement of $\mathcal{R} ( D^* )$ using three-prong $τ$ decays is currently ongoing at LHCb. The statistical precision of this analysis is 6.7%, i.e. the smallest statistical uncertainty for a single measurement of this observable. Therefore this measurement will be important to confirm or disprove the current discrepancy from the theoretical expectations.

hep-ex