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We consider the problem of designing distributed collision-avoidance multi-agent control in large-scale environments with potentially moving obstacles, where a large number of agents are required to maintain safety using only local information and reach their goals. This paper addresses the problem of collision avoidance, scalability, and generalizability by introducing graph control barrier functions (GCBFs) for distributed control. The newly introduced GCBF is based on the well-established CBF theory for safety guarantees but utilizes a graph structure for scalable and generalizable decentralized control. We use graph neural networks to learn both neural a GCBF certificate and distributed control. We also extend the framework from handling state-based models to directly taking point clouds from LiDAR for more practical robotics settings. We demonstrated the efficacy of GCBF in a variety of numerical experiments, where the number, density, and traveling distance of agents, as well as the number of unseen and uncontrolled obstacles increase. Empirical results show that GCBF outperforms leading methods such as MAPPO and multi-agent distributed CBF (MDCBF). Trained with only 16 agents, GCBF can achieve up to 3 times improvement of success rate (agents reach goals and never encountered in any collisions) on <500 agents, and still maintain more than 50 success rates for >1000 agents when other methods completely fail.more » « less
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Free, publicly-accessible full text available September 1, 2025
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A bstract A comprehensive study of the local and nonlocal amplitudes contributing to the decay
B 0→K *0(→K +π − )μ +μ − is performed by analysing the phase-space distribution of the decay products. The analysis is based onpp collision data corresponding to an integrated luminosity of 8.4 fb− 1collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient , responsible for vector dimuon currents, exhibits a 2.1$$ {\mathcal{C}}_9 $$ σ deviation from the Standard Model expectation. The Wilson Coefficients ,$$ {\mathcal{C}}_{10} $$ and$$ {\mathcal{C}}_9^{\prime } $$ are all in better agreement than$$ {\mathcal{C}}_{10}^{\prime } $$ with the Standard Model and the global significance is at the level of 1.5$$ {\mathcal{C}}_9 $$ σ . The model used also accounts for nonlocal contributions fromB 0→ K *0[τ +τ − → μ +μ − ] rescattering, resulting in the first direct measurement of thebsττ vector effective-coupling .$$ {\mathcal{C}}_{9\tau } $$ Free, publicly-accessible full text available September 1, 2025 -
A bstract A search for the fully reconstructed
$$ {B}_s^0 $$ → μ +μ − γ decay is performed at the LHCb experiment using proton-proton collisions at = 13 TeV corresponding to an integrated luminosity of 5$$ \sqrt{s} $$ . 4 fb− 1. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set$$ {\displaystyle \begin{array}{cc}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[2{m}_{\mu },1.70\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<7.7\times {10}^{-8},&\ m\left({\mu}^{+}{\mu}^{-}\right)\in \left[\textrm{1.70,2.88}\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[3.92,{m}_{B_s^0}\right]\textrm{GeV}/{c}^2,\end{array}} $$ at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2
m μ , 1. 70] GeV/c 2dimuon mass region excluding the contribution from the intermediateϕ (1020) meson, and in the region combining all dimuon-mass intervals.Free, publicly-accessible full text available July 1, 2025 -
Abstract A Large Ion Collider Experiment (ALICE) has been conceived and constructed as a heavy-ion experiment at the LHC. During LHC Runs 1 and 2, it has produced a wide range of physics results using all collision systems available at the LHC. In order to best exploit new physics opportunities opening up with the upgraded LHC and new detector technologies, the experiment has undergone a major upgrade during the LHC Long Shutdown 2 (2019–2022). This comprises the move to continuous readout, the complete overhaul of core detectors, as well as a new online event processing farm with a redesigned online-offline software framework. These improvements will allow to record Pb-Pb collisions at rates up to 50 kHz, while ensuring sensitivity for signals without a triggerable signature.
Free, publicly-accessible full text available May 1, 2025 -
Recent measurements of charm-baryon production in hadronic collisions have questioned the universality of charm-quark fragmentation across different collision systems. In this work the fragmentation of charm quarks into charm baryons is probed, by presenting the first measurement of the longitudinal jet momentum fraction carried bybaryons,, in hadronic collisions. The results are obtained in proton-proton () collisions atat the LHC, withbaryons and charged (track-based) jets reconstructed in the transverse momentum intervals ofand, respectively. Thedistribution is compared to a measurement of-tagged charged jets incollisions as well as to 8 simulations. The data hints that the fragmentation of charm quarks into charm baryons is softer with respect to charm mesons, in the measured kinematic interval, as predicted by hadronization models which include color correlations beyond leading-color in the string formation.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available April 1, 2025 -
Abstract Luminosity determination within the ALICE experiment is based on the measurement, in van der Meer scans, of the cross sections for visible processes involving one or more detectors (visible cross sections). In 2015 and 2018, the Large Hadron Collider provided Pb–Pb collisions at a centre-of-mass energy per nucleon pair of √
s NN= 5.02 TeV. Two visible cross sections, associated with particle detection in the Zero Degree Calorimeter (ZDC) and in the V0 detector, were measured in a van der Meer scan.This article describes the experimental set-up and the analysis procedure, and presents the measurement results. The analysis involves a comprehensive study of beam-related effects and an improved fitting procedure, compared to previous ALICE studies, for the extraction of the visible cross section. The resulting uncertainty of both the ZDC-based and the V0-based luminosity measurement for the full sample is 2.5%. The inelastic cross section for hadronic interactions in Pb–Pb collisions at √s NN= 5.02 TeV, obtained by efficiency correction of the V0-based visible cross section, was measured to be 7.67 ± 0.25 b, in agreement with predictions using the Glauber model.Free, publicly-accessible full text available February 1, 2025 -
The production of 𝜂 and 𝜂′ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of 5.02 and 13TeV and proton-lead collisions are studied at a center-of-mass energy per nucleon of 8.16TeV. The studies are performed in center-of-mass (c.m.) rapidity regions 2.5<𝑦c.m.<3.5 (forward rapidity) and −4.0<𝑦c.m.<−3.0 (backward rapidity) defined relative to the proton beam direction. The 𝜂 and 𝜂′ production cross sections are measured differentially as a function of transverse momentum for 1.5<𝑝T<10GeV and 3<𝑝T<10GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for 𝜂 and 𝜂′ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of 𝜂 mesons are also used to calculate 𝜂/𝜋0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as 𝜂 and 𝜂′ meson fragmentation.more » « lessFree, publicly-accessible full text available February 1, 2025
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The production of thecharmonium state was measured with ALICE in Pb-Pb collisions at, in the dimuon decay channel. A significant signal was observed for the first time at LHC energies down to zero transverse momentum, at forward rapidity (). The measurement of the ratio of the inclusive production cross sections of theandresonances is reported as a function of the centrality of the collisions and of transverse momentum, in the region. The results are compared with the corresponding measurements incollisions, by forming the double ratio. It is found that in Pb-Pb collisions theis suppressed by a factor ofwith respect to the. Thenuclear modification factorwas also obtained as a function of both centrality and. The results show that theresonance yield is strongly suppressed in Pb-Pb collisions, by a factor of up towith respect to. Comparisons of cross section ratios with previous Super Proton Synchrotron findings by the NA50 experiment and ofwith higher-results at LHC energy are also reported. These results and the corresponding comparisons with calculations of transport and statistical models address questions on the presence and properties of charmonium states in the quark-gluon plasma formed in nuclear collisions at the LHC.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available January 1, 2025