Guillaume Falmagne

The scaling property of large-$p_\perp$ hadron suppression, $R_{\rm{AA}}(p_\perp)$, measured in heavy ion collisions at RHIC and LHC leads to the determination of the average parton energy loss $\langle \epsilon \rangle$ in quark-gluon plasma produced in a variety of collision systems and centrality classes. Relating $\langle \epsilon \rangle$ to the particle multiplicity and collision geometry allows for probing the dependence of parton energy loss on the path-length $L$. We find that $\langle \epsilon \rangle \propto L^\beta$ with $\beta=1.02^{+0.09}_{-0.06}$, consistent with the pQCD expectation of parton energy loss in a longitudinally expanding quark-gluon plasma. We then demonstrate that the azimuthal anisotropy coefficient divided by the collision eccentricity, $v_2/\textrm{e}$, follows the same scaling property as $R_{\rm{AA}}$. This scaling is observed in data, which are reproduced by the model at large $p_\perp$. Finally, a linear relationship between $v_2/\textrm{e}$ and the logarithmic derivative of $R_{\rm{AA}}$ is found and confirmed in data, offering an additional way to probe the $L$ dependence of parton energy loss using coming measurements from LHC Run 3.

Understanding the emergent dynamics – in particular critical transitions – in complex social-ecological systems is key to foster positive social transformations in the Anthropocene era. Regime shifts in some ecosystems may be preceded by statistical early warning signals, but systems where such signals can be tested systematically are elusive. The r/place game hosted by Reddit is a social experiment that provides data for thousands of subsystems that can undergo critical transitions. It is therefore an excellent testbed for comparing the performance of various warning indicators. In r/place, millions of users collaborated to build many discernible drawings on a canvas of pixels. A drawing undergoes a transition when it is rapidly replaced by another. We build an early warning signal indicator that uses machine learning to combine the predictive power of a number of time-dependent and system-specific variables, and we show that its performance far exceeds that of standard indicators. For example, when training the algorithm and testing its performance on separate parts of the 2022 r/place, we detect half of the transitions coming in less than 20 minutes with only a 0.6% false positive rate. The performance only slightly decreases when training on 2022 data and testing on the 2023 experiment, showing that the predictive power holds across significantly different setups. We use SHAP values to elucidate the drivers of any given warning and highlight generic properties of warnings in online social systems. Some properties, such as a decreasing return time, are at odds with standard statistical indicators. Where sufficient data is available, our tool and resulting insights can contribute to warn of – and possibly trigger or avoid – macroscopic social and ecological change.

The B c + meson is observed in lead-lead and proton-proton collisions at a center-of-mass energy per nucleon pair of √ S NN = 5.02 TeV, via the B c + → (J/ψ → μ + μ − )μ + v μ decay and using 2017 and 2018 data from the CMS detector. The resulting B c + nuclear modification factor is measured in two bins of the trimuon transverse momentum and of the collision centrality. Less suppression is observed than for other quarkonia and most open heavy flavour mesons. This first observation of the B c + meson in heavy ion collisions will shed light on the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.

The $p_\perp$ dependence of the nuclear modification factor $R_{\text{AA}}$ measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. We update a former study by including in the analysis the recent CMS measurements on $J/\psi$ production in PbPb collisions at $\sqrt{s}=5.02$ TeV and charged hadron production in XeXe collisions at $\sqrt{s}=5.44$ TeV. The average parton energy loss extracted from minimum bias XeXe collisions is reduced typically by 20% compared to PbPb collisions, consistent with a length dependence $\langle\bar{\epsilon}\rangle \propto L^{1.3\pm0.5}$ with $L\propto A^{1/3}$.

The $p_{_\perp}$ dependence of the nuclear modification factor $R_{\text{AA}}$ measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. We update a former study by including in the analysis the recent CMS measurements on $J/\psi$ production in PbPb collisions at $\sqrt{s}=5.02$~TeV and charged hadron production in XeXe collisions at $\sqrt{s}=5.44$~TeV. The average parton energy loss extracted from minimum bias XeXe collisions is reduced typically by 20% compared to PbPb collisions, consistent with a length dependence $\langle\bar{\epsilon}\rangle \propto L^{1.3\pm0.5}$ with $L\propto A^{1/3}$.

Beauty quark production in heavy-ion collisions is considered to be one of the key measurements to address the flavour-dependence of in-medium energy loss in heavy-ion collisions.On the other hand, the measurement of the production of strange beauty mesons can provide fundamental insights into the relevance of mechanisms of beauty recombination in the quark-gluon plasma.In this talk, CMS results on the nuclear modification factor, R AA , of fully reconstructed B 0 s and B + mesons as a function of transverse momentum at √ s NN = 5.02 TeV in PbPb collisions will be presented for the first time.The R AA double ratio between B 0 s and B + will also be presented.