Measurement of CPCP violation in B0→D+D−{B^0}\rightarrow{D^{+}D^{-}} and Bs0→Ds+Ds−{B^{0}_{s}}\rightarrow{D^{+}_{s}D^{-}_{s}} decays

International audienceA time-dependent, flavour-tagged measurement of $CP$ violation is performed with ${B^0}\rightarrow{D^{+}D^{-}}$ and ${B^{0}_{s}}\rightarrow{D^{+}_{s}D^{-}_{s}}$ decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 6 fb$^{-1}$. In ${B^0}\rightarrow{D^{+}D^{-}}$ decays the $CP$-violation parameters are measured to be \begin{align} S_{D^{+}D^{-}} & = -0.552 \pm 0.100\,\text{(stat)} \pm 0.010\,\text{(syst)}, \nonumber \newline C_{D^{+}D^{-}} & = \phantom{-}0.128 \pm0.103\,\text{(stat)} \pm 0.010\,\text{(syst)}. \nonumber \end{align} In $B^{0}_{s} \rightarrow D^{+}_{s}D^{-}_{s}$ decays the $CP$-violating parameter formulation in terms of $\phi_{s}$ and $|\lambda|$ results in \begin{align} \phi_{s} & = -0.086 \pm 0.106 \,\text{(stat)} \pm 0.028\,\text{(syst)} \,\text{rad}, \nonumber \newline |\lambda_{D^{+}_{s}D^{-}_{s}}| & = \phantom{-}1.145 \pm 0.126\,\text{(stat)} \pm 0.031\,\text{(syst)}. \nonumber \end{align} These results represent the most precise single measurement of the $CP$-violation parameters in their respective channels. For the first time in a single measurement, $CP$ symmetry is observed to be violated in ${B^0}\rightarrow{D^{+}D^{-}}$ decays with a significance exceeding six standard deviations

Pseudorapidity distributions of charged hadrons in lead-lead collisions at sNN\sqrt{s_\mathrm{NN}} = 5.36 TeV

International audienceThe pseudorapidity ($\eta$) distributions of charged hadrons are measured using data collected at the highest ever nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV for collisions of lead-lead ions. The data were recorded by the CMS experiment at the LHC in 2022 and correspond to an integrated luminosity of 0.30 $\pm$ 0.03 $\mu$b$^{-1}$. Using the CMS silicon pixel detector, the yields of primary charged hadrons produced in the range $\vert\eta\vert$$\lt$ 2.6 are reported. The evolution of the midrapidity particle density as a function of collision centrality is also reported. In the 5% most central collisions, the charged-hadron $\eta$ density in the range $\vert\eta\vert$ $\lt$ 0.5 is found to be 2032 $\pm$ 91 (syst), with negligible statistical uncertainty. This result is consistent with an extrapolation from nucleus-nucleus collision data at lower center-of-mass energies. Comparisons are made to various Monte Carlo event generators and to previous measurements of lead-lead and xenon-xenon collisions at similar collision energies. These new data detail the dependence of particle production on the collision energy, initial collision geometry, and the size of the colliding nuclei

Projecting dynamical systems via a support bound

For a polynomial dynamical system, we study the problem of computing the minimal differential equation satisfied by a chosen coordinate (in other words, projecting the system on the coordinate). This problem can be viewed as a special case of the general elimination problem for systems of differential equations and appears in applications to modeling and control. We give a bound for the Newton polytope of such minimal equation and show that our bound is sharp in "more than half of the cases". We further use this bound to design an algorithm for computing the minimal equation following the evaluation-interpolation paradigm. We demonstrate that our implementation of the algorithm can tackle problems which are out of reach for the state-of-the-art software for differential elimination

Efficient (3,3)(3,3)-isogenies on fast Kummer surfaces

International audienceWe give an alternative derivation of $(N,N)$-isogenies between fast Kummer surfaces which complements existing works based on the theory oftheta functions. We use this framework to produce explicit formulae for the case of $N = 3$, and show that the resulting algorithms are more efficient than all prior $(3, 3)$-isogeny algorithms

Search for flavor-changing neutral current interactions of the top quark mediated by a Higgs boson in proton-proton collisions at 13 TeV

International audienceA search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on proton-proton collision data collected in 2016-2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of 138 fb$^{-1}$. Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction ($\mathcal{B}$) of the top quark decaying to a Higgs boson and an up (u) or charm (c) quark. No significant excess above the estimated background was found. The observed (expected) upper limits at 95% confidence level are found to be 0.072% (0.059%) for $\mathcal{B}$(t $\to$ Hu) and 0.043% (0.062%) for $\mathcal{B}$(t $\to$ Hc). These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states with a pair of photons or of bottom quarks. The resulting observed (expected) upper limits at 95% confidence level are 0.019% (0.027%) for $\mathcal{B}$(t $\to$ Hu) and 0.037% (0.035%) for $\mathcal{B}$(t $\to$ Hc). These results constitute the most stringent limits on these branching fractions to date

L'évolution de la motilité de gouttes actives est capturée par un modèle de marche aléatoire auto-évitante.

International audienceIn living matter, concentration gradients of nutrients carve the motility of microorganisms in a heterogeneous environment. Here, we use swimming droplets as a model system to study how swimmer-trail interactions guide locomotion. Combining experiments and theory, we show that our non-Markovian droplet model quantitatively captures droplet motility. The two fit parameters provide the first estimate of the effective temperature arising from hydrodynamic flows and the coupling strength of the propulsion force. This framework is general and explains memory effects, droplet hovering, and enhanced collective motion

Do Skilled Migrants Compete with Native Workers?

International audienceSkilled migration is seen as a solution against skill shortages, but its impact on native workers facing increased competition remains debated. To investigate the longer-term potential for displacement, this paper exploits a 2008 reform in France facilitating the hiring of foreign workers within a list of tight occupations. The analysis relies on administrative data and applies a difference-in-differences approach. Results show that the reform successfully boosted migrant hires without affecting native employment. In addition, the negative pressure on occupational wages is much larger among migrants than natives, suggesting that such policies can be a viable solution in the long run

Spectroscopic investigations of a filament reconnecting with coronal loops during a two-ribbon solar flare

International audienceContext. In the standard 2D model of eruption, the eruption of a magnetic flux rope is associated with magnetic reconnection occurring beneath it. However, in 3D, additional reconnection geometries are possible, in particular the AR – RF , where external reconnection involving the overlying arcades ( A ) and erupting flux rope ( R ) turns into another arcade and a flare loop ( F ). This process results in the drifting of the legs of the erupting flux rope. Aims. We investigate spectroscopic signatures of such AR – RF reconnection occurring in an erupting filament reconnecting with coronal arcades during a weak B3.2-class two-ribbon flare. Methods. We examined the evolution of the erupting filament eruption using imaging observations by the Atmospheric Imaging Assembly (AIA) as well as both imaging and spectroscopic observations by the Interface Region Imaging Spectrograph (IRIS). Results. As the filament rises into the corona, it reconnects with the surrounding arcade of coronal loops with localized brightenings, resulting in the disappearance of the coronal loops and formation of a hot flux rope, showing a slipping motion of its footpoints that extends to the previous footpoints of the coronal loops ( AR – RF reconnection), as was predicted by the 3D extensions to the standard solar flare model. These brightenings are accompanied by the presence of strong blueshifts in both the IRIS Si IV and Mg II lines, up to ≈200 km s −1 . The lines are also extremely wide, with nonthermal widths above 100 km s −1 . Furthermore, a strongly non-Gaussian profile of the most blueshifted component is detected at the start of the AR – RF reconnection, indicating the presence of accelerated particles and magnetohydrodynamic turbulence, and associated with the appearance of hot plasma in the AIA 94 Å passband. Results. For the first time, an observation has been reported in which the IRIS slit successfully captures AR – RF reconnection between a filament and overlying arcades, resulting in strong blueshifts and very broad line profiles

Initiation Route of Coronal Mass Ejections. II. The Role of Filament Mass

International audienceAbstract A thorough understanding of the initiation of coronal mass ejections (CMEs), which is manifested as a slow rise of pre-eruptive structures before the impulsive ejection in kinematics, is key for forecasting solar eruptions. In our previous work, we showed that the slow rise of a hot flux rope with coronal mass density is caused by the moderate magnetic reconnection occurring in the hyperbolic flux tube (HFT) combined with the torus instability. However, it remains unclear how the initiation process varies when a filament is present in the pre-eruptive flux rope. In this work, we reveal the complete initiation route of a CME containing filament mass with a state-of-the-art full-magnetohydrodynamics simulation. The comprehensive analyses show that the filament mass has an important impact on the CME initiation through triggering and driving the slow rise of flux rope with its drainage, besides the contributions of HFT reconnection and torus instability. Finally, in combination with our previous work, we propose that the enhanced drainage of filament mass and various features related to the HFT reconnection, such as the split of pre-eruptive structure and the preflare loops and X-ray emissions, can serve as precursors of CME initiation in observations

Anomalous summertime CO₂ sink in the subpolar Southern Ocean promoted by early 2021 sea ice retreat

International audienceThe physical and biogeochemical processes governing the air–sea CO2 flux in the Southern Ocean are still widely debated. The Southern Ocean Carbon and Heat Impact on Climate cruise in summer 2022 aimed at studying these processes in the Weddell Sea and in its vicinity. A CARbon Interface OCean Atmosphere (CARIOCA) drifting buoy was deployed in January 2022 in the subpolar Southern Ocean, providing hourly surface ocean observations of fCO2 (fugacity of CO2), dissolved oxygen, salinity, temperature, and chlorophyll a fluorescence for 17 months. An underwater glider was piloted with the buoy for the first 6 weeks of the deployment to provide vertical ocean profiles of hydrography and biogeochemistry. These datasets reveal an anomalously strong ocean carbon sink for over 2 months, occurring in the region of Bouvet Island and associated with large plumes of chlorophyll a (Chl a). Based on Lagrangian backward trajectories reconstructed using various surface currents fields, we identified that the water mass reaching the Bouvet Island region originated from the southwest, from the vicinity of the sea ice edge in spring 2021. A strong phytoplankton bloom developed there in November 2021. We propose that it was promoted by early sea ice retreat in 2021 in the Weddell Sea. These waters, depleted in carbon, then traveled to the position of the CARIOCA buoy. The very low values of ocean fCO2, measured by the buoy (down to 310 µatm), are consistent with net community production previously observed during blooms occurring near the sea ice edge, partly compensated by air–sea CO2 flux along the water mass trajectory. Early sea ice retreat might therefore have caused a large CO2 sink farther north than usual in summer 2022, in the Atlantic sector of the subpolar Southern Ocean. Such events might become more frequent in the future as a result of climate change