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Context.Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities).

Aims.We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30–150 mas range.

Methods.To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations.

Results.We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the starGaiaDR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of 8 × 10⁻⁴(ΔΚ= 7.7 mag) at a separation of 35 mas, and a contrast of 3 × 10⁻⁵(ΔΚ= 11 mag) at 100 mas from a bright primary (K< 6.5), for 30 min exposure time.

Conclusions.With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY andGaiafor the confirmation and characterization of substellar companions.

 

Aims. HD 206893 is a nearby debris disk star that hosts a previously identified brown dwarf companion with an orbital separation of ∼10 au. Long-term precise radial velocity (RV) monitoring, as well as anomalies in the system proper motion, has suggested the presence of an additional, inner companion in the system. Methods. Using information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we have undertaken a multi-epoch search for the purported additional planet using the VLTI/GRAVITY instrument. Results. We report a high-significance detection over three epochs of the companion HD 206893c, which shows clear evidence for Keplerian orbital motion. Our astrometry with ∼50−100 μarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7$ ^{+1.2}_{-1.0} $ M Jup and an orbital separation of 3.53$ ^{+0.08}_{-0.06} $ au for HD 206893c. Our fits to the orbits of both companions in the system use both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore allow us to derive an age of 155 ± 15 Myr for the system. We find that theoretical atmospheric and evolutionary models that incorporate deuterium burning for HD 206893c, parameterized by cloudy atmosphere models as well as a “hybrid sequence” (encompassing a transition from cloudy to cloud-free), provide a good simultaneous fit to the luminosity of both HD 206893B and c. Thus, accounting for both deuterium burning and clouds is crucial to understanding the luminosity evolution of HD 206893c. Conclusions. In addition to using long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part by Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward for identifying and characterizing additional directly imaged planets. In addition, HD 206893c is an example of an object narrowly straddling the deuterium-burning limit but unambiguously undergoing deuterium burning. Additional discoveries like this may therefore help clarify the discrimination between a brown dwarf and an extrasolar planet. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form, at ice-line orbital separations of 2−4 au. 

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high$p_{\mathrm{T}}$) charged hadron, in$pp$and central Pb-Pb collisions at center-of-mass energy per nucleon–nucleon collision$\sqrt{s_{\mathrm{NN}}}=5.02$TeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range in$p_{\mathrm{T},\mathrm{ch}\mathrm{jet}}$and jet resolution parameter$R$. Recoil jet yields are reported for$R=0.2$, 0.4, and 0.5 in the range$7<p_{\mathrm{T},\mathrm{ch}\mathrm{jet}}<140 \mathrm{GeV}/c$and$\pi /2<\mathrm{\Delta }\phi <\pi$, where$\mathrm{\Delta }\phi$is the azimuthal angular separation between hadron trigger and recoil jet. The low-$p_{\mathrm{T},\mathrm{ch}\mathrm{jet}}$reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark–gluon plasma generated in high-energy nuclear collisions. Comparison of$p_{\mathrm{T},\mathrm{ch}\mathrm{jet}}$distributions from$pp$and central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.

Results on the transverse spherocity dependence of light-flavor particle production (π, K, p,ϕ, K^*0,$$ {\textrm{K}}_{\textrm{S}}^0 $$$K_S^0$, Λ, Ξ) at midrapidity in high-multiplicity pp collisions at$$ \sqrt{s} $$$\sqrt{s}$= 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator$$ \left({S}_{\textrm{O}}^{p_{\textrm{T}}=1}\right) $$$\left(S_O^{p_T=1}\right)$categorizes events by their azimuthal topology. Utilizing narrow selections on$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$$S_O^{p_T=1}$, it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$$S_O^{p_T=1}$estimator is found to effectively constrain the hardness of the events when the midrapidity (|η| < 0.8) estimator is used.

The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced.

The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$$S_O^{p_T=1}$.

 

The production yields of the Σ(1385)^±and Ξ(1530)⁰resonances are measured in pp collisions at$$ \sqrt{s} $$$\sqrt{s}$= 13 TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity ⟨dN_ch/dη⟩, which is related to the energy density produced in the collision. The results include transverse momentum (p_T) distributions,p_T-integrated yields, mean transverse momenta of Σ(1385)^±and Ξ(1530)⁰, as well as ratios of thep_T-integrated resonance yields relative to yields of other hadron species. The Σ(1385)^±/π^±and Ξ(1530)⁰/π^±yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the Σ(1385)^±and Ξ(1530)⁰production in pp collisions at$$ \sqrt{s} $$$\sqrt{s}$= 13 TeV.

 

$K^{+}{K}^{-}$pairs may be produced in photonuclear collisions, either from the decays of photoproduced$\varphi (1020)$mesons or directly as nonresonant$K^{+}{K}^{-}$pairs. Measurements of$K^{+}{K}^{-}$photoproduction probe the couplings between the$\varphi (1020)$and charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction of$K^{+}{K}^{-}$pairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of direct$K^{+}{K}^{-}$production. There is significant$K^{+}{K}^{-}$production at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass range$1.1<M_{KK}<1.4\mathrm{GeV}/c^2$above the$\varphi (1020)$resonance, for rapidity$|y_{KK}|<0.8$and$p_{T,KK}<0.1\mathrm{GeV}/c$, the measured coherent photoproduction cross section is$\mathrm{d}\sigma /\mathrm{d}y=3.37\pm 0.61(\text{stat})\pm 0.15(\mathrm{syst})\mathrm{mb}$. The center-of-mass energy per nucleon of the photon-nucleus (Pb) system$W_{\gamma \mathrm{Pb},n}$ranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected for$\varphi (1020)$photoproduction alone. The mass spectrum is fit to a cocktail consisting of$\varphi (1020)$decays, direct$K^{+}{K}^{-}$photoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for direct$K^{+}{K}^{-}$photoproduction are presented.

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