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1. Observation of the Charged-Particle Multiplicity Dependence of ${\sigma }_{\psi \left(2S\right)}/{\sigma }_{J/\psi }$ in $p$ -Pb Collisions at 8.16 TeV

   https://doi.org/10.1103/c9wp-5tq3  

   Chekhovsky, V; Hayrapetyan, A; Makarenko, V; Tumasyan, A; Adam, W; Andrejkovic, J W; Benato, L; Bergauer, T; Chatterjee, S; Damanakis, K; et al (August 2025, Physical Review Letters)

   Bound states of charm and anticharm quarks, known as charmonia, have a rich spectroscopic structure that can be used to probe the dynamics of hadron production in high-energy hadron collisions. Here, the cross section ratio of excited $\left(\psi \left(2S\right)\right)$ and ground state $\left(J/\psi \right)$ vector mesons is measured as a function of the charged-particle multiplicity in proton-lead ( $p\mathrm{Pb}$ ) collisions at a center-of-mass (CM) energy per nucleon pair of 8.16 TeV. The data corresponding to an integrated luminosity of $175{\mathrm{nb}}^{-1}$ were collected using the CMS detector. The ratio is measured separately for prompt and nonprompt charmonia in the transverse momentum range $6.5<p_{\mathrm{T}}<30\mathrm{GeV}$ and in four rapidity ranges spanning $-2.865<y_{\mathrm{CM}}<1.935$ . For the first time, a statistically significant multiplicity dependence of the prompt cross section ratio is observed in proton-nucleus collisions. There is no clear rapidity dependence in the ratio. The prompt measurements are compared with a theoretical model which includes interactions with nearby particles during the evolution of the system. These results provide additional constraints on hadronization models of heavy quarks in nuclear collisions. 

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2. Study of Drell-Yan dimuon production in proton-lead collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

   https://doi.org/10.1007/JHEP05(2021)182  

   Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Erö, J.; Escalante Del Valle, A.; Frühwirth, R.; Jeitler, M.; et al (May 2021, Journal of High Energy Physics)

   null (Ed.)

   A bstract Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb − 1 . The differential cross section as a function of the dimuon mass is measured in the range 15–600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15–60 GeV and 60–120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum p T and of a geometric variable ϕ * are measured, where ϕ * highly correlates with p T but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions. 

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3. Active Galactic Nucleus Disks as Supernova Mufflers. I. Three-dimensional Local Hydrodynamic Models

   https://doi.org/10.3847/1538-4357/ae595c  

   Cook, Harrison E; Lyra, Wladimir; Mac_Low, Mordecai-Mark; Ford, K_E Saavik; McKernan, Barry (April 2026, The Astrophysical Journal)

   Supernova (SN) shocks that originate from stars on orbits embedded in dense active galactic nucleus (AGN) accretion disks evolve differently from those that occur in the interstellar medium. We aim to assess how shocks evolve in this dense stratified medium and understand where SNe are muffled and have their kinetic energy absorbed by an AGN disk versus escaping. We use Sirko–Goodman (SG) and Thompson–Quataert–Murray (TQM) AGN disk models for midplane radial profiles, generated with the pAGN code; we compare the disk pressure to the energy of a standard core-collapse SN (10^51 erg) to find radii where shock breakout can occur. For verification, we evolve three-dimensional hydrodynamic shearing box simulations of stratified Gaussian disks constructed from the midplane values that are injected with energy and mass from SNe placed at multiple radii and vertical locations, using the Athena code. We find SN shocks in SG disks around black holes with mass M_BH = 10^6 M⊙ become muffled beyond R ∼ 10^6 R_s, and that this muffling radius is inversely proportional to supermassive black hole mass with muffling occurring at R ∼ 10^2 R_s for M_BH = 10^9 M⊙. Around TQM disks, the muffling radius occurs at R ∼ 10^6 R_s, independent of M_BH. The largest determining factor for muffling an SN shock is the local scale height of the AGN disk. In conclusion, we developed a predictive analytic criterion to identify where AGN disks can muffle SN shocks depending on their density and vertical scale 

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4. Creation of quark–gluon plasma droplets with three distinct geometries

   https://doi.org/10.1038/s41567-018-0360-0  

   C. Aidala, 40 Y. (December 2018, Science et nature)

   Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons1–4. In this state, matter behaves as a nearly inviscid fluid5 that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium produced would be too small to form a QGP. Here we report on the observation of elliptic and triangular flow patterns of charged particles produced in proton–gold (p+Au), deuteron–gold (d+Au) and helium–gold (3He+Au) collisions at a nucleon–nucleon centre-of-mass energy sNN−−−√ = 200 GeV. The unique combination of three distinct initial geometries and two flow patterns provides unprecedented model discrimination. Hydrodynamical models, which include the formation of a short-lived QGP droplet, provide the best simultaneous description of these measurements. 

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5. Measurement of $d^2\sigma /d\left|\overrightarrow{q}\right|d{E}_{\text{avail}}$ in charged current ${\nu }_{\mu }$ -nucleus interactions at $⟨E_{\nu }⟩=1.86\mathrm{GeV}$ using the NOvA Near Detector

   https://doi.org/10.1103/PhysRevD.111.052009  

   Acero, M A; Acharya, B; Adamson, P; Aliaga, L; Anfimov, N; Antoshkin, A; Arrieta-Diaz, E; Asquith, L; Aurisano, A; Back, A; et al (March 2025, Physical Review D)

   Double- and single-differential cross sections for inclusive charged-current ${\nu }_{\mu }$ -nucleus scattering are reported for the kinematic domain 0 to $2\mathrm{GeV}/c$ in three-momentum transfer and 0 to 2 GeV in available energy, at a mean ${\nu }_{\mu }$ energy of 1.86 GeV. The measurements are based on an estimated 995,760 ${\nu }_{\mu }$ charged-current (CC) interactions in the scintillator medium of the NOvA Near Detector. The subdomain populated by 2-particle-2-hole (2p2h) reactions is identified by the cross section excess relative to predictions for ${\nu }_{\mu }$ -nucleus scattering that are constrained by a data control sample. Models for 2-particle-2-hole processes are rated by ${\chi }^2$ comparisons of the predicted-versus-measured ${\nu }_{\mu }$ CC inclusive cross section over the full phase space and in the restricted subdomain. Shortfalls are observed in neutrino generator predictions obtained using the theory-based València and SuSAv2 2p2h models. Published by the American Physical Society2025 

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