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1. The Kelvin–Helmholtz Instability at the Boundary of Relativistic Magnetized Jets

   https://doi.org/10.3847/2041-8213/acdfcf  

   Chow, Anthony; Davelaar, Jordy; Rowan, Michael E; Sironi, Lorenzo (July 2023, The Astrophysical Journal Letters)

   Abstract We study the linear stability of a planar interface separating two fluids in relative motion, focusing on conditions appropriate for the boundaries of relativistic jets. The jet is magnetically dominated, whereas the ambient wind is gas-pressure-dominated. We derive the most general form of the dispersion relation and provide an analytical approximation of its solution for an ambient sound speed much smaller than the jet Alfvén speedv_A, as appropriate for realistic systems. The stability properties are chiefly determined by the angleψbetween the wavevector and the jet magnetic field. Forψ=π/2, magnetic tension plays no role, and our solution resembles the one of a gas-pressure-dominated jet. Here, only sub-Alfvénic jets are unstable ( $0<M_e\equiv \left(v/v_{\mathrm{A}}\right)\cos \theta <1$, wherevis the shear velocity andθthe angle between the velocity and the wavevector). Forψ= 0, the free energy in the velocity shear needs to overcome the magnetic tension, and only super-Alfvénic jets are unstable ( $1<M_e<\sqrt{{(1+{\mathrm{\Gamma }}_w^2)/[1+(v_{\mathrm{A}}/c)}^2{\mathrm{\Gamma }}_w^2]}$, with Γ_wthe wind adiabatic index). Our results have important implications for the propagation and emission of relativistic magnetized jets. 

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2. Detection of Cosmological 21 cm Emission with the Canadian Hydrogen Intensity Mapping Experiment

   https://doi.org/10.3847/1538-4357/acb13f  

   The CHIME Collaboration; Amiri, Mandana; Bandura, Kevin; Chen, Tianyue; Deng, Meiling; Dobbs, Matt; Fandino, Mateus; Foreman, Simon; Halpern, Mark; Hill, Alex S.; et al (April 2023, The Astrophysical Journal)

   Abstract We present a detection of 21 cm emission from large-scale structure (LSS) between redshift 0.78 and 1.43 made with the Canadian Hydrogen Intensity Mapping Experiment. Radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (LRGs), emission-line galaxies (ELGs), and quasars (QSOs) from the eBOSS clustering catalogs. We find decisive evidence for a detection when stacking on all three tracers of LSS, with the logarithm of the Bayes factor equal to 18.9 (LRG), 10.8 (ELG), and 56.3 (QSO). An alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1σ(LRG), 5.7σ(ELG), and 11.1σ(QSO). These are the first 21 cm intensity mapping measurements made with an interferometer. We constrain the effective clustering amplitude of neutral hydrogen (Hi), defined as ${\mathit{}}_{\mathrm{H}\mathrm{I}}\equiv {10}^3{\mathrm{\Omega }}_{\mathrm{H}\mathrm{I}}\left(b_{\mathrm{H}\mathrm{I}}+〈f{\mu }^2〉\right)$, where Ω_Hiis the cosmic abundance of Hi,b_Hiis the linear bias of Hi, and 〈fμ²〉 = 0.552 encodes the effect of redshift-space distortions at linear order. We find ${\mathit{}}_{\mathrm{H}\mathrm{I}}={1.51}_{-0.97}^{+3.60}$for LRGs (z= 0.84), ${\mathit{}}_{\mathrm{H}\mathrm{I}}={6.76}_{-3.79}^{+9.04}$for ELGs (z= 0.96), and ${\mathit{}}_{\mathrm{H}\mathrm{I}}={1.68}_{-0.67}^{+1.10}$for QSOs (z= 1.20), with constraints limited by modeling uncertainties at nonlinear scales. We are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias Δv= − 66 ± 20 km s⁻¹for the QSOs. We split the QSO catalog into three redshift bins and have a decisive detection in each, with the upper bin atz= 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far. 

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3. Observation of Medium-Induced Yield Enhancement and Acoplanarity Broadening of Low- $p_{\mathrm{T}}$ Jets from Measurements in $pp$ and Central Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$

   https://doi.org/10.1103/PhysRevLett.133.022301  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (July 2024, Physical Review Letters)

   The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high $p_{\mathrm{T}}$) hadron trigger in proton-proton and central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter $R=0.2$, 0.4, and 0.5 in the range $7<p_{\mathrm{T},\text{jet}}<140\mathrm{GeV}/c$and trigger-recoil jet azimuthal separation $\pi /2<\mathrm{\Delta }\phi <\pi$. The measurements exhibit a marked medium-induced jet yield enhancement at low $p_{\mathrm{T}}$and at large azimuthal deviation from $\mathrm{\Delta }\phi \sim \pi$. The enhancement is characterized by its dependence on $\mathrm{\Delta }\phi$, which has a slope that differs from zero by $4.7\sigma$. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation. © 2024 CERN, for the ALICE Collaboration2024CERN 

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4. The metastable Q ³ Δ ₂ state of ThO: a new resource for the ACME electron EDM search

   https://doi.org/10.1088/1367-2630/ab6a3a  

   Wu, X.; Han, Z.; Chow, J.; Ang, D. G.; Meisenhelder, C.; Panda, C. D.; West, E. P.; Gabrielse, G.; Doyle, J. M.; DeMille, D. (February 2020, New Journal of Physics)

   Abstract The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable $H{(}^3{\mathrm{\Delta }}_1)$state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-lived $Q{(}^3{\mathrm{\Delta }}_2)$state of ThO, and show that this state is a very useful resource for both these purposes. TheQstate lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for theQstate, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of theQstate is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that theQstate has a large transition dipole moment to the $C{(}^1{\mathrm{\Pi }}_1)$state, which allows for efficient population transfer between the ground state $X{(}^1{\mathrm{\Sigma }}^{+})$and theQstate via $X-C-Q$Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate 90 % STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment ofCstate, the $X\to C$transition dipole moment, and branching ratios of decays from theCstate. 

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5. Measurements of jet quenching using semi-inclusive hadron+jet distributions in $pp$ and central Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

   https://doi.org/10.1103/PhysRevC.110.014906  

   Acharya, S; Adamová, D; Aglieri_Rinella, G; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; Ahuja, I; Akindinov, A; et al (July 2024, Physical Review C)

   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. ©2024 CERN, for the ALICE Collaboration2024CERN 

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