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1. Systematic study of flow vector fluctuations in $\sqrt{s_{NN}}=5.02$ TeV Pb-Pb collisions

   https://doi.org/10.1103/PhysRevC.109.065202  

   Acharya, S; Adamová, D; Agarwal, A; Aglieri_Rinella, G; Aglietta, L; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, S U; et al (June 2024, Physical Review C)

   Measurements of the $p_{\mathrm{T}}$-dependent flow vector fluctuations in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$using azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [ALICE Collaboration, ] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the $p_{\mathrm{T}}$-dependent flow vector fluctuations at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$with two-particle correlations. Significant $p_{\mathrm{T}}$-dependent fluctuations of the ${\vec{V}}_2$flow vector in Pb–Pb collisions are found across different centrality ranges, with the largest fluctuations of up to $\sim 15\%$being present in the 5% most central collisions. In parallel, no evidence of significant $p_{\mathrm{T}}$-dependent fluctuations of ${\vec{V}}_3$or ${\vec{V}}_4$is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than $5\sigma$significance in central collisions. These observations in $\text{Pb–Pb}$collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high $p_{\mathrm{T}}$, which might be biased by $p_{\mathrm{T}}$-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be reexamined to improve our understanding of initial conditions, quark–gluon plasma properties, and the dynamic evolution of the created system. ©2024 CERN, for the ALICE Collaboration2024CERN 

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2. Electrical conductivity of hot relativistic plasma in a strong magnetic field

   https://doi.org/10.1103/PhysRevD.110.096009  

   Ghosh, Ritesh; Shovkovy, Igor A (November 2024, Physical Review D)

   We employ first-principles quantum field theoretical methods to investigate the longitudinal and transverse electrical conductivities of a strongly magnetized hot quantum electrodynamics (QED) plasma at the leading order in coupling. The analysis employs the fermion damping rate in the Landau-level representation, calculated with full kinematics and exact amplitudes of one-to-two and two-to-one QED processes. In the relativistic regime, both conductivities exhibit an approximate scaling behavior described by ${\sigma }_{\parallel ,\perp }=T{\tilde{\sigma }}_{\parallel ,\perp }$, where ${\tilde{\sigma }}_{\parallel ,\perp }$are functions of the dimensionless ratio $\left|eB\right|/T^2$(with $T$denoting temperature and $B$magnetic field strength). We argue that the mechanisms for the transverse and longitudinal conductivities differ significantly, leading to a strong suppression of the former in comparison to the latter. Published by the American Physical Society2024 

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3. Measurement of Angular Coefficients of $\overline{B}\to D^{*}\ell {\overline{\nu }}_{\ell }$ : Implications for $\left|V_{cb}\right|$ and Tests of Lepton Flavor Universality

   https://doi.org/10.1103/PhysRevLett.133.131801  

   Prim, M T; Bernlochner, F; Metzner, F; Aihara, H; Asner, D M; Aushev, T; Ayad, R; Babu, V; Banerjee, Sw; Behera, P; et al (September 2024, Physical Review Letters)

   We measure the complete set of angular coefficients $J_i$for exclusive $\overline{B}\to D^{*}\ell {\overline{\nu }}_{\ell }$decays ( $\ell =e$, $\mu$). Our analysis uses the full $711{\mathrm{fb}}^{-1}$Belle dataset with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the $\overline{B}\to D^{*}$transition and the Cabibbo-Kobayashi-Maskawa matrix element $\left|V_{\mathrm{cb}}\right|$. Using recent lattice QCD calculations for the hadronic form factors, we find $\left|V_{\mathrm{cb}}\right|=(40.7\pm 0.7)\times {10}^{-3}$using the Boyd-Grinstein-Lebed parametrization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter $w$and investigate the differences of the electron and muon angular distributions. We find no deviation from standard model expectations. Published by the American Physical Society2024 

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4. Test of lepton flavor universality with a measurement of $R\left(D^{*}\right)$ using hadronic $B$ tagging at the Belle II experiment

   https://doi.org/10.1103/PhysRevD.110.072020  

   Adachi, I; Adamczyk, K; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; et al (October 2024, Physical Review D)

   The ratio of branching fractions $R\left(D^{*}\right)=\mathcal{B}(\overline{B}\to D^{*}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}(\overline{B}\to D^{*}{\ell }^{-}{\overline{\nu }}_{\ell })$, where $\ell$is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of $189{\mathrm{fb}}^{-1}$at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$collider. Data is collected at the $\mathrm{\Upsilon }\left(4\mathrm{S}\right)$resonance, and one $B$meson in the $\mathrm{\Upsilon }\left(4\mathrm{S}\right)\to B\overline{B}$decay is fully reconstructed in hadronic decay modes. The accompanying signal $B$meson is reconstructed as $\overline{B}\to D^{*}{\tau }^{-}{\overline{\nu }}_{\tau }$using leptonic $\tau$decays. The normalization decay, $\overline{B}\to D^{*}{\ell }^{-}{\overline{\nu }}_{\ell }$, produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields $R\left(D^{*}\right)={0.262}_{-0.039}^{+0.041}\left(\mathrm{stat}{)}_{-0.032}^{+0.035}\right(\mathrm{syst})$. This result is consistent with the current world average and with Standard Model predictions. Published by the American Physical Society2024 

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5. Photoproduction of the ${\mathrm{\Sigma }}^{+}$ hyperon using linearly polarized photons with CLAS

   https://doi.org/10.1103/PhysRevC.111.025204  

   Clark, L; McKinnon, B; Ireland, D G; Glazier, D I; Livingston, K; Rönchen, D; Acar, A G; Achenbach, P; Alvarado, J S; Amaryan, M J; et al (February 2025, Physical Review C)

   Measurements of the polarization observables $\mathrm{\Sigma },\mathbf{P},\mathbf{T},{\mathbf{O}}_{\mathbf{x}},{\mathbf{O}}_{\mathbf{z}}$for the reaction $\vec{\gamma }p\to K_S^0{\mathrm{\Sigma }}^{+}$using a linearly polarized photon beam of energy 1.1 to 2.1 GeV are reported. The measured data provide information on a channel that has not been studied extensively, but is required for a full coupled-channel analysis in the nucleon resonance region. Observables have been simultaneously extracted using likelihood sampling with a Markov-Chain Monte Carlo process. Angular distributions in bins of photon energy $E_{\gamma }$are produced for each polarization observable. $\mathbf{T},{\mathbf{O}}_{\mathbf{x}}$, and ${\mathbf{O}}_{\mathbf{z}}$are first time measurements of these observables in this reaction. The extraction of $\mathrm{\Sigma }$extends the energy range beyond a previous measurement. The measurement of $\mathbf{P}$, the recoil polarization, is consistent with previous measurements. The measured data are shown to be significant enough to affect the estimation of the nucleon resonance parameters when fitted within a coupled-channels model. Published by the American Physical Society2025 

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