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1. Spin density matrix elements in exclusive $$\rho ^0$$ meson muoproduction

   https://doi.org/10.1140/epjc/s10052-023-11359-4  

   Alexeev, G D; Alexeev, M G; Alice, C; Amoroso, A; Andrieux, V; Anosov, V; Augsten, K; Augustyniak, W; Azevedo, C_D R; Badelek, B; et al (October 2023, The European Physical Journal C)

   Abstract We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive$$\rho ^0$$ ${\rho }^0$meson muoproduction at COMPASS using 160 GeV/cpolarised$$ \mu ^{+}$$ ${\mu }^{+}$and$$ \mu ^{-}$$ ${\mu }^{-}$beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/$$c^2$$ $c^2$$$< W<$$ $<W<$17.0 GeV/$$c^2$$ $c^2$, 1.0 (GeV/c)$$^2$$ ${}^2$$$< Q^2<$$ $<Q^2<$10.0 (GeV/c)$$^2$$ ${}^2$and 0.01 (GeV/c)$$^2$$ ${}^2$$$< p_{\textrm{T}}^2<$$ $<p_{\text{T}}^2<$0.5 (GeV/c)$$^2$$ ${}^2$. Here,Wdenotes the mass of the final hadronic system,$$Q^2$$ $Q^2$the virtuality of the exchanged photon, and$$p_{\textrm{T}}$$ $p_{\text{T}}$the transverse momentum of the$$\rho ^0$$ ${\rho }^0$meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($$\gamma ^*_T \rightarrow V^{ }_L$$ ${\gamma }_T^{\ast }\to V_L^{}$) indicate a violation ofs-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive$$\rho ^0$$ ${\rho }^0$production. 

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2. Evidence of a liquid–liquid phase transition in H$$_2$$O and D$$_2$$O from path-integral molecular dynamics simulations

   https://doi.org/10.1038/s41598-022-09525-x  

   Eltareb, Ali; Lopez, Gustavo E.; Giovambattista, Nicolas (April 2022, Scientific Reports)

   Abstract We perform path-integral molecular dynamics (PIMD), ring-polymer MD (RPMD), and classical MD simulations of H$$_2$$ ${}_2$O and D$$_2$$ ${}_2$O using the q-TIP4P/F water model over a wide range of temperatures and pressures. The density$$\rho (T)$$ $\rho \left(T\right)$, isothermal compressibility$$\kappa _T(T)$$ ${\kappa }_T\left(T\right)$, and self-diffusion coefficientsD(T) of H$$_2$$ ${}_2$O and D$$_2$$ ${}_2$O are in excellent agreement with available experimental data; the isobaric heat capacity$$C_P(T)$$ $C_P\left(T\right)$obtained from PIMD and MD simulations agree qualitatively well with the experiments. Some of these thermodynamic properties exhibit anomalous maxima upon isobaric cooling, consistent with recent experiments and with the possibility that H$$_2$$ ${}_2$O and D$$_2$$ ${}_2$O exhibit a liquid-liquid critical point (LLCP) at low temperatures and positive pressures. The data from PIMD/MD for H$$_2$$ ${}_2$O and D$$_2$$ ${}_2$O can be fitted remarkably well using the Two-State-Equation-of-State (TSEOS). Using the TSEOS, we estimate that the LLCP for q-TIP4P/F H$$_2$$ ${}_2$O, from PIMD simulations, is located at$$P_c = 167 \pm 9$$ $P_c=167\pm 9$ MPa,$$T_c = 159 \pm 6$$ $T_c=159\pm 6$ K, and$$\rho _c = 1.02 \pm 0.01$$ ${\rho }_c=1.02\pm 0.01$ g/cm$$^3$$ ${}^3$. Isotope substitution effects are important; the LLCP location in q-TIP4P/F D$$_2$$ ${}_2$O is estimated to be$$P_c = 176 \pm 4$$ $P_c=176\pm 4$ MPa,$$T_c = 177 \pm 2$$ $T_c=177\pm 2$ K, and$$\rho _c = 1.13 \pm 0.01$$ ${\rho }_c=1.13\pm 0.01$ g/cm$$^3$$ ${}^3$. Interestingly, for the water model studied, differences in the LLCP location from PIMD and MD simulations suggest that nuclear quantum effects (i.e., atoms delocalization) play an important role in the thermodynamics of water around the LLCP (from the MD simulations of q-TIP4P/F water,$$P_c = 203 \pm 4$$ $P_c=203\pm 4$ MPa,$$T_c = 175 \pm 2$$ $T_c=175\pm 2$ K, and$$\rho _c = 1.03 \pm 0.01$$ ${\rho }_c=1.03\pm 0.01$ g/cm$$^3$$ ${}^3$). Overall, our results strongly support the LLPT scenario to explain water anomalous behavior, independently of the fundamental differences between classical MD and PIMD techniques. The reported values of$$T_c$$ $T_c$for D$$_2$$ ${}_2$O and, particularly, H$$_2$$ ${}_2$O suggest that improved water models are needed for the study of supercooled water. 

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3. Measurement of the branching fractions of $$ \overline{B} $$ → D(*)K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ and $$ \overline{B} $$ → D(*)$$ {D}_s^{-} $$ decays at Belle II

   https://doi.org/10.1007/JHEP08(2024)206  

   Adachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, T; et al (August 2024, Journal of High Energy Physics)

   Abstract We present measurements of the branching fractions of eight$$ {\overline{B}}^0 $$ ${\overline{B}}^0$→D^(*)+K⁻$$ {K}_{(S)}^{\left(\ast \right)0} $$ $K_{\left(S\right)}^{\left(\ast \right)0}$,B⁻→D^(*)0K⁻$$ {K}_{(S)}^{\left(\ast \right)0} $$ $K_{\left(S\right)}^{\left(\ast \right)0}$decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4S) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb⁻¹. The event yields are extracted from fits to the distributions of the difference between expected and observedBmeson energy, and are efficiency-corrected as a function ofm(K⁻$$ {K}_{(S)}^{\left(\ast \right)0} $$ $K_{\left(S\right)}^{\left(\ast \right)0}$) andm(D^(*)$$ {K}_{(S)}^{\left(\ast \right)0} $$ $K_{\left(S\right)}^{\left(\ast \right)0}$) in order to avoid dependence on the decay model. These results include the first observation of$$ {\overline{B}}^0 $$ ${\overline{B}}^0$→D⁺K⁻$$ {K}_S^0 $$ $K_S^0$,B⁻→D*⁰K⁻$$ {K}_S^0 $$ $K_S^0$, and$$ {\overline{B}}^0 $$ ${\overline{B}}^0$→D*⁺K⁻$$ {K}_S^0 $$ $K_S^0$decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of theK⁻$$ {K}_{(S)}^{\left(\ast \right)0} $$ $K_{\left(S\right)}^{\left(\ast \right)0}$systems are compatible with quasi-two-body decays via a resonant transition with spin-parityJ^P= 1⁻for theK⁻$$ {K}_S^0 $$ $K_S^0$systems andJ^P= 1⁺for theK⁻K*⁰systems. We also present measurements of the branching fractions of four$$ {\overline{B}}^0 $$ ${\overline{B}}^0$→D^(*)+$$ {D}_s^{-} $$ $D_s^{-}$,B⁻→D^(*)0$$ {D}_s^{-} $$ $D_s^{-}$decay channels with a precision compatible to the current world averages. 

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4. Photo-response of the $$N=Z$$ nucleus $$^{24}$$Mg

   https://doi.org/10.1140/epja/s10050-023-01111-7  

   Deary, J; Scheck, M; Schwengner, R; O’Donnell, D; Bemmerer, D; Beyer, R; Hensel, Th; Junghans, A R; Kögler, T; Müller, S E; et al (September 2023, The European Physical Journal A)

   Abstract The electricE1 and magneticM1 dipole responses of the$$N=Z$$ $N=Z$nucleus$$^{24}$$ ${}^{24}$Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the$$^{24}$$ ${}^{24}$Mg($$\gamma ,\gamma ^{\prime }$$ $\gamma ,{\gamma }^{\prime }$) reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one$$J^{\pi }=1^-$$ $J^{\pi }=1^{-}$, four$$J^{\pi }=1^+$$ $J^{\pi }=1^{+}$, and six$$J^{\pi }=2^+$$ $J^{\pi }=2^{+}$states in$$^{24}$$ ${}^{24}$Mg. De-excitation$$\gamma $$ $\gamma$rays were detected using the four high-purity germanium detectors of the$$\gamma $$ $\gamma$ELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total$$B(M1)\uparrow = 2.7(3)~\mu _N^2$$ $B\left(M1\right)\uparrow =2.7\left(3\right){\mu }_N^2$is observed, but this$$N=Z$$ $N=Z$nucleus exhibits only marginalE1 strength of less than$$\sum B(E1)\uparrow \le 0.61 \times 10^{-3}$$ $\sum B\left(E1\right)\uparrow \le 0.61\times {10}^{-3}$ e$$^2 \, $$ ${}^2$fm$$^2$$ ${}^2$. The$$B(\varPi 1, 1^{\pi }_i \rightarrow 2^+_1)/B(\varPi 1, 1^{\pi }_i \rightarrow 0^+_{gs})$$ $B(\Pi 1,1_i^{\pi }\to 2_1^{+})/B(\Pi 1,1_i^{\pi }\to 0_{\mathrm{gs}}^{+})$branching ratios in combination with the expected results from the Alaga rules demonstrate thatKis a good approximative quantum number for$$^{24}$$ ${}^{24}$Mg. The use of the known$$\rho ^2(E0, 0^+_2 \rightarrow 0^+_{gs})$$ ${\rho }^2(E0,0_2^{+}\to 0_{\mathrm{gs}}^{+})$strength and the measured$$B(M1, 1^+ \rightarrow 0^+_2)/B(M1, 1^+ \rightarrow 0^+_{gs})$$ $B(M1,1^{+}\to 0_2^{+})/B(M1,1^{+}\to 0_{\mathrm{gs}}^{+})$branching ratio of the 10.712 MeV$$1^+$$ $1^{+}$level allows, in a two-state mixing model, an extraction of the difference$$\varDelta \beta _2^2$$ $\Delta {\beta }_2^2$between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV$$0^+_2$$ $0_2^{+}$level. 

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5. Entanglement negativity and replica symmetry breaking in general holographic states

   https://doi.org/10.1007/JHEP01(2025)022  

   Dong, Xi; Kudler-Flam, Jonah; Rath, Pratik (January 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> The entanglement negativity$$ \mathcal{E} $$ $E$(A:B) is a useful measure of quantum entanglement in bipartite mixed states. In random tensor networks (RTNs), which are related to fixed-area states, it was found in ref. [1] that the dominant saddles computing the even Rényi negativity$$ {\mathcal{E}}^{(2k)} $$ $E^{\left(2k\right)}$generically break theℤ_2kreplica symmetry. This calls into question previous calculations of holographic negativity using 2D CFT techniques that assumedℤ_2kreplica symmetry and proposed that the negativity was related to the entanglement wedge cross section. In this paper, we resolve this issue by showing that in general holographic states, the saddles computing$$ {\mathcal{E}}^{(2k)} $$ $E^{\left(2k\right)}$indeed break theℤ_2kreplica symmetry. Our argument involves an identity relating$$ {\mathcal{E}}^{(2k)} $$ $E^{\left(2k\right)}$to thek-th Rényi entropy on subregionAB^∗in the doubled state$$ {\left.|{\rho}_{AB}\right\rangle}_{A{A}^{\ast }{BB}^{\ast }} $$ ${\left(,{\rho }_{\mathrm{AB}}\right)}_{A{A}^{\ast }{\mathrm{BB}}^{\ast }}$, from which we see that theℤ_2kreplica symmetry is broken down toℤ_k. Fork< 1, which includes the case of$$ \mathcal{E} $$ $E$(A:B) atk= 1/2, we use a modified cosmic brane proposal to derive a new holographic prescription for$$ {\mathcal{E}}^{(2k)} $$ $E^{\left(2k\right)}$and show that it is given by a new saddle with multiple cosmic branes anchored to subregionsAandBin the original state. Using our prescription, we reproduce known results for the PSSY model and show that our saddle dominates over previously proposed CFT calculations neark= 1. Moreover, we argue that theℤ_2ksymmetric configurations previously proposed are not gravitational saddles, unlike our proposal. Finally, we contrast holographic calculations with those arising from RTNs with non-maximally entangled links, demonstrating that the qualitative form of backreaction in such RTNs is different from that in gravity. 

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