Chinese Physics C

Charge Separation Measurements in Au+Au collisions at ${ \sqrt{{\boldsymbol s}_{\boldsymbol{NN}}}} $ = 7.7–200 GeV in Search of the Chiral Magnetic Effect

The STAR Collaboration

Published:

Abstract:
The chiral magnetic effect in heavy-ion collisions predicts an electric charge separation along the direction of a strong magnetic field, which indicates local parity (

\begin{document}$ {\cal{P}} $\end{document}

) and charge-conjugation-parity (

\begin{document}$ {\cal{CP}} $\end{document}

) violations in strong interactions. We report measurements of electric charge separation signals perpendicular to the spectator event plane in Au+Au collisions using high-statistics data from RHIC Beam Energy Scan II and top-RHIC energy (

\begin{document}$ \sqrt{s_{NN}}=200 $\end{document}

GeV) runs. A novel event shape selection method is employed to suppress the flow-induced background. The residual charge-separation signal fractions near the zero-flow limit are positive in Au+Au collisions within the 20%–50% centrality range. The significance levels are

\begin{document}$ 2.8\sigma $\end{document}

,

\begin{document}$ 3\sigma $\end{document}

, and

\begin{document}$ 3.2\sigma $\end{document}

at

\begin{document}$ \sqrt{s_{NN}} = $\end{document}

11.5, 14.6, and 19.6 GeV, respectively. At other beam energies, the signals are either statistically limited or consistent with zero.

The S-wave topped meson

Jun-Hao Zhang, Shuo Yang, Bing-Dong Wan

Published: , doi: 10.1088/1674-1137/ae7963

Abstract:
Motivated by the recent near-threshold enhancement in top-quark pair production reported by CMS and ATLAS, we study the S-wave spectral structure of heavy-light systems containing a single top quark, namely

\begin{document}$ t\bar{q} $\end{document}

,

\begin{document}$ t\bar{c} $\end{document}

, and

\begin{document}$ t\bar{b} $\end{document}

, within the instantaneous Bethe-Salpeter formalism. Because the top quark decays on a timescale much shorter than the typical hadronization time, the discrete eigenvalues we obtain should be interpreted as model-dependent reference positions of possible quasi-bound heavy-light configurations, rather than as predictions for fully formed conventional hadrons. The numerical results indicate that the masses of these configurations lie close to the top-quark mass. For the

\begin{document}$ t\bar{b} $\end{document}

system, the masses of the first four S-wave

\begin{document}$ 0^{-} $\end{document}

radial states are about

\begin{document}$ 5.1 $\end{document}

,

\begin{document}$ 5.4 $\end{document}

,

\begin{document}$ 5.6 $\end{document}

, and

\begin{document}$ 5.7 $\end{document}

GeV above the top-quark mass, respectively. For the

\begin{document}$ t\bar{c} $\end{document}

system, the corresponding values are about

\begin{document}$ 1.9 $\end{document}

,

\begin{document}$ 2.2 $\end{document}

,

\begin{document}$ 2.5 $\end{document}

, and

\begin{document}$ 2.6 $\end{document}

GeV. We also briefly discuss possible production and decay patterns at a qualitative level, which may serve as a reference for future dedicated phenomenological studies or for experimental constraints.

Quasi-two-body decays B⁺ → D_s⁺(R→)K⁺K^- in the perturbative QCD approach

Zhi-Tian Zou, Jun-Peng Wang, Rui Zhou, Ying Li

Published:

Abstract:
A search for the decay

\begin{document}$ B^+\to D_s^+ K^+K^- $\end{document}

has been reported by the LHCb Collaboration using

\begin{document}$ pp $\end{document}

collision data corresponding to an integrated luminosity of

\begin{document}$ 4.8\,{\rm{fb}}^{-1} $\end{document}

, collected at center-of-mass energies of 7, 8, and 13 TeV, in which no amplitude analysis of the

\begin{document}$ K^+K^- $\end{document}

subsystem was performed. In this work, we study the resonant contributions to the decay

\begin{document}$ B^+\to D_s^+ K^+K^- $\end{document}

within the perturbative QCD (PQCD) factorization framework. Contributions from the S-wave resonances

\begin{document}$ f_0(980) $\end{document}

,

\begin{document}$ f_0(1370) $\end{document}

, and

\begin{document}$ f_0(1500) $\end{document}

, the P-wave resonance

\begin{document}$ \phi(1020) $\end{document}

, and the D-wave resonances

\begin{document}$ f_2(1270) $\end{document}

and

\begin{document}$ f_2(1525) $\end{document}

are taken into account. By introducing the corresponding two-meson distribution amplitudes for the

\begin{document}$ K^+K^- $\end{document}

system, we perform a complete perturbative analysis of the quasi-two-body decays

\begin{document}$ B^+\to D_s^+(R\to)K^+K^- $\end{document}

, where R denotes an intermediate resonance, and present the first PQCD predictions for the associated branching fractions. Using the narrow-width approximation, we further extract the branching fractions of the corresponding two-body decays

\begin{document}$ B^+\to D_s^+R $\end{document}

. Our results are consistent with the available experimental measurements and previous theoretical studies. Finally, we find that direct CP asymmetries vanish for these quasi-two-body decays within the Standard Model, so that any experimentally observed nonzero CP asymmetry would constitute a clear signal of physics beyond the Standard Model.

Strong Gravitational Lensing and Shadow Signatures of Anisotropic Black Holes in Plasma

Pakhlavon Yovkochev, Atamurotov Farruh, Abdujabbarov Ahmadjon, Yerzhanov Koblandy, Bauyrzhan Gulnur, Chengxun Yuan

Published: , doi: 10.1088/1674-1137/ae7706

Abstract:
We study strong gravitational lensing and black hole shadow in a static, spherically symmetric spacetime sourced by anisotropic matter with exponentially decaying hair, in the presence of a non-magnetized plasma. The geometry is characterized by deformation parameters

\begin{document}$\tilde{v}_2$\end{document}

and

\begin{document}$\tilde{v}_c$\end{document}

, which influence the photon sphere and shadow in opposing ways:

\begin{document}$\tilde{v}_2$\end{document}

shrinks both while

\begin{document}$\tilde{v}_c$\end{document}

enlarges them. Plasma effects systematically increase the shadow size and suppress the deflection angle. Using EHT observations of Sgr A*, we constrain the parameter space of the model. Our analysis demonstrates that anisotropic matter hair and plasma environments produce distinguishable signatures in strong-field gravitational optics, offering potential probes for testing deviations from the standard gravity.

LHC Shines on Positivity

Zhen Liu, Kun-Feng Lyu, Tong Arthur Wu

Published:

Abstract:
We show that hadron colliders have an excellent reach for positivity tests on a class of diphoton operators. Due to the helicity selection rules, the relevant dimension-6 operators either do not contribute or are highly constrained by other experimental observables. We demonstrate, for the first time, that the LHC can probe the positivity of the dimension-8 operators involving colored particles. The kinematic differential distributions of the diphoton final states are utilized to perform the

\begin{document}$ \chi^2$\end{document}

analysis. Through a global fit, the effective scale for these operators can be inclusively probed up to around 2 TeV at HL-LHC and over 5 TeV at future 100 TeV FCC-hh at 95% C.L., providing a powerful test of the positivity bounds up to the multi-TeV scale.

Quasinormal modes of an electrically charged Kalb-Ramond black hole

Yun-Tao Gu, Wen-Di Guo, Yu-Xiao Liu

Published: , doi: 10.1088/1674-1137/ae6ed3

Abstract:
Lorentz violation serves as a significant feature in many modified theories of gravity. In particular, spontaneous Lorentz violation induced by the Kalb-Ramond field has attracted considerable attention. Recently, an electrically charged black hole solution within the Kalb-Ramond framework was proposed. In this study, we investigate the odd-parity quasinormal modes of the resulting non-decouplable system of the gravitational and electromagnetic perturbations using both the matrix-valued continued fraction method and the matrix-valued direct integration method. Additionally, we develop a new approach to distinguish between different modes in such non-decouplable systems. An error analysis is performed, and the influence of Lorentz violation on the fundamental quasinormal modes is systematically analyzed within a suitable parameter range.

The resonance effect for the CP asymmetry associated with the process ${\boldsymbol\omega{\bf\to}{\boldsymbol\pi}^+{\boldsymbol\pi}^-{\boldsymbol\pi}^{\bf 0} }$

Xi-Liang Yuan, Gang Lü, Na Wang, Chao Wang

Published: , doi: 10.1088/1674-1137/ad8ec2

Abstract:
The direct CP asymmetry in the weak decay process of hadrons is commonly attributed to the weak phase of the CKM matrix and the indeterminate strong phase. We propose a method to generate a significant phase difference through the interference between ρ and ω mesons, taking into account the G-parity allowed decay process of

\begin{document}$\omega \rightarrow \pi^{+}\pi^{-}\pi^{0}$\end{document}

and the G-parity-suppressed decay process of

\begin{document}$\rho^{0} \rightarrow \pi^{+}\pi^{-}\pi^{0}$\end{document}

in B meson decays. This interference can lead to notable changes in the CP asymmetry within the interference region. Additionally, we calculate the integral results for different phase space regions of the four-body decay process. We hope that our work provides valuable theoretical guidance for future experimental investigations on CP asymmetry in these decays.

Just Accepted