Highlights
• Charmless two-body B meson decays in the perturbative QCD factorization approach
2022, 46(12): 123103. doi: 10.1088/1674-1137/ac88bd
The perturbative quantum chromodynamics (PQCD) approach based on $k_T$ factorization has resulted in great achievements in the QCD calculation of hadronic B decays. By regulating the endpoint divergence by the transverse momentum of quarks in the propagators, one can perform the perturbation calculation for various diagrams, including annihilation type diagrams. In this paper, we review the current status of the PQCD factorization calculation of two-body charmless $B\to PP, PV, VV$U decays up to next-to-leading order (NLO) QCD corrections. Two new power suppressed terms in the decaying amplitudes are also considered. Using universal input (non-perturbative) parameters, we collect the branching ratios and ${C P}$ asymmetry parameters of all charmless two body B decays, which are calculated in the PQCD approach up to NLO. The results are compared with those of the QCD factorization approach, soft-collinear effective theory approach, and current experimental measurements. For most of the considered B meson decays, the PQCD results for branching ratios agree well with those of other approaches and experimental data. The PQCD predictions for the ${C P}$ asymmetry parameters of many of the decay channels do not agree with those of other approaches but have better agreement with experimental data. The longstanding $K \pi$ puzzle regarding the pattern of the direct CP asymmetries of penguin-dominated $B \to K \pi$ decays can be understood after the inclusion of NLO contributions in PQCD. The NLO corrections and power suppressed terms play an important role in color suppressed and pure annihilation type B decay modes. These rare decays are more sensitive to different types of corrections, providing an opportunity to examine the factorization approach with more precise experimental measurements.
• Influence of the neck parameter on the fission dynamics within the two-center shell model parametrization
2022, 46(12): 124101. doi: 10.1088/1674-1137/ac8867
The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach, in which the nuclear shape is described with the two-center shell model (TCSM) parametrization, and the elongation, mass asymmetry, and fragment deformation are set to be the generalized coordinates of the Langevin equation. We first study the influence of the neck parameter on the scission configuration. We find that there is almost no obvious correlation between the neck parameter $\epsilon$ and mass asymmetry η at the scission point, indicating that $\epsilon$ has no evident impact on the fragment mass distribution. The elongation $Z_0/R_0$ and its correlation with the mass asymmetry η at the scission point are clearly influenced by the neck parameter $\epsilon$, which has a strong effect on the total kinetic energy (TKE) distribution of the fragments. The pre-neutron emission fragment mass distributions for 14 MeV n+ $^{233,235,238}$U and $^{239}$Pu are calculated, and then, based on these results, the post-neutron emission fragment mass distributions are obtained by using the experimental data of prompt neutron emission. The calculated post-neutron emission fragment mass distributions can reproduce the experimental data well. The TKE distributions for 14 MeV n+ $^{235}$U fission are calculated for $\epsilon$=0.25, 0.35, and 0.45, and the results show that the TKE distribution cannot be described very well for the three cases. However, the trend of the calculated TKE distribution with $\epsilon$ is just as expected from the scission configuration calculations. The results with $\epsilon$=0.35 present a better agreement with the experiment data compared with the other two cases.
• Speculations on the W-mass measurement at CDF
2022, 46(12): 123107. doi: 10.1088/1674-1137/ac8cd5
The W mass determination at the Tevatron CDF experiment reported a deviation from the SM expectation at the 7σ level. We discuss a few possible interpretations and their collider implications. We perform electroweak global fits under various frameworks and assumptions. We consider three types of electroweak global fits in the effective-field-theory framework: the S-T, S-T-$\delta G_F$, and eight-parameter flavor-universal one. We discuss the amounts of tensions between different $m_W$ measurements reflected in these fits and the corresponding shifts in central values of these parameters. With these electroweak fit pictures in hand, we present a few different classes of models and discuss their compatibility with these results. We find that while explaining the $m_W$ discrepancy, the single gauge boson extensions face strong LHC direct search constraints unless the $Z'$ is fermiophobic (leptophobic), which can be realized if extra vector fermions (leptons) mix with the SM fermions (leptons). Vector-like top partners can partially generate the needed shift to the electroweak observables. The compatibility with the top squark is also studied in detail. We find that the non-degenerate top squark soft masses enhance the needed operator coefficients, enabling an allowed explanation compatible with current LHC measurements. Overall, more theoretical and experimental developments are highly in demand to reveal the physics behind this discrepancy.
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• Analysis of Pcs(4338) and related pentaquark molecular states via QCD sum rules
Published: 2022-11-26, doi: 10.1088/1674-1137/ac9aab
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In this study, we tentatively identify $P_{cs}(4338)$ as the $\bar{D}\Xi_c$molecular state and distinguish the isospins of current operators to explore in detail the$\bar{D}\Xi_c$, $\bar{D}\Lambda_c$, $\bar{D}_s\Xi_c$, $\bar{D}_s\Lambda_c$, $\bar{D}^*\Xi_c$, $\bar{D}^*\Lambda_c$, $\bar{D}^*_s\Xi_c$, and $\bar{D}^*_s\Lambda_c$ molecular states without strange, with strange, and with double strange in the framework of QCD sum rules. The present exploration favors identifying $P_{cs}(4338)$ ($P_{cs}(4459)$) as the $\bar{D}\Xi_c$ ($\bar{D}^*\Xi_c$) molecular state with the spin-parity $J^P={\dfrac{1}{2}}^-$ (${\dfrac{3}{2}}^-$) and isospin $(I,I_3)=(0,0)$, and the observation of their cousins with the isospin $(I,I_3)=(1,0)$ in the $J/\psi\Sigma^0/\eta_c\Sigma^0$ invariant mass distributions would decipher their inner structures.
• Deuteron electromagnetic form factors and tensor polarization observables in the framework of the hard-wall AdS/QCD model
Published: 2022-11-25, doi: 10.1088/1674-1137/ac957a
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We study the electromagnetic form factors and tensor polarization observables of the deuteron in the framework of the hard-wall AdS/QCD model. We find a profile function for the bulk twist $\tau=6$ vector field, which describes the deuteron on the boundary and fix the infrared boundary cut-off of AdS space in accordance with the ground state mass of the deuteron. We obtain the deuteron charge monopole, quadrupole, and magnetic dipole form factors and tensor polarization observables from the bulk Lagrangians for the deuteron and photon field interactions. We plot the momentum transfer dependence of the form factors and tensor polarization observables and compare our numerical results with those in the soft-wall model and experimental data.
• Thermodynamics of black holes in the quintessential phase space
Published: 2022-11-24, doi: 10.1088/1674-1137/ac9b2b
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Considering that the negative pressure of the accelerated expansion of the universe results from the cosmological constant or the dark energy quintessence, we use the dark energy quintessence to construct the "quintessential" phase space. In contrast to the previous discussion in which the cosmological constant is considered as the black hole (BH) phase transition pressure, in this analysis, we believe that the pressure results from quintessence. The characteristics of critical behavior, Gibbs free energy, and temperature behavior in quintessential phase space are investigated. We observe that the phase transition belongs to van der Waals phase transition within$-1 <\omega_{\rm q}<-2/3$. If $\omega_{\rm q}$is within (–2/3, –1/3), the phase transition loses the large BH phase transition characteristics, which is caused by the later stage of the phase transition being completely dominated by quintessence dark energy with negative pressure. These results suggest that the quintessential phase space can be constructed with the pressure from the thermal quintessence, and it can be used as a new probe to explore the thermodynamics of BHs.
Current Issued
2022 Vol. 46, No. 12
Published: 30 November 2022
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