Motivated by the very important discovery of CP violation in charm-decays for the first time, by the LHCb collaboration, the role of nearby resonances such as the scalar $f_0(1710)$ in accounting for the observed CP is discussed. It is suggested that the influence of such a resonance may also explain the long-standing puzzle of such a large breaking of SU(3) seen in its decays. It is also explained that intervention of such resonance(s) will render first principles calculations of $ΔA_{CP}$ rather difficult. Instead, it is proposed that searches for CP violation in simple radiative final states, such as $D^0 \to γϕ[\to K^+ K^-]$, $D^0 \to l^+ l^- π$ etc. has much better chance of theoretical precision studies and therefore theoretical and experimental investigations therein are strongly urged.
In this article, we study the radiative decays among the charmonium states with the heavy quark effective theory, and make predictions for the ratios among the radiative decay widths of an special multiplet to another multiplet. The predictions can be confronted with the experimental data in the future and put additional constraints in identifying the $X$, $Y$, $Z$ charmonium-like mesons.
Assuming that $X(3872)$ is a mixture between $2P$ charmonium and $\bar{D}D^{*}$ molecular states with $J^{PC}=1^{++}$, an analysis of $X(3872)$ radiative decays into $J/ψγ$ and $ψ(2S)γ$ is presented. The modification of the radiative branching ratio due to possible constructive or destructive interferences between the meson-loop and the short-distance contact term, which is modeled by a charm quark loop, is shown. The model predictions are shown to be compatible with the experimentally determined ratio of the mentioned branching fractions for a wide range of the $X(3872)$ charmonium content. I…
The radiative decays of the p-wave charmed heavy baryons to the ground state baryon states are studied in the framework of the light cone QCD sum rules method. Firstly, the transition form factors that describe these transitions are estimated, and then using these form factors the corresponding decay widths are calculated. A comparison of our results on the decay widths with those predicted by the other approaches existing in literature is performed.
We apply a phenomenological Lagrangian approach to the radiative decay Y(4260) -> X(3872) + gamma. The Y(4260) and X(3872) resonances are considered as composite states containing both molecular hadronic and charmonium components. Having a leading molecular component in the X(3872) and a sole molecular configuration for the Y(4260) results in a prediction compatible with present data.
We analyze the theoretical description of radiative decays in charmonium. We use an elementary emission decay model to build the most general electromagnetic transition operator. We show that accurate results for the widths can be obtained from a simple quark potential model reasonably fitting the spectroscopy if the complete form of the operator is used instead of its standard p/m approximation and the experimental masses are properly implemented in the calculation.
Motivated by the recent measurement of $D^0\toρ^0γ$ improved standard model (SM) predictions for branching ratios and CP asymmetries of radiative charm decay are given. Weak annihilation induced decays are probes of non-perturbative QCD approaches. Rare decays probe the SM and physics beyond the SM, e.g. leptoquark and supersymmetric models. Opportunities with $Λ_c\to pγ$ for future polarization measurements are presented.
We determine the radiative decay amplitudes for decay into $D^*$ and $\bar{D} γ$, or $D^*_s$ and $\bar{D}_s γ$ of some of the charmonium like states classified as X,Y,Z resonances, plus some other hidden charm states which are dynamically generated from the interaction of vector mesons with charm. The mass distributions as a function of the $\bar{D} γ$ or $\bar{D}_s γ$ invariant mass show a peculiar behavior as a consequence of the $D^* \bar{D}^*$ nature of these states. The experimental search of these magnitudes can shed light on the nature of these states.
结合重夸克有效理论和手征拉格朗日方法，我们研究了D介子的辐射衰变。首先，我们重新分析$D^{*} \rightarrow D γ$衰变使用重夸克自旋对称性，手征对称性拉格朗日，但也包括轻矢量介子。然后，我们计算分支比$D \rightarrow V γ$。本文对Cabbibo抑制的$D \to ρ/ ωγ$衰变和$D \rightarrow P P γ$衰变的分支比作了一些评论。
The presented paper is devoted to theoretical analysis of charmonium mesons $η_c$, $J/ψ$, $χ_{c0,1,2}$, and $h_c$ production in exclusive radiative $Z$ boson decays in the frameworks of Nonrelativistic Chromodynamic and amplitude expansion on the light-cone. In the framework of light-cone expansion amplitudes and widths of all processes are described with one universal relation. It is interesting to note that from this relation it follows automatically which component of $Z$ boson (either vector or axial) gives contribution to the width of the particular decay. It is shown that the effect of i…
The $c \to u γ$ Contribution to Weak Radiative Charm Decay
$c \to u γ$转换不会发生在标准模型的树级别，并且在一个循环中受到强烈的GIM抑制。已知领先的QCD振幅可以提高两个数量级。我们指出，振幅进一步增加了两个数量级后，包括完整的2圈QCD的贡献。尽管如此，粲强子的$ΔS =0$辐射衰变仍然由$c \to d \bar{d} u γ$和$c \to s \bar{s} u γ$夸克子过程控制。
We have systematically studied the strong and radiative decays of the low-lying $1P$-wave doubly charmed baryons. Some interesting observations are: (i) The states $Ξ_{cc}^*$ and $Ω_{cc}^*$ with $J^P=3/2^+$ have a fairly large decay rate into the $Ξ_{cc}γ$ and $Ω_{cc}γ$ channels with a width $\sim 15$ and $\sim7$ keV, respectively. (ii) The lowest lying excited doubly charmed baryons are dominated by the $1P$ $ρ$ mode excitations, which should be quite narrow states. They decay into the ground state with $J^P=1/2^+$ through the radiative transitions with a significant ratio. (iii) The total de…
Using the dynamical diquark model, we calculate the electric-dipole radiative decay widths to $X(3872)$ of the lightest negative-parity exotic candidates, including the four $I=0$, $J^{PC} \! = \! 1^{--}$ ("$Y$") states. The $O$(100--1000 keV) values obtained test the hypothesis of a common substructure shared by all of these states. We also calculate the magnetic-dipole radiative decay width for $Z_c(4020)^0 \! \to \! γX(3872)$, and find it to be rather smaller ($<$~10 keV) than its predicted value in molecular models.
In this work we present our model that dynamically generates resonances from charmed and light pseudoscalar and vector mesons. The model generates a rich spectrum of charmed and hidden charm scalar and axial resonances, most of them which can be associated with observed states. Other states are predicted, in particular a hidden charm scalar resonance with mass close to the $D\bar D$ threshold. For this resonance we present calculations which show that an observed enhancement in the $D\bar D$ mass spectrum measured by Belle in reactions producing $D\bar D J/ψ$ in the final state could be origin…
We use QCD sum rules to calculate the width of the radiative decay of the meson X(3872), assumed to be a mixture between charmonium and exotic molecular $[c\bar{q}][q\bar{c}]$ states with $J^{PC}=1^{++}$. We find that in a small range for the values of the mixing angle, $5^0\leqθ\leq13^0$, we get the branching ratio $Γ(X\to J/ψγ)/Γ(X\to J/ψπ^+π^-)=0.19\pm0.13$, which is in agreement, with the experimental value. This result is compatible with the analysis of the mass and decay width of the mode $J/ψ(nπ)$ performed in the same approach.
The X(3872) radiative decay is discussed by employing a two-meson multichannel model with the charmonium components, which explains many of the other observed features of X(3872). We have found that the ratio of the branching fractions of the X(3872) radiative decays, $R_γ=\text{Br}(X(3872)\rightarrowψ(2S)γ)$ / Br$(X(3872)\rightarrow J/ψγ)$, is 1.1 $\sim$ 3.4 if one assumes that the decay occurs only from the charmonium components. The invariant mass spectra of $cc^{bar}$($2P$)$\rightarrow J/ψγ$ and $cc^{bar}$($2P$)$\rightarrow ψ(2S) γ$ are also investigated. It is found that an enhancement ap…
In this work we study the radiative decay of dynamically generated $J^P=\oh^-$ charm baryons into the ground state $J^P=\oh^+$ baryons. Since different theoretical interpretations of these baryonic resonances, and in particular of the $Λ_c(2595)$, give different predictions, a precise experimental measurement of these decays would be an important step for understanding their nature.
Using the helicity formalism, we calculate the combined angular distribution function of the two gamma photons ($γ_1$ and $γ_2$) and the electron ($e^-$) in the triple cascade process $\bar{p}p\rightarrow{}^3D_3\rightarrow{}^3P_2+γ_1\rightarrow(ψ+γ_2) +γ_1 \rightarrow (e^- + e^+) +γ_2 +γ_1$, when $\bar{p}$ and $p$ are arbitrarily polarized. We also derive six different partially integrated angular distribution functions which give the angular distributions of one or two particles in the final state. Our results show that by measuring the two-particle angular distribution of $γ_1$ and $γ_2$ and…
We study weak radiative $|Δc|=|Δu|=1$ decays of the charmed anti-triplett ($Λ_c$, $Ξ_c^{+}$, $Ξ_c^{0}$) and sextet ($Σ_c^{++}$, $Σ_c^+$, $Σ_c^0$, $Ξ_c^{\prime +}$, $Ξ_c^{\prime 0}$, $Ω_c$) baryons in the standard model (SM) and beyond. We work out $SU(2)$ and $SU(3)_F$-symmetry relations. We propose to study self-analyzing decay chains such as $Ξ_c^+ \to Σ^+ (\to p π^0) γ$ and $Ξ_c^0 \to Λ(\to p π^-) γ$, which enable new physics sensitive polarization studies. SM contributions can be controlled by corresponding analysis of the Cabibbo-favored decays $Λ_c^+ \to Σ^+ (\to p π^0) γ$ and $Ξ_c^0 \to…
We study the photon spectrum in the radiative decays of the charmonium $\frac{1}Γ\frac{dΓ(J/ψ\rightarrowγgg)}{dz}$ as an excellent scene for hunting the exotic mesons (hybrids $q\bar{q}g$ and glueballs $gg$) and an ideal frame for the theoretical and phenomenological investigations of the gluon nature in IR, by subtle estimation of its non-zero effective mass which seems required in Quark-Gluon Constituent Model (QGCM) for identifying the nature of these exotic species.
Recent experimental bounds on rare charm decays offer a chance to improve our theoretical understanding of physics present in $c \to u γ$ and $c \to u l^+ l^-$ transitions. Standard Model and New Physics contributions are reviewed for inclusive and exclusive $D \to Vγ$, $D^+ \to π^+ l^+ l^-$, $D \to l^+ l^-$ decays. Observables important for search of New Physics are discussed. Possibility to observe CP violation in rare charm decays is questioned.
In this work, we investigate the decay widths and the line shapes of the open-charm radiative and pionic decays of Y(4274) with the $D_s\bar{D}_{s0}(2317)$ molecular charmonium assignment. Our calculation indicates that the decay widths of $Y(4274)\to D^{+}_{s}D^{*-}_{s}γ$ and $Y(4274)\to D^+_{s}D^-_{s}π^0$ can reach up to 0.05 keV and 0.75 keV, respectively. In addition, the result of the line shape of the photon spectrum of $Y(4274)\to D_s^+ {D}_s^{*-} γ$ shows that there exists a very sharp peak near the large end point of photon energy. The line shape of the pion spectrum of $Y(4274)\to D_…
In the present work, we perform systematic estimations for the radiative decays of the charmed mesons in a modified relativistic quark model. Our estimations indicate that the branching ratios of the process of $D_2^0(1^3P_2) \to D^{\ast 0}(1^3S_1) γ$, $D_3^0(1D_3) \to D_2^0(1^3P_2) γ$, $D_2^0(2D_2^\prime) \to D_1^{0}(2P_1) γ$, $D_3^0(2^3D_3) \to D_2^0(2^3P_2) γ$, and $D^{\ast 0}(1^3S_1) \to D^0(1^1S_0) γ$ are of the order of $10^{-2}$, which are sizable to be detected experimentally. Moreover, the branching ratios of some channels, for example, $D_1^0(1P_1) \to D(1^1S_0)^0 γ$, $D^0(3^1S_0) \t…
In this work we study the radiative decay widths of vector quarkonia for the process of $J/ψ(nS)\rightarrowη_{c}(nS)γ$ and $Υ(nS)\rightarrowη_{b}(nS)γ$ (for principal quantum numbers $n=1, 2, 3$) in the framework of Bethe-Salpeter equation under the covariant instantaneous ansatz using a $4\times 4$ form of BSE. The parameters of the framework were determined by a fit to the mass spectrum of ground states of pseudoscalar and vector quarkonia, such as; $η_{c}$, $η_{b}$, $J/ψ$ and $Υ$. These input parameters so fixed were found to give good agreements with data on mass spectra of ground and exci…
Studying the hidden-charm dipion decays of the charmoniumlike state Y(4360), we show that there exist charged charmoniumlike structures near $D\bar{D}^*$ and $D^*\bar{D}^*$ thresholds in the $J/ψπ^+$, $ψ(2S)π^+$ and $h_c(1P)π^+$ invariant mass spectra of the corresponding hidden-charm dipion decays of Y(4360) using the {\it{Initial Single Pion Emission} mechanism}. We suggest to do further experimental study on these predicted charged enhancement structures, especially by BESIII, Belle, and the forthcoming BelleII.
A brief review of the theoretical description of exclusive and inclusive semileptonic charm decays is given. In light of the recent experimental puzzles in leptonic charm decays, the complementary role of semileptonic modes is emphasized. The relevance of semileptonic charm decay studies to the precise determination of the Vub CKM matrix element from semileptonic B decays is also discussed. Some interesting and important theoretical challenges are mentioned.
The importance of charm decays in the context of flavor is motivated. A theory overview on recent developments in leptonic and semileptonic decays, hadronic two-body decays, and rare decays is presented. Standard Model (SM) predictions as well as tests of the SM are pointed out, {\it e.g.}~how to discover direct CP violation in charm decays and how to search for physics beyond the SM. Differences between rare charm and beauty decays are discussed.
Motivated by very recent measurement of the radiative decays of $Υ(1S)$ to $χ_{c1}$ at Belle, we use the nonrelativistic QCD factorization theory and calculate the branching fractions of the radiative decays of bottomonium into S-wave and P-wave charmonium, i.e. $Υ(nS) \to η_c(nS)+γ$ and $Υ(nS)\to χ_{cJ}+γ$. We systematically studied the branching fractions of the radiative decays of bottomonium into charmonium. Compared to the previous calculation, we obtained the analytical expression for the decay widths and considered the color-octet contributions. For $Υ(nS) \to η_c(nS)+γ$, the relativist…
We discuss the possibilities of producing the X(3872), which is assumed to be a D \bar D^* bound state, in radiative decays of charmonia. We argue that the ideal energy regions to observe the X(3872) associated with a photon in e^+e^- annihilations are around the Y(4260) mass and around 4.45 GeV, due to the presence of the S-wave D \bar D_1(2420) and D^* \bar D_1(2420) threshold, respectively. Especially, if the Y(4260) is dominantly a D \bar D_1 molecule and the X(3872) a D \bar D^* molecule, the radiative transition strength will be quite large.
