238 research outputs found

### Revisiting the $D$-meson twist-2, 3 distribution amplitudes

Due to the significant difference between the experimental measurements and
the theoretical predictions of standard model (SM) for the value of
$\mathcal{R}(D)$ of the semileptonic decay $B\to D\ell\bar{\nu}_{\ell}$, people
speculate that it may be the evidence of new physics beyond the SM. Usually,
the $D$-meson twist-2, 3 distribution amplitudes (DAs) $\phi_{2;D}(x,\mu)$,
$\phi_{3;D}^p(x,\mu)$ and $\phi_{3;D}^\sigma(x,\mu)$ are the main error sources
when using perturbative QCD factorization and light-cone QCD sum rules to study
$B\to D\ell\bar{\nu}_{\ell}$. Therefore, it is important to get more reasonable
and accurate behaviors for those DAs. Motivated by our previous work [Phys.
Rev. D 104, no.1, 016021 (2021)] on pionic leading-twist DA, we revisit
$D$-meson twist-2, 3 DAs $\phi_{2;D}(x,\mu)$, $\phi_{3;D}^p(x,\mu)$ and
$\phi_{3;D}^\sigma(x,\mu)$. New sum rules formulae for the $\xi$-moments of
these three DAs are suggested to obtain more accurate values. The light-cone
harmonic oscillator models for those DAs are improved, and whose model
parameters are determined by fitting the values of $\xi$-moments with the least
squares method.Comment: 9 pages, 2 figure

### Investigation for $Z$-boson decay into $\Xi_{bc}$ and $\Xi_{bb}$ baryon with the NRQCD factorizations approach

The $Z$-boson decay provides good opportunities for the research on
$\Xi_{bQ'}$ baryon due to large quantity of $Z$ events that can be collected at
the high-energy colliders. We performed a completed investigation of the
indirect production of the $\Xi_{bc}$ and $\Xi_{bb}$ baryon via $Z$-boson decay
$Z\to \Xi_{bQ'}+\bar b +\bar Q'$ with $Q'= (c, b)$ quark according to NRQCD
factorizations approach. After considering the contribution of the diquark
states $\langle bc\rangle [^3S_1]_{\bar 3/6}$, $\langle bc\rangle [^1S_0]_{\bar
3/6}$, $\langle bb\rangle [^1S_0]_{6}$ and $\langle bb\rangle [^3S_1]_{\bar
3}$, the calculated branching ratio for $Z\to\Xi_{bQ'}+X$ are ${\cal
B}(Z\to\Xi_{bc}+X) = 3.595\times 10^{-5}$ and ${\cal B}(Z\to\Xi_{bc}+X) =
1.213\times 10^{-6}$. Moreover, the $\Xi_{bc}$ events produced are predicted to
be of the $10^4(10^7)$ order at the LHC(CEPC), while the $\Xi_{bb}$ events
produced are forecasted to be of the $10^3(10^6)$ order. Furthermore, we have
estimated the production ratio ${\cal R}(Z_Q\to\Xi^{+,0}_{bc})$ with four
$Z$-boson decay channels. The ${\cal R}(Z_Q\to\Xi^{+,0}_{bc})$ up to $10^{-6}$
for $Z\to c\bar c$ channel and $10^{-5}$ for $Z\to b\bar b$ channel,
respectively. Finally, we present the differential decay widths of
$\Xi_{bc}(\Xi_{bb})$ with respect to $s_{23}$ and $z$ distributions, and
analysis the uncertainties.Comment: 9 pages, 4 figures. Some ambiguous sentences have been modified and
discussion extende

### Heavy Pseudoscalar Twist-3 Distribution Amplitudes within QCD Theory in Background Fields

In this paper, we study the properties of the twist-3 distribution amplitude
(DA) of the heavy pseudo-scalars such as $\eta_c$, $B_c$ and $\eta_b$. New sum
rules for the twist-3 DA moments \left_{\rm HP} and
\left_{\rm HP} up to sixth orders and up to dimension-six
condensates are deduced under the framework of the background field theory.
Based on the sum rules for the twist-3 DA moments, we construct a new model for
the two twist-3 DAs of the heavy pseudo-scalar with the help of the
Brodsky-Huang-Lepage prescription. Furthermore, we apply them to the
$B_c\to\eta_c$ transition form factor ($f^{B_c\to\eta_c}_+(q^2)$) within the
light-cone sum rules approach, and the results are comparable with other
approaches. It has been found that the twist-3 DAs $\phi^P_{3;\eta_c}$ and
$\phi^\sigma_{3;\eta_c}$ are important for a reliable prediction of
$f^{B_c\to\eta_c}_+(q^2)$. For example, at the maximum recoil region, we have
$f^{B_c\to\eta_c}_+(0) = 0.674 \pm 0.066$, in which those two twist-3 terms
provide $\sim33\%$ and $\sim22\%$ contributions. Also we calculate the
branching ratio of the semi-leptonic decay $B_c \to\eta_c l\nu$ as $Br(B_c
\to\eta_c l\nu) = \left( 9.31^{+2.27}_{-2.01} \right) \times 10^{-3}$.Comment: 12 pages, 16 figure

### Further study on the production of P-wave doubly heavy baryons from Z-boson decays

In this paper, we carried out a systematic investigation about the excited
doubly heavy baryons production in $Z$-boson decays within the framework of
NRQCD. Our investigation accounts for all the intermediate diquark states,
including those in $P$-wave such as $\langle cc\rangle[^1P_1]_{\bar 3}$,
$\langle cc\rangle[^3P_J]_{6}$, $\langle bc\rangle[^1P_1]_{\bar 3/6}$, $\langle
bc\rangle[^3P_J]_{\bar 3/6}$, $\langle bb\rangle[^1P_1]_{\bar 3}$, and $\langle
bb\rangle[^3P_J]_{6}$ with $J = (0, 1, 2)$, were taken into account. The
results show that the contributions of the all diquark state in $P$-wave were
$7\%$, $8\%$, and $3\%$, respectively, when compared to $S$-wave. Based on
these results, we anticipate that about $0.539\times 10^3(10^6)$ events of
excited $\Xi_{cc}$, $1.827\times 10^3(10^6)$ events of excited $\Xi_{bc}$ and
$0.036\times 10^3(10^6)$ events of excited $\Xi_{bb}$ can be produced annually
at the LHC (CEPC). Additionally, we plot the differential decay widths of
$\Xi_{cc}$, $\Xi_{bc}$ and $\Xi_{bb}$ as a function of the invariant mass
$s_{23}$ and energy fuction $z$ distributions, and analyze the theoretical
uncertainties decay width arising from the mass parameters of heavy quark.Comment: 11 pages, 4 figure

### The $D\to \rho$ semileptonic and radiative decays within the light-cone sum rules

The measured branching ratio of the $D$ meson semileptonic decay $D \to \rho
e^+ \nu_e$, which is based on the $0.82~{\rm fb^{-1}}$ CLEO data taken at the
peak of $\psi(3770)$ resonance, disagrees with the traditional SVZ sum rules
analysis by about three times. In the paper, we show that this discrepancy can
be eliminated by applying the QCD light-cone sum rules (LCSR) approach to
calculate the $D\to \rho$ transition form factors $A_{1,2}(q^2)$ and $V(q^2)$.
After extrapolating the LCSR predictions of these TFFs to whole $q^2$-region,
we obtain $1/|V_{\rm cd}|^2 \times \Gamma(D \to \rho e \nu_e)
=(55.45^{+13.34}_{-9.41})\times 10^{-15}~{\rm GeV}$. Using the CKM matrix
element and the $D^0(D^+)$ lifetime from the Particle Data Group, we obtain
${\cal B} (D^0\to \rho^- e^+ \nu_e) = (1.749^{+0.421}_{-0.297}\pm 0.006)\times
10^{-3}$ and ${\cal B} (D^+ \to \rho^0 e^+ \nu_e) = (2.217^{+0.534}_{-0.376}\pm
0.015)\times 10^{-3}$, which agree with the CLEO measurements within errors. We
also calculate the branching ratios of the two $D$ meson radiative processes
and obtain ${\cal B}(D^0\to \rho^0 \gamma)= (1.744^{+0.598}_{-0.704})\times
10^{-5}$ and ${\cal B}(D^+ \to \rho^+ \gamma) = (5.034^{+0.939}_{-0.958})\times
10^{-5}$, which also agree with the Belle measurements within errors. Thus we
think the LCSR approach is applicable for dealing with the $D$ meson decays.Comment: 12 pages, 7 figures, version to be published in EPJ

### Next-to-leading-order QCD correction to the exclusive double charmonium production via $Z$ decays

In this paper, we preformed a further research on the exclusive productions
of double charmonium via $Z$-boson decay by using nonrelativistic QCD
factorizations approach, where the single-photon fragmentation topologies of
the QED diagrams, the interference terms between the QCD and full QED diagrams,
the next-to-leading-order calculations of the interference terms are preformed.
For the production of $J/\psi+J/\psi$ in $Z$-boson decay, the interference
terms show a significantly phenomenological effect due to the addition of the
newly calculated NLO QCD corrections. After adding together all contributions,
the branching fraction $\mathcal{B}_{Z\to J/\psi J/\psi}$ still undershoots the
CMS collaboration data obviously. In addition, we simultaneously complete the
next-to-leading-order calculations for $Z\to J/\psi+\eta_c (\chi_{cJ})$ with
$J=(0,1,2)$. The calculated results show that the newly-calculated complete QED
and cross terms will have obvious effective on the total decay widths.Comment: 8 pages, 4 figure

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