arXiv subjects

Hai-Bing Fu

Publications and source records attributed to Hai-Bing Fu.

At least 73 records · Page 4Linked to original sources

arXiv2018

The $B \to ρ$ helicity form factors within the QCD light-cone sum rules

We study the $B \to ρ$ helicity form factors (HFFs) by applying the light-cone sum rules up to twist-4 accuracy. The HFF has some advantages in comparison to the conventionally calculated transition form factors, such as the HFF parameterization can be achieved via diagonalizable unitarity relations and etc. At the large recoil point, only the $ρ$-meson longitudinal component contributes to the HFFs, and we have $\mathcal{H}_{ρ,0}(0)=0.435^{+0.055}_{-0.045}$ and $\mathcal{H}_{ρ,\{1,2\}}(0)\equiv 0$. We extrapolate the HFFs to physically allowable $q^2$-region and apply them to the $B \to ρ$ semileptonic decay. We observe that the $ρ$-meson longitudinal component dominates its differential decay width in low $q^2$-region, and its transverse component dominates the high $q^2$-region. Two ratios $R_{\rm low}$ and $R_{\rm high}$ are used to characterize those properties, and our LCSR calculation gives, $R_{\rm low}=0.967^{+0.305}_{-0.284}$ and $R_{\rm high}=0.219^{+0.058}_{-0.070}$, which agree with the BaBar measurements within errors.

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arXiv2018

The Ratio $\mathcal{R}(D)$ and the $D$-meson Distribution Amplitude

In this paper, we calculate the $B\to D$ transition form factors (TFFs) within the light-cone sum rules (LCSR) and predict the ratio $\mathcal{R}(D)$. More accurate $D$-meson distribution amplitudes (DAs) are essential to get a more accurate theoretical prediction. We construct a new model for the twist-3 DAs $ϕ^p_{3;D}$ and $ϕ^σ_{3;D}$ based on the QCD sum rules under the background field theory for their moments as we have done for constructing the leading-twist DA $ϕ_{2;D}$. As an application, we observe that the twist-3 contributions are sizable in whole $q^2$-region. Taking the twist-2 and twist-3 DAs into consideration, we obtain $f^{B\to D}_{+,0}(0) = 0.659^{+0.029}_{-0.032}$. As a combination of the Lattice QCD and the QCD LCSR predictions on the TFFs $f^{B\to D}_{+,0}(q^2)$, we predict $\mathcal{R}(D) = 0.320^{+0.018}_{-0.021}$, which improves is about $1.5σ$ deviation from the HFAG average of the Belle and BABAR data. At present the data are still of large errors, and we need further accurate measurements of the experiment to confirm whether there is signal of new physics from the ratio $\mathcal{R}(D)$.

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arXiv2018

The asymmetries of the $B \to K^* μ^+ μ^-$ decay and the search of new physics beyond the Standard Model

In this paper, we compute the forward-backward asymmetry and the isospin asymmetry of the $B \to K^* μ^+ μ^-$ decay. The $B \to K^*$ transition form factors (TFFs) are key components of the decay. To achieve a more accurate QCD prediction, we adopt a chiral correlator for calculating the QCD light-cone sum rules for those TFFs with the purpose of suppressing the uncertain high-twist distribution amplitudes. Our predictions show that the asymmetries under the Standard Model and the Minimal Supersymmetric Standard Model with minimal flavor violation are close in shape for $q^2 \ge 6~{\rm GeV}^2$ and are consistent with the Belle, LHCb and CDF data within errors. When $q^2 < 2~{\rm GeV}^2$, their predictions behave quite differently. Thus a careful study on the $B \to K^* μ^+ μ^-$ decay within small $q^2$-region could be helpful for searching new physics beyond the Standard Model. As a further application, we also apply the $B \to K^*$ TFFs to the branching ratio and longitudinal polarization fraction of the $B\to K^*ν\barν$ decay within different models.

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arXiv2018

The longitudinal leading-twist distribution amplitude of $J/ψ$ meson within background field theory

We make a detailed study on the $J/ψ$ meson longitudinal leading-twist distribution amplitude $ϕ_{2;J/ψ}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langleξ_{n;J/ψ}^\|\rangle$. The first three ones are $\langleξ_{2;J/ψ}^\|\rangle=0.083(12)$, $\langleξ_{4;J/ψ}^\|\rangle=0.015(5)$ and $\langleξ_{6;J/ψ}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $ϕ_{2;J/ψ}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an application, we adopt the QCD light-cone sum rules to calculate the $B_c$ meson semileptonic decay $B_c^+ \to J/ψ\ell^+ ν_\ell$. We obtain $Γ(B_c^+ \to J/ψ\ell^+ ν_\ell) = (89.67^{+24.76}_{-19.06}) \times 10^{-15}~{\rm GeV}$ and $\Re(J/ψ\ell^+ ν_\ell) = 0.217^{+0.069}_{-0.057}$, which agree with the next-to-leading order pQCD prediction and the new CDF measurement within errors.

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arXiv2017

Uncertainties of the $B\to D$ transition form factor from the $D$-Meson Leading-Twist Distribution Amplitude

The $B\to D$ transition form factor (TFF) $f^{B\to D}_+(q^2)$ is determined mainly by the $D$-meson leading-twist distribution amplitude (DA) , $ϕ_{2;D}$, if the proper chiral current correlation function is adopted within the light-cone QCD sum rules. It is therefore significant to make a comprehensive study of DA $ϕ_{2;D}$ and its impact on $f^{B\to D}_+(q^2)$. In this paper, we calculate the moments of $ϕ_{2;D}$ with the QCD sum rules under the framework of the background field theory. New sum rules for the leading-twist DA moments $\left<ξ^n\right>_D$ up to fourth order and up to dimension-six condensates are presented. At the scale $μ= 2 \rm GeV$, the values of the first four moments are: $\left<ξ^1\right>_D = -0.418^{+0.021}_{-0.022}$, $\left<ξ^2\right>_D = 0.289^{+0.023}_{-0.022}$, $\left<ξ^3\right>_D = -0.178 \pm 0.010$ and $\left<ξ^4\right>_D = 0.142^{+0.013}_{-0.012}$. Basing on the values of $\left<ξ^n\right>_D(n=1,2,3,4)$, a better model of $ϕ_{2;D}$ is constructed. Applying this model for the TFF $f^{B\to D}_+(q^2)$ under the light cone sum rules, we obtain $f^{B\to D}_+(0) = 0.673^{+0.038}_{-0.041}$ and $f^{B\to D}_+(q^2_{\rm max}) = 1.124^{+0.053}_{-0.058}$. The uncertainty of $f^{B\to D}_+(q^2)$ from $ϕ_{2;D}$ is estimated and we find its impact should be taken into account, especially in low and central energy region. The branching ratio $\mathcal{B}(B\to Dl\barν_l)$ is calculated, which is consistent with experimental data.

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arXiv2017

Reconsideration of the $B \to K^*$ Transition Form Factors within the QCD Light-Cone Sum Rules

In this paper, we study the $B \to K^*$ transition form factors (TFFs) within the QCD light-cone sum rules (LCSR) approach. Two correlators, i.e. the usual one and the right-handed one, are adopted in the LCSR calculation. The resultant LCSRs for the $B \to K^*$ TFFs are arranged according to the twist structure of the $K^*$-meson light-cone distribution amplitudes (LCDAs), whose twist-2, twist-3 and twist-4 terms behave quite differently by using different correlators. We observe that the twist-4 LCDAs, though generally small, shall have sizable contributions to the TFFs $A_{1/2}$, $V$ and $T_1$, thus the twist-4 terms should be kept for a sound prediction. We also observe that even though different choices of the correlator lead to different LCSRs with different twist contributions, the large correlation coefficients for most of the TFFs indicate that the LCSRs for different correlators are close to each order, not only for their values at the large recoil point $q^2=0$ but also for their ascending trends in whole $q^2$-region. Such a high degree of correlation is confirmed by their application to the branching fraction of the semi-leptonic decay $B \to K^* μ^+ μ^-$. Thus, a proper choice of correlator may inversely provide a chance for probing uncertain LCDAs, i.e. the contributions from those LCDAs can be amplified to a certain degree via a proper choice of correlator, thus amplifying the sensitivity of the TFFs, and hence their related observables, to those LCDAs.

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arXiv2016

The $ρ$-meson longitudinal leading-twist distribution amplitude within QCD background field theory

We revisit the $ρ$-meson longitudinal leading-twist distribution amplitude (DA) $ϕ_{2;ρ}^\|$ by using the QCD sum rules approach within the background field theory. To improve the accuracy of the sum rules for its moments $\langleξ_{n;ρ}^\|\rangle$, we include the next-to-leading order QCD correction to the perturbative part and keep all non-perturbative condensates up to dimension-six consistently within the background field theory. The first two moments read $\langle ξ_{2;ρ}^\| \rangle|_{1{\rm GeV}} = 0.241(28)$ and $\langle ξ_{4;ρ}^\| \rangle|_{1{\rm GeV}} = 0.109(10)$, indicating a double humped behavior for $ϕ_{2;ρ}^\|$ at small energy scale. As an application, we apply them to the $B\to ρ$ transition form factors within the QCD light-cone sum rules, which are key components for the decay width $Γ(B\to ρ\ell ν_\ell)$. To compare with the world-average of $Γ(B\to ρ\ell ν_\ell)$ issued by Particle Data Group, we predict $|V_{\rm ub}| = 3.19^{+0.65}_{-0.62}$, which agrees with the BABAR and Omnès parameterization prediction within errors.

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arXiv2016

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 $η_c$, $B_c$ and $η_b$. New sum rules for the twist-3 DA moments $\left<ξ^n_P\right>_{\rm HP}$ and $\left<ξ^n_σ\right>_{\rm HP}$ 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 $B_c\toη_c$ transition form factor ($f^{B_c\toη_c}_+(q^2)$) within the light-cone sum rules approach, and the results are comparable with other approaches. It has been found that the twist-3 DAs $ϕ^P_{3;η_c}$ and $ϕ^σ_{3;η_c}$ are important for a reliable prediction of $f^{B_c\toη_c}_+(q^2)$. For example, at the maximum recoil region, we have $f^{B_c\toη_c}_+(0) = 0.674 \pm 0.066$, in which those two twist-3 terms provide $\sim33\%$ and $\sim22\%$ contributions. Also we calculate the branching ratio of the semi-leptonic decay $B_c \toη_c lν$ as $Br(B_c \toη_c lν) = \left( 9.31^{+2.27}_{-2.01} \right) \times 10^{-3}$.

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arXiv2015

$B\to K^$ Transition Form Factors and the Semi-leptonic Decay $B \to K^ μ^+ μ^-$

We present a detailed calculation on the $B\to K^*$ transition form factors (TFFs), $A_{0,1,2}$, $V$ and $T_{1,2,3}$, within the QCD light-cone sum rules (LCSR). To suppress the contributions from high-twist light-cone distribution amplitudes, we adopt a right-handed chiral correlator to do the LCSR calculation. In the resultant LCSRs for the TFFs, the transverse leading-twist distribution amplitude $ϕ_{2;K^*}^\bot$ provides over $90\%$ contribution, thus those TFFs provide good platforms for testing the property of $ϕ_{2;K^*}^\bot$. We suggest a model for $ϕ_{2;K^*}^\bot$, in which two parameters $B_{2;K^*}^\bot$ and $C_{2;K^*}^\bot$ dominantly control its longitudinal distribution. With a proper choice of $B_{2;K^*}^\bot$ and $C_{2;K^*}^\bot$, our predictions on $B\to K^*$ TFFs are consistent with those of lattice QCD predictions. As an application, we also calculate the branching fraction of the $B$-meson rare decay $B \to K^* μ^+ μ^-$. The predicted differential branching fraction $d{\cal B}/dq^2(B\to K^{*}μ^+μ^-)$ is consistent with the LHCb and Belle measurements within errors. After integrating over the allowable $q^2$-region, we get the branching fraction, ${\cal B}(B\to K^*μ^+μ^-) = \left(1.088^{+0.261}_{-0.205} \right)\times 10^{-6}$, where the errors are squared average of the mentioned error sources. When the precision of experimental measurements or the other source of theoretical uncertainties for this process have been further improved in the future, we may get a definite conclusion on the behavior of $ϕ_{2;K^*}^\bot$.

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arXiv2015

Renormalization Group Invariance and Optimal QCD Renormalization Scale-Setting

A valid prediction for a physical observable from quantum field theory should be independent of the choice of renormalization scheme -- this is the primary requirement of renormalization group invariance (RGI). Satisfying scheme invariance is a challenging problem for perturbative QCD (pQCD), since a truncated perturbation series does not automatically satisfy the requirements of the renormalization group. Two distinct approaches for satisfying the RGI principle have been suggested in the literature. One is the "Principle of Maximum Conformality" (PMC) in which the terms associated with the $β$-function are absorbed into the scale of the running coupling at each perturbative order; its predictions are scheme and scale independent at every finite order. The other approach is the "Principle of Minimum Sensitivity" (PMS), which is based on local RGI; the PMS approach determines the optimal renormalization scale by requiring the slope of the approximant of an observable to vanish. In this paper, we present a detailed comparison of the PMC and PMS procedures by analyzing two physical observables $R_{e+e-}$ and $Γ(H\to b\bar{b})$ up to four-loop order in pQCD. At the four-loop level, the PMC and PMS predictions for both observables agree within small errors with those of conventional scale setting assuming a physically-motivated scale, and each prediction shows small scale dependences. However, the convergence of the pQCD series at high orders, behaves quite differently: The PMC displays the best pQCD convergence since it eliminates divergent renormalon terms; in contrast, the convergence of the PMS prediction is questionable, often even worse than the conventional prediction based on an arbitrary guess for the renormalization scale. ......

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arXiv2015

$B\to ρ$ transition form factors within the QCD light-cone sum rules and the $ρ$-meson leading-twist distribution amplitude

The QCD light-cone sum rules (LCSR) provides an effective way for dealing with the heavy-to-light transition form factors (TFFs), whose non-perturbative dynamics are parameterized into the light-meson's light-cone distribution amplitudes (LCDAs) with various twist structures. By taking the chiral correlator as the starting point, we calculate the LCSRs for the $B\toρ$ TFFs up to twist-4 accuracy. As for the TFFs at the large recoil region, we observe that the twist-2 transverse DA $ϕ_{2;ρ}^\bot$ provides the dominant contribution, while the contributions from the remaining twist-3 and twist-4 terms are $δ^2$-suppressed. Thus, our present improved LCSRs provides a good platform for testing the $ϕ_{2;ρ}^\bot$ behavior. For the purpose, we suggest a convenient WH-model for the $ρ$-meson leading-twist wavefunction, in which the parameter $B_{2;ρ}^\bot\sim a^\bot_2$ dominantly controls its longitudinal distribution. Typically, its DA $ϕ_{2;ρ}^\bot$ is CZ-like as $B_{2;ρ}^\bot\simeq-0.20$, which changes to be asymptotic-like as $B_{2;ρ}^\bot\simeq0.00$. By varying $B_{2;ρ}^\bot\in[-0.20,0.20]$, we present a detailed comparison of the LCSR estimation for the $B\toρ$ TFFs with those of pQCD and Lattice QCD predictions. Furthermore, by using the extrapolated TFFs, we estimate the CKM-matrix element $|V_{\rm ub}|$ with the help of two $B\toρ$ semi-leptonic decays. The predicted value for $|V_{\rm ub}|$ increases with the increment of $B_{2;ρ}^\bot$, i.e. we have $\Vub=(2.91\pm0.19)\times 10^{-3}$ for $B_{2;ρ}^\bot=-0.20$ and $\Vub=(3.11\pm0.19)\times 10^{-3}$ for $B_{2;ρ}^\bot=0.00$. If using the BABAR prediction as a criteria, we observe that $B^{\perp}_{2;ρ}\in[-0.2,0.10]$, which indicates that the $ρ$-meson DA $ϕ_{2;ρ}^\bot$ prefers a single-peak behavior rather than a double-humped behavior.

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arXiv2014

Photoproduction of doubly heavy baryon at the ILC

In the present paper, we make a detailed study on the doubly heavy baryon photoproduction in the future $e^+e^-$ International Linear Collider (ILC). The baryons $Ξ_{cc}$, $Ξ_{bc}$, and $Ξ_{bb}$ are produced via the channel $γγ\to Ξ_{QQ'} +\bar{Q'} +\bar{Q}$, where $Q$ and $Q'$ stand for heavy $c$ or $b$ quark, respectively. As for the $Ξ_{QQ'}$-baryon production, it shall first generate a $(QQ')[n]$-diquark and then form the final baryon via fragmentation, where $[n]$ stands for the color- and spin- configurations for the $(QQ')$-diquark states. According to the non-relativistic QCD theory, four diquark configurations shall provide sizable contributions to the baryon production, e.g., $[n]$ equals $[^3S_1]_{\bar{\textbf{3}}}$, $[^1S_0]_{\textbf{6}}$, $[^3S_1]_{\textbf{6}}$, or $[^1S_0]_{\bar{\textbf{3}}}$, respectively. We adopt the improved helicity amplitude approach for the hard scattering amplitude to improve the calculation efficiency. Total and differential cross sections of those channels, as well as the theoretical uncertainties, are presented. We show that sizable amounts of baryon events can be generated at the ILC, i.e., about $2.0\times 10^{6}$ $Ξ_{cc}$, $2.2\times 10^{5}$ $Ξ_{bc}$, as well as $3.0\times 10^{3}\;Ξ_{bb}$ events are to be generated in one operation year for $\sqrt{S}=500$ GeV and ${\cal L}\simeq 10^{36}$cm$^{-2}$s$^{-1}$.

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arXiv2014

Photoproduction of the heavy quarkonium at the ILC

We study the photoproduction of the heavy quarkonium at the future International Linear Collider (ILC) within the nonrelativistic QCD theory. We focus on the production channel via the subprocess $γγ\to |[Q\bar{Q'}]_{\bf 1}(n)>+Q'+\bar{Q}$, where $Q$ and $Q'$ stand for heavy $c$- or $b$-quark, respectively. $|[Q\bar{Q'}]_{\bf 1}(n)>$ stands for color-singlet $S$-wave quarkonium, i.e., $η_{c}(|[c\bar{c}]_{\bf 1}(^1S_0)>)$, $J/ψ(|[c\bar{c}]_{\bf 1}(^3S_1)>)$, $B_{c}(|[c\bar{b}]_{\bf 1}(^1S_0)>)$, $B^*_{c}(|[c\bar{b}]_{\bf 1}(^3S_1)>)$, $η_{b}(|[b\bar{b}]_{\bf 1}(^1S_0)>)$, and $Υ(|[b\bar{b}]_{\bf 1}(^3S_1)>)$, respectively. To improve the calculation efficiency, we adopt the improved helicity amplitude approach to deal with the difficulty of calculating the expressions for the yields when the quark masses cannot be neglected. Total and differential photoproduction cross sections, together with their uncertainties, have been presented. It is noted that sizable amount of $|c\bar{c}>$-charmonium and $|c\bar{b}>$-quarkonium events can be generated at the ILC. More specifically, we predict $(2.8^{+1.0}_{-0.7})\times 10^{6}$ $η_c$, $(5.4^{+1.9}_{-1.3})\times 10^{6}$ $J/ψ$, $(8.3^{+2.2}_{-1.8})\times 10^{4}$ $B_c$, $(4.3^{+1.1}_{-0.9})\times 10^{5}$ $B_c^*$, $(9.0^{+1.7}_{-1.4})\times 10^{3}$ $η_b$, and $(1.6\pm0.3)\times 10^{4}$ $Υ$ events to be generated in one operation year at the ILC under the condition of $\sqrt{S}=500$ GeV and ${\cal L}\simeq 10^{36}$cm$^{-2}$s$^{-1}$.

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arXiv2014

The $ρ$-meson longitudinal leading-twist distribution amplitude

In the present paper, we suggest a convenient model for the vector $ρ$-meson longitudinal leading-twist distribution amplitude $ϕ_{2;ρ}^\|$, whose distribution is controlled by a single parameter $B^\|_{2;ρ}$. By choosing proper chiral current in the correlator, we obtain new light-cone sum rules (LCSR) for the $B\toρ$ TFFs $A_1$, $A_2$ and $V$, in which the $δ^1$-order $ϕ_{2;ρ}^\|$ provides dominant contributions. Then we make a detailed discussion on the $ϕ_{2;ρ}^\|$ properties via those $B\toρ$ TFFs. A proper choice of $B^\|_{2;ρ}$ can make all the TFFs agree with the lattice QCD predictions. A prediction of $|V_{\rm ub}|$ has also been presented by using the extrapolated TFFs, which indicates that a larger $B^{\|}_{2;ρ}$ leads to a larger $|V_{\rm ub}|$. To compare with the BABAR data on $|V_{\rm ub}|$, the longitudinal leading-twist DA $ϕ_{2;ρ}^\|$ prefers a doubly-humped behavior.

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arXiv2014

Revisiting the Pion Leading-Twist Distribution Amplitude within the QCD Background Field Theory

We study the pion leading-twist distribution amplitude (DA) within the framework of SVZ sum rules under the background field theory. To improve the accuracy of the sum rules, we expand both the quark propagator and the vertex $(z\cdot \tensor{D})^n$ of the correlator up to dimension-six operators in the background field theory. The sum rules for the pion DA moments are obtained, in which all condensates up to dimension-six have been taken into consideration. Using the sum rules, we obtain $\left<ξ^2\right>|_{\rm 1\;GeV} = 0.338 \pm 0.032$, $\left<ξ^4\right>|_{\rm 1\;GeV} = 0.211 \pm 0.030$ and $\left<ξ^6\right>|_{\rm 1\;GeV} = 0.163 \pm 0.030$. It is shown that the dimension-six condensates shall provide sizable contributions to the pion DA moments. We show that the first Gegenbauer moment of the pion leading-twist DA is $a^π_2|_{\rm 1\;GeV} = 0.403 \pm 0.093$, which is consistent with those obtained in the literature within errors but prefers a larger central value as indicated by lattice QCD predictions.

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arXiv2014

$V_{cb}$ from the semileptonic decay $B\to D \ell \barν_{\ell}$ and the properties of the $D$ meson distribution amplitude

The improved QCD light-cone sum rule (LCSR) provides an effective way to deal with the heavy-to-light transition form factors (TFFs). Firstly, we adopt the improved LCSR approach to deal with the $B\to D$ TFF $f^{+}(q^2)$ up to twist-4 accuracy. Due to the elimination of the most uncertain twist-3 contribution and the large suppression of the twist-4 contribution, the obtained LCSR shall provide us a good platform for testing the $D$-meson leading-twist DA. For the purpose, we suggest a new model for the $D$-meson leading-twist DA ($ϕ_{3D}$), whose longitudinal behavior is dominantly determined by a parameter $B$. Moreover, we find its second Gegenbauer moment $a^D_2\sim B$. Varying $B$ within certain region, one can conveniently mimic the $D$-meson DA behavior suggested in the literature. Inversely, by comparing the estimations with the experimental data on the $D$-meson involved processes, one can get a possible range for the parameter $B$ and a determined behavior for the $D$-meson DA. Secondly, we discuss the $B\to D$ TFF at the maximum recoil region and present a detailed comparison of it with the pQCD estimation and the experimental measurements. Thirdly, by applying the LCSR on $f^{+}(q^2)$, we study the CKM matrix element $\Vcb$ together with its uncertainties by adopting two types of processes, i.e. the $B^0/\bar{B}^0$-type and the $B^{\pm}$-type. It is noted that a smaller $B \precsim 0.20$ shows a better agreement with the experimental value on $\Vcb$. For example, for the case of $B=0.00$, we obtain $|V_{cb}|(B^0/\bar{B}^0-{\rm type})=(41.28 {^{+5.68}_{-4.82}} {^{+1.13}_{-1.16}}) \times 10^{-3}$ and $|V_{cb}|(B^{\pm}-{\rm type})=(40.44 {^{+5.56}_{-4.72}} {^{+0.98}_{-1.00}}) \times 10^{-3}$, whose first (second) uncertainty comes from the squared average of the mentioned theoretical (experimental) uncertainties.

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arXiv2014

Hadronic decays of the spin-singlet heavy quarkomium under the principle of maximum conformality

The principle of maximum conformality (PMC) provides a way to eliminate the conventional renormalization scale ambiguity in a systematic way. By applying the PMC scale setting, all non-conformal terms in perturbative series are summed into the running coupling, and one obtains a unique, scale-fixed prediction at any finite order. In the paper, we make a detailed PMC analysis for the spin-singlet heavy quarkoniums decay (into light hadrons) at the next-to-leading order. After applying the PMC scale setting, the decay widths for all those cases are almost independent of the initial renormalization scales. The PMC scales for $η_c$ and $h_c$ decays are below $1$ GeV, in order to achieve a confidential pQCD estimation, we adopt several low-energy running coupling models to do the estimation. By taking the MPT model, we obtain: $Γ(η_{c} \to LH)=25.09^{+5.52}_{-4.28}$ MeV, $Γ(η_{b} \to LH)=14.34^{+0.92}_{-0.84}$ MeV, $Γ(h_{c} \to LH)=0.54^{+0.06}_{-0.04}$ MeV and $Γ(h_{b} \to LH)=39.89^{+0.28}_{-0.46}$ KeV, where the errors are calculated by taking $m_{c}\in[1.40\rm GeV,1.60\rm GeV]$ and $m_{b}\in[4.50\rm GeV,4.70\rm GeV]$. These decay widths agree with the principle of minimum sensitivity estimations, in which the decay widths of $η_{c,b}$ are also consistent with the measured ones.

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arXiv2014

Hadronic production of $Ξ_{cc}$ at a fixed-target experiment at the LHC

In the paper, we present a detailed discussion on the $Ξ_{cc}$ production at a fixed target experiment at the LHC (After@LHC). The doubly charmed baryon $Ξ_{cc}$ is produced via the channel, ${\rm Proton} + {\rm Proton}\toΞ_{cc}+X$. In estimating its hadroproduction, we discuss three dominant subprocesses, e.g. $g+g\to Ξ_{cc} +\bar{c} +\bar{c}$, $g+c\to Ξ_{cc}+\bar{c}$ and $c+c\to Ξ_{cc}+g$. During the production, it shall first generate a binding diquark and then form the $Ξ_{cc}$ baryon by grabbing soft light-quarks or gluons. We observe that both the two diquark configurations $(cc)[^3S_1]_{\bf\bar 3}$ and $(cc)[^1S_0]_{\bf 6}$ can have sizable contributions to the $Ξ_{cc}$ production. Large number of $Ξ_{cc}$ events can be generated at the After@LHC, whose total production cross section is larger than that of the SELEX experiment by about thirty-five times. It may also possible to study the properties of $Ξ_{bc}$ at the After@LHC. More specifically, we shall have about $8.3 \times 10^6$ $Ξ_{cc}$ events/year and $1.8 \times 10^4$ $Ξ_{bc}$ events/year when its integrated luminosity approaches to $2$ fb$^{-1}$/year. Thus, in addition to SELEX and LHC, the After@LHC shall provide another useful platform for studying the baryon properties.

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