arXiv subjects

Rui-Lin Zhu

Publications and source records attributed to Rui-Lin Zhu.

12 recordsLinked to original sources

arXiv2024

Probing $B^+ \to K^+$ semi-leptonic FCNC decay with new physics effects under PQCD approach

Recently, the Belle II Collaboration reported the branching fraction $\mathcal{B}(B^+ \to K^+ \nu \bar{\nu})=(2.3\pm0.7)\times10^{-5}$ with a significance of $3.5\sigma$, which is $2.7\sigma$ above the SM expectation. Motivated by this measurement, we calculate this decay channel at the NLO and twist-3 level using the PQCD approach. By combining the lattice QCD data and our results, we obtain form factors with improved accuracy. Using these form factors, we precisely estimate the branching ratios of $B^+ \to K^+$ semileptonic FCNC decays, including $B^+ \to K^+\nu\bar\nu$ and $B^+ \to K^+\ell^+\ell^-$. To explain the anomalies in these two processes, we introduce a leptoquark model as a new physics scenario. Using five possible types of leptoquarks, we successfully explain the latest experimental measurements, and further constraints on the leptoquarks are derived.

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arXiv2017

Interpretation of the newly observed $Ω_c^0$ resonances

We study the charmed and bottomed doubly strange baryons within the heavy-quark-light-diquark framework. The two strange quarks are assumed to lie in $S$ wave and thus their total spin is 1. We calculate the mass spectra of the $S$ and $P$ wave orbitally excited states and find the $Ω_c^0 (2695)$ and $Ω_c^0 (2770)$ fit well as the $S$ wave states of charmed doubly strange baryons. The five newly $Ω_c^0(X)$ resonances observed by the LHCb Collaboration, i.e. $Ω_c^0(3000)$, $Ω_c^0(3050)$, $Ω_c^0(3066)$, $Ω_c^0(3090)$, and $Ω_c^0(3119)$, can be interpreted as the $P$ wave orbitally excited states. In heavy quark effective theory, we analyze their decays into the $Ξ^+_c K^-$ and $Ξ_c'^+ K^-$, and point out that decays of the five P-wave $Ω_c^0$ states into the $Ξ_c^+ K^-$ and $Ξ_c'^+K^-$ are suppressed by either heavy quark symmetry or phase space. The narrowness of the five newly observed $Ω_c^0(X)$ states can then be naturally interpreted with heavy quark symmetry.

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arXiv2016

Production of Charmed Tetraquarks from $B_c$ and $B$ decays

Hadronic states composed of multi-quark flavors may exist in reality since they are not prohibited by QCD. Compact four quark systems of color singlet are classified as tetraquarks. To understand the properties of these states, more theoretical and experimental efforts are needed. In this work, we study charmed tetraquarks with three light flavors using flavor $SU(3)$ symmetry. States with three different light quarks must be in a ${\bf \bar 6 }$ or a ${\bf 15}$ multiplet. We investigate the production of charmed tetraquarks $X_c$ in $B\to X_c (\overline {X}_c) P$ and $B_c \to X_c P$ decays. Whether the states with three light quarks belong to ${\bf \bar 6}$ or ${\bf 15}$ can be determined by studying various tetraquark $B$ and $B_c$ decays. We demonstrate that the decay amplitudes for these decays can be parametrized by a few irreducible SU(3) invariant amplitudes. We then derive relations for decay widths and CP violating rate difference which can be examined experimentally. Although no experimental measurement is available yet, they might be accessed at the ongoing and forthcoming experiments like the LHCb and Belle-II. Measurements of these observables can not only provide useful information for the study of exotics spectroscopy but are also valuable information towards a better understanding of some non-perturbative aspects of QCD.

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arXiv2015

A Possible Solution to the $B\to ππ$ Puzzle Using the Principle of Maximum Conformality

The measured $B_d \to π^0π^0$ branching fraction deviates significantly from conventional QCD predictions, a puzzle which has persisted for more than 10 years. This may be a hint of new physics beyond the Standard Model; however, as we shall show in this paper, the pQCD prediction is highly sensitive to the choice of the renormalization scales which enter the decay amplitude. In the present paper, we show that the renormalization scale uncertainties for $B\to ππ$ can be greatly reduced by applying the Principle of Maximum Conformality (PMC), and more precise predictions for CP-averaged branching ratios ${\cal B}(B\toππ)$ can be achieved. Combining the errors in quadrature, we obtain ${\cal B}(B_{d}\to π^0π^0)|_{\rm PMC} = \left(0.98^{+0.44}_{-0.31}\right) \times10^{-6}$ by using the light-front holographic low-energy model for the running coupling. All of the CP-averaged $B\toππ$ branching fractions predicted by the PMC are consistent with the Particle Data Group average values and the recent Belle data. Thus, the PMC provides a possible solution for the $B_d \to π^0π^0$ puzzle.

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arXiv2015

Radiative Leptonic $B_c\to γ\ell\barν$ Decay in Effective Field Theory beyond Leading Order

We study the radiative leptonic $B_c\to γ\ell\barν$ decays in the nonrelativistic QCD effective field theory, and consider a fast-moving photon. As a result the interactions with the heavy quarks can be integrated out, and thus we arrive at a factorization formula for the decay amplitude. We calculate not only the relevant short-distance coefficients at leading order and next-to-leading order in $α_s$, but also the nonrelativistic corrections at the order $|\bold{v}|^2$ in our analysis. We find out that the QCD corrections can sizably decrease the branching ratio and thus is of great importance in extracting the long-distance operator matrix elements of $B_c$. For the phenomenological application, we present our results for the photon energy, lepton energy and lepton-neutrino invariant mass distribution.

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arXiv2015

To understand the rare decay $B_s\toπ^+π^-\ell^+\ell^-$

Motivated by the LHCb measurement, we analyze the $B_s\to π^+π^-\ell^+\ell^-$ decay in the kinematics region where the pion pairs have invariant mass in the range $0.5$-$1.3$ GeV and muon pairs do not originate from a resonance. The scalar $π^+π^-$ form factor induced by the strange $\bar ss$ current is predicted by the unitarized approach rooted in the chiral perturbation theory. Using the two-hadron light-cone distribution amplitude, we then can derive the $B_s\to π^+π^-$ transition form factor in the light-cone sum rules approach. Merging these quantities, we present our results for differential decay width which can generally agree with the experimental data. More accurate measurements at the LHC and KEKB in future are helpful to validate our formalism and determine the inputs in this approach.

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arXiv2014

Understanding the cross section of $e^+e^-\to ηJ/ψ$ process via nonrelativistic QCD

Motivated by the large cross section of $e^+e^-\to ηJ/ψ$ process measured by the BESIII and Belle Collaborations recently, we evaluate this process at $\mathcal{O}(α_s^4)$ accuracy in the framework of nonrelativistic QCD. We find that the cross section at the center-of-mass energy $\sqrt{s}=4.009$ {GeV} is $34.6\mathrm{pb}$, which is consistent with the BESIII data. The comparison with the Belle data in the region from $4.0\ \mathrm{GeV}$ to $5.3\ \mathrm{GeV}$ is also presented. Concerning the $η$ and $η^\prime$ mixing and the potential gluonium component of $η^\prime$, we also estimate the rate of $e^+e^-\to η^\prime J/ψ$ process, which can be checked within the updated Belle data.

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arXiv2013

$B_c$ Exclusive Decays to Charmonium and a Light Meson at Next-to-Leading Order Accuracy

In this paper the next-to-leading order (NLO) corrections to $B_c$ meson exclusive decays to S-wave charmonia and light pseudoscalar or vector mesons, i.e. $π$, $K$, $ρ$, and $K^*$, are performed within non-relativistic (NR) QCD approach. The non-factorizable contribution is included, which is absent in traditional naive factorization (NF). And the theoretical uncertainties for their branching ratios are reduced compared with that of direct tree level calculation. Numerical results show that NLO QCD corrections markedly enhance the branching ratio with a K factor of 1.75 for $B_{c}^{\pm}\to η_{c} π^{\pm}$ and 1.31 for $B_{c}^{\pm}\to J/ψπ^{\pm}$. In order to investigate the asymptotic behavior, the analytic form is obtained in the heavy quark limit, i.e. $m_b \to \infty$. We note that annihilation topologies contribute trivia in this limit, and the corrections at leading order in $z= m_c/m_b$ expansion come from form factors and hard spectator interactions. At last, some related phenomenologies are also discussed.

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arXiv2013

Reconstructing the 125 GeV SM Higgs Boson Through $\ell\bar{\ell}γ$

To ascertain the new boson with mass near 125 {GeV} observed recently by ATLAS and CMS Collaborations to be the Standard Model Higgs, and to determine its intrinsic properties, more measurements on its various decay channels are still necessary. In this work we reanalyze the processes of the Standard Model Higgs radiative decays to lepton pairs. We find that when photon and leptons are hard, that is possessing energies larger than 1 {GeV}, the branching fractions of $H\rightarrow \ell\bar{\ell}γ(\ell=e~or~μ)$ processes are about two-thirds of the $H\rightarrowμ^+μ^-$ process. Since the lepton-pair yields of the radiative processes mainly come from the Z-boson conversion, which will greatly suppress the backgrounds, we believe the signal should be observable in presently accumulated data or in the next run of the LHC experiment, provided the Standard Model Higgs is indeed light.

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arXiv2013

Estimation of Semileptonic Decays of $B_c$ Meson to S-wave Charmonia with NRQCD

We study the semileptonic differential decay rates of $B_c$ meson to S-wave charmonia, $η_c$ and $J/Ψ$, at the next-to-leading order accuracy in the framework of NRQCD. In the heavy quark limit, $m_b \to \infty$, we obtain analytically the asymptotic expression for the ratio of NLO form factor to LO form factor. Numerical results show that the convergence of the ratio is perfect. At the maximum recoil region, we analyze the differential decay rates in detail with various input parameters and polarizations of $J/ψ$, which can now be checked in the LHCb experiment. Phenomenologically, the form factors are extrapolated to the minimal recoil region, and then the $B_c$ to charmonium semileptonic decay rates are estimated.

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arXiv2012

W Boson Inclusive Decays to Quarkonium at the LHC

In this paper, the production rates of quarkonia eta_c, J/psi, eta_b, Upsilon, B_c and B_c^* through W boson decay at the LHC are calculated, at the leading order in both the QCD coupling constant and in v, the typical velocity of the heavy quark inside of mesons. It shows that a sizable number of quarkonia from W boson decay will be produced at the LHC. Comparison with the predictions by using quark fragmentation mechanism is also discussed. Results show that, for the charmonium production through W decay, the difference between predictions by the fragmentation mechanism and complete leading order calculation is around 3%, and it is insensitive to the uncertainties of theoretical parameters; however, for the bottomonium and B_c^(*) productions, the difference cannot be ignored as the fragmentation mechanism is less applicable here due to the relatively large ratio mb/mw.

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arXiv2011

The NLO QCD Corrections to $B_c$ Meson Production in $Z^0$ Decays

The decay width of $Z^0$ to $B_c$ meson is evaluated at the next-to-leading order(NLO) accuracy in strong interaction. Numerical calculation shows that the NLO correction to this process is remarkable. The quantum chromodynamics(QCD)renormalization scale dependence of the results is obviously depressed, and hence the uncertainties lying in the leading order calculation are reduced.

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