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Cheng-Ping Shen

Publications and source records attributed to Cheng-Ping Shen.

12 recordsLinked to original sources
arXiv2025

Emergence of the exotic bottomoniumlike state $Y(10650)$ and support from Belle and Belle II data

Near-threshold exotic hadrons are usually associated with $S$-wave hadron-hadron dynamics, while higher partial waves are expected to be strongly suppressed by the centrifugal barrier. We show that this expectation can be overturned in the bottomonium sector. In a coupled-channel meson exchange framework combined with the complex scaling method, we find a $J^{PC}=1^{--}$ pole, denoted as $Y(10650)$, generated dominantly by the $P$-wave $B^*\bar B^*$ interaction and located close to the $B^*\bar B^*$ threshold. This pole naturally accounts for the anomalous enhancement observed just above the opening of the $B^*\bar B^*$ threshold in $e^+e^-\to B^*\bar B^*$. Once its production strength is fixed by this threshold enhancement, the corresponding cross sections of $\sigma[e^+e^-\to Y(10650)\to B\bar B^*]$ are predicted by the pole residues and phase-space factors, giving a characteristic dip-or-peak structure consistent with the available Belle (II) data. We further study the hidden-bottom transition $Y(10650)\to \Upsilon(2S)\eta$ through a near-threshold $B^*\bar B^*$ loop mechanism. The resulting $\mathcal{O}(10\sim100~\mathrm{keV})$ width for $Y(10650)\to \Upsilon(2S)\eta$ is sufficient to account for the corresponding cross sections measured by Belle II. The simultaneous appearance of this state in open- and hidden-bottom channels provides a direct experimental path to test a $P$-wave near-threshold mechanism and makes $Y(10650)$ a strong candidate for the first neutral isoscalar exotic bottomoniumlike state in the spectral gap between $\Upsilon(4S)$ and $\Upsilon(5S)$.

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arXiv2024

Toponium: the smallest bound state and simplest hadron in quantum mechanics

We explore toponium, the smallest known quantum bound state of a top quark and its antiparticle, bound by the strong force. With a Bohr radius of $8\times 10^{-18}$~m and a lifetime of $2.5 \times 10^{-25}$~s, toponium uniquely probes microphysics. Unlike all other hadrons, it is governed by ultraviolet freedom. This distinction offers novel insights into quantum chromodynamics. Our analysis reveals a toponium signal exceeding $5\sigma$ in the distribution of the cross section ratio between $e^+e^- \rightarrow b\bar{b}$ and $e^+e^- \rightarrow q\bar{q}$ ($q=b,c,s,d,u$), based on 400~fb$^{-1}$ of data collected at $\sqrt{s}\approx 341~{\rm GeV}$. This discovery enables a top quark mass measurement with an uncertainty reduced by a factor of ten compared to current precision levels. Moreover, this method improves the systematic uncertainty by at least a factor of 2.7 compared to any other possible methods.

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arXiv2024

Production of exotic hadrons in $pp$ and nuclear collisions

Exotic hadrons beyond the conventional quark model have been discovered in the past two decades. Investigations of these states can lead to deep understanding of nonperturbative dynamics of the strong interaction. In this concise review, we focus on the productions of exotic hadrons in $pp$, $p\bar p$, and nuclear collisions. Experimental observations of light nuclei and hypernuclei, as prototypes of hadronic molecules, in heavy ion collisions will also be briefly discussed.

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arXiv2024

Novel method for identifying the heaviest QED atom

The bound state of a $τ^+τ^-$ pair by the electromagnetic force is the heaviest and smallest QED atom. Since the discovery of the two lightest QED atoms more than 60 years ago, no evidence for the third one has been found. We demonstrate that the $J_τ$ ($τ^+τ^-$ atom with $J^{PC}=1^{--}$) resonance signal can be observed with a significance larger than $5σ$ including both statistical and systematic uncertainties, via the process $e^+e^-\to X^+ Y^- \slashed{E}$ ($X,\,Y=e$, $μ$, $π$, $K$, or $ρ$, and $\slashed{E}$ is the missing energy) with $1.5~{\rm ab^{-1}}$ data taken around the $τ$ pair production threshold. The $τ$ lepton mass can be measured in a precision of 2 keV with the same data sample. This is within one year's running time of the proposed super tau-charm factory or super charm-tau factory.

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arXiv2022

Mass Spectra and Semileptonic Decays of Doubly Heavy $ Ξ$ and $ Ω$ Baryons

In the framework of a non-relativistic quark model, the mass spectra of the ground and excited states of doubly heavy $Ξ$ and $Ω$ baryons are calculated. We estimate the mass difference between the $ Ω$ and corresponding $ Ξ$ baryons as $M_Ω-M_Ξ\simeq178 $ MeV for all the states containing $ cc,~bc $, or $ bb $ quarks. A simple form of the universal Isgur-Wise function, as the transition form factor between the doubly heavy baryons, is introduced. Working in the close-to-zero recoil limit, we investigate the $ b \rightarrow c $ semileptonic decay widths and branching fractions of the doubly heavy baryons. The obtained results are compared with other theoretical predictions.

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arXiv2020

The $XYZ$ states: experimental and theoretical status and perspectives

The quark model was formulated in 1964 to classify mesons as bound states made of a quark-antiquark pair, and baryons as bound states made of three quarks. For a long time all known mesons and baryons could be classified within this scheme. Quantum Chromodynamics (QCD), however, in principle also allows the existence of more complex structures, generically called exotic hadrons or simply exotics. These include four-quark hadrons (tetraquarks and hadronic molecules), five-quark hadrons (pentaquarks) and states with active gluonic degrees of freedom (hybrids), and even states of pure glue (glueballs). Exotic hadrons have been systematically searched for in numerous experiments for many years. Remarkably, in the past fifteen years, many new hadrons that do not exhibit the expected properties of ordinary (not exotic) hadrons have been discovered in the quarkonium spectrum. These hadrons are collectively known as $XYZ$ states. Some of them, like the charged states, are undoubtedly exotic. Parallel to the experimental progress, the last decades have also witnessed an enormous theoretical effort to reach a theoretical understanding of the $XYZ$ states. Theoretical approaches include not only phenomenological extensions of the quark model to exotics, but also modern non-relativistic effective field theories and lattice QCD calculations. The present work aims at reviewing the rapid progress in the field of exotic $XYZ$ hadrons over the past few years both in experiments and theory. It concludes with a summary on future prospects and challenges.

hep-ex↗
arXiv2019

QCD sum rule studies on the $s s \bar s \bar s$ tetraquark states with $J^{PC} = 1^{+-}$

We apply the method of QCD sum rules to study the structure $X$ newly observed by the BESIII Collaboration in the $ϕη^\prime$ mass spectrum in 2.0-2.1 GeV region in the $J/ψ\rightarrow ϕηη^\prime$ decay. We construct all the $s s \bar s \bar s$ tetraquark currents with $J^{PC} = 1^{+-}$, and use them to perform QCD sum rule analyses. One current leads to reliable QCD sum rule results and the mass is extracted to be $2.00^{+0.10}_{-0.09}$ GeV, suggesting that the structure $X$ can be interpreted as an $s s \bar s \bar s$ tetraquark state with $J^{PC} = 1^{+-}$. The $Y(2175)$ can be interpreted as its $s s \bar s \bar s$ partner having $J^{PC} = 1^{--}$, and we propose to search for the other two partners, the $s s \bar s \bar s$ tetraquark states with $J^{PC} = 1^{++}$ and $1^{-+}$, in the $η^\prime f_0(980)$, $η^\prime K \bar K$, and $η^\prime K \bar K^*$ mass spectra.

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arXiv2018

A possible partner state of the $Y(2175)$

We study the $Y(2175)$ using the method of QCD sum rules. There are two independent $ss\bar s\bar s$ interpolating currents with $J^{PC} = 1^{--}$, and we calculate both their diagonal and off-diagonal correlation functions. We obtain two new currents which do not strongly correlate to each other, so they may couple to two different physical states: one of them couples to the $Y(2175)$, while the other may couple to another state whose mass is about $71 ^{+172}_{-~48}$ MeV larger. Evidences of the latter state can be found in the BaBar, BESII, Belle, and BESIII experiments.

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arXiv2016

$B^*_{s,d} \to μ^+ μ^-$ and its impact on $B_{s,d} \to μ^+ μ^-$

The decay of $B^*_{s,d} \to μ^+ μ^-$~ and its impact on $B_{s,d} \to μ^+ μ^-$ is studied here. The $ μ^+ μ^-$ decay widths of vector mesons $B^*_{s,d}$ are about a factor of 700 larger than the corresponding scalar mesons $B_{s,d}$. The obtained ratio of the branching fractions $Br({B_{s,d}^*\to μ^+μ^-})/{Br({B_{s,d}\toμ^+μ^-})}$ is about $\frac{0.3 \times {\rm eV}}{{Γ(B^*_{s,d} \to B_{s,d} γ)}}$. At the same time, the hadronic contribution $B_{s,d} \to B^*_{s,d} γ\to μ^+ μ^-$ is estimated too. The relative increase of the amplitude of $B_{s,d}\to μ^+μ^-$ is about $(0.01\pm 0.006) \sqrt{\frac{{Γ(B^*_{s,d} \to B_{s,d} γ)}}{100~ {\rm eV}}}$. If we choose $Γ(B^*_{s,d} \to B_{s,d} γ)=2~$eV, the branching fractions of the vector mesons to lepton pair are $(6.2 \pm 0.6) \times 10^{-10}$ and $(1.7 \pm 0.2) \times 10^{-11}$ for $B^*_{s}$ and $B^*_{d}$ respectively. If we choose $Γ(B^*_{s,d} \to B_{s,d} γ)=200~$eV, the updated branching fractions of the scalar mesons to muon pair are $(3.78 \pm 0.25)\times 10^{-9}$ and $(1.09 \pm 0.09)\times 10^{-10}$ for $B_{s}$ and $B_{d}$ respectively. Further studies on $B^*_{s,d}$ are usefully here, including dielectron decay, two-body decay with $J/ψ$, and so on.

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arXiv2016

Sensitivity Study of Searching for $τ^- \to γμ^-$ at HIEPA

The charged lepton flavor violation process is a clean and sensitive probe of new physics beyond the Standard Model. A sensitivity study is performed to the process $τ^- \to γμ^-$ based on a 3~fb$^{-1}$ inclusive Monte Carlo sample of $e^+e^-$ collisions at a center-of-mass energy of 4.26 or 4.6~GeV, in the framework of the BESIII software system. The 90\% confidence level upper limits on $\BR(τ^- \to γμ^-)$ are estimated assuming no signal is produced. We also obtain the sensitivity on $\BR(τ^- \to γμ^-)$ as a function of the integrated luminosity, to serve as a reference for the HIEPA being proposed in China. It is found that 6.34~ab$^{-1}$ are needed to reach the current best upper limit of $4.4\times 10^{-8}$ and about 2510~ab$^{-1}$ are needed to reach a sensitivity of $10^{-9}$ if the detector design is similar to that of BESIII.

hep-ex↗
arXiv2014

Enhanced breaking of heavy quark spin symmetry

Heavy quark spin symmetry is useful to make predictions on ratios of decay or production rates of systems involving heavy quarks. The breaking of spin symmetry is generally of the order of $O({Λ_{\rm QCD}/m_Q})$, with $Λ_{\rm QCD}$ the scale of QCD and $m_Q$ the heavy quark mass. In this paper, we will show that a small $S$- and $D$-wave mixing in the wave function of the heavy quarkonium could induce a large breaking in the ratios of partial decay widths. As an example, we consider the decays of the $Υ(10860)$ into the $χ_{bJ}ω\, (J=0,1,2)$, which were recently measured by the Belle Collaboration. These decays exhibit a huge breaking of the spin symmetry relation were the $Υ(10860)$ a pure $5S$ bottomonium state. We propose that this could be a consequence of a mixing of the $S$-wave and $D$-wave components in the $Υ(10860)$. Prediction on the ratio $Γ(Υ(10860)\toχ_{b0}ω)/Γ(Υ(10860)\toχ_{b2}ω)$ is presented assuming that the decay of the $D$-wave component is dominated by the coupled-channel effects.

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