We investigate various search strategies for light vector boson $X$ in $\mathcal{O}(10)~{\rm MeV}$ mass range using $J/Ψ$ associated channels at BESIII and Belle II: (i) $J/Ψ\to η_c X$ with $10^{10} J/Ψ$s at BESIII, (ii) $J/Ψ(η_c +X) +\ell \bar{\ell}$ production at Belle~II, and (iii) $J/Ψ+X$ with the displaced vertex in $X\to e^+e^-$ decay are analyzed and the future sensitivities at Belle II with 50 ${\rm ab}^{-1}$ luminosity are comprehensively studied. By requiring the displaced vertex to be within the beam pipe, the third method results in nearly background-free analysis, and the vector boson-electron coupling and the vector boson mass can be probed in the unprecedented range, $10^{-4}\leq |\varepsilon_e| \leq 10^{-3}$ and $9~{\rm MeV}\leq m_X\leq 100 {\rm MeV}$ with 50 ${\rm ab}^{-1}$ at Belle II. This covers the favored signal region of $^8{\rm Be}^*$ anomaly recently reported by Atomki experiment with $m_X \simeq 17~{\rm MeV}$.
A brief report of some recent experimental developments concerning the $X$, $Y$ and $Z$ charmoniumlike mesons states and other puzzling states from the BaBar, Belle, BESIII and CDF experiments is presented.
We present precise theoretical predictions for the absolute branching fractions of $Λ_c^+ \to Λ\ell^+ ν_\ell\,(\ell=e,μ)$ decays in the covariant confined quark model. This study is motivated by two recent and accurate measurements of the absolute branching fractions of $Λ_c^+ \to p K^- π^+$ and $Λ_c^+ \to Λe^+ ν_e$ by the Belle Collaboration at the KEKB and by the BESIII Collaboration at the BEPCII. Our predictions for the branching fractions are consistent with both experimental results. We also provide detailed numerical results for differential decay distributions and polarization observab…
We present, how a systematic study of $B \to D\ell N$ ($D \to K \ell N$) decays with $\ell=μ,τ$, at Belle II (BESIII) can provide unambiguous signature of a heavy neutrino $N$ and/or constrain its mixing with active neutrinos $ν_\ell$, which is parameterized by $|U_{\ell N}|^2$. Our constraint on $|U_{μN}|^2$ that can be achieved from the full Belle II data is comparable with what can be obtained from the much larger data set of the upgraded LHCb. Additionally, our method offers better constraint on $|U_{μN}|^2$ for mass of sterile neutrino $m_N < 2$ GeV. We can also probe the Dirac and Majora…
The $O$(MeV) spin-1 U-boson has been proposed to mediate the interaction among electron-positron and $O$(MeV) dark matter, in order to account for the 511 keV $γ$-ray observation by SPI/INTEGRAL. In this paper the observability of such kind of U-boson at BESIII is investigated through the processes $e^+e^- \to U γ$ and $e^+e^- \to J/Ψ\to e^+e^- U$. We find that BESIII and high luminosity B-factories have the comparable capacity to detect such U-boson. If U-boson decays mainly into dark matter, i.e. invisibly, BESIII can measure the coupling among U-boson and electron-positron $g_{eR}$ (see tex…
A new charged state, called $Z_c(3900)$ has been recently observed by BESIII collaboration in $J/ψπ^{\pm}$ channel. The same has been confirmed by Belle (called Z(3894.5 in the Belle paper). In this short note we discuss probable interpretations of this charmonium like state which we call Z(3900).
We present a comprehensive investigation on the possibility of the search for new force mediator $X$ boson in $e^+e^-$ collision and $J/ψ$ decay at the BESIII experiment. The typical interactions of $X$ boson coupling to leptons and quarks are explored. The production and decay properties of this $X$ particle, the product/decay chains $e^+e^-\to Xγ\to e^+e^-γ$ and $J/ψ\to Xγ\toμ^+μ^-γ$, and exclusion limits on the reduced coupling strength parameters as functions of $X$ boson mass are presented. With the data set of tens of fb$^{-1}~e^+e^-$ or $10^{10}~J/ψ$, we find that the exclusion limits o…
With a design luminosity of 50 ab$^{-1}$ and detectors with tracking capabilities extending beyond 1 m, the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more. We show that for models of dark photons and other light vector bosons, Belle II will be successful in probing regions of parameter space which are as of now unexplored by any experiment. In addition, for models where the vector boson couples sub-dominantly to the electron and quarks as compared to muons, e…
We study the possibilities on the search of the light and weakly interacting gauge boson in the gauged $L_μ- L_τ$ model. Introducing the kinetic mixing at the tree-level, the allowed parameter regions for the gauge coupling and kinetic mixing parameter are presented. Then, we analyze one photon plus missing event within the allowed region and show that search for the light gauge boson will be possible at Belle-II experiment. We also analyze neutrino trident production process in neutrino beam experiments.
The large rate of the $J/ψ+η_c$ production observed by the Belle collaboration has posed a serious challenge to our understanding of the quarkonium. We examine a scenario that there exists a light scalar boson around 5 GeV, with an enhanced coupling solely to the charm quark. Such a scenario would explain the Belle anomaly. It also predicts a significant increase in $J/ψ$ plus open charm pair production. An immediate test for the scalar boson is to look for a peak around 5 GeV in the recoil mass spectrum of $J/ψ$, because the scalar boson can also be produced in association with the $J/ψ$. Fin…
The $ O(GeV)$ extra $ U(1)$ gauge boson named U-boson, has been proposed to mediate the interaction among leptons and dark matter (DM), in order to account for the observations by PAMELA and ATIC. In such kind of models, the extra U(1) gauge group can be chosen as $U(1)_{L_i-L_j}$ with $L_i$ the $i-$th generation lepton number. This anomaly-free model provides appropriate dark matter relic density and boost factor required by experiments. In this work the observability of such kind of U-boson at BESIII detector is investigated through the processes $ e^ + e^ - \to Uγ$, followed by $U\to e^+e^-…
We discuss the feasibility of detecting the gauge boson of the $U(1)_{L_μ-L_τ}$ symmetry, which possesses a mass in the range between MeV and GeV, at the Belle-II experiment. The kinetic mixing between the new gauge boson $Z'$ and photon is forbidden at the tree level and is radiatively induced. The leptonic force mediated by such a light boson is motivated by the discrepancy in muon anomalous magnetic moment and also the gap in the energy spectrum of cosmic neutrino. Defining the process $e^{+} e^{-} \rightarrow γZ' \rightarrow γν\barν~(missing~energy)$ to be the signal, we estimate the numbe…
$L_μ-L_τ$ gauge boson ($Z'$) with a mass in the MeV to GeV region can resolve not only the muon $g-2$ excess, but also the gap in the high-energy cosmic neutrino spectrum at IceCube. It was recently proposed that such a light gauge boson can be detected during the Belle II experiment with a luminosity of 50 ab$^{-1}$ by the $e^+ e^- \to γ+\slashed{E}$ process through the kinetic mixing with the photon, where the missing energy $\slashed{E}$ is from the $Z' \to \barνν$ decays. We study the phenomenological implications when a pair of singlet vector-like leptons carrying different $L_μ- L_τ$ cha…
We propose that the $γ+ E \hspace{-.5em}/\;\:$ signal at the Belle-II will be a smoking gun for supersymmetry (SUSY) in the presence of a gauged $U(1)_{L_μ-L_τ}$ symmetry. A striking consequence of breaking the enhanced symmetry in the limit of degenerate (s)leptons is the nondecoupling of the radiative contribution of heavy charged sleptons, appearing in SUSY, to the $γ- Z^\prime$ kinetic mixing. The signal process, $e^+ e^- \rightarrow γZ^\prime \rightarrow γ+ E \hspace{-.5em}/\;\:$, is an outcome of this ubiquitous feature. We take into account the severe constraints on gauged $U(1)_{L_μ-L_…
Motivated by the long-lasting $3.5σ$ discrepancy in the anomalous magnetic moment of muon, we consider a new muon-specific force mediated by a light gauge boson, $X$, with mass $m_X < 2m_μ$ and the coupling constant $g_X \sim (10^{-4}, 10^{-3})$. We show that the Belle~II experiment has a robust chance to probe such a light boson in $e^+ e^- \to μ^+ μ^- + X$ channel and cover the most interesting parameter space explaining the discrepancy with the planned target luminosity, $\int dt \ {\cal L}=50~{\rm ab^{-1}}$. The clean signal of muon-pair plus missing energy at Belle II can be a smoking gun…
Experimental measurements collected by the BABAR, Belle, and LHCb experiments on different observables associated with the semileptonic transition $b \to c τ\barν_τ$, indicate the existence of disagreement respect with the Standard Model predictions. We analyse the charged scalar boson contributions to these charged-current $B$ meson anomalies within the framework of two Higgs doublet model with the most general Yukawa couplings to quarks and leptons from the third generation, involving left-handed and right-handed (sterile) neutrinos. We perform a phenomenological study of the Yukawa coupling…
A careful reanalysis is made on $e^+e^-\to X(4660)\to (Λ_c\barΛ_c)/(ψ'ππ)$ processes, aiming at resolving the apparent conflicts between Belle and BESIII data above $Λ_c\barΛ_c$ threshold. We use a model containing a Breit-Wigner resonance and $Λ_c\barΛ_c$ four-point contact interactions, with which the enhancement right above the $Λ_c\barΛ_c$ threshold is well explained by a virtual pole generated by $Λ_c\barΛ_c$ attractive final state interaction, located at $M_V=4.566\pm0.007$ GeV. Meanwhile, $X(4660)$ remains to be a typical Breit-Wigner resonance, and is hence of confinement nature. Our a…
In this talk, we present the recent study on the charmoniumlike states from the e^+e^- colliders, including BESIII, Belle, BaBar, and CLEOc. The talk covers the X(3872) from the Y(4260) radiative transition, the Y states from the initial-state-radiation processes and from e+e- to pi+pi-h_c, and the charged Z_c states.
Very recent experimental information obtained from the Belle experiment, along with that accumulated by the BABAR and LHCb experiments, has shown the existence of anomalies in the ratios $R(D)$ and $R(D^{*})$ associated with the charged-current transition $b \to c τ\barν_τ$. Although the Belle measurements are in agreement with the standard model (SM) predictions, the new experimental world averages still exhibit a tension. In addition, the $D^\ast$ longitudinal polarization $F_L(D^\ast)$ related with the channel $B \to D^\ast τ\barν_τ$ observed by the Belle Collaboration and the ratio $R(J/ψ)…
In this work, we present the mass spectrum of higher charomona around and above 4.6 GeV by adopting the unquenched potential model. We perform a combined fit to the updated experimental data of $e^+e^- \to ψ(2S)π^+π^-$ and $e^+e^-\to Λ_c\barΛ_c$. To understand the "platform" structure observed in the range of $4.57 \sim 4.60$ GeV existing in the $Λ_c\barΛ_c$ invariant mass spectrum of $e^+e^-\to Λ_c\barΛ_c$ of BESIII, we introduce two resonances in this combined fit to the $e^+e^- \to ψ(2S)π^+π^-$ and $e^+e^-\to Λ_c\barΛ_c$, which have resonance parameters, $m_{Y_1}=4585\pm2$ MeV, $Γ_{Y_1}=29.…
Motivated by the newly observed resonance $X(2600)$ by BESIII Collaboration, we examine the trigluon glueball interpretation for it in the framework of QCD sum rules. We evaluate the mass spectra of the trigluon glueballs with quantum numbers $0^{-+}$ and $2^{-+}$ up to dimension 8 condensate in the operator product expansion. Our numerical results indicate that the mass of the $2^{-+}$ trigluon glueball is about $2.66\pm 0.06$ GeV, which is consistent with the mass of the X(2600) within the uncertainties, while $0^{-+}$ has a mass of $2.01\pm0.14$ GeV. The possible decay channels of the $2^{-…
Many new states in the charmonium mass region were recently discovered by BaBar, Belle, CLEO-c, CDF, D0, BESIII, LHCb and CMS Collaborations. We use the QCD Sum Rule approach to study the possible structure of some of these states.
Dark showers from strongly interacting dark sectors that confine at the GeV scale can give rise to novel signatures at $e^+e^-$ colliders. In this work, we study the sensitivity of $B$ factory experiments to dark showers produced through an effective interaction arising from a heavy off-shell mediator. We show that a prospective search for displaced vertices from GeV-scale long-lived particles at Belle II can improve the sensitivity to dark showers substantially compared to an existing search at BaBar. We compare the sensitivity of searches for displaced signals to searches for promptly produc…
In this work, we predict the spectroscopy behavior of these light unflavored vector mesons with masses at the range of $2.4\sim 3$ GeV, which are still missing in the experiment. By presenting their mass spectrum and studying their two-body Okubo-Zweig-lizuka allowed decay widths, we discuss the possible experimental evidences of these discussed states combining with the present experimental data. Especially, we strongly suggest that our experimental colleagues carry out the exploration of these higher states via the $e^+e^-$ annihilation into light mesons. It is obvious that BESIII and Belle …
Inspired by the observed Y(2175) state, we predict its non-strange partner Y(1915), which has a resonance structure with mass around 1915 MeV and width about $317\sim 354$ MeV. Experimental search for Y(1915) is proposed by analyzing the $ωf_0(980)$ or $ωππ$ invariant mass spectrum of the $e^+e^-\to ωf_0(980), ωππ$ and $J/ψ\to ηωf_0(980)$ processes, which are accessible at Belle, BaBar, BESIII and forthcoming BelleII. Considering similarity between two families, the comparison of the mass spectra of $ω$ and $ϕ$ families can provide important information on the 1D state of $ϕ$ family, $ϕ(1910)$…
Dalitz decays of vector heavy quarkonia into $χ_{QJ}(1P)$ in the Bethe-Salpeter approach
Hebei University（河北大学）；Hebei Vocational University of Industry and Technology（河北工业职业技术大学）；Harbin Institute of Technology（哈尔滨工业大学）；Northwestern Polytechnical University（西北工业大学）
The properties of the light vector meson states around 2.0 GeV have been poorly understood for a long time, which has become a barrier to the expansion to higher light vector meson spectrum. Recently, the BESIII collaboration released the measurements of the $e^+ e^- \to ωπ^0$ and $e^+ e^- \to ρη^{\prime}$ reactions above 2.0 GeV, both of which are ideal processes to study the isovector $ρ$ meson family. In this work, through carrying out a combined analysis of the Born cross section data for the above two processes with the theoretical support on mass spectrum, and production and strong decay…
We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/ψ$, $Υ$, $ρ^0$, $ω,ϕ$, \ldots) into four charged leptons ($2(e^+e^-)$, $2(μ^+μ^-)$, $2(τ^+τ^-)$, $e^+e^-μ^+μ^-$, $e^+e^-τ^+τ^-$, \ldots) at lowest order in QED. In contrast to the case of vector meson decay into a single pair of leptons, the lepton mass must be retained in these four-lepton decay channels to cutoff the mass singularity. Owing to more pronounced collinear enhancement, the branching fractions of vector mesons decays into $ 2(e^+e^-)$ are considerably greater than those for decays into $2(μ…
The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the $μτ$ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the $τ$ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensi…
Inelastic dark matter is an interesting scenario for light thermal dark matter which is fully consistent with all cosmological probes as well as direct and indirect dark matter detection. The required mass splitting between dark matter $χ_1$ and its heavier twin $χ_2$ is naturally induced by a dark Higgs field which also provides a simple mechanism to give mass to the dark photon $A'$ present in the setup. The corresponding dark Higgs boson $h'$ is naturally the lightest dark sector state and therefore decays into Standard Model particles via Higgs mixing. In this work we study signatures with…
In this work, we provide a simultaneous and accurate description of the $π^+π^-$ and $π^{\pm} J/ψ$ invariant mass distributions of the recent BESIII data on $e^+ e^- \to J/ψ\; π^+ π^-$ together with the $e^+ e^- \to J/ψ\; K^+K^-$ cross sections at $e^+e^-$ center-of-mass energies $q=4.23$ GeV and $q=4.26$ GeV. The rescattering effects between pions in the S and D-waves are taken into account through the Muskhelishvili-Omnès formalism. Since the physical region of the $ππ$ invariant mass extends above 1 GeV, the important $K\bar{K}$ intermediate state in the S-wave is implemented through couple…
We analyze the flavor structure of composite vector bosons arising in a model of vectorlike technicolor, often called hypercolor (HC), with eight flavors that form a one-family content of HC fermions. Dynamics of the composite vector bosons, referred to as HC rho in this paper, are formulated together with HC pions by the hidden local symmetry (HLS), in a way analogous to QCD vector mesons. Then coupling properties to the standard model (SM) fermions, which respect the HLS gauge symmetry, are described in a way that couplings of the HC rhos to the left-handed SM quarks and leptons are given by…
A detailed analysis to find a missing $ψ(4S)$ is made by utilizing the recent precise mesurements of the cross section for the process $e^+e^-\to ψ(2S)π^+π^-$ by Belle. Assuming three resonances $Y(4360)$, $Y(4660)$, and $ψ(4S)$ to fit the data, we obtain the resonance parameters for $ψ(4S)$ as $m=4243$ MeV and $Γ=16 \pm 31$ MeV showing a narrow state as predicted before. A combined fit to the data $e^+ e^- \to ψ(2S) π^+ π^-, \ h_c π^+ π^-$, and $χ_{c0} ω$ is also performed to obtain the similar resonance parameters of $ψ(4S)$. The upper limit of the branching ratio is fitted to be $\mathcal{B…
The anomaly found in the excited $^8\text{Be}$ nuclear transition to its ground state is attributed to a spin-1 gauge boson $X(16.7)$. To hunt for this boson, we propose two traps: $e^+e^-\to Xγ$ and $J/ψ\to Xγ$, both following with $X\to e^+e^-$ decay. We adopt the "vector minus axial-vector" interaction hypothesis. Analysis on the $X(16.7)$ decay length, production rates, differential distribution with respect to the $e^+e^-$ invariant-mass spectrum, and the signal-to-noise ratios (SNR) after the smearing at BESIII detector are discussed in detail. Given the coupling strength of $X$ to vecto…
We study the $B_s \to π^+ π^-$ and $B_d \to K^+ K^-$ decays in the standard model and the family non-universal $Z^\prime$ model. Since none of the quarks in final states is the same as the initial quark, these decay modes can occur only via power-suppressed annihilation diagrams. Despite the consistence of the standard model prediction with the available data, there is a surviving room for a light $Z^\prime$ boson. Taking into account the $Z^\prime$ contribution, we find theoretical results for branching fractions can better accommodate the data. With the relevant data, we also derive a constr…
We propose a search for $B$ meson decays to a baryon plus missing energy at the Belle II experiment to probe supersymmetry with a GeV-scale lightest neutralino ${\tildeχ_1^0}$ and $R$-parity violation (RPV). We perform analytic computations of the signal branching fractions in the framework of effective field theory, with a single nonzero RPV operator $λ''_{ij3}\bar{U}_{i}^c\bar{D}_{j}^c\bar{D}_3^c$, where $i,j=1,2$. The hadronic form factors are calculated using an SU(3) phenomenological Lagrangian approach for the proton, as well as several hyperons and charmed baryons. Since the decay of th…
We study here the interaction of $D \bar D^*$ in the isospin $I=1$ channel in the light of recent theoretical advances that allow to combine elements of the local hidden gauge approach with heavy quark spin symmetry. We find that the exchange of light $q \bar q$ is OZI suppressed and, thus, we concentrate on the exchange of heavy vectors and of two pion exchange. The latter is found to be small compared to the exchange of heavy vectors, which then determines the strength of the interaction. A barely $D\bar{D}^*$ bound state decaying into $η_cρ$ and $πJ/ψ$ is found. At the same time we reanalyz…
We consider the strangeness-changing decays of hyperons into another baryon and missing energy which is carried away by a pair of invisible spinless bosons. Pursuing a model-independent approach and taking into account constraints from the kaon sector, we find that these hyperon modes can have large rates, especially if the bosons have parity-odd effective couplings to light quarks. In that case the rates could attain values which are well within the expected reach of the currently running BESIII experiment. Since the branching fractions of hyperon decays with missing energy are tiny in the st…
The observation of $Z_c(3900)$ by the BESIII collaboration in the invariant mass spectrum of $J/ψπ^\pm$ in $e^+e^-\to J/ψπ^+π^-$ at the center of mass 4.260 GeV suggests the existence of a charged $\bar D D^*+D\bar D^*$ molecular state with $I(J^P)=1(1^+)$, which could be an isovector brother of the famous X(3872) and an analogue of $Z_b(10610)$ claimed by the Belle Collaboration. We demonstrate that this observation provides strong evidence that the mysterious Y(4260) is a $\bar{D}D_1(2420) +D\bar{D}_1(2420)$ molecular state. Especially, we show that the decay of this molecule naturally popul…
We consider low-scale leptogenesis via right-handed neutrinos $N$ coupled to a $Z'$ boson, with gauged $U(1)_{B-L}$ as a simple realization. Keeping the neutrinos sufficiently out of equilibrium puts strong bounds on the $Z'$ coupling strength and mass, our focus being on light $Z'$ and $N$, testable in the near future by SHiP, HPS, Belle II, and at the LHC. We show that leptogenesis could be robustly falsified in a large region of parameter space by the double observation of $Z'$ and $N$, e.g. in the channel $pp\to Z' \to NN$ with displaced $N$-decay vertex, and by several experiments searchi…
A $Σ^*$ state with spin-parity $J^P = 1/2^-$ with mass and width around $1380$ MeV and $120$ MeV, refereed to as the $Σ^*_{1/2^-}(1380)$, has been predicted in several pentaquark models and inferred from the analysis of CLAS $γp$ data. In the present work, we discuss how one can employ the $Λ^+_c \to ηπ^+ Λ$ decay to test its existence, as well as to study the $Σ^*(1385)$ state with $J^P = 3/2^+$. Because the final $π^+ Λ$ system is in a pure isospin $I = 1$ combination, the $Λ^+_c \to ηπ^+ Λ$ decay can be an ideal process to study these $Σ^*$ resonances. In particular, we show that the decay …
Probing the isospin structure and low-lying resonances in $Λ_c^+ \to n\bar{K}^0 π^+$ decays
School of Physics, Zhengzhou University（郑州大学物理学院）；School of Physics and Electronics, Henan University（河南大学物理与电子学院）；School of Physics, Henan Normal University（河南师范大学物理学院）
通过研究Λ_c^+ → n ar{K}^0 π^+衰变，探索低能重子光谱中的未解之谜和ar{K}N系统的异ospin动力学，利用耦合通道的chiral单元ary方法分析该衰变过程，揭示N(1535)和Λ(1670)的动态生成，并发现N(1535)的窄峰和Λ(1670)的深凹结构，支持其分子解释。
The cross section of $e^+e^- \rightarrow ηJ/ψ$ has been measured by BESIII and Belle experiments. Fit to the $e^+e^- \rightarrow ηJ/ψ$ line shape, three resonant structures are evident. The parameters for the three resonant structures are $M_{1}=(3980\pm17\pm7)$ MeV/$c^{2}$, $Γ_{1}=(104\pm32\pm13)$ MeV; $M_{2}=(4219\pm5\pm4)$ MeV/$c^{2}$, $Γ_{2}=(63\pm9\pm3)$ MeV; $M_{3}=(4401\pm12\pm4)$ MeV/$c^{2}$, $Γ_{3}=(49\pm19\pm4)$ MeV, where the first uncertainties are statistical and the second systematic. We attribute the three structures to $ψ(4040)$, $Y(4220)$ and $ψ(4415)$ states. The branching fr…
