arXiv subjects

Zheng-Tao Wei

Publications and source records attributed to Zheng-Tao Wei.

At least 19 recordsLinked to original sources

arXiv2018

The semi-leptonic and non-leptonic weak decays of $Λ_b^0$

The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon $Λ_b^0$. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of $Λ^0_b$ into baryons $Λ^+_c$, $Λ$, $p$, and $n$. The diquark approximation is adopted so that the methods developed in the $B$ meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors $f_3, ~g_3$ can be extracted and are found to be non-negligible. The semi-leptonic processes of $Λ^0_b\to Λ^+_c(p)l^-\barν_l$ are calculated and the results are consistent with the experiment. We study the non-leptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant $α_s$. We calculate the non-leptonic decays of $Λ^0_b$ into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

hep-ph↗

arXiv2016

The decay of $Λ_b\rightarrow p~K^-$ in QCD factorization approach

With only the tree level operator, the decay of $Λ_b\rightarrow pK$ is predicted to be one order smaller than the experimental data. The QCD penguin effects should be taken into account. In this paper, we explore the one-loop QCD corrections to the decay of $Λ_b\to pK$ within the framework of QCD factorization approach. For the baryon system, the diquark approximation is adopted. The transition hadronic matrix elements between $Λ_b$ and $p$ are calculated in the light front quark model. The branching ratio of $Λ_b\rightarrow pK$ is predicted to be about $4.85\times 10^{-6}$ which is consistent with experimental data $(4.9\pm 0.9)\times 10^{-6}$. The CP violation is about 5\% in theory.

hep-ph↗

arXiv2013

Is $Z_c(3900)$ a molecular state

Assuming the newly observed $Z_c(3900)$ to be a molecular state of $D\bar D^*(D^{*} \bar D)$, we calculate the partial widths of $Z_c(3900)\to J/ψ+π;\; ψ'+π;\; η_c+ρ$ and $D\bar D^*$ within the light front model (LFM). $Z_c(3900)\to J/ψ+π$ is the channel by which $Z_c(3900)$ was observed, our calculation indicates that it is indeed one of the dominant modes whose width can be in the range of a few MeV depending on the model parameters. Similar to $Z_b$ and $Z_b'$, Voloshin suggested that there should be a resonance $Z_c'$ at 4030 MeV which can be a molecular state of $D^*\bar D^*$. Then we go on calculating its decay rates to all the aforementioned final states and as well the $D^*\bar D^*$. It is found that if $Z_c(3900)$ is a molecular state of ${1\over\sqrt 2}(D\bar D^*+D^*\bar D)$, the partial width of $Z_c(3900)\to D\bar D^*$ is rather small, but the rate of $Z_c(3900)\toψ(2s)π$ is even larger than $Z_c(3900)\to J/ψπ$. The implications are discussed and it is indicated that with the luminosity of BES and BELLE, the experiments may finally determine if $Z_c(3900)$ is a molecular state or a tetraquark.

hep-ph↗

arXiv2013

Constraints of unparticle physics parameters from $K^0-\bar K^0$ mixing

The neutral kaon meson mixing plays an important role in test of the Standard Model (SM) and new physics beyond it. Scale invariant unparticle physics induces a flavor changing neutral current (FCNC) transition of $K^0-\bar K^0$ oscillation at the tree level. In this study, we investigate the scale invariant unparticle physics effects on the $K^0-\bar K^0$ mixing. Based on the current experimental data, we give constraints of $K^0-\bar K^0$ mixing on the unparticle parameters.

hep-ph↗

arXiv2012

$Σ_{b}\toΣ_c$ and $Ω_b\toΩ_c$ weak decays in the light-front quark model

The successful operation of LHC provides a great opportunity to study the processes where heavy baryons are involved. {In this work we mainly study} the weak transitions of $Σ_b\to Σ_c$. Assuming the reasonable quark-diquark structure where the two light quarks constitute an axial vector, we calculate the widths of semi-leptonic decay $Σ_{b}\toΣ_c eν_e$ and non-leptonic decay modes $Σ_{b}\toΣ_c +M$ (light mesons) in terms of the light front quark model. We first construct the vertex function for the concerned baryons and then deduce the form factors which are related to two Isgur-Wise functions for the $Σ_{b}\toΣ_c$ transition under the heavy quark limit. Our numerical results indicate that $Γ(Σ_{b}\toΣ_c eν_e)$ is about $1.38\times10^{10}{\rm s}^{-1}$ and $Γ(Σ_{b}\toΣ_c +M)$ is slightly below $1\times10^{10}{\rm s}^{-1}$ which may be accessed at the LHCb detector. By the flavor SU(3) symmetry we estimate the rates of $Ω_b\toΩ_c$. We suggest to measure weak decays of $Ω_b\toΩ_c$, because $Ω_b$ does not decay via strong interaction, the advantage is obvious.

hep-ph↗

arXiv2011

A solution to Higgs naturalness

The Standard Model (SM) is usually considered to be unnatural because the scalar Higgs mass receives a quadratic divergent correction. We suggest a new way to solve the naturalness problem from point of view of renormalization group method. Our approach is illustrated through the familiar $ϕ^4$ theory. A renormalization group equation for scalar field mass is proposed by introducing a subtraction scale. We give a non-trivial prediction: the Higss mass at short-distance is a damping exponential function of the energy scale. It follows from a characteristic of the SM that the couplings to Higgs are proportional to field masses, in particular the Higgs self-interactions. In the ultraviolent limit, the Higgs mass approaches to a mass called by Veltman mass which is at the order of the electroweak scale. The fine-tuning is not necessary. The Higgs naturalness problem is solved by radiative corrections themselves.

hep-ph↗

arXiv2010

Re-Study on the wave functions of $Υ(nS)$ states in LFQM and the radiative decays of $Υ(nS)\to η_b+γ$

The Light-front quark model (LFQM) has been applied to calculate the transition matrix elements of heavy hadron decays. However, it is noted that using the traditional wave functions of the LFQM given in literature, the theoretically determined decay constants of the $Υ(nS)$ obviously contradict to the data. It implies that the wave functions must be modified. Keeping the orthogonality among the $nS$ states and fitting their decay constants we obtain a series of the wave functions for $Υ(nS)$. Based on these wave functions and by analogy to the hydrogen atom, we suggest a modified analytical form for the $Υ(nS)$ wave functions. By use of the modified wave functions, the obtained decay constants are close to the experimental data. Then we calculate the rates of radiative decays of $Υ(nS)\to η_b+γ$. Our predictions are consistent with the experimental data on decays $Υ(3S)\to η_b+γ$ within the theoretical and experimental errors.

hep-ph↗

arXiv2010

Determining the $η-η'$ mixing by the newly measured $BR(D(D_s)\toη(η')+\bar l+ν_l$

The mixing of $η-η'$ or $η-η'-G$ is of a great theoretical interest, because it concerns many aspects of the underlying dynamics and hadronic structure of pseudoscalar mesons and glueball. Determining the mixing parameters by fitting data is by no means trivial. In order to extract the mixing parameters from the available processes where hadrons are involved, theoretical evaluation of hadronic matrix elements is necessary. Therefore model-dependence is somehow unavoidable. In fact, it is impossible to extract the mixing angle from a unique experiment because the model parameters must be obtained by fitting other experiments. Recently $BR(D\toη+\bar l+ν_l)$ and $BR(D_s\toη(η')+\bar l+ν_l)$ have been measured, thus we are able to determine the $η-η'$ mixing solely from the semileptonic decays of D-mesons where contamination from the final state interactions is absent. Thus we hope that the model-dependence of the extraction can be somehow alleviated. Once $BR(D\toη'+\bar l+ν_l)$ is measured, we can further determine all the mixing parameters for $η-η'-G$. As more data are accumulated, the determination will be more accurate. In this work, we obtain the transition matrix elements of $D_{(s)}\to η^{(\prime)}$ using the light-front quark model whose feasibility and reasonability for such processes have been tested.

hep-ph↗

arXiv2009

Evaluating decay Rates and Asymmetries of $Λ_b$ into Light Baryons in LFQM

In this work we calculate the branching ratios of semi-leptonic and non-leptonic decays of $Λ_b$ into light baryons ($p$ and $Λ$), as well as the measurable asymmetries which appear in the processes, in the light front quark model (LFQM). In the calculation, we adopt the diquark picture and discuss the justifiability of applying the picture in our case. Our result on the branching ratio of $Λ_b\toΛ+J/ψ$ is in good agreement with data. More predictions are made in the same model and the results will be tested in the future experiments which will be conducted at LHCb and even ILC.

hep-ph↗

arXiv2009

Whether new data on $D_s\to f_0(980) e^+ ν_e$ can be understood if $f_0(980)$ consists of only the conventional $q\bar{q}$ structure

Only two isospin-singlet scalar mesons $f_0(600)$ ($σ$) and $f_0(980)$ exist below 1 GeV, so that it is natural to suppose that they are two energy eigenstates which are mixtures of ${1\over\sqrt 2}(u\bar u+d\bar d)$ and $s\bar s$. Is this picture right? Generally, it is considered that $f_0(600)$ mainly consists of ${1\over\sqrt 2}(u\bar u+d\bar d)$, if so, the dominant component of $f_0(980)$ should be $s\bar s$. The recent measurement of the CLEO collaboration on the branching ratio of $D_s\to f_0(980) e^+ ν_e$ provides an excellent opportunity to testify the structure of $f_0(980)$, namely whether the data can be understood as long as it consists of mainly the conventional $q\bar q$ structure. We calculate the form factors of $D_s\to f_0(980)$ in the light-front quark model (LFQM) and the corresponding branching ratio of the semileptonic decay. By fitting the data, we obtain the mixing angle $ϕ$. The obtained mixing angle shows that the $s\bar s$ component in $f_0(980)$ may not be dominant.

hep-ph↗

arXiv2009

Interpretation of the "$f_{D_s}$ puzzle" in SM and beyond

The recent measurement on the decay constant of $D_s$ shows a discrepancy between theory and experiment. We study the leptonic and semileptonic decays of $D$ and $D_s$ simultaneously within the standard model by employing a lightfront quark model. There is space by tuning phenomenological parameters which can explain the "$f_{D_s}$ puzzle" and do not contradict other experiments on the semileptonic decays. We also investigate the leptonic decays of D and $D_{s}$ with a new physics scenario, unparticle physics. The unparticle effects induce a constructive interference with the standard model contribution. The nontrivial phase in unparticle physics could produce direct CP violation which may distinguish it from other new physics scenarios.

hep-ph↗

arXiv2009

Probing unparticle theory via lepton flavor violating process $J/ψ\to ll'$ at BESIII

The lepton flavor violating process $J/ψ\to ll' (l\neq l')$ serves as an ideal place to probe the unparticle theory. Such process can only occur at loop level in the Standard model (SM), so that should be very suppressed, by contrast in unparticle scenario, it happens at tree level and its contribution may be sizable for practical measurement. Moreover, the BESIII will offer the largest database on $J/ψ$ which makes more accurate measurements possible. Furthermore, for such purely leptonic decays background is relatively low and signal would be cleaner. Our work carefully investigates the possibility of observing such processes from both theoretical and experimental aspects.

hep-ph↗

arXiv2008

FCNC-induced semileptonic decays of $J/ψ$ in the Standard Model

In this work, we calculate the form factors for $J/ψ\to \bar{D}^{(*)0}$ induced by the flavor changing neutral currents (FCNC) in terms of the QCD sum rules. Making use of these form factors, we further calculate the branching fractions of semileptonic decays $J/ψ\to \bar{D}^{(*)0} l ^+ l^-$ ($l=e, μ$). In particular, we formulate the matrix element $ $ with $T_{μν}$ being a tensor current, which was not fully discussed in previous literature. Our analysis indicates that if only the standard model (SM) applies, the production of single charmed mesons at the present electron-positron colliders is too small to be observed even the resonance effects are included, therefore if an anomalous production rates are observed, it would be a hint of new physics beyond SM. Even though the predicted branching ratios are beyond the reach of present facilities which can be seen from a rough order estimate, the more accurate formulation of the three point correlation function derived in this work has theoretical significance and the technique can also be applied to other places. In analog to some complicated theoretical derivations which do not have immediate phenomenological application yet, if the future experiments can provide sufficient luminosity and accuracy, the results would be helpful.

hep-ph↗

arXiv2008

Charm Physics - A Field Full with Challenges and Opportunities

In this review, we discuss some interesting issues in charm physics which is full with puzzles and challenges. So far in the field there exist many problems which have not obtained satisfactory answers yet and more unexpected phenomena have been observed at the present facilities of high energy physics. Charm physics may become an ideal place for searching new resonances and studying non-perturbative QCD effects, moreover probably is an area to explore new physics beyond the Standard Model. More data will be available at BESIII, B-factories, LHC and even future ILC which may open a wide window to a better understanding of the nature.

hep-ph↗

arXiv2008

Contribution of final state interaction to the branching ratio of $B\to J/ψD$

To testify the validity of the perturbative QCD (pQCD) and investigate its application range, one should look for a suitable process to do the job. $B\to J/ψD$ is a promising candidate. The linear momentum of the products is relatively small, so that there may exist a region where exchanged gluons are soft and the perturbative treatment may fail, so that the non-perturbative effect would be significant. We attribute such non-perturbative QCD effects into the long-distance final state interaction (FSI) which is estimated in this work. We find that the contribution from the FSI to the branching ratio is indeed sizable and may span a rather wide range of $10^{-6}\sim 10^{-5}$, and cover a region where the pQCD prediction has the same order. A more accurate measurement on its branching ratio may provide important information about the application region of pQCD and help to clarify the picture of the inelastic rescattering (i.e. FSI) which is generally believed to play an important role in B decays.

hep-ph↗

arXiv2008

Neutrino decay as a possible interpretation to the MiniBooNE observation with unparticle scenario

In a new measurement on neutrino oscillation $ν_μ\toν_e$, the MiniBooNE Collaboration observes an excess of electron-like events at low energy and the phenomenon may demand an explanation which obviously is beyond the oscillation picuture. We propose that heavier neutrino $ν_2$ decaying into a lighter one $ν_1$ via the transition process $ν_μ\to ν_e+X$ where $X$ denotes any light products, could be a natural mechanism. The theoretical model we employ here is the unparticle scenario established by Georgi. We have studied two particular modes $ν_μ\to ν_e+\Un$ and $ν_μ\to ν_e+\barν_e+ν_e$. Unfortunately, the number coming out from the computation is too small to explain the observation. Moreover, our results are consistent with the cosmology constraint on the neutrino lifetime and the theoretical estimation made by other groups, therefore we can conclude that even though neutrino decay seems plausible in this case, it indeed cannot be the source of the peak at lower energy observed by the MiniBooNE collaboration and there should be other mechanisms responsible for the phenomenon.

hep-ph↗

arXiv2008

Weak decays of $J/ψ$: the non-leptonic case

In our previous study, we calculated the transition from factors of $J/ψ\to D^{(*)}_{(s)}$ using the QCD sum rules. Based on the factorization approximation, the obtained form factors can be applied to evaluate the weak non-leptonic decay rates of $J/ψ\to D^{(*)}_{(s)}+M$, where $M$ stands for a light pseudoscalar or vector meson. We predict that the branching ratio for inclusive non-leptonic two-body weak decays of $J/ψ$ which are realized via the spectator mechanism, can be as large as $1.3 \times 10^{-8}$, in particular, the branching ratio of $J/ψ\to D^{*\pm}_s+ρ^\mp$ can reach $5.3 \times 10^{-9}$. Such values will be marginally accessed by the ability of BESIII which will begin running very soon.

hep-ph↗

arXiv2008

A Possibility of Search for New Physics at LHCb

It is interesting to search for new physics beyond the standard model at LHCb. We suggest that weak decays of doubly charmed baryon such as $Ξ_{cc}(3520)^+, Ξ_{cc}^{++}$ to charmless final states would be a possible signal for new physics. In this work, we consider two models, i.e. the unparticle and $Z'$ as examples to study such possibilities. We also discuss the cases for $Ξ^0_{bb}, Ξ_{bb}^-$ which have not been observed yet, but one can expect to find them when LHCb begins running. Our numerical results show that these two models cannot result in sufficiently large decay widths, therefore if such modes are observed at LHCb, there must be a new physics other than the unparticle or $Z'$ models.

hep-ph↗