We present measurements of $pi^-$ and $pi^+$ elliptic flow, $v_2$, at midrapidity in Au+Au collisions at $sqrt{s_{_{rm NN}}} =$ 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry, $A_{ch}$, based on data from
the STAR experiment at RHIC. We find that $pi^-$ ($pi^+$) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins at $sqrt{s_{_{rm NN}}} = text{27 GeV}$ and higher. At $sqrt{s_{_{rm NN}}} = text{200 GeV}$, the slope of the difference of $v_2$ between $pi^-$ and $pi^+$ as a function of $A_{ch}$ exhibits a centrality dependence, which is qualitatively similar to calculations that incorporate a chiral magnetic wave effect. Similar centrality dependence is also observed at lower energies.
Assuming the newly observed $Z_c(3900)$ to be a molecular state of $Dbar D^*(D^{*} bar D)$, we calculate the partial widths of $Z_c(3900)to J/psi+pi;; psi+pi;; eta_c+rho$ and $Dbar D^*$ within the light front model (LFM). $Z_c(3900)to J/psi+pi$ is th
e 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 ${1oversqrt 2}(Dbar D^*+D^*bar D)$, the partial width of $Z_c(3900)to Dbar D^*$ is rather small, but the rate of $Z_c(3900)topsi(2s)pi$ is even larger than $Z_c(3900)to J/psipi$. 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.
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 $Sigma_bto Sigma_c$. Assuming the reasonable quark-diquark structure where th
e two light quarks constitute an axial vector, we calculate the widths of semi-leptonic decay $Sigma_{b}toSigma_c e u_e$ and non-leptonic decay modes $Sigma_{b}toSigma_c +M$ (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 $Sigma_{b}toSigma_c$ transition under the heavy quark limit. Our numerical results indicate that $Gamma(Sigma_{b}toSigma_c e u_e)$ is about $1.38times10^{10}{rm s}^{-1}$ and $Gamma(Sigma_{b}toSigma_c +M)$ is slightly below $1times10^{10}{rm s}^{-1}$ which may be accessed at the LHCb detector. By the flavor SU(3) symmetry we estimate the rates of $Omega_btoOmega_c$. We suggest to measure weak decays of $Omega_btoOmega_c$, because $Omega_b$ does not decay via strong interaction, the advantage is obvious.
The mixing of $eta-eta$ or $eta-eta-G$ 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 $BR(Dtoeta+bar l+ u_l)$ and $BR(D_stoeta(eta)+bar l+ u_l)$ have been measured, thus we are able to determine the $eta-eta$ 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 $BR(Dtoeta+bar l+ u_l)$ is measured, we can further determine all the mixing parameters for $eta-eta-G$. As more data are accumulated, the determination will be more accurate. In this work, we obtain the transition matrix elements of $D_{(s)}to eta^{(prime)}$ using the light-front quark model whose feasibility and reasonability for such processes have been tested.
In this work we calculate the branching ratios of semi-leptonic and non-leptonic decays of $Lambda_b$ into light baryons ($p$ and $Lambda$), as well as the measurable asymmetries which appear in the processes, in the light front quark model (LFQM). I
n 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 $Lambda_btoLambda+J/psi$ 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.
Only two isospin-singlet scalar mesons $f_0(600)$ ($sigma$) 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 ${1oversqrt 2}(ubar u+dbar d)$ and $sbar s$. Is this picture rig
ht? Generally, it is considered that $f_0(600)$ mainly consists of ${1oversqrt 2}(ubar u+dbar d)$, if so, the dominant component of $f_0(980)$ should be $sbar s$. The recent measurement of the CLEO collaboration on the branching ratio of $D_sto f_0(980) e^+ u_e$ 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 $qbar q$ structure. We calculate the form factors of $D_sto f_0(980)$ 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 $phi$. The obtained mixing angle shows that the $sbar s$ component in $f_0(980)$ may not be dominant.
It has been suggested that the high symmetries in the Schrodinger equation with the Coulomb or harmonic oscillator potentials may remain in the corresponding relativistic Dirac equation. If the principle is correct, in the Dirac equation the potentia
l should have a form as ${(1+beta)over 2}V(r)$ where $V(r)$ is ${-e^2over r}$ for hydrogen atom and $kappa r^2$ for harmonic oscillator. However, in the case of hydrogen atom, by this combination the spin-orbit coupling term would not exist and it is inconsistent with the observational spectra of hydrogen atom, so that the symmetry of SO(4) must reduce into SU(2). The governing mechanisms QED and QCD which induce potential are vector-like theories, so at the leading order only vector potential exists. However, the higher order effects may cause a scalar fraction. In this work, we show that for QED, the symmetry restoration is very small and some discussions on the symmetry breaking are made. At the end, we briefly discuss the QCD case and indicate that the situation for QCD is much more complicated and interesting.
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. Th
ere 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.
In this work we evaluate the cross section of the process $e^+e^-to J/psi eta_c$ at energy $sqrt{s}approx 10.6$ GeV in the Bethe-Salpeter formalism. To simplify our calculation, the heavy quark limit is employed. Without taking the beyond-leading-ord
er contribution(s) into account, the cross section calculated in this scenario is comparable with the experimental data. We also present our prediction for the cross section of double bottomonium production $e^+e^-to Upsilon(1S)eta_b$ for the energy range of $sqrt{s}approx (25 hbox{-} 30)$ GeV which may be experimentally tested, even though there is no facility of this range available at present yet.
In this work we investigate the weak $Lambda_{b}toLambda_c$ semi-leptonic and non-leptonic decays. The light-front quark model and diquark picture for heavy baryons are adopted to evaluate the $Lambda_{b}toLambda_c$ transition form factors. In the he
avy quark limit we study the Isgur-Wise function. By fitting the data of the semi-leptonic process we obtain the mass of the light scalar diquark as 817 MeV. The numerical predictions on the branching ratios of non-leptonic decay modes $Lambda_{b}toLambda_c M$ and various polarization asymmetries are made. A comparison with other approaches is discussed.
