arXiv subjects

Bo-Qiang Ma

Publications and source records attributed to Bo-Qiang Ma.

At least 253 records · Page 14Linked to original sources

arXiv2005

Photon-meson transition form factors of light pseudoscalar mesons

The photon-meson transition form factors of light pseudoscalar mesons $π^{0}$, $η$, and $η^{\prime}$ are systematically calculated in a light-cone framework, which is applicable as a light-cone quark model at low $Q^{2}$ and is also physically in accordance with the light-cone pQCD approach at large $Q^{2}$. The calculated results agree with the available experimental data at high energy scale. We also predict the low $Q^{2}$ behaviors of the photon-meson transition form factors of $π^{0}$, $η$ and $η^{\prime }$, which are measurable in $e+A({Nucleus})\to e+A+M$ process via Primakoff effect at JLab and DESY.

hep-ph↗

arXiv2004

Effect of Asymmetric Strange-Antistrange Sea to the NuTeV Anomaly

We calculate the strange quark and antiquark distributions of the nucleon by using the effective chiral quark model, and find that the strange-antistrange asymmetry can bring a contribution of about 60--100% to the NuTeV deviation of $\sin^{2}θ_{w}$ from the standard value measured in other electroweak processes. The results are insensitive to different inputs. The light-flavor quark asymmetry of $\bar{d}-\bar{u}$ is also investigated and found to be consistent with the experimental measurements. Therefore the chiral quark model provides a successful picture to understand the NuTeV anomaly, as well as the light-flavor quark asymmetry and the proton spin problem in previous studies.

hep-ph↗

arXiv2004

Parametrization of Neutrino Mixing Matrix in Tri-bimaximal Mixing Pattern

The neutrino mixing matrix is expanded in powers of a small parameter $λ$ in tri-bimaximal mixing pattern. We also present some applications of this parametrization, such as to the expression of the Jarlskog parameter $J$. Comparing with other parametrizations (such as the parametrization in bimaximal mixing pattern), this parametrization converges more quickly, but is of less symmetry.

hep-ph↗

arXiv2004

A New Parametrization of the Neutrino Mixing Matrix

The neutrino mixing matrix is expanded in powers of a small parameter $λ$, which approximately equals to 0.1. The meaning of every order of the expansion is discussed respectively, and the range of $λ$ is carefully calculated. We also present some applications of this new parametrization, such as to the expression of the Jarlskog parameter $J$, in which the simplicities and advantages of this parametrization are shown.

hep-ph↗

arXiv2004

Non-zero transversity distribution of the pion in a quark-spectator-antiquark model

We calculate the non-zero (naïve) T-odd transverse momentum dependent transversity distribution $h_1^{\perp}(x,\kp^2)$ of the pion in a quark-spectator-antiquark model. The final-state interaction is modelled by the approximation of one gluon exchange between the quark and the antiquark spectator. Using our model result we estimate the unsuppressed cos2$ϕ$ azimuthal asymmetry in unpolarized $π^-p$ Drell-Yan process. We find that the transverse momentum dependence of $h_1^{\perp}(x,\kp^2)$ of the pion is the same as that of $h_1^{\perp}(x,\kp^2)$ of the proton calculated from the quark-scalar-diquark model, although the $x$ dependencies of them are different from each other. This suggests a connection between cos2$ϕ$ asymmetries in Drell-Yan processes with different initial hadrons.

hep-ph↗

arXiv2004

Sigma Meson Cloud and Proton's Light Flavor Sea Quarks

We take into account the sigma meson cloud effect in the meson cloud model to calculate the distributions of light flavor sea quarks in the proton. Our calculation gives a better description of the data for $\bar{d}(x)/\bar{u}(x)$. We also provide a picture that the probability of finding a physical proton in a Fock state $|Nω> $ is reasonable small with a smaller cutoff $Λ_ω$.

hep-ph↗

arXiv2004

Exotic baryons with charm number $\pm1$ from Skyrme model

We illustrate the exotic SU(3) baryon sub-multiplets in the SU(4) baryon multiplets predicted from the flavor SU(4) collective-coordinate quantization, and investigate the exotic states with charm number $C=\pm1$ up to leading order of $1/N_c$ under chiral $SU(3)_L\times SU(3)_R$ symmetry and the heavy quark limit from bound state approach. We find that there exist the $\bar{15}$-plets and 24-plets with C=1 and the $\bar{6}$-plets, 15-plets and $15^{\prime}$-plets with $C=-1$ bounded in this approach, qualitatively consistent with predictions from the flavor SU(4) collective-coordinate quantization. By fitting one unique parameter of leading SU(3) flavor symmetry breaking term with the mass difference between $Ξ_c$ and $Σ_c$ and up to $O(m_Q^0N_c^{-1})$, we give all the average masses of baryons in $\bar{6}$-plet and 15-plet. Several general relations of these masses without any parameter are also introduced.

hep-ph↗

arXiv2004

The 35-plet Baryons from Chiral Soliton Models

We investigate the 35-plet baryons from the chiral soliton models. We find that the coupling constant for the decay of 35-plet baryons with spin 3/2 to the decuplet baryons is surprisingly small, but that for the decay to 27-plet baryons with spin 3/2 is larger. We give all the masses and widths of 35-plet baryons with spin 5/2 and suggest candidates for all nonexotic members from the available particle listings. We also focus on $Δ_{5/2}$ and $Θ_2$, which are the lightest two baryons of 35-plet with spin 5/2 and with simplest minimal pentaquark configurations. Calculations show that $Γ_{Δ_{5/2}}<$380 MeV, compared with the results from SU(2) Skyrme Model ($Γ_{Δ_{5/2}}>$800 MeV), and $Γ_{Θ_{2}}<100$ MeV if we assume that their widths are dominated by two-body decay and that $Θ^+$ has a width $Γ_{Θ^+}<25$ MeV.

hep-ph↗

arXiv2004

Decay Probability Ratio of Pentaquark Theta^+ State

The pentaquark state of $Θ^{+}(uudd\bar{s})$ has been observed to decay with two decay modes: $Θ^+\to n K^+$ and $Θ^+ \to p K^0$. The decay probability ratio of the two decay modes is studied with general symmetry consideration of isospin, spin, and parity. We arrive at a result of the ratio $\frac{Γ(Θ^+\to nK^+)}{Γ(Θ^+\to pK^0)} =\frac{(α-β)^2}{(α+β)^2}(\frac{k_1}{k_2})^{2L+1}$, which is valid for the $Θ^+$ state to be a pure isoscalar or isovector state, or an isoscalar and isovector mixing state, or an isotensor state with mixture of isoscalar and isovector components with coefficients $α$ and $β$. The dependence on spin and parity of the pentaquark $Θ^+$ state is found to be small due to small difference between the center of mass decay momenta $k_1$ and $k_2$ of the two decay modes. We also provide an analysis on the constraint of the isospin of $Θ^+$ from the absence of a peak in the $pK^+$ invariant mass distribution in the $γp \to pK^+K^-$ process. Future experimental results about the decay probability ratio may provide information about the properties of the pentaquark $Θ^+$ state.

hep-ph↗

arXiv2004

Particle-Antiparticle Asymmetries of $Λ$ Production in Hadron-Nucleon Collisions

The particle-antiparticle asymmetries of $Λ$ production in 250 GeV/c $π^{\pm}$, $K^{\pm}$, and $p$ --nucleon collisions are studied with two model parametrizations of quark to $Λ$ fragmentation functions. It is shown that the available data can be qualitatively explained by the calculated results in both the quark-diquark model and a pQCD based analysis of fragmentation functions. The differences in the two model predictions are significant for $K^{\pm}$ beams, and high precision measurements of the asymmetries with detailed $x_F$ and $P_T$ information can discriminate between different predictions.

hep-ph↗

arXiv2004

Parity of Anti-Decuplet Baryons Revisited from Chiral Soliton Models

We recalculate masses and widths of anti-decuplet baryons in the case of positive parity from chiral soliton models, provided that the member $Ξ_{3/2}$ of the anti-decuplet has a mass 1.86 GeV as reported recently. Calculations show that there are no convincing candidates for the nonexotic members of the anti-decuplet available in the baryon listings. Up to the leading order of $m_s$ and 1/$N_c$, the width formula for the decay of the anti-decuplet baryons to the octet depends only on SU(3) symmetry model-independently, except the coupling constant. Similarly we give a width formula for the decay of negative parity baryons belong to certain SU(3) baryon multiplet by pure symmetry consideration. By this formula, we find that if we have an anti-decuplet with negative parity and that the masses are the same as those given by chiral soltion models, the identification of N(1650) as $N_{\bar{10}}$ are inconsistent with experiments for $N(1650)\to Nπ$ while the widths agree with other two decay channels involving strangeness. And $Σ(1750)$ seems to be a reasonable candidate for $Σ_{\bar{10}}$.

hep-ph↗

arXiv2004

Sivers function in light-cone quark model and azimuthal spin asymmetries in pion electroproduction

We perform a calculation of Sivers function in a light-cone SU(6) quark-diquark model with both scalar diquark and vector diquark spectators. We derive the transverse momentum dependent light-cone wave function of the proton by taking into account the Melosh-Wigner rotation. By adopting one-gluon exchange, we obtain a non-vanishing Sivers function of $down$ quark from interference of proton spin amplitudes. We analyze the $\frac{|P_{h\perp}|}{M}$ weighted Sivers asymmetries in $π^+$, $π^-$ and $π^0$ electroproduction off transverse polarized proton target, averaged and not averaged by the kinematics of HERMES experiment.

hep-ph↗

arXiv2004

Contribution of asymmetric strange-antistrange sea to the Paschos-Wolfenstein relation

The NuTeV Collaboration reported a value of $\sin^{2}θ_{w}$ measured in neutrino-nucleon deep inelastic scattering, and found that the value is three standard deviations from the standard model prediction. This result is obtained under the assumption that the strange-antistrange sea quarks of nucleons are symmetric, and that the up and down quark distributions are symmetric with the simultaneous interchange of $u$$\leftrightarrow$$d$ and $p$$\leftrightarrow$$n$. We discuss the contribution of asymmetric strange-antistrange sea to the Paschos-Wolfenstein relation in the extraction of weak mixing angle $\sin^{2}θ_{w}$. We also point out that the contribution of asymmetric strange-antistrange sea should remove roughly 30--80% of the discrepancy between the NuTeV result and other determinations of $\sin^{2}θ_{w}$, when using the light-cone meson-baryon model to calculate the contribution of the strange-antistrange sea.

hep-ph↗

arXiv2004

Ratio of $\barΛ/Λ$ in Semi-inclusive Electroproduction

It is shown that the $\barΛ/Λ$ cross section ratio in semi-inclusive electroproduction of $Λ$ and $\barΛ$ hyperons in deep inelastic scattering of charged lepton on a nucleon target, can provide useful information on the quark to $Λ$ fragmentation functions. This ratio is calculated explicitly in a quark-diquark model, a pQCD based analysis, and an SU(3) symmetry model, with three different options for the contribution from the unfavored fragmentation functions. The $x$-dependence of this ratio is sensitive to the ratio of unfavored fragmentation functions over favored fragmentation functions, $D_{\bar{u}}^Λ(z)/D_{u}^Λ(z)$, whereas the $z$-dependence is sensitive to the flavor structure of the fragmentation functions, i.e., the ratio $D_u^Λ(z)/D_s^Λ(z)$. Future measurements by the HERMES Collaboration at DESY can discriminate between various cases.

hep-ph↗

arXiv2004

The 27-plet Baryons from Chiral Soliton Models

We use the perturbation method to calculate the masses and widths for 27-plet baryons with spin 3/2 from chiral soliton models. According to the masses and quantum numbers, we find all the candidates for non-exotic members of 27-plet. The calculation of the widths shows that these candidates manifest an approximate symmetry of the 27 representation of the SU(3) group, and the quantum numbers of $Ξ(1950)$ seem to be $I(J^P)={1/2}({3/2}^+)$. Up to leading order of the strange quark mass, we find that the exotic members have widths much larger than those of the anti-decuplet members.

hep-ph↗

arXiv2004

Pentaquark $Θ^*$ States in {27} Baryon Multiplet from Chiral Soliton Model

We estimate the mass and the width of pentaquark $Θ^*$ states in the 27-plet from chiral soliton models. The calculations show that the mass of $Θ^*$ is about 1.60 GeV and the width for the process $Θ^*\to {KN}$ is less than 43 MeV. We also discuss the search for the existence of $Θ^*$ states in physical processes.

hep-ph↗

arXiv2003

Pion-photon and photon-pion transition form factors in light-cone formalism

We derive the minimal Fock-state expansions of the pion and the photon wave functions in light-cone formalism, then we calculate the pion-photon and the photon-pion transition form factors of $γ^{\ast}π^{0}\to γ$ and $γ^{\ast}γ\to π^{0}$ processes by employing these quark-antiquark wave functions of the pion and the photon. We find that our calculation for the $γ^{\ast}γ\to π^{0}$ transition form factor agrees with the experimental data at low and moderately high energy scale. Moreover, the physical differences and inherent connections between the transition form factors of $γ^{\ast}π^{0}\to γ$ and $ γ^{\ast}γ\to π^{0}$ have been illustrated, which indicate that these two physical processes are intrinsically related. In addition, we also discuss the $π^{0}\to γγ$ form factor and the decay width $ \mathitΓ(π\to γγ)$ at $Q^{2}=0$.

hep-ph↗

arXiv2003

Applicability of Perturbative QCD to Pion Virtual Compton Scattering

We study explicitly the applicability of perturbative QCD (pQCD) to the pion virtual Compton scattering. It is found that there are central-region singularities introduced by the QCD running coupling constant, in addition to the end-point singularities generally existed in other exclusive processes such as the pion form factor. We introduce a simple technique to evaluate the contributions from these singularities, so that we can arrive at a judgement that these contributions will be unharmful to the applicability of pQCD at certain energy scale, i.e., the ``work point'' which is defined to determine when pQCD is applicable to exclusive processes. The applicability of pQCD for different pion distribution amplitudes are explored in detail. We show that pQCD begins to work at 10 ${GeV}^2$. If we relax our constraint to a weak sense, the work point may be as low as 4 ${GeV}^2$.

hep-ph↗