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Search Results: 1 - 10 of 275095 matches for " Q. B. Li "
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Sea-quark effects in the pion charge form factor
Li, Q. B.;Riska, D. O.
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevC.77.045207
Abstract: It is shown that the data on the pion charge form factor admit the possibility for a substantial sea-quark components in the pion wave function. If the charge form factor is calculated with instant form kinematics in a constituent quark model that is extended to include explicit $(q\bar q)^2$ components in the pion wave function, that component will give the dominant contribution to the calculated $\pi^+$ charge form factor at large values of momentum transfer. The present experimental values $Q^2$ can be described well with $(q\bar q)^2$ component admixtures of up to 50%. The sensitivity of the calculated $\pi^+$ charge form factor to whether one of the quarks or one of the antiquarks is taken to be in the P-state is small.
XANES and XPS Study on Microstructure of Mn-Doped ZnO Films  [PDF]
B. Zhang, M. Li, J. Z. Wang, L. Q. Shi, H. S. Cheng
Materials Sciences and Applications (MSA) , 2013, DOI: 10.4236/msa.2013.45039
Abstract:

Microstructure of ZnO:Mn films with various Mn concentration was investigated with XANES and XPS. The experimental results revealed a substitution of Mn in ZnO and also excluded the existence of Mn oxides or metallic manganese clusters. The substitutional Mn presented a divalent state and all the ZnO:Mn films were n-type. Room temperature ferromagnetism monotonously decreases with the decrease of the electron carrier concentration. The observed ferrmagnetism should come from the carrier-mediated exchange.

Inelastic Rescattering and CP Asymmetries in D -> pi+ pi-, pi0 pi0
X. Q. Li,B. S. Zou
Physics , 1997, DOI: 10.1103/PhysRevD.57.1518
Abstract: We study the direct CP violation induced by inelastic final state interaction (FSI) rescattering in $D\to\pi\pi$ modes, and find that the resultant CP asymmetry is about $10^{-4}$ which is larger than $\epsilon'$ in the K-system. Our estimation is based on well-established theories and experiment measured data, so there are almost no free parameters except the weak phase $\delta_{13}$ in the CKM matrix.
Significance of Single Pion Exchange Inelastic Final State Interaction for D->VP Processes
X. Q. Li,B. S. Zou
Physics , 1996, DOI: 10.1016/S0370-2693(97)00308-0
Abstract: We evaluate the contribution of the final state interaction (FSI) due to single pion exchange inelastic scattering for $D^+\rightarrow \bar {K}^{0*}\pi^+$ and $D^+\rightarrow \bar K^0\rho^+$ processes. The effects are found to be very significant. The hadronic matrix elements of the weak transition are calculated in terms of the heavy quark effective theory (HQET), so are less model-dependent and more reliable.
Five-quark components in $Δ(1232)\to Nπ$ decay
Q. B. Li,D. O. Riska
Physics , 2005, DOI: 10.1103/PhysRevC.73.035201
Abstract: Five-quark $qqqq\bar q$ components in the $\Delta(1232)$ are shown to contribute significantly to $\Delta(1232)\to N\pi$ decay through quark-antiquark annihilation transitions. These involve the overlap between the $qqq$ and $qqqq\bar q$ components and may be triggered by the confining interaction between the quarks. With a $\sim$ 10% admixture of five-quark components in the $\Delta(1232)$ the decay width can be larger by factors 2 - 3 over that calculated in the quark model with 3 valence quarks, depending on the details of the confining interaction. The effect of transitions between the $qqqq\bar q$ components themselves on the calculated decay width is however small. The large contribution of the quark-antiquark annihilation transitions thus may compensate the underprediction of the width of the $\Delta(1232)$ by the valence quark model, once the $\Delta(1232)$ contains $qqqq\bar q$ components with $\sim$ 10% probability.
The Role of 5-quark Components on the Nucleon Form Factors
Q. B. Li,D. O. Riska
Physics , 2007, DOI: 10.1016/j.nuclphysa.2007.05.002
Abstract: The covariant quark model is shown to allow a phenomenological description of the neutron electric form factor, G_E^n(Q^2), in the impulse approximation, provided that the wave function contains minor (~ 3 %) admixtures of the lowest sea-quark configurations. While that form factor is not very sensitive to whether the \bar q in the qqqq\bar q component is in the P-state or in the S-state, the calculated nucleon magnetic form factors are much closer to the empirical values in the case of the former configuration. In the case of the electric form factor of the proton, G_E^p(Q^2), a zero appears in the impulse approximation close to 9 GeV^2, when the \bar q is in the P-state. That configuration, which may be interpreted as a pion loop ("cloud") fluctuation, also leads to a clearly better description of the nucleon magnetic moments. When the amplitude of the sea-quark admixtures are set so as to describe the electric form factor of the neutron, the qqqq\bar q admixtures have the phenomenologically desirable feature, that the electric form factor of the proton falls at a more rapid rate with momentum transfer than the magnetic form factor.
Possible $ΔΔ$ dibaryons in the quark cluster model
Q. B. Li,P. N. Shen
Physics , 1999, DOI: 10.1088/0954-3899/26/8/308
Abstract: In the framework of RGM, the binding energy of one channel $\Delta\Delta_{(3,0)}$($d^*$) and $\Delta\Delta_{(0,3)}$ are studied in the chiral SU(3) quark cluster model. It is shown that the binding energies of the systems are a few tens of MeV. The behavior of the chiral field is also investigated by comparing the results with those in the SU(2) and the extended SU(2) chiral quark models. It is found that the symmetry property of the $\Delta\Delta$ system makes the contribution of the relative kinetic energy operator between two clusters attractive. This is very beneficial for forming the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very important role on binding. The S-wave phase shifts and the corresponding scattering lengths of the systems are also given.
$NΩ$ and $ΔΩ$ dibaryons in SU(3) chiral quark model
Q. B. Li,P. N. Shen
Physics , 1999, DOI: 10.1007/s10050-000-5080-y
Abstract: The binding energy of the six quark system with strangeness s=-3 is investigated under the chiral SU(3) constituent quark model in the framework of $RGM$. The calculations of the single $N\Omega$ channel with spin S=2 and the single $\Delta\Omega$ channel with spin S=3 are performed. The results show that both systems could be dibaryons and the interaction induced by the chiral field plays a very important role on forming bound states in the systems considered. The phase shifts and scattering lengths in corresponding channels are also given.
Quark model approach to the $η$ meson electroproduction on the proton
Q. Zhao,B. Saghai,Z. -P. Li
Physics , 2000, DOI: 10.1088/0954-3899/28/6/312
Abstract: A recently developed quark model approach to pseudoscalar meson photoproduction is extended to electroproduction process for the $\eta$ meson in the kinematics of momentum transfer $Q^2 \leq$ 4 (GeV/c)$^2$ and total center of mass energy $W \leq$ 1.6 GeV. Existing data are well reproduced and the roles of the $S_{11}(1535)$ and $D_{13}(1520)$ resonances are closely investigated. In the study of the longitudinal excitation of the $S_{11}(1535)$ resonance, a reliable constraint on the $S_{11}(1535)$ properties is obtained by cleanly removing the electromagnetic transition from the $\gamma_{(v)} p \to S_{11}(1535) \to \eta p$ amplitude. Thus, the fitted quantities can be determined with an uncertainty of about 15%. This could be the first direct constraint on the $S_{11}(1535)$ properties in theory.
Possible Dibaryons with Strangeness s=-5
Q. B. Li,P. N. Shen
Physics , 1999, DOI: 10.1103/PhysRevC.62.028202
Abstract: In the framework of $RGM$, the binding energy of the six quark system with strangeness s=-5 is systematically investigated under the SU(3) chiral constituent quark model. The single $\Xi^*\Omega$ channel calculation with spins S=0 and 3 and the coupled $\Xi\Omega$ and $\Xi^*\Omega$ channel calculation with spins S=1 and 2 are considered, respectively. The results show following observations: In the spin=0 case, $\Xi^* \Omega$ is a bound dibaryon with the binding energy being $80.0 \sim 92.4 MeV$. In the S=1 case, $\Xi\Omega$ is also a bound dibaryon. Its binding energy is ranged from $26.2 MeV$ to $32.9 MeV$. In the S=2 and S=3 cases, no evidence of bound dibaryons are found. The phase shifts and scattering lengths in the S=0 and S=1 cases are also given.
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