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1.
Coupling constants of all vector mesons are determined in QCD by means of a new QCD sum-rule method. The results are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainf =202 MeV,f K*=216 MeV,f D*=212±22 MeV,f B*=138±42 MeV, and . Based on this approach the spin-flavour symmetry for the heavy quark systems are also discussed.Supported by Bundesministerium für Forschung und Technologie  相似文献   

2.
It is suggested that a low-mass magnetic monopole of Dirac chargeg=(137/2)e may be interacting with ac-quark's magnetic dipole moment to produce Zeeman splitting of meson states. The massM 0=2397 MeV of the monopole is in contrast to the 1016-GeV monopoles of grand unification theories (GUT). It is shown that shell structure of energyE n =M 0+1/4nM 0+ exists for meson states. The presence of symmetric meson states leads to the identification of the shell structure. The possible existence of the 2397-MeV magnetic monopole is shown to quantize quark masses in agreement with calculations of quantum chromodynamics (QCD). From the shell structure of meson states, the existence of two new mesons is predicted:(1814±50 MeV) withI G(J PC =0+(0–+) and c (3907±100 MeV) withJ PC =0–+. The presence of shell structure for baryon states is shown.  相似文献   

3.
The strange quark mass is calculated from QCD sum rules for the divergence of the vector as well as axialvector current in the next-next-to-leading logarithmic approximation. The determination for the divergence of the axial-vector current is found to be unreliable due to large uncertainties in the hadronic parametrisation of the two-point function.From the sum rule for the divergence of the vector current, we obtain a value of (1 GeV)=189±32 MeV, where the error is dominated by the unknown perturbativeO( s 3 ) correction. Assuming a continued geometric growth of the perturbation series, we findm s =178±18 MeV. Using both determinations ofm s , together with quark-mass ratios from chiral perturbation theory, we also give estimates of the light quark massesm u andm d.  相似文献   

4.
A K Giri  R Mohanta 《Pramana》1997,49(2):231-238
We have studied some of the two body nonleptonic decays ofB meson in the context of heavy quark effective theory using factorization hypothesis. Treatinga 1 as a free parameter, we have obtained its value asa 1=0.822±0.045, by correlating the experimental and predicted branching ratio for process. With this value ofa 1 the branching ratios obtained for other decay channels are in good agreement with the experiment. The decay constant ofD meson is extracted to be 280.82 MeV. Heavy quark spin symmetry has also been tested.  相似文献   

5.
We study the flavour-singlet pseudoscalar mesons from first principles using lattice QCD. With N f=2 flavours of light quarks, this is the so-called η 2 meson and we discuss the phenomenological status of this meson. Using maximally twisted-mass lattice QCD, we extract the mass of the η 2 meson at two values of the lattice spacing for lighter quarks than previously discussed in the literature. We are able to estimate the mass value in the limit of light quarks with their physical masses.  相似文献   

6.
The study of the properties of inclusive production ofD s mesons and of events in which a and a muon are present in the same jet provides two independent measurements of the probability,f s w , for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ 0 decays. The combined value of these measurements isf s w =0.19±0.06±0.08. From the flight distance distributions ofD s and of (-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB s 0 meson lifetime. Combining these measurements with a previous result based on the study ofD s- events, theB s 0 meson lifetime is measured to be: 0.96±0.37 ps.  相似文献   

7.
8.
At a qualitative level, it is well known that QCD featuring a large number of quark flavors must differ drastically from actual QCD. However, it is possible to consider the large-Nf limit (where Nf is the number of light flavors in QCD) such that the basic dynamics of the system remains unchanged. This is the region of chiral perturbation theory, where the limit Nf → ∞ is simultaneously the limit of a large number of colors, Nc. Features are indicated that make it possible, in such a situation, to compare analytically the same quantity in a simplified model of actual QCD and in the large-Nf limit, and methods are proposed for calculating these features. Calculations in the limit Nf → ∞ are of no use in assessing quantities of the theory at small N f.  相似文献   

9.
We calculate the , (P is the light pseudoscalar meson, V the light vector meson) form factors in the large-recoil limit in the perturbative QCD approach, including both the vector (axial vector) and tensor operators. In general there are two leading components and for the B meson wave functions. We consider both contributions of them. Sudakov effects ( and threshold resummation) are included to regulate the soft end-point singularity. By choosing the hard scale as the maximum virtualities of the internal particles in the hard b quark decay amplitudes, Sudakov factors can effectively suppress the long-distance soft contribution. The hard contribution can be dominant in these approaches. Received: 27 December 2002 / Published online: 5 May 2003 RID="a" ID="a" e-mail: lucd@mail.ihep.ac.cn RID="b" ID="b" e-mail: yangmz@mail.ihep.ac.cn  相似文献   

10.
We have studied the andK systems centrally produced in proton proton collisions at 300 GeV/c and +/p proton collisions at 85 GeV/c using the CERN spectrometer. Clear evidence forS */f o(975) production is observed. An analysis performed on the + mass spectrum in the 1.0 GeV region, using a coupled channel formalism, shows that it is possible to describe theS */f o(975) effect with one single resonance once interference of theS */f o(975) with theS-wave background is introduced. The resultingS */f o(975) parameters arem o =979±4MeV,g =0.28±0.04,g K =0.56±0.18 corresponding to a pole position on sheet II at (1001±2)–i(36±4) MeV. Evidence is also found for a structure having a mass of 1472±12 MeV and a width of 195±33 MeV.  相似文献   

11.
TheW andQ 2 dependence of the transverse momentum of the forward-going hadrons in deep inelastic neutrino charged current interactions on neon is studied. The data were obtained by exposing BEBC filled with a Ne/H2 mixture to the CERN SPS wide-band neutrino beam. The data on average transverse momentum are compared to a model which includes first order QCD, intrinsic quark momentum in the nucleon and Fermi motion, as well as a simple model for hadronization. The model is found to describe the data well. Values of s =0.16±0.02(stat)±0.02(syst.)±0.03(frag.) at an averageQ 2 of 15.4±0.4 GeV2/c2 and (stat.) –90 +100 (syst.) –90 +130 , (frag.) MeV/v for three flavours are extracted.  相似文献   

12.
13.
Using an operator product expansion (OPE) in the inverse of the heavy quark massM Q and a dispersive approach, we rederive theB andB * couplings and the Isgur-Wise function predicted by the infinite mass effective theory (IMET). We find that, at the subtraction pointM Q and using VDM for the spectral function, these observables are governed by the universal light quark condensate. We also find that the corrections induced by finite values ofM c andM b are large and are due to the splitting b between the ground state and its radial excitation. We review the determinations of the different decay constants, couplings and masses from QCD spectral sum rules (QSSR). Forf B andf D , we conclude the optimum average:f B =(1.59±0.09±0.27)f andf D =(1.31±0.12)f , where the main error is due to the quark mass, while the first one inf B is due to the non-perturbative terms and to the choice of the continuum thresholdt c from the onset of sum rule variable stability until thet c -stability regions. We also find that the vector coupling V satisfies approximately the IMETM Q 3/2 mass dependence scaling law, whilef P obeys in units of GeV:f P/f(4.6±0.4)M Q –1/2 (1–1.56/M Q +0.88/M Q 2 ), forM Q M c . We also predict the flavour independence:M P -M Q 0.6-0.7 GeV andM V -M Q 0.7-0.8 GeV of the mass differences between the mesons and the corresponding quark. Finally we find that theBDev e form factorf +(0)(0.55±0.10) deviates from the naive expectation (f +(0)=1).  相似文献   

14.
We study the behavior of the QCD effective coupling α s in the low-energy region by exploiting the conventional meson spectrum within a relativistic quantum-field model based on analytical confinement of quarks and gluons. The spectra of quark-antiquark and two-gluon bound states are defined by using a master equation similar to the ladder Bethe-Salpeter equation. A new, independent and specific infrared-finite behavior of QCD coupling is found below energy scale ∼1 GeV. Particularly, an infrared-fixed point is extracted at α s (0) ≅ 0.757 for confinement scale Λ = 345 MeV. We provide a new analytic estimate of the lowest-state glueball mass. As applications, we also estimate masses of some intermediate and heavy mesons as well as the weak-decay constants of light mesons. By introducing only a minimal set of parameters (the quark masses m f and Λ) we obtain results in reasonable agreement with recent experimental data in a wide range of energy scale ∼0.1–10 GeV. We demonstrate that global properties of some low-energy phenomena may be explained reasonably in the framework of a simple relativistic quantum-field model if one guesses correct symmetry structure of the quark-gluon interaction in the confinement region and uses simple forms of propagators in the hadronisation regime. The model may serve a reasonable framework to describe simultaneously different sectors in low-energy particle physics.  相似文献   

15.
We extend our previous investigation about the flavor mixing or the OZI violating process in the light quark systems with the use of the generalized Nambu-Jona-Lasinio model incorporating theU A (1) anomaly. The OZI breaking effects newly studied in the meson sector include the and meson decay constants, their couplings with nucleon as well as the masses and the mixing property of the scalar mesons. As for the baryon sector, we reexamine the strangeness content of the proton and the -N sigma term N by taking into account the interactions between the constituent quarks. It is found that the short-range spin-spin interaction between the quarks gives anO(10 MeV)-enhancement for the theoretical value of the sigma term. Anomalous quark contents of other octet and decuplet baryons (hyperons) are also examined. It is shown that the axial anomaly induces the anomalous quark contents which are not expected in the naive quark model, while the short-range interaction between the quarks acts to suppress (enhance) the quark contents of the decuplet (octet) baryons. All the results indicate that the following picture holds systematically:m s is so large that (i) the strangeness mixing induced by the anomaly is considerably suppressed and that (ii) the naive chiral perturbation does not work in the strange sector even in the tree level of the meson fields (largeN c limit). The spin problem of nucleon, which is another subject related to the flavor mixing, is also examined with the use of our effective model.This paper is a modified version of the paper SUNY-NTG-89-49, RYU-THP-89-2 (August 1989)  相似文献   

16.
17.
We perform a QCD sum rule analysis for the light scalar meson σ   (f0(600)f0(600)) with a tetraquark current related to the instanton picture for QCD vacuum. We demonstrate that instanton current, including equal weights of scalar and pseudoscalar diquark–antidiquarks, leads to a strong cancelation between the contributions of high dimension operators in the operator product expansion (OPE). Furthermore, in the case of this current direct instanton contributions do not spoil the sum rules. Our calculation, obtained from the OPE up to dimension 10 operators, gives the mass of σ-meson around 780 MeV.  相似文献   

18.
From the pole dominance approximation for transformation an estimate of the M d or the mass difference of D L 0 and D s 0 meson has been found out. The results obtained are close to that of Donoghue et al. Two gamma decay width of D0 meson has also been calculated. Further calculations from the box diagram approach for this meson have been carried out by modifying the CKM matrix in the light of recent observation of top quark massm t=174 GeV while maintaining the prediction for the K0 meson undisturbed.  相似文献   

19.
We calculate the leptonic constant for the pseudoscalar ground state of the B c meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy quark current in nonrelativistic QCD as matched with full QCD.  相似文献   

20.
From a number of qualitative conjectures, the constantsm e ,c, , and a spin(8) gauge field theory, I derive the following particle masses (quark masses are constituent masses) and force constants: up quark mass=312.7542 MeV; down quark mass=312.7542 MeV; proton mass=938.2626 MeV; neutrino masses (all types)=0; muon mass=104.76 MeV; strange quark mass=523 MeV; charmed quark mass=1989 MeV; tauon mass=1877 MeV; bottom quark mass=5631 MeV; top quark mass=129.5 GeV;W + mass=80.87 GeV;W mass=80.87 GeV;W 0 mass=99.04 GeV; fine structure constant= 1/137.036082; weak constant times the proton mass squared M p 2 =0.97×10–5; color constant=0.6286. From the pion mass in addition, I derive the Planck mass (1–1.6)×1019 GeV, so that the gravitational constant times the proton mass squared GM p 2 (3.6–8.8)×10–39.  相似文献   

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