The Riddle of the f0(980) and a0(980): Are They the Quark-Antiquark States?
A list of arguments favouring quark-antiquark nature of a0(980) and f0(980) is presented.
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arXiv subjects
V. A. Nikonov
Publications and source records attributed to V. A. Nikonov.
Photoproduction of Baryons Decaying into N pi and N eta
A combined analysis of photoproduction data on γp to πN, eta N was performed including the data on K Lambda and K Sigma. The data are interpreted in an isobar model with s--channel baryon resonances and pi, rho,(omega), K, and K^* exchange in the t--channel. Three baryon resonances have a substantial coupling to eta N, the well known N(1535)S_{11}, N(1720)P_{13}, and N(2070)D_{15}. The inclusion of data with open strangeness reveals the presence of further new resonances, N(1840)P_{11}, N(1875)D_{13} and N(2170)D_{13}.
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Decays of Baryon Resonances into K Lambda, K^+ Sigma^0 and K^0 Sigma^+
Cross sections, beam asymmetries, and recoil polarisations for the reactions gamma p to K^+ Lambda ; gamma to K^+ Sigma^0, and gamma p to K^0 Sigma^+ have been measured by the SAPHIR, CLAS, and LEPS collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from pi and eta photoproduction reveals evidence for new baryon resonances in this energy region. A new P_{11} state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D_{13} states at 1870 and 2170 MeV.
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Decay $ϕ(1020)\to γf_0(980)$: analysis in the non-relativistic quark model approach
We demonstrate the possibility of a good description of the processes $ϕ(1020)\to γππ$ and $ϕ(1020)\to γf_0(980)$ within the framework of non-relativistic quark model assuming $f_0(980)$ to be dominantly quark--antiquark system. Different mechanisms of the radiative decay, that is, the emission of photon by the constituent quark (additive quark model) and charge-exchange current, are considered. We also discuss the status of the threshold theorem applied to the studied reactions, namely, the behaviour of the decay amplitude at $M_{ππ} \to m_ϕ$ and $m_{f_0}\to m_ϕ$. In conclusion the arguments favouring the $q\bar q$ origin of $f_0(980)$ are listed.
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Charmed quark component of the photon wave function
We determine the c-anti-c component of the photon wave function on the basis of (i) the data on the transitions e+ e- -> J/psi(3096), psi(3686), psi(4040), psi(4415), (ii) partial widths of the two-photon decays eta_{c0}(2979), chi_{c0}(3415), chi_{c2}(3556) -> gamma-gamma, and (iii) wave functions of the charmonium states obtained by solving the Bethe-Salpeter equation for the c-anti-c system. Using the obtained c-anti-c component of the photon wave function we calculate the gamma-gamma decay partial widths for radial excitation 2S state, eta_{c0}(3594) -> gamma-gamma, and 2P states chi_{c0}(3849), chi_{c2}(3950) -> gamma-gamma.
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Determination of quark-antiquark component of the photon wave function for u, d, s quarks
Based on the data for the transitions pi0, eta, eta' -> gamma gamma^*(Q^2) and reactions of the e^+ e^- -annihilations, e^+ e^- -> rho0, omega, phi and e^+ e^--> hadrons at 1 q anti-q (q= u, d, s) for the region 0< Q^2 <1 (GeV/c)^2.
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Observation of the Second Tensor Nonet with the L3 Experiment
This paper was withdrawn by arXiv administrators upon request of the Chairperson and Spokesperson of the L3 Collaboration.
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Radiative decays of mesons in the quark model: relativistic and non-relativistic approaches
Different conclusions about quark nature of f0(980) based on the analysis of data on the reaction phi(1020) -> gamma f0(980) make it necessary to perform detailed comparison of formulae used by various groups for the calculation of partial widths of radiative decays. We carry out a comparative analysis of methods of calculation of radiative decays like phi -> gamma f0 and phi -> gamma eta performed by F.E.Close et al., Phys. Rev. D 65, 092003 (2002), and A.V.Anisovich et al., Eur. Phys. J. A 12, 103 (2001); Yad. Fiz. 65, 523 (2002).
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D^+_s -> pi^+ pi^+ pi^- decay: the 1^3P_0 s anti-s component in scalar-isoscalar mesons
On the basis of data on the decay D^+_s -> pi^+ pi^+ pi^-, which goes dominantly via the transition D_s -> pi^+ s anti-s, we evaluate the 1^3P_0 s anti-s components in the scalar-isoscalar resonances f0(980), f0(1300), f0(1500) and broad state f0(1200-1600)$. The data point to a large s anti-s component in the f0(980): 40% < s anti-s < 70%. Nearly 30% of the 1^3P_0 s anti-s component flows to the mass region 1300-1500 MeV being shared by f0(1300), f0(1500) and broad state f0(1200-1600): the interference of these states results in a peak near 1400 MeV with the width around 200 MeV.
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Two-photon partial widths of tensor mesons
We calculate partial widths of the gamma-gamma decay of the tensor q\bar q states a_2(1320), f_2(1270), f_2(1525), their radial excitations a_2(1660), f_2(1640), f_2(1800) as well as ^3F_2 q\bar q states. Calculations are performed in the framework of the same approach which was used before for the study of radiative decays f_0(980) -> gamma-gamma, a_0(980) -> gamma-gamma and phi(1020) -> gamma-f_0(980): the assumption made is that of q\bar q structure of f_0(980) and a_0(980) [A.V. Anisovich et al., Phys. Lett. B 456, 80 (1999); Eur. Phys. J. A 12, 103 (2001)]. The description of the decay partial widths for a_2(1320), f_2(1270), f_2(1525) and f_0(980), a_0(980) is reached with the approximately equal radial wave functions, thus giving a strong argument in favour of the fact that these scalar and tensor mesons are to be classified as members of the same P-wave q\bar q multiplet.
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Radiative decays of basic scalar, vector and tensor mesons and the determination of the P-wave q\bar q multiplet
We perform simultaneous calculations of the radiative decays of scalar mesons f_0(980)-> γγ, a_0(980)-> γγ, vector meson ϕ(1020)-> γf_0(980), γa_0(980), γπ^0, γη, γη' and tensor mesons a_2(1320)-> γγ, f_2(1270)-> γγ, f_2(1525)-> γγassuming all these states to be dominantly the q\bar q ones. A good description of the considered radiative decays is reached by using almost the same radial wave functions for scalar and tensor mesons that supports the idea for the f_0(980), a_0(980) and a_2(1320), f_2(1270), f_2(1525) to belong to the same P -wave q\bar q multiplet.
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Quark-gluonium content of the scalar-isoscalar states f_0(980), f_0(1300), f_0(1500), f_0(1750), f_0(1420 ^{+150}_{- 70}) from hadronic decays
On the basis of the decay couplings f_0 -> ππ, K\bar K, ηη, ηη', which had been found before, in the study of analytical (IJ^{PC}=00^{++})-amplitude in the mass range 450-1900 MeV, we analyse the quark-gluonium content of resonances f_0(980), f_0(1300), f_0(1500), f_0(1750) and the broad state f_0(1420 ^{+ 150}_{-70}). The K-matrix technique used in the analysis makes it possible to evaluate the quark-gluonium content both for the states with switched-off decay channels (bare states, f^{bare}_0) and the real resonances. We observe significant change of the quark-gluonium composition in the evolution from bare states to real resonances, that is due to the mixing of states in the transitions f_0(m_1)-> real mesons-> f_0(m_2) responsible for the decay processes as well. For the f_0(980), the analysis confirmed the dominance of q\bar q component thus proving the n\bar n/s\bar s composition found in the study of the radiative decays. For the mesons f_0(1300), f_0(1500) and f_0(1750), the hadronic decays do not allow one to determine uniquely the n\bar n, s\bar s and gluonium components providing relative pecentage only. The analysis shows that the broad state f_0(1420 ^{+ 150}_{-70}) can mix with the flavour singlet q\bar q component only, that is consistent with gluonium origin of the broad resonance.
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Quark structure of f0(980) from the radiative decays phi(1020)->gamma f0(980), gamma eta, gamma eta', gamma pi0 and f0(980)->gamma gamma
Partial widths of the radiative decays $ϕ(1020)\toγf_0(980)$, $γη$, $γη'$, $γπ^0$ and $f_0(980)\toγγ$ are calculated assuming all mesons under consideration to be $q\bar q$ states: $ϕ(1020)$ is dominantly an $s\bar s$ state ($n\bar n$ component $\lesssim 1%$), $η$, $η'$ and $π^0$ are standard $q\bar q$ states, $η= n\bar n\cosθ- s\bar s\sinθ$ and $η'=n\bar n\sinθ+ s\bar s\cosθ$ with $θ\simeq 37^\circ$, and $f_0(980)$ is the $q\bar q$ meson with the flavour wave function $n\bar n\cosϕ+ s\bar s \sinϕ$. Calculated partial widths for the decays $ϕ\toγη$, $γη'$, $γπ^0$ are in a reasonable agreement with experiment. The measured value of the branching ratio $BR(ϕ\toγf_0(980))$ requires $25^\circ\le |ϕ|\le 90^\circ$; for the decay $f_0(980)\toγγ$ the agreement with data is reached at either $77^\circ\leϕ\le 93^\circ$ or $(-54^\circ)\leϕ\le (-38^\circ)$. Simultaneous analysis of the decays $ϕ(1020)\toγf_0(980)$ and $f_0(980)\toγγ$ provides arguments in favour of the solution with negative mixing angle $ϕ=-48^\circ\pm 6^\circ$.
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Determination of hadronic partial widths for scalar-isoscalar resonances f0(980), f0(1300), f0(1500), f_0(1750) and the broad state f0(1530^{+90}_{-250})
In the article of V.V. Anisovich et al., Yad. Fiz. 63, 1489 (2000), the K-matrix solutions for the wave IJ^{PC}=00^{++} were obtained in the mass region 450 - 1900 MeV where four resonances f0(980), f0(1300), f0(1500), f0(1750) and the broad state f0(1530^{+90}_{-250}) are located. Based on these solutions, we determine partial widths for scalar-isoscalar states decaying into the channels pi-pi, K-anti K, eta-eta, eta-eta', pi-pi-pi-pi and corresponding decay couplings.
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Quark combinatorics and meson production ratios in hadronic Z^0 decays
Rich experimental data accumulated in the past few years in the hadronic $Z^0$ decays allow one to check the quark combinatorics relations for a new type of processes, namely: quark jets in the decays $Z^0 \to q\bar q \to hadrons$. In this paper we review quark combinatorics rules for the yields of vector and pseudoscalar mesons, $V/P$, in the central and fragmentation regions of the hadronic $Z^0$ decays. It is stressed that in the central region a direct verification of quark combinatorics rules is rather problematic because of a considerable background related to the decay of highly excited resonances; however such a verification is possible in the fragmentation region, at $x_{hadron} \sim 0.5-1$, where the contribution of resonance decays is suppressed due to the rapid decrease of spectra with increasing $x_{hadron}$. It is shown that the experimental data in the fragmentation region for $ρ^0/π^0$ and $p/π^+$ are in a reasonable agreement with the predictions of quark combinatorics. The ratios of the heavy meson yields, $B^*/B$ and $D^*/D$, are also discussed: the data demonstrate a good agreement with the quark combinatorial results. We analyse the structure of the suppression parameters for strange and heavy quark productions in soft processes and estimate their order of magnitudes in the multiperipheral processes; the ratio $K^{\pm}/π^{\pm}$ at $x_{hadron}\sim 0.5-0.8$ and production probabilities of the $c\bar c$ and $b \bar b$ mesons are in a good agreement with the estimates.
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Quark combinatorics for production ratios in hadronic Z^0 decays
Model independent verification of the quark combinatorics rules, which govern the ratios of the yields of secondaries, is presented for jet processes. Because of a large number of produced resonances in the hadron jets, a test of the quark combinatorics rules is hardly possible in the central region, x_{hadron} < 0.2. However, a model-independent verification is plausible at x_{hadron} \sim 1. It is shown that for the large x_{hadron} kinematical region the quark combinatorial relations are in a reasonable agreement with data for ρ^0/π^0 and p/π^+ ratios.
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The light sigma meson
In the framework of the dispersion relation N/D-approach, we restore the low-energy pi-pi (IJ^{PC}=00^{++})-wave amplitude sewing it with the previously obtained K-matrix solution for the region 450-1900 MeV. The restored N/D-amplitude has a pole on the second sheet of the complex-s plane near the pi-pi threshold, that is the light sigma meson.
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The low-mass sigma-meson: Is it an eyewitness of confinement?
In the framework of the dispersion relation N/D-method we restore the low-energy pi-pi (IJ^{PC}=00^{++})-wave amplitude sewing it with the previously obtained K-matrix solution for the region 450--1900 MeV [V.V. Anisovich, Yu.D. Prokoshkin and A.V. Sarantsev, Phys. Lett. B389, 388 (1996)]. The restored N/D-amplitude has a pole on the second sheet of the complex-s plane, near the pi-pi threshold. We discuss the hypothesis that this low-mass pole, or the low-mass sigma-meson, corresponds to the dynamical state related to the confinement forces, that is the eyewitness of confinement.
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