Searcharxiv⌕ Search

arXiv subjects

N. N. Achasov

Publications and source records attributed to N. N. Achasov.

At least 91 records · Page 5Linked to original sources
arXiv2005

Shape of the $f_0(980)$ in $γγ\toπ^+π^-$

The Belle Collaboration results on the observation of the $f_0(980)$ resonance in the reaction $γγ\toπ^+π^-$ are analyzed. It is argued that they point to the presence of mechanisms which give rise to a strong distortion of the $f_0(980)$ resonance shape in comparison with the shape of a solitary Breit-Wigner resonance. It is shown that the main factors responsible for the formation of the specific, steplike, shape of the $f_0(980)$ resonance in the $γγ\toπ^+π^-$ reaction cross section are the $K^+K^-$ loop mechanism of the $f_0(980)$ coupling to the $γγ$ system and the destructive interference between the background and $f_0(980)$ resonance contributions in the $π^+π^-$ invariant mass region below the $K^+K^-$ threshold.

hep-ph↗
arXiv2005

Branching ratios of the decays of psi(3770) and Upsilon(10580) into light hadrons

Taking into account the new data on the full width of D^{\ast\pm}(2010) and the mass difference of the charged and neutral beauty mesons B^\pm, B^0,\bar B^0, the branching ratios of the decays psi(3770), Upsilon(10580) to pi^+pi^-, K bar K, rho(omega)pi, rho(omega)eta, rho(omega)eta^prime, K^ast bar K+ c.c, rho^+ rho^-, and K^ast bar K^ast are re-evaluated in the model in which the Okubo-Zweig-Iizuka rule is violated due to the real intermediate state D\bar D in case of psi(3770) and B\bar B in case of Upsilon(10580). The inclusive annihilation of psi(3770) and Upsilon(10580) into light hadrons is discussed.

hep-ph↗
arXiv2005

Role of a_1(1260) resonance in multipion decays of light vector mesons

The contribution of the a_1(1260) meson to the amplitudes of the decays rho(770) to 4 pi, omega(782) to 5 pi, and phi(1020) to 5 pi is analyzed in the chiral model of pseudoscalar, vector, and axial vector mesons based on the generalized hidden local symmetry added with the anomalous terms. The analysis shows that inclusion of a_1 meson in the intermediate states results in enhancement of the branching ratios of the above decays by the factor ranging from 1.3 to 1.9 depending on the mass of a_1 meson ranging from 1.23 GeV to m_{a_1}=m_rho sqrt{2}=1.09 GeV, the greater factor standing in case of lower mass of the a_1.

hep-ph↗
arXiv2004

Propagators of light scalar mesons

For the first time, as far as we know, in field theory are found explicit forms of propagators satisfying the Källen -- Lehmann representation. To be exact, it is shown that scalar meson propagators, taking into account a virtual intermediate state contribution to the resonance self-energy, satisfy the Källen -- Lehmann representation in the wide domain of coupling constants of the light scalar mesons with the two-particle states. It is proposed to use these propagators in routine fitting data about light scalar mesons to reveal physics underlying the light scalar mesons.

hep-ph↗
arXiv2004

Light Scalar Mesons

The crucial points of physics of light scalar mesons are discussed. The special attention is given to the chiral shielding of lightest scalar mesons and the production of the well established light scalar mesons in the ϕradiative decays. Arguments in favor of the four-quark model of the a0(980) and f0(980) mesons are given.

hep-ph↗
arXiv2004

Manifestation of the $a^0_0(980)-f_0(980)$ mixing in the reaction $π^-p\toηπ^0n$ on a polarized target

It is argued that the single-spin asymmetry in the reaction $π^-p\to a_0^0(980)n\to(ηπ^0)_S n$ is extremely sensitive to the mixing of the $a^0_0(980)$ and $f_0(980)$ resonances. It is shown that at low momentum transfers (namely, in any one of the intervals $0\leq-t\leq0.025,...,0.1$ GeV$^2$) the normalized asymmetry, which can take the values from -1 to 1, must undergo a jump in magnitude close to 1 in the $ηπ^0$ invariant mass region between 0.965 GeV and 1.01 GeV. The strong asymmetry jump is the straightforward manifestation of the $a^0_0(980)-f_0(980)$ mixing. For observing the jump, any very high quality $ηπ^0$ mass resolution is not required. The energy dependence of the polarization effect is expected to be rather weak. Therefore, it can be investigated at any high energy, for example, in the range from eight to 100 GeV.

hep-ph↗
arXiv2004

Problem of Light Scalar Mesons

The following topics are considered. 1. Confinement, chiral dynamics and light scalar mesons. 2. $ϕ$-meson radiative decays about nature of light scalar resonances. Arguments in favor of the four-quark model of the $a_0(980)$ and $f_0(980)$ mesons are given.

hep-ph↗
arXiv2004

Proposed Search for $a^0_0(980)-f_0(980)$ Mixing in Polarization Phenomena

The $K^+$ and $K^0$ meson mass difference induces the mixing of the $a^0_0(980)$ and $f_0(980)$ resonances, the amplitude of which, between the $K^+K^-$ and $K^0\bar K^0$ thresholds, is large in magnitude, of the order of $ m_{K}\sqrt{m^2_{K^0}-m^2_{K^+}}\approx\sqrtαm^2_K$, and possesses the phase sharply varying by about 90$^\circ$. We suggest performing the polarized target experiments on the reaction $π^-p\toηπ^0n$ at high energy in which the fact of the existence of $a^0_0(980)-f_0(980)$ mixing can be unambiguously and very easily established through the presence of a strong jump in the azimuthal asymmetry of the $ηπ^0$ $S$ wave production cross section near the $K\bar K$ thresholds. The presented estimates of the polarization effect to be expected in experiment are to a great extent model independent.

hep-ph↗
arXiv2003

Radiative decays of phi-meson about nature of light scalar resonances

We show on gauge invariance grounds that the fine threshold phenomenon is discovered in the radiative decays phi->gamma a0->gamma pi0 eta and phi->gamma f0->gamma pi0pi0. This enables to conclude that production of the lightest scalar mesons a0(980) and f0(980) in these decays is caused by the four-quark transitions, resulting in strong restrictions on the large NC expansions of the decay amplitudes. The analysis shows that these constraints give new evidences in favor of the four-quark nature of a0(980) and f0(980) mesons.

hep-ph↗
arXiv2003

The decays omega(782), phi(1020) to 5 pi in the hidden local symmetry approach

The decays omega -> 2pi^+ 2pi^- pi^0 and omega -> pi^+ pi^- 3pi^0 are reconsidered in the hidden local symmetry approach (HLS) added with the anomalous terms. The decay amplitudes are analyzed in detail, paying the special attention to the Adler condition of vanishing the whole amplitude at vanishing momentum of any final pion. Combining the Okubo-Zweig-Iizuka (OZI) rule applied to the five pion final state, with the Adler condition, we calculate also the phi -> 2pi^+ 2pi^-pi^0 and phi -> pi^+ pi^- 3pi^0 decay amplitudes. The partial widths of the above decays are evaluated, and the excitation curves in e^+e^- annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B(phi -> pi^+ pi^- 3pi^0)~2x10^{-7} and B(phi -> 2pi^+ 2pi^- pi^0)~7x10^{-7} are such that with the luminosity L=500 pb^{-1} attained at DAFNE phi factory, one may already possess about 1685 events of the decays phi -> 5pi.

hep-ph↗
arXiv2003

The perspectives of decoding the nature of the a0(980) and f0(980) mesons and of defining the relative phase between the three-gluon and one-photon amplitudes in the J/psi decays

It is argued that the search of the J/psi --> f0(980)omega and J/psi --> a0(980)rho decays and the more precise definition of B(J/psi --> f0(980)phi) are the urgent purposes in the J/ψspectroscopy. It is shown that the study of the omega-rho0 interference pattern in the J/psi --> (ρ^0+ω)eta --> pi+pi-eta decay provides evidence for the large (nearly pi/2) relative phase between the isovector one-photon and three-gluon decay amplitudes .

hep-ph↗
arXiv2003

$ππ$ scattering S wave from the data on the reaction $π^-p\toπ^0π^0n$

The results of the recent experiments on the reaction $π^-p\toπ^0π^0n$ performed at KEK, BNL, IHEP, and CERN are analyzed in detail. For the I=0 $ππ$ S wave phase shift $δ^0_0$ and inelasticity $η^0_0$ a new set of data is obtained. Difficulties emerging when using the physical solutions for the $π^0π^0$ S and D wave amplitudes extracted with the partial wave analyses are discussed. Attention is drawn to the fact that, for the $π^0π^0$ invariant mass, m, above 1 GeV, the other solutions, in principle, are found to be more preferred. For clarifying the situation and further studying the $f_0(980)$ resonance thorough experimental investigations of the reaction $π^-p\toπ^0π^0n$ in the m region near the $K\bar K$ threshold are required.

hep-ph↗
arXiv2003

Investigation of light scalar resonances at COSY

The $a_0$(980) and $f_0$(980) resonances are two well established states in the excited meson spectrum. We review the most prominent theoretical models which try to explain the structure of these states. It is discussed whether data from COSY on $a_0$ and $f_0$ production in $pp$, $pn$, $pd$ and $dd$ collisions allow to distinguish between the different approaches. Very promising in this respect seems to be the measurement of the reaction $dd \to (\mathrm{^4He} a_0^0 \to) \mathrm{^4He} π^0η$ which violates isospin conservation and can be related to $a_0$-$f_0$ mixing.

hep-ph↗
arXiv2002

The new analysis of the KLOE data on the phi->eta pi0 gamma decay

In this paper we present the fit to the recent high-statistical KLOE data on the phi -> eta pi^0 gamma decay. This decay mainly goes through the a_0 gamma intermediate state. The obtained results differ from those of the previous fits: data prefer a high a_0 mass and a considerably large a_0 coupling to the K\bar K}.

hep-ph↗
arXiv2002

Contribution to muon g-2 from the \pi0γand ηγintermediate states in the vacuum polarization

Using new experimental data, we have calculated the contribution to the anomalous magnetic moment of the muon from the \pi0γand ηγintermediate states in the vacuum polarization with high precision: aμ(\pi0γ)+aμ(ηγ)=(54.7\pm 1.5)\times 10^{-11}. We have also found the small contribution from e+e-\pi0, e+e-ηand μ+μ-\pi0 intermediate states equal to 0.5\times 10^{-11}.

hep-ph↗
arXiv2002

Radiative decays of ϕ-meson and nature of light scalar resonances

Based on gauge invariance, we show that the new threshold phenomenon is discovered in the ϕradiative decays ϕ\toγa0\toγ\pi0ηand ϕ\toγf0\toγ\pi0\pi0. This enables to conclude that production of the lightest scalar mesons a0(980) and f0(980) in these decays is caused by the four-quark transitions, resulting in strong restrictions on the large Nc expansions of the decay amplitudes. The analysis shows that these constraints give new evidences in favor of the four-quark nature of a0(980) and f0(980) mesons.

hep-ph↗
arXiv2001

Search for $a_0(980)$ and $f_0(980)$ mesons in $ϕ\toγK\bar K$

We study the decay $ϕ\toγK^+K^-$ taking into account the scalar mesons production $ϕ\toγ(f_0+a_0) \toγK^+K^-$ and the final state radiation. We note that the relative sign between the final state radiation amplitude and the scalar meson production amplitude is fixed in the $K^+K^-$ loop model which describes data on the $ϕ\to γf_0\toγππ$ and $ϕ\toγa_0\toγπη$ decays. As consequence this model predicts the definite interference between the final state radiation and the scalar resonance production amplitudes. We calculate the mass spectra of the $ϕ\toγK^+K^-$ decay and the differential cross-sections for $e^+e^-\toϕ\toγK^+K^-$ and for $e^+e^-\toϕ\toγK^0\bar K^0$ reactions.

hep-ph↗