Nature Of Light Scalar Mesons Research Articles

Evidence of the four-quark nature of f0(980) and f0(500)

There exists a great deal of concrete evidence in favor of the exotic four-quark nature of light scalars. At the same time, the further expansion of the area of the $q^2\bar q^2$ model validity for light scalars on ever new processes seems extremely interesting and important. We analyze the BESIII data on the decay $J/\psi\to \gamma\pi^0\pi^0$ and show that the results of this high-statistics experiment can be interpreted in favor of the four-quark nature of light scalar mesons $f_0(980)$ and $f_0(500)$.

Semileptonic decays D→π+π−e+νe and Ds→π+π−e+νe as the probe of constituent quark-antiquark pairs in the light scalar mesons

Decays $D\to\pi^+\pi^-e^+\nu_e$ and $D_s\to\pi^+ \pi^-e^+\nu_e$ serve as probes that check the existence of constituent $q\bar q$ components in the wave functions of scalar mesons decaying into $\pi^+\pi^-$. There exists a great deal of concrete evidence in favor of the exotic four-quark nature of light scalars. At the same time, the further expansion of the area of the $q^2\bar q^2$ model validity for light scalars on ever new processes seems extremely interesting and important. We analyze the BESIII and CLEO data on the decays $D^+\to \pi^+\pi^- e^+\nu_e$ and $D^+_s\to \pi^+\pi^- e^+\nu_e$ and show that the results of these experiments together can be interpreted in favor of the four-quark nature of light scalar mesons $\sigma(500)$ and $f_0(980)$. Our approach can also be applied to the description of other similar decays involving light scalars.

New information on the strong isospin symmetry breaking in the reactions of the a00(980) and f0(980) resonance production

We discuss the isotopic symmetry breaking as a tool of studying the production mechanisms and nature of light scalar mesons. The anomalous isospin breaking effects can appear not only due to the $ a_0^0(980) - {f_0}(980) $ mixing, but also for any mechanism of the production of the $ \bar{K} $ pairs with a definite isospin in the S wave.

Strong isospin breaking at production of light scalars

It is discussed breaking the isotopic symmetry as the tool of studying the production and nature of light scalar mesons.

Study of Light Scalars in Photon-Photon Collisions, the learned Lessons

After a short review of the nature of light scalar mesons, we dwell on the investigation of the high-statistics Belle data on two-photon productionof light scalar mesons and ascertain that these data allow us to establish their production mechanisms. We show that light scalars are produced in two-photon collisions via four-quark transitions in contrast to the classic P -wave tensor q q ¯ mesons which are produced via two-quark transitions γ γ → q q ¯ . In particular, we show that the ideal q q ¯ model prediction g f 0 γ γ 2 : g a 0 γ γ 2 = 25 : 9 is excluded by experiment. Thus we get new strong evidence of the four-quark nature of these states. A programme of further investigations is presented.

Physics with the KLOE-2 experiment at the upgraded DAΦNE

Investigation at a $\phi$--factory can shed light on several debated issues in particle physics. We discuss: i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled kaon states, iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and eta/eta$^\prime$ mesons, iv) the contribution to understand the nature of light scalar mesons, and v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the $e^+ e^-$ physics in the continuum with the measurements of (multi)hadronic cross sections and the study of gamma gamma processes.

On the high-statistics investigation of the a 0(980) resonance in the γγ → π0η reaction

High-statistics data on the γγ → π0η reaction will make it possible to conclude whether the K+K−-loop rescattering mechanism, γγ → K+K− → a0(980) → π0η, is the main mechanism of the production of a0(980) isovector resonance. This mechanism provides a reasonable value of 20–30 nb at the maximum for the manifestation of a0(980) in the γγ → π0η cross section. It also gives rise to a noticeable narrowing of the a0(980) peak to its effective (observed) width ≈20–30 MeV in the γγ → π0η channel. The decay width averaged over the resonance mass distribution is 〈Γα0 → K+K− → γγ〉πη ≈ 0.13 keV. The experimental confirmation of this scenario would be important evidence in favor of the q2\( \bar q \)2 nature of light scalar mesons.

Scalar Mesons in D and B Decays

The decays of D and B mesons provide new insights into the nature of light scalar mesons. Several recent measurements are presented.

Thee+e−→P1P2γ processes close to the Φ peak: toward a model-independent analysis

We discuss the general decomposition and possible general parameterizations of the processes $e^+ e^- \to \gamma^* \to P_1 P_2 \gamma$, where $P_1 P_2=\pi^0 \pi^0$, $\pi^0\eta$, or $\pi^+\pi^-$, for $\sqrt{s}\approx M_\Phi$. Particular attention is devoted to the amplitude where the two pseudoscalar mesons are in a $J^{CP}= 0^{++}$ state, where we propose a general parameterization which should help to shed light on the nature of light scalar mesons.

Erratum: Semileptonic decay ofBandD→K0*(1430)ℓ¯νfrom QCD sum rule [Phys. Rev. D73, 034027 (2006)

We calculate $B_{(s)}$, and $D_{(s)}$ to $K^*_0(1430)$ transition form factors, and study semileptonic decays of $B_{(s)}$ and $D_{(s)}\to K_0^*(1430) \bar{\ell}\nu$ based on QCD sum rule. Measuring these semileptonic decays with high statistics will give valuable information on the nature of light scalar mesons.

Semileptonic decay ofBandD→K0*(1430)ℓ¯νfrom QCD sum rule

We calculate ${B}_{(s)}$ and ${D}_{(s)}$ to ${K}_{0}^{*}(1430)$ transition form factors, and study semileptonic decays of ${B}_{(s)}$ and ${D}_{(s)}\ensuremath{\rightarrow}{K}_{0}^{*}(1430)\overline{\ensuremath{\ell}}\ensuremath{\nu}$ based on QCD sum rule. Measuring these semileptonic decays with high statistics will give valuable information on the nature of light scalar mesons.