Decay X(3872)→π0π+π− and S

Abstract

The isospin-breaking decay Xð3872Þ → ðD ÃD þD Ã DÞ → π 0 DD → π 0 π þ π − is discussed. In its amplitude there is a triangle logarithmic singularity, due to which the dominant contribution to BRðXð3872Þ → π 0 π þ π − Þ comes from the production of the π þ π − system in a narrow interval of the invariant mass m π þ π − near the value of 2m D 0 ≈ 3.73 GeV. The analysis shows that BRðXð3872Þ → π 0 π þ π − Þ can be expected at the level of 10 −3 − 10 −4. This estimate includes, in particular, the assumption that the S-wave inelastic scattering length jα 00 D 0D0 →π þ π − j ≈ 1=ð2m D Ãþ Þ ≈ 0.25 GeV −1 .

Study of the process $$e^+e^- \rightarrow \eta \eta \gamma $$ in the energy range $$\sqrt{s} = \text{1.17--2.00 }$$ GeV with the SND detector

“…The total number of signal events is a free fit parameter. The fractions of the processes (11) in the sum are calculated using their measured cross sections [4,21,22] and the branching fractions of the decays φ, ρ, ω → ηγ [10]. The energy dependences of the cross sections for the processes (11) are shown in Fig.…”

“…2. The calculation is based on the approximation of the experimental data [4,21,22]. Above 1.6 GeV, the main contribution to the cross section arises from the φη mechanism, while below 1.6 GeV, the Fig.…”

“…In Fig. 2, the measured cross section is compared with the calculation for the mechanisms φη, ωη and ρη based on the approximation of the experimental data [4,21,22]. Figure 2 also shows the measurement of the cross section for the dominant mechanism e + e − → φη performed by CMD-3 in decay mode φ → K + K − [4].…”

Study of the reactions $e^+e^-\toπ^+π^-π^0π^0π^0π^0$ and $π^+π^-π^0π^0π^0η$ at center-of-mass energies from threshold to 4.5 GeV using initial-state radiation

“…To determine the contribution of the ηπ + π − π 0 intermediate state, we fit the events of Fig. 11(a) using a triple-Gaussian function to describe the signal peak, as in for the e + e − → π + π − π 0 η cross section with those from the SND experiment with η → γγ, shown by squares [33] and with those from the CMD-3 experiment, also based on η → γγ, shown by triangles [35]. The insert shows an expanded view of the resonant region.…”

Forming molecular states with hadronic rescattering

“…Lying within 0.2 MeV of the D 0 D * 0 threshold, the χ c1 (3872) resonance is oftentimes interpreted as such a molecular state [15]. Alternative interpretations of the χ c1 (3872) include a fourquark state, or the χ c1 (2P) meson [16], but the molecular interpretation remains as the preferred model [17][18][19][20][21][22][23]. The P + c (4312), P + c (4440) and P + c (4457) pentaquarks observed by LHCb may also be described by a molecular state of * c D0 or * c D * 0 [24][25][26][27][28][29][30][31][32].…”