Possible mechanism for producing the threshold enhancement inJ/ψ→γpp¯

Abstract

In the J/ψ radiative decay channels J/ψ → γVV , the result of partial wave analysis indicates that the VV systems are predominately pseudoscalar component, and most of these channels have relatively large branching ratios at an order of 10 −3 . Meanwhile, vector mesons, such as ρ, ω and K * , have strong couplings with nucleons and/or hyperons. This suggests a dynamical mechanism describing the ηpp form factors for higher η mesons, such as η(1405/1475) and η(1760). It is thus natural to expect that rescatterings of these vector meson pairs into pp of 0 − partial wave could be an important source contributing to J/ψ → γpp of which the branching ratio is at the order of 10 −4 . Our calculation justifies this point. In particular, we find that interferences between different rescattering amplitudes can produce a significant threshold enhancement in the invariant mass spectrum of pp. Without introducing dramatic ingredients, our model provides a natural explanation for the peculiar threshold enhancement observed by BES-II in J/ψ → γpp. Additional experimental constraints on the VV → pp transitions are examined. This mechanism in J/ψ → ωpp is also discussed.

X(1835)and the new resonancesX(2120)andXLiu1, Ding2, Yan3 2010Phys. Rev. D382420View full textAdd to dashboardCite

“…Some interpret Xð1835Þ as a p " p bound state [4][5][6][7][8], a glueball candidate [9][10][11][12], or the radial excitation of 0 [13,14], and some others interpret it as final state interaction or a rescattering effect [15][16][17]. Naïvely the observation of Xð2120Þ and Xð2370Þ seems to indicate that all the three resonances Xð1835Þ, Xð2120Þ, and Xð2370Þ are possibly the radial excitations of or 0 ; they jump to the ground state 0 through emitting two [18].…”

Observation of an Anomalous Line Shape of the η′π+π− Mass Spectrum near the pp¯ Mass Threshold in J/ψ→γη′π+π−

“…This enhancement structure was subsequently determined to have spin parity J P ¼ 0 − by BESIII [7]. Among the various theoretical interpretations on the nature of the Xð1835Þ and XðppÞ [8][9][10][11][12], a particularly intriguing one suggests that the two structures originate from a pp bound state [13][14][15][16][17]. If the Xð1835Þ is really a pp bound state, it should have a strong coupling to 0 − pp systems, in which case the line shape of Xð1835Þ at the pp mass threshold would be affected by the opening of the Xð1835Þ → pp decay mode.…”

“…Some theoretical models are proposed to interpret their internal structures, e.g. a pp bound state [3][4][5][6], a pseudoscalar glueball [7][8][9], or a radial excitation of the η ′ meson [10]. Subsequently these resonances were confirmed by BESIII [11,12] and CLEO [13] experiments and found to have the same J P C of 0 −+ [14,15].…”

Measurement of the branching fraction of J/ψ→ωη′π+π− and search for Ablikim1, Ачасов2, Adlarson3 et al. 2019Phys. Rev. D

“…A partial wave analysis of the pp mass-threshold enhancement was performed [10], and the J PC quantum number were determined to be the same as for the Xð1835Þ. theoretical speculations on their nature, such as a pp bound state [11][12][13][14], a pseudoscalar glueball [15][16][17], a radial excitation of the η 0 meson [18], etc. Thanks to the world's largest e þ e − → J∕ψ dataset collected by BESIII, it has been possible to study in detail the significant abrupt change in the line shape of the Xð1835Þ → η 0 π þ π − in correspondence of the pp mass threshold [19], which could be originated from the opening of the pp additional decay channel (threshold effect) or by the interference between two different resonances.…”