How resonances can synchronize with thresholds

Abstract

The mechanism by which a threshold may capture a resonance is examined. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t-and u-channel exchanges. The f 0 (980), X(3872) and Z(4430) are studied in detail. The f 0 (980) provides a valuable model of the locking mechanism. The X(3872) is too narrow to be fitted by a cusp, and requires either a resonance or virtual state. The Z(4430) can be fitted as a resonance but also can be fitted successfully by a cusp with no nearby resonant pole.

Charged charmonium-like states as rescattering effects in B¯→DsJ−D(⁎)Pakhlov1 2011Physics Letters B10250View full textAdd to dashboardCite

“…Many attempts of explanation of Z + 's follow these observations including molecular [5,6], tetraquark [7], hadrocharmonium states [8] or cusp effects [9]. In this Letter we demonstrate that the observed peaks can be explained by the effect of rescattering in the decay chain (Fig.…”

The hidden-charm pentaquark and tetraquark states

“…Whether the X(3872) is due to the cusp effect and threshold effect was discussed in Refs. [614,615,616,519,400,617]. Since the X(3872) is very close to the D * 0D0 threshold, the rescattering effects of the D and D * mesons were studied in Refs.…”

“…Various final state interactions may generate enhancement structures. For example, the cusp effect was proposed to explain the Z + c (4430) [519], Z b (10610) and Z b (10650) [449,451]. The initial single pion emission mechanism was applied to interpret the charged Z b and Z c structures [452,491].…”

Observation of e+e−→ηhc at center-of-mass energies from 4.085

“…Therefore, it is hard to explain all these resonances as charmonia, and they are named "charmoniumlike states" collectively. Several unconventional explanations, such as hybrid charmonium [17][18][19], tetraquark [20][21][22], hadronic molecule [23][24][25], diquarks [26,27] or kinematical effects [28][29][30][31] have been suggested. See also Ref.…”