Publication

Observation of Three Resonant Structures in the Cross Section of e+e- →π+π-hc

2025

Abstract

Using e+e- collision data collected with the BESIII detector operating at the Beijing electron positron collider, the cross section of e+e-→π+π-hc is measured at 59 points with center-of-mass energy s ranging from 4.009 to 4.950 GeV with a total integrated luminosity of 22.2 fb-1. The cross section between 4.3 and 4.45 GeV exhibits a plateaulike shape and drops sharply around 4.5 GeV, which cannot be described by two resonances only. Three coherent Breit-Wigner functions are used to parametrize the s-dependent cross section line shape. The masses and widths are determined to be M1=(4223.6-3.7-2.9+3.6+2.6) MeV/c2, Γ1=(58.5-11.4-6.5+10.8+6.7) MeV, M2=(4327.4-18.8-9.3+20.1+10.7) MeV/c2, Γ2=(244.1-27.1-18.3+34.0+24.2) MeV, and M3=(4467.4-5.4-2.7+7.2+3.2) MeV/c2, and Γ3=(62.8-14.4-7.0+19.2+9.9) MeV. The first uncertainties are statistical and the second are systematic. The inclusion of the relatively narrower third component proves crucial for reproducing the drop at around 4.5 GeV. The statistical significance of the three-resonance assumption over the two-resonance assumption is greater than 5σ.

Official source

https://infoscience.epfl.ch/entities/publication/37029c73-6dc4-45b5-856e-cf36021be7dc

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2025

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/37029c73-6dc4-45b5-856e-cf36021be7dc

About this result

Related concepts (32)

Invariant mass

The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system. More precisely, it is a characteristic of the system's total energy and momentum that is the same in all frames of reference related by Lorentz transformations. If a center-of-momentum frame exists for the system, then the invariant mass of a system is equal to its total mass in that "rest frame".

Mass in special relativity

The word "mass" has two meanings in special relativity: invariant mass (also called rest mass) is an invariant quantity which is the same for all observers in all reference frames, while the relativistic mass is dependent on the velocity of the observer. According to the concept of mass–energy equivalence, invariant mass is equivalent to rest energy, while relativistic mass is equivalent to relativistic energy (also called total energy).

Energy–momentum relation

In physics, the energy–momentum relation, or relativistic dispersion relation, is the relativistic equation relating total energy (which is also called relativistic energy) to invariant mass (which is also called rest mass) and momentum. It is the extension of mass–energy equivalence for bodies or systems with non-zero momentum. It can be written as the following equation: This equation holds for a body or system, such as one or more particles, with total energy E, invariant mass m0, and momentum of magnitude p; the constant c is the speed of light.

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Observation of Three Resonant Structures in the Cross Section of e+e- →π+π-hc

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