Study of γ γ → γ ψ ( 2 S ) at Belle

Abstract

Using 980

fb − 1 of data at and around the Υ ( n S ) ( n = 1 , 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e + e − collider, the two-photon process γ γ → γ ψ ( 2 S ) is studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of γ ψ ( 2 S ) : one at M R 1 = 3922.4 ± 6.5 ± 2.0

MeV / c 2 with a width of Γ R 1 = 22 ± 17 ± 4

MeV , and another at M R 2 = 4014.3 ± 4.0 ± 1.5

MeV / c 2 with a width of Γ R 2 = 4 ± 11 ± 6

MeV ; the signals are parametrized with the incoherent sum of two Breit-Wigner functions. The first structure is consistent with the X ( 3915 ) or the χ c 2 ( 3930 ) , and the local statistical significance is determined to be 3.1 σ with the systematic uncertainties included. The second matches none of the known charmonium or charmoniumlike states, and its global significance is determined to be 2.8 σ including the look-elsewhere effect. The production rates are Γ γ γ B ( R 1 → γ ψ ( 2 S ) ) = 9.8 ± 3.6 ± 1.3

eV assuming ( J P C , | λ | ) = ( 0 + + , 0 ) or 2.0 ± 0.7 ± 0.2

eV with ( 2 + + , 2 ) for the first structure and Γ γ γ B ( R 2 → γ ψ ( 2 S ) ) = 6.2 ± 2.2 ± 0.8

eV with ( 0 + + , 0 ) or 1.2 ± 0.4 ± 0.2

eV with ( 2 + + , 2 ) for the second. Here, the first errors are statistical and the second systematic, and λ is the helicity.