Abstract
The radiative decayJ/ψ → γ π+ π− has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe +e− storage rings at Orsay. The π+ π− mass spectrum shows a cleanf 2 (1270) signal, and the possible presence of two other states at thef 2 (1720) andf 4 (2030) masses. For thef 2 (1270), the branching ratio BR(J/ψ →γf)xBR(f→π+ π−) is measured to be (7.50±0.30±1.12)×10−4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.
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A specific analysis of this channel will appear in a forthcoming paper. A fit to the π+π- mass spectrum between 1075 and 1550 MeV/c2 gives, assuming the presence off 2(1270) on the low mass side, with mass and width fixed to 1270 and 176 MeV/c2:m x=1372±10 MeV/c2 andΓ X =106±13MeV/c2 withχ 2=54 for 15 d.o.f. The agreement is still bad if the two Breit-Wigner functions are allowed to interfere with a relative phase of about 180°:m x=1445±9 MeV/c2 andΓ X =139±16MeV/c2 withχ 2=41 for 15 d.o.f.
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DM2 Collaboration., Augustin, J.E., Cosme, G. et al. Radiative decay ofJ/ψ into γ π+ π− . Z. Phys. C - Particles and Fields 36, 369–376 (1987). https://doi.org/10.1007/BF01573930
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DOI: https://doi.org/10.1007/BF01573930