Phys. Rev. D 58, 052004 (1998) [15 pages]

Hadronic transitions Υ(2S)→Υ(1S)

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J. P. Alexander et al. (CLEO Collaboration)
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Received 26 February 1998; published 7 August 1998

Using a 73.6 pb-1 data sample of Υ(2S) events collected with the CLEO II detector at the Cornell Electron Storage Ring, we have investigated the hadronic transitions between the Υ(2S) and the Υ(1S). The dipion transition Υ(2S)→Υ(1S+π- was studied using two different analysis techniques. Selecting events in which Υ(1S)→e+e-+μ- (“exclusive” analysis), and using the Υ(1S) leptonic branching fractions world averages from the PDG review, we obtained B(Υ(2S)→Υ(1S+π-)=0.189±0.004±0.010, while using a method allowing Υ(1S)→anything (“inclusive” analysis) we obtained B(Υ(2S)→Υ(1S+π-)=0.196±0.002±0.010. The appropriate weighted average of the two measurements gives B(Υ(2S)→Υ(1S+π-)=0.192±0.002±0.010. Combining the exclusive and inclusive results we derive the Υ(1S) leptonic branching fractions Bee=0.0229±0.0008±0.0011 and Bμμ=0.0249±0.0008±0.0013. We also studied Υ(2S)→Υ(1S0π0 and obtained B(Υ(2S)→Υ(1S0π0)=0.092±0.006±0.008. Parameters of the ππ system (dipion invariant mass spectra, angular distributions) were analyzed and found to be consistent with current theoretical models. Lastly, we searched for the η and single π0 transitions and obtained the 90% confidence level upper limits B(Υ(2S)→Υ(1S)η)<0.0028 and B(Υ(2S)→Υ(1S0)<0.0011.


©1998 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevD.58.052004
DOI: 10.1103/PhysRevD.58.052004
PACS: 13.20.Gd, 13.25.-k

* Permanent address: University of Texas, Austin, TX 78712.
Permanent address: Lawrence Livermore National Laboratory, Livermore, CA 94551.
Permanent address: BINP, RU-630090 Novosibirsk, Russia.
§ Permanent address: Yonsei University, Seoul 120-749, Korea.
** Permanent address: Brookhaven National Laboratory, Upton, NY 11973.

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