Measurement of Bs→J/ψf0(980) Branching Fraction

Primary Author: Michal Kreps


Since the Bs mixing observation in 2006 particle physics community is excited by searches for CP violation in Bs→J/ψφ decays. The first results, which used flavor tagging to separate Bs and anti-Bs, showed about 1.5σ deviations from the standard model. In the initial measurements of both Tevatron experiments as well as in the subsequent CDF update a possible contribution from the so-called S-wave contribution was neglected. The S-wave component itself can be non-resonant Bs→J/ψ K+K- decay or decay Bs→J/ψf0(980) with f0(980)→K+K-. It was argued that the mild deviation from the SM could have been due to ignoring the S-wave contribution rather than real genuine effect. A summary of the discussion can be find in work of Stone (arXiv:1009.4939). It is also suggested that sufficient signal for the decay Bs→J/ψf0(980) with f0(980)→π+π- can be used to measure CP violating phase βsJ/ψφ without need of angular analysis. All this generated interest in the decay Bs→J/ψf0(980).

Several estimations for Rf0, the ratio of branching fractions between Bs→J/ψf0(980) and Bs→J/ψφ, exist based on theoretical calculations as well as on comparison to Ds decays. They vary in wide range of 0.1 to 0.5. Here we present observation of the Bs→J/ψf0(980) decay with f0(980)→π+π- in CDF data and a measurement of Rf0. The analysis is based on 3.8 fb-1 of data collected by dimuon trigger.

Further information can be found in the arXiv:1106.3682.


We observe signal of Bs→J/ψf0(980) with f0(980)→π+π- with a 502±37(stat)±18(sys) signal events. The J/ψπ+π- invariant mass distribution is shown in following figure:

We measure
Rf0=[BF(Bs→J/ψf0(980))BF(f0(980)→π+π-)]/ [BF(Bs→J/ψφ)BF(φ→K+K-)]=0.257±0.020(stat)±0.014(sys)
from which we derive
BF(Bs→J/ψf0(980))BF(f0(980)→π+π-)= (1.63±0.12(stat)±0.09(sys)±0.50(pdg))10-4.

List of Figures