First evidence of B0s→π+π- decays.

Primary authors: M.J. Morello, G. Punzi, F. Ruffini

This webpage collects the links to the CDF public note and to the relevant supporting plots for the measurement of the branching fractions of the B0s →π+π- and B0 →K+K- decays. These preliminary results were approved on May 19th,2011 by the CDF collaboration.


Most effective models used in predictions of non-leptonic B meson decay amplitudes rely on perturbative expansions in the inverse of the b quark mass. These provide accurate results for decays dominated by tree-level amplitudes, but suffer from significant uncertainties when penguin amplitudes or other sources of large strong phases intervene. These uncertainties frequently limit the accuracy and predictivity of tests of CKM dynamics using these decays. One of the largest sources of uncertainty is the size of penguin-annihilation topologies. These are processes where the two quarks composing the B meson annihilate yielding a final state made of completely different quarks. Their amplitudes are difficult to calculate and experimental input is crucial to constrain their magnitude. The B0s→π+π- mode proceeds only through annihilation amplitudes and a measurement of its branching ratio would gauge the size of annihilation topologies improving the precision of predictions of a vaste class of hadronic B decays. Its features are similar to the as yet unobserved B0→K+K- mode, but it has a larger predicted branching fraction; a measurement of both modes would provide an even more accurate determination of the strength of penguin-annihilation.

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Data and analysis

The data have been collected by the hadronic B trigger designed to select events containing track pairs exiting from a common displaced vertex and correspond to about 6 fb-1 of integrated luminosity. This is an improvement of the measurement performed on 1 fb-1 ( public web page and CDF Public note 8579 ) published on Phys. Rev. Lett. 103, 031801 (2009) and Phys. Rev. Lett. 106, 181802 (2011) .

A complete description of the analysis is available here: CDF Public note 10498.

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We report the first evidence of the B0s→π+π- with a significance of 3.7σ, including statistical and systematic uncertainties. No firm evidence for the B0→K+K- is found but the measured rate excludes zero at the 90% C.L."

We measured:

Using the (PDG 2010) input we obtained:

We set a 90% C.L. interval for the B0→K+K-. Both modes are annhilation dominated decays.

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Tables and figures

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