Probing the symmetry of nature (CP violation in B mesons decaying to J/psi Kaon-long)

Abstract

In this work we present a measurement of the CP-violation parameter sin2&phis;₁ determined through the difference between the time-dependent decay rates for the B⁰ → J/ψ K_L and B¯ ⁰ → J/ψ K_L transitions.

We also show improved selection criteria, which allow us to increase the reconstruction efficiency by 40% and decrease the statistical error in sin2&phis;₁ by 25%. In addition, we will present a detailed overview of the K_L and J/ψ detection and reconstruction.

Using 78 fb⁻¹ of e⁺ e⁻ collision data, collected with the Belle detector at the KEKB accelerator, we reconstruct 2054 J/ψ K_L candidates, with an estimated signal purity of 57 ± 3%. Using 1714 of these candidates, we measure sin2&phis;₁ = 0.51 ± 0.12(statistical) ± 0.07(systematic).

The measurements presented take advantage of the excellent design of the Belle KLM detector. They are in good agreement with the results from other experiments.