Study of B^{+-} -> K^{+-}(K_S K pi)^0 Decay and Determination of eta_c and eta_c(2S) Parameters

TL;DR

This study measures the branching fractions, masses, and widths of $\\eta_c$ and $\\eta_c(2S)$ charmonium states through $B^{\pm} o K^{\pm} \\eta_c$ decays using Belle data, accounting for interference effects to improve accuracy.

Contribution

First precise measurement of $\\eta_c$ and $\\eta_c(2S)$ parameters with interference effects considered in $B$ decay analysis.

Findings

Branching fraction for $B^{\pm} o K^{\pm} \\eta_c$ measured as $(26.7 \\pm 1.4(stat)^{+2.9}_{-2.6}(syst) \\pm 4.9(model)) imes 10^{-6}$.

Mass of $\\eta_c$ determined as $(2985.4 \\pm 1.5(stat)^{+0.5}_{-2.0}(syst))$ MeV/$c^2$.

Mass of $\\eta_c(2S)$ determined as $(3636.1^{+3.9}_{-4.2}(stat+model)^{+0.7}_{-2.0}(syst))$ MeV/$c^2$.

Abstract

We report the results of a study of $B^{\pm}\to K^{\pm}\eta_c$ and $B^{\pm}\to K^{\pm}\eta_c(2S)$ decays followed by $\eta_c$ and $\eta_c(2S)$ decays to $(K_SK\pi)^0$. The results are obtained from a data sample containing 535 million $B\bar{B}$-meson pairs collected by the Belle experiment at the KEKB $e^+e^-$ collider. We measure the products of the branching fractions ${\mathcal B}(B^{\pm}\to K^{\pm}\eta_c){\mathcal B}(\eta_c\to K_S K^{\pm}\pi^{\mp})=(26.7\pm 1.4(stat)^{+2.9}_{-2.6}(syst)\pm 4.9(model))\times 10^{-6}$ and ${\mathcal B}(B^{\pm}\to K^{\pm}\eta_c(2S)){\mathcal B}(\eta_c(2S)\to K_S K^{\pm}\pi^{\mp})=(3.4^{+2.2}_{-1.5}(stat+model)^{+0.5}_{-0.4} syst))\times 10^{-6}$. Interference with the non-resonant component leads to significant model uncertainty in the measurement of these product branching fractions. Our analysis accounts for this interference and allows the model uncertainty to be reduced. We also obtain the following charmonia masses and widths: $M(\eta_c)=(2985.4\pm 1.5(stat)^{+0.5}_{-2.0}(syst))$ MeV/$c^2$, $\Gamma(\eta_c)=(35.1\pm 3.1(stat)^{+1.0}_{-1.6}(syst))$ MeV/$c^2$, $M(\eta_c(2S))=(3636.1^{+3.9}_{-4.2}(stat+model)^{+0.7}_{-2.0}(syst))$ MeV/$c^2$, $\Gamma(\eta_c(2S))=(6.6^{+8.4}_{-5.1}(stat+model)^{+2.6}_{-0.9}(syst))$ MeV/$c^2$.