Experimental Study of chi_b(2P) --> pi pi chi_b(1P)

TL;DR

This study searches for the di-pion transition between chi_b(2P) and chi_b(1P) states in Upsilon(3S) decays, providing evidence for this decay mode and measuring its partial width.

Contribution

First experimental evidence for the chi_b(2P) to pi pi chi_b(1P) transition with a measured partial decay width.

Findings

Partial decay width measured as approximately 0.83 keV.

Null hypothesis rejected, indicating the decay occurs.

Analysis includes both charged and neutral pion channels.

Abstract

We have searched for the di-pion transition chi_b(2P) -> pi pi chi_b(1P) in the CLEO III sample of Upsilon(3S) decays in the exclusive decay chain: Upsilon(3S) -> gamma chi_b(2P), chi_b(2P) -> pi pi chi_b(1P), chi_b(1P) -> gamma Upsilon(1S), Upsilon(1S) -> lepton pairs. Our studies include both pi+ pi- and pi0 pi0, each analyzed both in fully reconstructed events and in events with one pion undetected. We show that the null hypothesis is not substantiated. Under reasonable assumptions, we find the partial decay width to be Gamma[chi_b(2P) -> pi pi chi_b(1P)] = (0.83 +/- 0.22 +/- 0.08 +/- 0.19) keV, with the uncertainties being statistical, internal CLEO systematics, and common systematics from outside sources.