Evidence for the exclusive decay Bc+- to J/psi pi+- and measurement of the mass of the Bc meson

TL;DR

This paper presents the first evidence of the B_c^{ ext{±}} meson decaying into J/psi pi^{ ext{±}} and measures its mass using data from proton-antiproton collisions at Fermilab.

Contribution

It provides the first reconstructed decay mode of the B_c^{ ext{±}} meson and measures its mass with statistical and systematic uncertainties.

Findings

Observed 14.6 ± 4.6 signal events

Measured B_c^{ ext{±}} mass as 6285.7 ± 5.3 (stat) ± 1.2 (syst) MeV/c^2

Estimated probability of background fluctuation as 0.012%

Abstract

We report first evidence for a fully reconstructed decay mode of the B_c^{\pm} meson in the channel B_c^{\pm} \to J/psi \pi^{\pm}, with J/psi \to mu^+mu^-. The analysis is based on an integrated luminosity of 360 pb$^{-1} in p\bar{p} collisions at 1.96 TeV center of mass energy collected by the Collider Detector at Fermilab. We observe 14.6 \pm 4.6 signal events with a background of 7.1 \pm 0.9 events, and a fit to the J/psi pi^{\pm} mass spectrum yields a B_c^{\pm} mass of 6285.7 \pm 5.3(stat) \pm 1.2(syst) MeV/c^2. The probability of a peak of this magnitude occurring by random fluctuation in the search region is estimated as 0.012%.