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Observation of gamma(2S) -> gamma eta(b)(1S) Decay

Abstract

We report the observation of gamma(2S) -> gamma eta(b)(1S) based on an analysis of the inclusive photon spectrum of 24.7 fb(-1) of e(+)e(-) collisions at the gamma(2s) center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We measure a branching fraction of B [gamma(2S) -> gamma eta(b)(1S)] = (6.1(-0.7-0.6)(+0.6+0.9) x 10(-4) and derive an eta(b) (1S) mass of 9394.8(-3.1-2.7)(+2.7+4.5) MeV/c(2), where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

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Abstract

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Related concepts (20)

Standard deviation

In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the values are spread out over a wider range. Standard deviation may be abbreviated SD, and is most commonly represented in mathematical texts and equations by the lower case Greek letter σ (sigma), for the population standard deviation, or the Latin letter s, for the sample standard deviation.

Radioactive decay

Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay, all of which involve emitting particles. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.

Beta decay

In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission.

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