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First observation of (B)over-bar(0) -> J/psi K+K- and search for (B)over-bar(0) -> J/psi phi decays

Abstract

The first observation of the (B) over bar (0) -> J/psi K+K- decay is presented with a data sample corresponding to an integrated luminosity of 1.0 fb(-1) of pp collisions at a center-of-mass energy of 7 TeV collected with the LHCb detector. The branching fraction is measured to be B((B) over bar (0) -> J/psi K+K-) = (2.53 +/- 0.31 +/- 0.19) x 10(-6), where the first uncertainty is statistical and the second is systematic. An amplitude analysis of the final state in the (B) over bar (0) -> J/psi K+K- decay is performed to separate resonant and nonresonant contributions in the K+K- spectrum. Evidence of the a(0)(980) resonance is reported with statistical significance of 3.9 standard deviations. The corresponding product branching fraction is measured to be B((B) over bar (0) -> J/psi a(0)(980), a(0)(980) -> K+K-) = (4.70 +/- 3.31 +/- 0.72) x 10(-7), yielding an upper limit of B((B) over bar (0) -> J/psi a(0)(980), a(0)(980) -> K+K-) < 9.0 x 10(-7) at 90% confidence level. No evidence of the resonant decay (0) J/psi phi is found, and an upper limit on its branching fraction is set to be B((B) over bar (0) -> J/psi phi)

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Abstract

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Related concepts (32)

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.

LHCb experiment

The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark). Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region.

Median absolute deviation

In statistics, the median absolute deviation (MAD) is a robust measure of the variability of a univariate sample of quantitative data. It can also refer to the population parameter that is estimated by the MAD calculated from a sample. For a univariate data set X1, X2, ..., Xn, the MAD is defined as the median of the absolute deviations from the data's median : that is, starting with the residuals (deviations) from the data's median, the MAD is the median of their absolute values. Consider the data (1, 1, 2, 2, 4, 6, 9).

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