Measurement of the dipion mass spectrum in the decay X(3872) [right arrow] J/ [psi] [pi]⁺ [pi]⁻ at the CDFII experiment

Abstract

We present a measurement of the dipion mass spectrum in the decay X(3872) [right arrow] J/ [psi] [pi]⁺ [pi]⁻ using a 360 pb-1 sample of pp collisions at av [square root]s = 1.96 TeV collected with the CDF II detector at the Fermnilab Tevatron Collider. As a benchmark, we also extract the dipion mass distribution for [psi] (2s) [right arrow] J/ [psi] [pi]⁺ [pi]⁻ decay. The X(3872) dipion mass spectrum is compared to QCD multipole expansion predictions for various charmonium states, as well as to the hypothesis [right arrow] J/ [psi] po. We find that the measured spectrum is compatible with 3S1 charmonium decaying to J/ [psi] [pi]⁺ [pi]⁻ - and with the X(3872) - J/po hypothesis. There is, however, no 3S1 charmonium state available for assignment to the X(3872). The multipole expansion calculations for 1P1 and 3DJ states are in clear disagreement with the X(3872) data. For the [psi] (2S) the data agrees well with previously published results and to multipole expansion calculations for 3S1 charmonium. Other, non-charmonium, models for the X(3872) are described too. We conclude that since the dipion mass spectrum for X(3872) is compatible with J/pO hypothesis, the X(3872) should be C-positive. This conclusion is supported by recent results from Belle Collaboration which observed X(3872) -+ J/7y decay. We argue that if X(3872) is a charmonium, then it should be either ... state, decaying into J/ [psi] [pi]⁺ [pi]⁻ in violation of isospin conservation. A non-charmonium assignment, such as DD* molecule, is also quite possible.