Abstract
We present various properties of the production of the $X(3872)$ and $\psi(2S)$ states based on 10.4 fb$^{-1}$ collected by D0 experiment in Tevatron $p \bar p$ collisions at $\sqrt{s}$ = 1.96 TeV. For both states, we measure the nonprompt fraction $f_{NP}$ of the inclusive production rate due to decays of $b$-flavored hadrons. We find the $f_{NP}$ values systematically below those obtained at the LHC. The $f_{NP}$ fraction for $\psi(2S)$ increases with transverse momentum whereas for the X(3872) it is constant within large uncertainties, in agreement with the LHC results. The ratio of prompt to nonprompt $\psi(2S)$ production, $(1 - f_{NP}) / f_{NP}$, decreases only slightly going from the Tevatron to the LHC, but for the $X(3872)$ this ratio decreases by a factor of about 3. We test the soft-pion signature of the $X(3872)$ modeled as a weakly-bound charm-meson pair by studying the production of the $X(3872)$ as a function of the kinetic energy of the $X(3872)$ and the pion in the $X(3872)\pi$ center-of-mass frame. For a subsample consistent with prompt production, the results are incompatible with a strong enhancement in the production of the $X(3872)$ at small kinetic energy of the $X(3872)$ and the $\pi$ in the $X(3872)\pi$ center-of-mass frame expected for the $X$+soft-pion production mechanism. For events consistent with being due to decays of $b$ hadrons, there is no significant evidence for the soft-pion effect but its presence at the level expected for the binding energy of 0.17 MeV and the momentum scale $\Lambda=M(\pi)$ is not ruled out.
Highlights
Fifteen years after the discovery of the state Xð3872Þ [1], its nature is still debated
The two-pion mass for each accepted J=ψπþπ− candidate is required to be greater than 0.35 GeV (0.5 GeV) for ψð2SÞ ðXð3872ÞÞ candidates
Tevatron values tend to be somewhat smaller than those measured by ATLAS and CMS. (2) The ratio of prompt to nonprompt ψð2SÞ production, Rp=np 1⁄4 ð1 − fNPÞ=fNP, increases only slightly going from the LHC to the Tevatron
Summary
Fifteen years after the discovery of the state Xð3872Þ [1] ( named χc1ð3872Þ [2]), its nature is still debated. According to the authors, such a process should be observable at hadron colliders as an increased event rate at small values of the kinetic energy TðXπÞ of the Xð3872Þ and the “soft” pion in the Xð3872Þπ center-of-mass frame and should provide a clean test of the molecular structure of the Xð3872Þ. In this Xð3872Þ article, we present production properties in Tevatron ppcollisions at the energy opf ffisffith1⁄4e. The fits yield 126891 Æ 770 and 16423 Æ 1031 events of ψð2SÞ and Xð3872Þ, with mass parameters of 3684.88 Æ 0.07 MeV and 3871.0 Æ 0.2 MeV, and mass
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