${\chi }_{c1}$ and ${\chi }_{c2}$ polarization as a probe of color octet channel

Abstract

We analyze the first LHC data on ${\chi }_{c1}$ and ${\chi }_{c2}$ polarization obtained very recently by the CMS Collaboration at $\sqrt{s}=8$~TeV. We describe the perturbative production of $c\bar{c}$ pair with $k_T$-factorization approach and use nonrelativistic QCD formalism for the formation of bound states. We demonstrate that the polar anisotropy of ${\chi }_{c1}$ and ${\chi }_{c2}$ mesons is strongly sensitive to the color octet contributions. We extract the long-distance matrix elements for ${\chi }_{c1}$ and ${\chi }_{c2}$ mesons from the first CMS polarization measurement %on the polarization parameters ${\lambda }_{\theta }^{{\chi }_{c1}}$ and ${\lambda }_{\theta }^{{\chi }_{c2}}$ obtained at $\sqrt{s}=8$~TeV together with available LHC data on the ${\chi }_{c1}$ and ${\chi }_{c2}$ transverse momentum distributions (and their ratios) collected at $\sqrt{s}=7$~TeV. Our fit points to unequal color singlet wave functions of ${\chi }_{c1}$ and ${\chi }_{c2}$ states.

12 pages, 5 figures, 1 table

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Cited by in corpus (2)

• Bottomonium production and polarization in the NRQCD with $k_T$-factorization. III: ${\rm Y}(1S)$ and ${\chi }_b(1P)$ mesons
• Bottomonia production and polarization in the NRQCD with $k_T$-factorization. II: ${\rm Y}(2S)$ and ${\chi }_b(2P)$ mesons