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Register a new userInclusive $chi_{cJ}$ production in $Upsilon$ decay at $mathcal{O}(alpha_s^5)$ in NRQCD factorization
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Inclusive $chi_{cJ}$ $(J=0,1,2)$ production from $Upsilon(1S)$ decay is studied within the framework of nonrelativistic QCD (NRQCD) factorization at leading order in $v_Q^2$, which includes the contributions of $bbar{b}({}^3S_1^{[1]})to cbar{c}(^3P_J^{[1]})+X$ and $bbar{b}({}^3S_1^{[1]})to cbar{c}(^3S_1^{[8]})+X$. For both channels, the short-distance coefficients are calculated through ${cal O}(alpha_s^5)$, which is next-to-leading order for the second one. By fitting to the measured $Upsilon(1S)$ branching fractions to $chi_{c1}$ and $chi_{c2}$, we obtain the color-octet long-distance matrix element (LDME) $langlemathcal{O}^{chi_{c0}}({}^3S_1^{[8]})rangle =(4.04pm0.47_{-0.34}^{+0.67})times10^{-3}$ GeV$^3$, where the first error is experimental and the second one due to the renormalization scale dependence, if we use as input $langlemathcal{O}^{chi_{c0}}({}^3P_0^{[1]})rangle=0.107$ GeV$^5$ as obtained via potential-model analysis. Previous LDME sets, extracted from data of prompt $chi_{cJ}$ hadroproduction, yield theoretical predictions that systematically undershoot or mildly overshoot the experimental values of $mathcal{B}(Upsilonto chi_{cJ}+X)$.
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We study $J/psi$ and $eta_c$ inclusive production in $Upsilon$ decay within the framework of nonrelativistic-QCD (NRQCD) factorization. In the latter case, for which no experimental data exist so far, we also include the $h_c$ feed-down contribution. We calculate the short distance coefficients completely through $mathcal{O}(alpha_s^5)$. The NRQCD predictions for the branching fraction $mathcal{B}(Upsilonto J/psi+X)$ via direct production, evaluated with different sets of long-distance matrix elements (LDMEs), all agree with the experimental data in a reasonable range of renormalization scale. Using $eta_c$ and $h_c$ LDMEs obtained from $J/psi$ and $chi_c$ ones via heavy-quark spin symmetry, we find that the bulk of $mathcal{B}(Upsilontoeta_c+X)$ via prompt production arises from the $cbar{c}({}^3!S_1^{[8]})$ Fock state. The experimental study of this decay process would, therefore, provide a particularly clean probe of the color octet mechanism of heavy-quarkonium production.
In this paper, we present a comprehensive study of $Upsilon$ inclusive production in $Z$ boson decay, including the first complete next-to-leading-order calculations of the color-octet (CO) contributions. With the inclusion of the newly-calculated remarkable QCD corrections, the CO processes exhibit crucially phenomenological influence on the existing predictions built on the color-singlet mechanism. We also include the exhaustive evaluations of the feed-down contributions, which remained ignored in the literature, and find them to be considerable. Summing up all the contributions, the $mathcal{B}_{Z to Upsilon(nS)+X}$ still notably undershoot the data released by the L3 Collaboration.
We discuss factorization in heavy quarkonium production in high energy collisions using NRQCD. Infrared divergences at NNLO are not matched by conventional NRQCD matrix elements. However, we show that gauge invariance and factorization require that conventional NRQCD production matrix elements be modified to include Wilson lines or non-abelian gauge links. With this modification NRQCD factorization for heavy quarkonium production is restored at NNLO.
Precise predictions are provided for the production of a $mathrm{Z}$-boson and a $mathrm{b}$-jet in hadron-hadron collisions within the framework of perturbative QCD, at $mathcal{O}(alpha_s^3)$. To obtain these predictions we perform the first calculation of a hadronic scattering process involving the direct production of a flavoured-jet at next-to-next-to-leading order accuracy in massless QCD, and extend techniques to also account for the impact of finite heavy-quark mass effects. The predictions are compared to CMS data obtained in $mathrm{pp}$ collisions at a centre-of-mass energy of $8~mathrm{TeV}$, which are the most precise data from Run I of the LHC for this process, where a good description of the data is achieved. To allow this comparison we have performed an unfolding of the data, which overcomes the long-standing issue that the experimental and theoretical definitions of jet flavour are incompatible.
The inclusive production of jets in the central region of rapidity is studied in $k_T$-factorization at next-to-leading order (NLO) in QCD perturbation theory. Calculations are performed in the Regge limit making use of the NLO BFKL results. A jet cone definition is introduced and a proper phase--space separation into multi-Regge and quasi-multi-Regge kinematic regions is carried out. Two situations are discussed: scattering of highly virtual photons, which requires a symmetric energy scale to separate the impact factors from the gluon Greens function, and hadron-hadron collisions, where a non--symmetric scale choice is needed.
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