A unique feature of quantum chromodynamics (QCD), the theory of strong interactions, is the possibility for gluonic degrees of freedom to participate in the construction of physical hadrons, which are color singlets, in an analogous manner to valence quarks. Hadrons with no valence quarks are called glueballs, while hadrons where both gluons and valence quarks combine to form a color singlet are called hybrids. The unambiguous identification of such states among the experimental hadron spectrum has been thus far not possible. Glueballs are particularly difficult to establish experimentally since the lowest lying ones are expected to strongly mix with conventional mesons. On the other hand, hybrids should be easier to single out because the set of quantum numbers available to their lowest excitations may be exotic, i.e., not realized in conventional quark-antiquark systems. Particularly promising for discovery appear to be heavy hybrids, which are made of gluons and a heavy-quark-antiquark pair (charm or bottom). In the heavy-quark sector systematic tools can be used that are not available in the light-quark sector. In this paper we use a nonrelativistic effective field theory to uncover for the first time the full spin structure of heavy-quark hybrids up to 1/m 2 -terms in the heavy-quark-mass expansion. We show that such terms display novel characteristics at variance with our consolidated experience on the fine and hyperfine splittings in atomic, molecular and nuclear physics. We determine the nonperturbative contributions to the matching coefficients of the effective field theory by fitting our results to lattice-QCD determinations of the charmonium hybrid spectrum and extrapolate the results to the bottomonium hybrid sector where lattice-QCD determinations are still challenging.

The spin-dependent operators for heavy quarkonium hybrids have been recently obtained in a nonrelativistic effective field theory approach up to next-to-leading order in the heavy-quark mass expansion. In the effective field theory for hybrids several operators not found in standard quarkonia appear, including an operator suppressed by only one power of the heavy-quark mass. We compute the matching coefficients for these operators in the short heavy-quark-antiquark distance regime, r ≪ 1=Λ QCD , by matching weakly coupled potential nonrelativistic QCD to the effective field theory for hybrids. In this regime the perturbative and nonperturbative contributions to the matching coefficients factorize, and the latter can be expressed in terms of purely gluonic correlators whose form we explicitly calculate with the aid of the transformation properties of the gluon fields under discrete symmetries. We detail our previous comparison with direct lattice computations of the charmonium hybrid spectrum, from which the unknown nonperturbative contributions can be obtained, and extend it to datasets with different light-quark masses.

Fixed-order QCD radiative corrections to the vector-boson and Higgs associated production channels, pp → V H (V = W ± , Z), at hadron colliders are well understood. We combine higher order perturbative QCD calculations with soft-gluon resummation of both threshold logarithms and logarithms which are important at low transverse momentum of the V H pair. We study the effects of both types of logarithms on the scale dependence of the total cross section and on various kinematic distributions. The next-to-next-to-next-to-leading logarithmic (NNNLL) resummed total cross sections at the LHC are almost identical to the fixed-order perturbative next-to-next-toleading order (NNLO) rates, indicating the excellent convergence of the perturbative QCD series.Resummation of the V H transverse momentum (p T ) spectrum provides reliable results for small values of p T and suggests that implementing a jet-veto will significantly decrease the cross sections.

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The process H → J/ψ + γ, where H is the Higgs particle, provides a way to probe the size and the sign of the Higgs-charm coupling. In order to improve the theoretical control of the decay rate, we compute order v 4 corrections to the decay rate based on the nonrelativistic QCD factorization formalism. The perturbative calculation is carried out by using automated computer codes. We also resum logarithms of the ratio of the masses of the Higgs boson and the J/ψ to all orders in the strong coupling constant α s to next-to-leading logarithmic accuracy. In our numerical result for the decay rate, we improve the theoretical uncertainty, while our central value is in agreement with previous studies within errors. We also present numerical results for H → Υ(nS) + γ for n = 1, 2, and 3, which turn out to be extremely sensitive to the Higgs bottom coupling. PACS numbers:Recently there have been many efforts to improve the theoretical prediction of the decay rate within the Standard Model [4][5][6][7][8]. Especially, approaches based on nonrelativistic effective field theories allow a systematic improvement of theoretical accuracy [4,5,7,8]. In the nonrelativistic QCD (NRQCD) effective field theory [9], decay and production processes involving a heavy quarkonium are given by a double series in α s and v, where v is the typical velocity of a heavy quark Q in a heavy quarkonium; for charmonium, v 2 ≈ 0.3, and for bottomonium, v 2 ≈ 0.1. Currently, the decay rates Γ(H → V +γ) for V = J/ψ or Υ(nS) for n = 1, 2, and 3 have been computed to relative order α s v 0 and v 2 accuracy [5,7,8,10]. In Refs. [5,7,8], the large logarithms of m 2 H /m 2 V that appear in higher order corrections in α s , where m H is the Higgs mass and m V is the mass of the quarkonium V , have been resummed to all orders in α s by combining the NRQCD and the light-cone formalisms [11][12][13].