We compare the transverse-momentum (pT) distribution of inclusive light-charged-particle production measured by the CDF Collaboration at the Fermilab Tevatron with the theoretical prediction ...evaluated at next-to-leading order in quantum chromodynamics using fragmentation functions recently determined through a global data fit. While in the lower pT range the data agree with the prediction within the theoretical error or slightly undershoot it, they significantly exceed it in the upper pT range, by several orders of magnitude at the largest values of pT, potentially challenging the factorization theorem.
An approach valid to any order which unifies the fixed order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution of fragmentation functions at large x with soft gluon logarithmic resummation at ...small x is proposed. At lowest order, this approach, implemented with the double logarithmic approximation, reproduces exactly the modified leading logarithm approximation but is more complete due to the degrees of freedom given to the quark sector and the inclusion of the fixed order terms. We find that data from the largest x values to the peak region can be better fitted than with other approaches.
In this Letter, we extend the known results for the QCD potential between a static quark and its antiquark by computing the two-loop corrections to the colour-octet state.
If quantum chromodynamics (QCD) is renormalized by minimal subtraction (MS), at higher orders, the strong coupling constant
α
s
and the quark masses
m
q
exhibit discontinuities at the flavour ...thresholds, which are controlled by so-called decoupling constants,
ζ
g
and
ζ
m
, respectively. Adopting the modified MS (
MS
) scheme, we derive simple formulae which reduce the calculation of
ζ
g
and
ζ
m
to the solution of vacuum integrals. This allows us to evaluate
ζ
g
and
ζ
m
through three loops. We also establish low-energy theorems, valid to all orders, which relate the effective couplings of the Higgs boson to gluons and light quarks, due to the virtual presence of a heavy quark
h, to the logarithmic derivatives with respect to
m
h
, of
ζ
g
and
ζ
m
, respectively. Fully exploiting the present knowledge of the anomalous dimensions of
α
s
and
m
q
, we thus calculate these effective couplings through four loops. Finally, we perform a similar analysis for the coupling of the Higgs boson to photons.
The next-to-next-to-next-to-leading order (N
3LO) Hamiltonian of potential nonrelativistic QCD is derived. The complete matching of the Hamiltonian and the contribution from the ultrasoft dynamical ...gluons relevant for perturbative bound-state calculations is performed including one-, two-, and three-loop contributions. The threshold expansion is used to disentangle and match contributions of different scales in the effective-theory calculations. As a physical application, the heavy-quarkonium spectrum is obtained at N
3LO for the case of vanishing QCD beta function. Our results set the stage for a full N
3LO analysis of the heavy-quarkonium system.
We study the photoproduction of isolated prompt photons associated with hadron jets in the framework of the parton Reggeization approach. The main improvements with respect to previous studies in the ...kT-factorization framework include the application of the Reggeized-quark formalism, the generation of exactly gauge-invariant amplitudes with off-shell initial-state quarks, and the exact treatment of the γR→γg box contribution with off-shell initial-state gluons. In this proceedings, the new data set, published recently by ZEUS collaboration is analyzed, were the distributions in photon and jet rapidity, transverse energy, azimuthal angle between photon and jet and proton momentum fraction are presented for different values of measured photon momentum fraction xγmeas<0.7,0.8 and xγmeas agreement of measured distributions with our predictions is observed for the direct-dominating part of the data set. The comparison with the previous calculations in kT-factorization, role of nonfactorizable higher-order and hadronization corrections is discussed.
We study the production of a prompt J/ψ meson in association with a prompt photon in ep deep-inelastic scattering within the factorisation formalism of non-relativistic quantum chromodynamics (NRQCD) ...and demonstrate that this process provides a clean probe of the colour-octet mechanism at DESY HERA. Our analysis is based on an updated set of non-perturbative NRQCD matrix elements obtained through a joint fit to data on charmonium inclusive hadroproduction from runs I and II at the Fermilab Tevatron.
In the virtual presence of a heavy quark
t, the interactiions of a
CP-odd scalar boson
A, with mass
M
A
⪡ 2
M
t
, with gluons and light quarks can be described by an effective Lagrangian. We ...analytically derive the coefficient functions of the respective physical operators to three loops in quantum chromodynamics (QCD), adopting the modified minimal-subtraction (
MS
) scheme of dimensional regularization. Special attention is paid to the proper treatment of the
γ5 matrix and the Levi-Civita ϵ tensor in
D dimensions. In the case of the effective
ggA coupling, we find agreement with an all-order prediction based on a low-energy theorem in connection with the Adler-Bardeen non-renormalization theorem. This effective Lagrangian allows us to analytically evaluate the next-to-leading QCD correction to the
A →
gg partial decay width by considering massless diagrams. For
MA = 100 GeV, the resulting correction factor reads
1 + (
221
12
) α
s
(5) (MA) /π + 165.9 (α
s
(5)(M
A) / π)
2 ≈ 1 + 0.68 + 0.23
. We compare this result with predictions based on various scale-optimization methods.
PDF
