Bound state effects in transverse momentum parton distributions

We use a non-gaussian intrinsic transverse momentum distribution, associated with the wavefunction of the partonic ground state inside the proton, to calculate the production of π0 with intermediate transverse momentum values in p − p collisions at high energies. It is shown that a perfect description of the experimental data for different experiments is achieved using an almost constant value for the mean transverse momentum of the initial partons, compatible with Heisenberg’s uncertainty relation (⟨kT ⟩ ≈ 0.3 GeV ). Our analysis suggests the presence of a non-vanishing, non-perturbative contribution from partonic bound states to the pp → πo(γ) + X and pp → p + X cross section.

Upsilon Transverse Momentum at Hadron Colliders

We predict the shape of the transverse momentum pT spectrum of ϒ production. The distribution at low pT is dominated by the region of small impact parameter b and may be computed reliably in perturbation theory. We resum to all orders in the strong coupling αs the process-independent large logarithmic contributions that arise from initial-state gluon showers in the small pT(≤ Mϒ) region. The cross section at large pT is represented by the [Formula: see text] lowest-order non-vanishing perturbative contribution.

IMPLICATIONS OF GLUON RADIATION EFFECTS AND SOFT TRANSVERSE MOMENTA FOR THE NUCLEON SUBSTRUCTURE IN QCD

The proton and neutron helicity-conserving form factors in the spacelike region are studied within a convolution scheme which takes into account: (i) soft-gluon radiative corrections via Sudakov-type form factors, and (ii) the intrinsic k⊥-dependence of the nucleon wave function. Results are presented for a complete set of nucleon distribution amplitudes which comply with QCD sum rules. Implications for the end point behavior of nucleon distribution amplitudes are discussed in the context of Appell decompositions. The calculated leading-order perturbative contribution to both form factors falls short compared to the existing data, indicating substantial higher-order perturbative corrections (i.e. a large K factor) and/or sizeable soft contributions, e.g., higher-twist effects, at presently accessible momentum-transfer values.