Unintegrated parton distributions and prompt photon hadroproduction

Abstract

We introduce a general expression which enables the parton distribution, unintegrated over the parton transverse momentum, to be obtained from the conventional parton densities. We use the formalism to study the effects of the transverse momentum q t of the incoming partonic system on the calculation of the transverse momentum spectra of prompt photons produced in high energy pp and pp collisions. For the purposes of illustration, we use the double logarithm approximation. For large q t we calculate the effect directly from the perturbative formalism, whereas for small q t we bound the effect using two extreme hypotheses. In both q t domains we find that the shapes of the prompt photon spectra are not significantly modified, although the cross sections are enhanced.

Off-shell amplitudes and four-jet production inkT-factorization

“…We find that the pairs (1, 1), (1, 2), (1, 3), (1, 7), (1, 8), (3, 3) (3, 7), (3,8) together account for more than 95 % of the total cross section. This was tested for all the sets of cuts considered in this paper.…”

“…The new degree of freedom is introduced via the transverse k T k , which is perpendicular to the collision axis. The formula is valid when the x's are not too large and not too small and, in order to construct a full set of TMD parton densities, we apply the Kimber-MartinRyskin (KMR) prescription [7,8], which, at the end of the day, amounts to applying the Sudakov form factor onto the PDFs. M (i * , j * → 4 part.)…”

Low mass Drell-Yan production of lepton pairs at forward directions at the LHC: A hybrid approach

“…Kimber-Martin-Ryskin distributions [29] make a simple link to collinear distributions. In this approach the transverse momentum distribution of "initial" gluons originates from the last emission in the ladder.…”

“…Similar contribution of the g(q/q) → l + l − j subprocess would be trivially symmetric around the (y + = 0, y − = 0) point. The calculation was done with the leading-order MSTW08 quark/antiquark distributions and the Kimber-Martin-Ryskin UGDF [29]. The figure clearly shows that including only one of the contributions is not sufficient but we wish to stress that this is routinely done in the dipole approach (see e.g.…”

Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA

“…The magnitude of <k T > has been taken to reflect the confinement of quarks and the known size of the proton, with the assumption that these non-perturbative effects may be combined in a straightforward way with a perturbative calculation of the parton scattering. However, it has more recently been argued that when partons undergo hard scattering, the presence of additional initialstate gluon radiation beyond NLO in QCD can increase their effective <k T > value and that this may be a major contribution to the effects observed [8][9][10][11][12][13]. Within PYTHIA, both of these contributions are allowed for: there is an 'intrinsic' component together with a parton-shower component, and their combination is referred to here as the effective value of <k T > .…”