QCD prediction of transverse momentum distribution of partons

A general method to compute the development of the transverse momentum distributions of the partons as Q² increases is presented. As an example, the average 〈p_⊥²〉 is computed for the valence, charmed, sea and gluonic partons in the Q² range from 1 GeV² to 120 GeV². The results show a fast increase of the gluonic contribution, a slow increase of the valence contribution and an almost flat sea contribution.     

QCD predictions for jet transverse momentum in leptoproduction

QCD predictions for distributions in the jet variable Σ_T  [Σ_hadp_T|]² are calculated for incident ν, $\text{ν}$ and μ. Estimates of the nonperturbative background are constructed.     

Probing the transverse momentum structure of QCD jets

Large logarithms are resummed to give QCD predictions for the differing transverse momentum structure of quark and gluon jets.     

Inclusive production at large transverse momentum in QCD

We calculate the cross section for the process quark + quark → quark (with large transverse momentum) + anything, up to order g⁶ in the cross section and in the leading-logarithm approximation. The result is suggestive of a simple ansatz for the calculation of the asymptotic behaviour of cross sections for the production of particles or jets with large transverse momenta.     

Hadron production at large transverse momentum and QCD

The predictions of a QCD-based hardscattering model for large p_T hadronic processes are investigated. Not only quark-quark scattering but all contributions in lowest order are considered. At low x_T, gluon-gluon and quark-gluon scattering are found to dominate the quark-quark term. At present energies the QCD predictions lie below the data but already come very close at the highest ISR energy. Predictions for higher p_T values and higher energies are made.     

Rapidity and transverse momentum distributions of heavy quarks produced by double pomeron exchange

Zeitschrift für Physik C Particles and Fields - Rapidity and transverse momentum distributions of heavy quarks produced by double exchange of Donnachie-Landshoff pomeron are presented and...     

Small transverse momentum distributions in hard processes

The effects of soft gluon brehmsstrahlung on the k_⊥ distributions of μ pairs produced in hadron-hadron collisions are studied using the Block-Nordsiek method. At moderate energies we obtain a good fit to present experimental data by adjusting the values of two phenomenological parameters. At quite large energies the predictions are independent of specific values assigned to the parameters and the whole p_⊥ distribution, including $\text{p}{}_{\mathrm{\perp }}\text{? 0}$, turns out to be computable.     

Lepton pair production at large transverse momentum in second order QCD

The production of Drell-Yan pairs at large transverse momentum is calculated up to O(α_s²) for a non-singlet combination defined as the cross section for an incident particle minus the analogous cross section for an incident antiparticle. Analytic results are presented for all cross sections and numerical estimates are given at various energies of experimental interest.     

Nuclear effects at large transverse momentum in a QCD parton model

Production of single mesons and opposite side pairs of mesons in hadron-nucleus and nucleusnucleus collisions are calculated in the framework of the QCD parton model, with the assumption that quarks and gluons undergo multiple scattering in the nucleus. A comparison with all available data is made. It is also shown that the anomalous nuclear enhancement, especially its dependence on the flavour, can be quantitatively described within the model. Furthermore, we predict no enhancement for symmetric pairs as it seems to be indicated by the data. Predictions for largep _T production in α?α scattering at ISR are made.     

A method of experimentally probing transverse momentum dependent distributions

We calculate the double spin asymmetry A_LL$A_{LL}$ for the π⁰${\pi }^0$ production in semi-inclusive deep inelastic lepton–proton scattering with a spectator model of power-law and a model based on the factorization ansatz. We also calculate the double spin asymmetry for the integration over parts of the kinematic range for the setups of the experiments of COMPASS, HERMES, and JLab. We find that the results are characteristically dependent on the model used. Therefore, we suggest that the measurements of the double spin asymmetry provides a method of experimentally probing the transverse momentum dependent distributions.     

Optimisation of variables for studying dilepton transverse momentum distributions at hadron colliders

In future measurements of the dilepton (Z/γ ^∗) transverse momentum, Q _T , at both the Tevatron and LHC, the achievable bin widths and the ultimate precision of the measurements will be limited by experimental resolution rather than by the available event statistics. In a recent paper the variable a _T , which corresponds to the component of Q _T that is transverse to the dilepton thrust axis, has been studied in this regard. In the region, Q _T < 30 GeV, a _T has been shown to be less susceptible to experimental resolution and efficiency effects than the Q _T . Extending over all Q _T , we now demonstrate that dividing a _T (or Q _T ) by the measured dilepton invariant mass further improves the resolution. In addition, we propose a new variable, f_h^*phi _{rm eta }^{*}, that is determined exclusively from the measured lepton directions; this is even more precisely determined experimentally than the above variables and is similarly sensitive to the Q _T . The greater precision achievable using such variables will enable more stringent tests of QCD and tighter constraints on Monte Carlo event generator tunes.     

QCD off the lightcone and the demise of the transverse momentum cut-off

Criteria are given for the applicability of the asymptotic freedom of QCD. Perturbative QCD has a much broader range of utility than lightcone dominated phenomena. The most striking predictions pertain to transverse momenta that scale, i.e. grow proportionately to the large invariants. While hints of these unlimited transverse momenta are already visible in existing data, the predictions are unmistakable for μ-p, e⁺-e⁻, and hadron-hadron experiments now planned.     

Unintegrated CCFM parton distributions and transverse momentum of gauge bosons

Transverse momentum distribution of gauge bosons W^± and Z⁰ is calculated using unintegrated parton distributions obtained by solving leading order CCFM equation(s) in the impact parameter space. For illustration we compare the results of the fixed-order collinear, soft-gluon resummation and CCFM approaches. A parameter of a nonperturbative form factor is adjusted to the D0 data. In contrast to the collinear approach, the leading order calculation based on the unintegrated CCFM parton distributions generates transverse momentum distributions of gauge bosons, which are almost consistent with experimental data provided the parameter of the nonperturbative form factor is appropriately adjusted. The W⁺–W⁻ asymmetry is calculated as a function of the boson rapidity and transverse momentum. Predictions are given for RHIC and LHC.     

Fluctuations and transverse momentum distributions in the color clustering approach

We present our results on transverse momentum fluctuations, multiplicity fluctuations and transverse momentum distributions for baryons and mesons in the framework of the clustering of color sources. We determine under what conditions the initial state configurations can lead to color connection, and more specifically, if variations of the initial state can lead to a transition from disconnected to connected color clusters, modifying the number of effective sources. We find that beyond a critical point, one has a condensate, containing interacting and hence color-connected sources. This point thus specifies the onset of color deconfinement. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. We obtain a non-monotonic dependence of the p _T and multiplicity fluctuations with the number of participants. We present our results for the fluctuations and the transverse momentum distributions at RHIC energies compared to the existing experimental data and our predictions for LHC energies.