Yan Lepton Pairs Research Articles

Production of Drell–Yan lepton pairs in hadron collisions: Transverse-momentum resummation at next-to-next-to-leading logarithmic accuracy

We consider the transverse-momentum (qT) distribution of Drell–Yan lepton pairs produced in hadron collisions. At small values of qT, we resum the logarithmically-enhanced perturbative QCD contributions up to next-to-next-to-leading logarithmic accuracy. At intermediate and large values of qT, we consistently combine resummation with the known next-to-leading order perturbative result. All perturbative terms up to order αS2 are included in our computation which, after integration over qT, reproduces the known next-to-next-to-leading order result for the Drell–Yan total cross section. We show and discuss the reduction in the scale dependence of the results with respect to lower-order calculations, estimating the corresponding perturbative uncertainty. We present a preliminary comparison with Tevatron Run II data.

Drell–Yan lepton pair azimuthal asymmetry in hadronic processes

We study the azimuthal asymmetry (cos2ϕ) in the Drell–Yan lepton pair production in hadronic scattering processes at moderate transverse momentum region, taking into account the contributions from the twist-three quark–gluon correlations from the unpolarized hadrons. The contributions are found to dominate the asymmetry, and are not power suppressed by q⊥/Q at small q⊥ where q⊥ and Q are the transverse momentum and invariant mass of the lepton pair. Accordingly, the Lam–Tung relation will be violated at this momentum region, and its violation depends on the twist-three functions. However, at large transverse momentum q⊥∼Q, the Lam–Tung relation still holds because all corrections are power suppressed by Λ2/q⊥2∼Λ2/Q2 where Λ is the typical nonperturbative scale.

Transverse-momentum resummation: A perturbative study of Z production at the Tevatron

We consider transverse-momentum ( q T ) resummation for Drell–Yan lepton pair production in hadron collisions. At small values of q T , the logarithmically-enhanced QCD contributions are resummed up to next-to-leading logarithmic accuracy. At intermediate and large values of q T , resummation is consistently combined with the fixed-order perturbative result. We present numerical results for e + e − pairs from the decay of Z bosons produced at Tevatron energies. We perform a detailed study of the scale dependence of the results to estimate the corresponding perturbative uncertainty. We comment on the comparison with the available Tevatron data.

Resummation of threshold logarithms in effective field theory for DIS, Drell–Yan and Higgs production

We apply the effective field theoretic (EFT) approach to resum the large perturbative logarithms arising when partonic hard scattering cross sections are taken to the threshold limit. We consider deep inelastic scattering, Drell–Yan lepton pair production and the standard model Higgs production through gluon–gluon fusion via a heavy-top quark loop. We demonstrate the equivalence of the EFT approach with the more conventional, factorization-based methods to all logarithmic accuracies and to all orders in perturbation theory. Specific EFT results are shown for the resummation up to next-to-next-to-next-to leading logarithmic accuracy for the above-mentioned processes. We emphasize the relative simplicity by which we derive most of the results and more importantly their clear physical origin. We find a new relation between the functions f ( q , g ) in the quark and gluon form factors and the matching coefficients in Drell–Yan and Higgs production, which may explain their universality believed to hold to all orders in perturbation theory.

Universality of the Collins–Soper–Sterman nonperturbative function in vector boson production

We revise the b∗ model for the Collins–Soper–Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. This revision leads to excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell–Yan lepton pair and Z boson production. The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis.

Quark Energy Loss and Shadowing in Nuclear Drell–Yan Process**Theproject partially supported by National NaturalScience Foundation of China under Grant Nos. 90103020, 10075057, and 10175074, CAS Knowledge Innovation Project under Grant No. KJCX2-SW-N02, the StateKey Basic Research Development Program under Grant No. G20000774,and the Natural ScienceFoundation of Hebei Province of China under Grant No. 103143

The energy loss effect in nuclear matter is another nucleareffect apart from the nuclear effects on the parton distributionas in deep inelastic scattering process. The quark energy loss canbe measured best by the nuclear dependence of the high energynuclear Drell–Yan process. By means of three kinds of quarkenergy loss parameterizations given in literature and thenuclear parton distribution extracted only with lepton-nucleusdeep inelastic scattering experimental data, measured Drell–Yanproduction cross sections are analyzed for 800 GeV proton incidenton a variety of nuclear targets from FNAL E866. It is shown thatour results with considering the energy loss effect are muchdifferent from those of the FNAL E866, who analyzes theexperimental data with the nuclear parton distribution functionsobtained by using the deep inelastic lA collisions and pA nuclearDrell–Yan data. Considering the existence of energy loss effect inDrell–Yan lepton pairs production, we suggest that the extractionof nuclear parton distribution functions should notinclude Drell–Yan experimental data.

Effect of quark off-shellness in DIS and the Drell–Yan process

We study higher twist corrections to the perturbative QCD cross sections for e p deep inelastic scattering and the Drell–Yan lepton pair production in p p collision. The corrections arise due to the initial state interaction of the active quarks with the spectator partons. The effect of this interaction is calculated by dressing the incoming quark lines with phenomenological single parameter Breit–Wigner spectral functions and taking into account full off-shell kinematics. The quark width in the proton is estimated by analyzing the data on Drell–Yan triple differential cross section from the experiment E866 at Fermilab.

Global analysis of eeqq contact interactions and future prospects for high energy physics

Data from HERA, LEP and the Tevatron as well as from low energy experiments are used to constrain the scale of possible electron–quark contact interactions. Different models are considered, including the most general one, in which all new couplings can vary independently. Limits on couplings and mass scales are extracted and upper limits on possible effects to be observed in future HERA, LEP and Tevatron runnings are estimated. The total hadronic cross section at LEP and the \(e^{-}p\) scattering cross section at HERA are strongly constrained by the existing data, whereas large cross section deviations are still possible for Drell–Yan lepton pair production at the Tevatron.