Drell-Yan Cross Section Research Articles

Flavor asymmetry of the nucleon sea

We discuss the relation between the ratio of the proton-deuteron (pd) Drell–Yan cross section to the proton-proton (pp) one Δ(T)σpd/2Δ(T)σpp and the flavor asymmetry in polarized light-antiquark distributions. Using a recent formalism of the polarized pd Drell–Yan process, we show that the difference between the pp and pd cross sections is valuable for finding not only the flavor asymmetry in longitudinally polarized antiquark distributions but also the one in transversity distributions. It is especially important that we point out the possibility of measuring the flavor asymmetry in the transversity distributions because it cannot be found in W production processes and inclusive lepton scattering due to the chiral-odd property.

The color dipole picture of the Drell–Yan process

At high energies, Drell–Yan (DY) dilepton production viewed in the target rest frame should be interpreted as bremsstrahlung and can be expressed in terms of the same color dipole cross section as DIS. We compute DY cross sections on a nucleon target with the realistic parameterization for the dipole cross section saturated at large separations. The results are compared to experimental data and predictions for RHIC are presented. The transverse momentum distribution of the DY process is calculated and energy growth is expected to be steeper at large than at small transverse momenta. We also calculate the DY angular distribution and investigate deviations from the 1+cos 2 θ shape.

Next-to-next-to-leading logarithmic threshold resummation for deep-inelastic scattering and the Drell–Yan process

The soft-gluon resummation exponents G N in moment space are investigated for the quark coefficient functions in deep-inelastic structure functions and the quark–antiquark contribution to the Drell–Yan cross section dσ/ dM. Employing results from two- and three-loop calculations we obtain the next-to-next-to-leading logarithmic terms α s ( α s ln N) n of G N to all orders in the strong coupling constant α s . These new contributions facilitate a reliable assessment of the numerical effect and the stability of the large- N expansion.

Nuclear enhanced higher-twist effects in the Drell–Yan process

Abstract We calculate the Drell–Yan cross section, resolving the full kinematics of the lepton pair, at high transverse momentum for hadron nucleus collisions. We use the general framework of Luo, Qiu and Sterman to calculate double scattering contributions that are of twist-4 and demonstrate their nuclear enhancement. By comparing single and double scattering at RHIC energies we find that double scattering gives contributions of comparable size. We also show that the angular dependence of the Drell–Yan pair discriminates between the various double scattering contributions.

Proton-deuteron asymmetry in Drell–Yan processes and polarized light-antiquark distributions

We discuss the relation between the ratio of the proton-deuteron (pd) Drell–Yan cross section to the proton-proton (pp) one Δ ( T) σ pd/2 Δ ( T) σ pp and the flavor asymmetry in polarized light-antiquark distributions. Using a recent formalism of the polarized pd Drell–Yan process, we show that the difference between the pp and pd cross sections is valuable for finding not only the flavor asymmetry in longitudinally polarized antiquark distributions but also the one in transversity distributions. It is especially important that we point out the possibility of measuring the flavor asymmetry in the transversity distributions because it cannot be found in W production processes and inclusive lepton scattering due to the chiral-odd property.

Color gauge invariance in the Drell–Yan process

We consider the color gauge invariance of a factorized description of the Drell–Yan process cross section. In particular, we focus on the next-to-leading twist contributions for polarized scattering and on the cross section differential in the transverse momentum of the lepton pair in the region where the transverse momentum is small compared to the hard scale. The hadron tensor is expressed in terms of manifestly color gauge invariant, non-local operator matrix elements and a color gauge invariant treatment of soft gluon poles is given. Also, we clarify the discrepancy between two published results for a single spin asymmetry in the Drell–Yan cross section. This asymmetry arises if such a soft gluon pole is present in a specific twist-three hadronic matrix element.

Power corrections to the differential Drell Yan cross section

We estimate the power corrections (infrared renormalon contributions) to the coefficient functions for the differential Drell-Yan cross-section $d^2\sigma/dQ^2dy$, where $Q^2$ is the mass squared and $y$ the rapidity of the produced lepton pair. We employ the dispersive method based on the analysis of one-loop Feynman graphs containing a massive gluon.

Drell-Yan and J/ψ production in high energy proton-nucleus and nucleus-nucleus collisions

The distributions of outgoing protons and charged hadrons in high energy proton-nucleus collisions are described rather well by a linear extrapolation from proton-proton collisions. This linear extrapolation is applied to precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets. The deviation from linear scaling in the atomic number A can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4±0.1 fm/c. Then we apply the linear extrapolation to measured J/ψ production cross sections for 200 and 450 GeV/c protons incident on a variety of nuclear targets. Our analysis takes into account energy loss of the beam proton, the time delay of particle production due to quantum coherence, and absorption of the J/ψ on nucleons. The best representation is obtained for a coherence time of 0.5 fm/c, which is consistent with Drell-Yan production, and an absorption cross section of 3.6 mb, which is consistent with the value deduced from photoproduction of the J/ψ on nuclear targets. Finally, we compare to recent J/ψ data from S+U and Pb+Pb collisions at the SPS. The former are reproduced reasonably well with no new parameters, but not the latter.

Intrinsic transverse momentum and transverse spin asymmetries

We investigate leading twist transverse momentum dependent origins of transverse spin asymmetries in hadron-hadron collisions. The chiral-odd T-odd distribution function with intrinsic transverse momentum dependence, which would signal an intrinsic handedness of quarks inside a hadron, could account for single spin asymmetries and at the same time for the large cos 2φ asymmetry in the unpolarized Drell-Yan cross section, which still lacks understanding. We show explicitly how it would relate unpolarized and polarized observables measurable with proton-proton collisions at RHIC. It would offer a new possibility to access the transversity distribution function.

Parton Energy Loss Limits and Shadowing in Drell-Yan Dimuon Production

A precise measurement of the ratios of the Drell-Yan cross section per nucleon for an 800 GeV/{ital c} proton beam incident on Be, Fe, and W targets is reported. The behavior of the Drell-Yan ratios at small target-parton momentum fraction is well described by an existing fit to the shadowing observed in deep-inelastic scattering. The cross-section ratios as a function of the incident-parton momentum fraction set tight limits on the energy loss of quarks passing through a cold nucleus. {copyright} {ital 1999} {ital The American Physical Society}

Measurement of the High-Mass Drell-Yan Cross Section and Limits on Quark-Electron Compositeness Scales

We present a measurement of the Drell-Yan cross section at high dielectron invariant mass using 120/pb of data collected in pbar-p collisions at sqrt(s) = 1.8 TeV by the D0 collaboration during 1992-96. No deviation from standard model expectations is observed. We use the data to set limits on the energy scale of quark-electron compositeness with common constituents. The 95% confidence level lower limits on the compositeness scale vary between 3.3 TeV and 6.1 TeV depending on the assumed form of the effective contact interaction.

Investigating the origins of transverse spin asymmetries at BNL RHIC

We discuss possible origins of transverse spin asymmetries in hadron-hadron collisions and propose an explanation in terms of a chiral-odd T-odd distribution function with intrinsic transverse momentum dependence, which would signal a correlation between the transverse spin and the transverse momentum of quarks inside an unpolarized hadron. We will argue that despite its conceptual problems, it can account for single spin asymmetries, for example in ${\mathrm{pp}}^{\ensuremath{\uparrow}}\ensuremath{\rightarrow}\ensuremath{\pi}X,$ and at the same time for the large $\mathrm{cos}2\ensuremath{\varphi}$ asymmetry in the unpolarized Drell-Yan cross section, which still lacks understanding. We use the latter asymmetry to arrive at a crude model for this function and show explicitly how it relates unpolarized and polarized observables in the Drell-Yan process, as could be measured with the proton-proton collisions at BNL RHIC. Moreover, it would provide an alternative method of accessing the transversity distribution function ${h}_{1}.$ For future reference we also list the complete set of azimuthal asymmetries in the unpolarized and polarized Drell-Yan process at leading order involving T-odd distribution functions with intrinsic transverse momentum dependence.

Coherence Time in High Energy Proton-Nucleus Collisions

Precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets exhibit a deviation from linear scaling in the atomic number A. We show that this deviation can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4 +- 0.1 fm/c, corresponding to a coherence path length of 8 +- 2 fm in the rest frame of the nucleus.

Diffractive production of Drell–Yan pairs and heavy flavors

Partonic interpretation of high-energy reactions is known to depend on a reference frame. Particularly, in the rest frame of the target Drell–Yan process looks like a freeing of the projectile l l ̄ fluctuation, rather than q q ̄ →l l ̄ annihilation. The light-cone representation for Drell–Yan reaction is very similar to that in DIS and exposes a substantial contamination of soft interactions which turns out to be dominant in diffractive production of lepton pairs and in nuclear shadowing. We estimate the fraction of diffractive events in the total Drell–Yan cross section, which scales in M 2, and find a substantial deviation from factorization. An analogous approach is developed for diffractive production of heavy flavors.

Measurement ofZ0and Drell-Yan production cross sections using dimuons inp¯pcollisions ats=1.8TeV

We present a measurement of Z 0 boson and Drell-Yan production cross sections in pp collisions at √s =1.8TeV using a sample of 107 pb -1 accumulated by the Collider Detector at Fermilab. The Drell-Yan cross section is measured in the mass range of M μμ > 40GeV/c 2 . We compare the measurements with the predictions of quantum chromodynamics in both leading order and next-to-leading order, incorporating the recent parton distribution functions. The measurements are consistent with the standard model expectations. ©1999 The American Physical Society.

Mesonic and binding contributions to the nuclear Drell-Yan process

We have evaluated the Drell-Yan cross section in nuclei paying special attention to the meson cloud contribution from pions and ϱ-mesons, for which an accurate calculation using the meson nuclear spectral functions is used. Similarly, the nucleonic contribution is evaluated in terms of a relativistic nucleon spectral function. Fair agreement with experiment is found for different nuclei and the results show a sizeable contribution from the renormalized meson cloud. In order to reproduce the experiment a novel element is introduced, consisting of a gradual energy loss of the incoming proton in its pass through the nucleus which produces a strong A dependence at x 1 large.

J/ ψ, ψ′ and Drell-Yan production in pp and pd interactions at 450 GeV/c

J/ ψ and ψ′ production cross-sections are measured in pp and pd collisions at 450 GeV/ c at the CERN-SPS. The Drell-Yan cross section for muon pairs in the mass range [4.3–8.0] GeV/ c 2 is also determined in the same experiment.

D¯/ūasymmetry and the origin of the nucleon sea

The Drell-Yan cross section ratios, {sigma}(p+d)/{sigma}(p+p), measured in Fermilab E866, have led to the first determination of {bar d}(x)/{bar u}(x), {bar d}(x){minus}{bar u}(x), and the integral of {bar d}(x){minus}{bar u}(x) for the proton over the range 0.02{le}x{le}0.345. The E866 results are compared with predictions based on parton distribution functions and various theoretical models. The relationship between the E866 results and the NMC measurement of the Gottfried integral is discussed. The agreement between the E866 results and models employing virtual mesons indicates that these non-perturbative processes play an important role in the origin of the {bar d},{bar u} asymmetry in the nucleon sea. {copyright} {ital 1998} {ital The American Physical Society}

And Drell-Yan cross-sections in PbPb interactions at 158 GeV/c per nucleon

Abstract First results are reported on J ψ and Drell-Yan cross-sections in PbPb reactions at 158 GeV/ c per nucleon. The ratio of cross-sections σ J/ψ /σ DY is studied as a function of the impact parameter of the collision estimated from the measured transverse energy.

QCD corrections to the longitudinally polarized Drell-Yan process

In this paper we calculate the O( α s ) corrections to the χ F and y distributions of lepton pairs produced in collisions of longitudinally polarized hadrons. The numerical importance of these corrections is studied and consequences for the extraction of the polarized sea-quark distributions from a measurement of the longitudinally polarized Drell-Yan cross section are discussed.