arXiv subjects

S. J. Brodsky

Publications and source records attributed to S. J. Brodsky.

130 records · Page 8Linked to original sources

arXiv1994

Hadroproduction and Polarization of Charmonium

In the limit of heavy quark mass, the production cross section and polarization of quarkonia can be calculated in perturbative QCD. We study the $p_\perp$-averaged production of charmonium states in $πN$ collisions at fixed target energies. The data on the relative production rates of $\jp$ and $χ_J$ is found to disagree with leading twist QCD. The polarization of the $\jp$ indicates that the discrepancy is not due to poorly known parton distributions nor to the size of higher order effects ($K$-factors). Rather, the disagreement suggests important higher twist corrections, as has been surmised earlier from the nuclear target $A$-dependence of the production cross section.

hep-ph↗

arXiv1994

Polarization as a Probe to the Production Mechanisms of Charmonium in $πN$ Collisions

Measurements of the polarization of $\jp$ produced in pion-nucleus collisions are in disagreement with leading twist QCD prediction where $\jp$ is observed to have negligible polarization whereas theory predicts substantial polarization. We argue that this discrepancy cannot be due to poorly known structure functions nor the relative production rates of $\jp$ and $χ_J$. The disagreement between theory and experiment suggests important higher twist corrections, as has earlier been surmised from the anomalous non-factorized nuclear $A$-dependence of the $\jp$ cross section.

hep-ph↗

arXiv1994

Angular Distributions in the Drell-Yan Process: A Closer Look at Higher Twist Effects

We calculate the angular distribution of the lepton produced in the Drell-Yan reaction taking into account pion bound state effects. We work in the kinematic region where one of the pion constituents goes far off-shell, which allows us to treat the bound state problem perturbatively. We show that the angular distribution is very sensitive to the shape of the pion distribution amplitude. The model we discuss fits the data if we choose a two-humped pion distribution amplitude suggested by QCD sum rules.

hep-ph↗

arXiv1994

QCD and Intrinsic Heavy Quark Predictions for Leading Charm and Beauty Hadroproduction

Recent experiments at Fermilab and CERN have observed a strong asymmetry between the hadroproduction cross sections of leading $D$ mesons, containing projectile valence quarks, and nonleading charmed mesons, without projectile valence quarks. The observed correlations of the $π^{\pm} N \to D^\pm X$ cross section with the projectile charge violates the usual assumption that heavy quark jet fragmentation factorizes. We examine the asymmetry between leading and nonleading charm production as a function of $x_f$ and $p_T^2$ assuming a two-component model combining leading-twist fusion subprocesses and charm production from intrinsic heavy quark Fock states. We predict a sizable asymmetry at low $p_T^2$ and high $x_f$ from coalescence of the charm quarks with the comoving spectator quarks of the projectile. An intrinsic $c \overline c$ production cross section of 0.5 $μ$b is sufficient to explain both the magnitude and kinematic dependence of the asymmetry. In contrast, the charm jet hadronization mechanisms contained in PYTHIA predict a sizeable leading charm asymmetry even at low $x_F.$ The two-component model is extended to predict the asymmetry in $B$ meson production in proton-proton and pion-proton interactions.

hep-ph↗