120877951
Sister trajectories in the dual resonance model
Abstract The existence of a Regge tranjectory γ = α /3 − 1 in the eight-point amplitude of the Dual Resonance Model set of demonstrated. It is suggested that the three presently known trajectories α, β and γ are part of an infinite set of “sister” trajectories, the expected properties of which are discussed.
125123165
Systematics of charm production in hadronic collisions
Charmed particles produced in hadron collisions have a harder momentum spectrum than predicted by QCD at leading twist. This and related features of the data can be understood as resulting from coalescence of the charm quark with co‐moving light quarks, and a contribution of intrinsic charm at large values of xF.
125593487
NEW DUALITY CONSTRAINTS ON MESON AMPLITUDES
35241283
Mass limits on particles from pulsed sources: How reliable are they?
It is widely believed that the arrival at Earth of pulsed emission from a cosmic accelerator such as Cygnus X-3 puts mass limits on the particles carrying the radiation of order 1 GeV. We show that these simple kinematic estimates are unreliable and can often be avoided. The actual mass limit depends critically on the detailed structure of the pulse, i.e., on (i) the shape of the flux as a function of energy and (ii) the minimum and maximum energies. We illustrate this by showing that masses of 100 GeV or more for the ''cygnets'' responsible for the unexplained pulsed muon signal from Cygnus X-3 can be made consistent with present experiments. These masses are large enough to accommodate the 3/sup 0/ angular spread of the muon pulses and to exclude the production of cygnets in accelerator experiments.
7918302
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⊥-averaged production of charmonium states in πN collisions at fixed target energies. The data on the relative production rates of J/ψ and χJ is found to disagree with leading twist QCD. The polarization of the J/ψ 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.
120494867
Parton evolution as a branching process
Abstract The evolution of parton distributions in high-energy scattering is described using the methods of branching processes. Exclusive, inclusive and multiplicity distributions can be simply obtained from a functional form of the evolution equations. Previous results derived from leading logarithmic terms in perturbation theory are verified. As a new application, we calculate the multiplicity distribution of partons with momenta above a given cutoff.
7794876
QCD Green functions in a gluon field
We formulate a dressed perturbative expansion of QCD, where the standard diagrams are evaluated in the presence of a constant external gluon field whose magnitude is gaussian distributed. The approach is Poincare and gauge invariant, and modifies the usual results for hard processes only by power suppressed contributions. Long distance propagation of quarks and gluons turns out to be inhibited due to a branch point singularity instead of a pole at p 2 = 0 in the quark and gluon propagators. The dressing keeps the (massless) quarks in q fluctuations of the photon at a finite distance from each other.
119307830
Bound states at lowest order in hbar
Bound states poles in scattering amplitudes are generated by the divergence of the perturbative series due to enhanced Coulomb scattering near thresholds. This suggests to organize bound state calculations according to an expansion in hbar, i.e., in the number of loops. I study QED and QCD bound states at lowest order in hbar, which are analogous to Born amplitudes. The absence of loops allows the use of retarded boundary conditions where particles only propagate forward in time, making a hamiltonian approach feasible. The instantaneous A^0 field is determined by the equations of motion separately for each Fock component of the bound state. The field equations are compatible with a linear A^0 potential as a homogeneous, non-perturbative solution. Stationarity of the action determines the direction of the ensuing constant electric field in each Fock state. Applying this approach to relativistic qqbar and qqq states in QCD results in a bound state equation which provides a reasonable description of the spectrum, including linear Regge trajectories. The equal-time wave functions have unique Lorentz transformation properties, which ensure the correct dependence of the bound state energy on the center-of-mass momentum. The qqq potential is gauge covariant and confines the three quarks in a symmetric way.
829521
The Unexpected Role of Final State Interactions in Deep Inelastic Scattering
Rescattering of the struck quark in Deep Inelastic Scattering implies that measured parton distributions are not directly related to the Fock state probabilities of the target wave function. The production amplitudes acquire dynamical phases, which gives rise to shadowing and diffraction in DIS. I review the kinematics and dynamics of DIS as seen in various frames and gauges.
118656657
Hadron Structure
I discuss a Born (~ → 0) approximation of hadrons, motivated by a general feature of the data: The spectra of hadrons reflect their valence (qq̄ or qqq) constituents, whereas hard scattering reveals a prominent sea quark distribution. Why do the sea quark d.o.f’s not imply a richer spectrum? I look for an approach that can reconcile the quark and parton model descriptions of hadrons, and consider how this physics could emerge from the QCD Lagrangian. The possibilities are reduced by insisting that the approximation should be simple, yet adhere to the rules of quantum field theory. One might suspect that no such method exists – but the Born approximation presents itself. The description of relativistic bound states that it brings has interesting features which merit further exploration.
119448188
Structure functions are not Parton probabilities
Abstract Parton distributions given by deep inelastic lepton scattering (DIS) are not equal to the probabilities of finding those partons in the parent wave function. Soft rescattering of the struck parton within the coherence length of the hard process influences the DIS cross section and gives dynamical phases to the scattering amplitudes. This gives rise to diffractive DIS, shadowing in nuclear targets and transverse spin asymmetry.