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.
121596214
Test of duality in baryon--antibaryon amplitudes from Reggeon--particle scattering
Abstract By studying the backward production data for meson resonances we investigate the dual properties of baryon-Reggeised antibaryon elastic scattering. We find strong support for the duality prediction that meson resonances in the baryon antibaryon channel should be dual to an exotic trajectory.
120719039
Duality constraints for mesons
Abstract A new method of imposing semi-local duality constraints is discussed, which satisfies the theoretical requirements of crossing symmetry and self-consistency. The duality relations involve only physical on-shell particles, and give many conditions on their masses and couplings. All constraints from PP→PP and PV→PP amplitudes with ordinary and strange particles give compatible results and are in good agreement with experiment. In particular, the near linearity of Regge trajectories is explained. The internal consistency of constraints with charmed particles is not as good, and implies stronger contributions from daughter resonances.
6876910
Structure Functions Are Not Parton Probabilities
The common view that structure functions measured in deep inelastic lepton scattering are determined by the probability distribution of quarks and gluons in the target is not correct. We show that the leading-twist cross section is affected by the rescattering of the struck quark in the target. This is consistent with the Glauber-Gribov interpretation of shadowing as a rescattering effect.
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.
119081579
Perturbative QCD with quark and gluon condensates
The quark 〈 ψ ¯ ψ 〉 and gluon ( F μν F μν ) vacuum expectation values are non-vanishing at low orders in α s when the perturbative ground state includes quark and gluon pairs. This offers possibilities of studying the effects of a non-trivial vacuum using formally exact perturbative methods. The QCD Feynman rules are modified only for the free, on-shell quark and gluon propagators at zero four-momentum. Gauge and lorentz invariance is maintained, while chiral symmetry is spontaneously broken by the ground state.
119250582
Inclusive Perspectives
I discuss the relation between inclusive and exclusive dynamics suggested by Bloom-Gilman duality. Duality implies the simultaneous applicability of two distinct limits, the standard DIS limit of hard inclusive processes taken at fixed xB and a limit where the hadronic mass is held fixed. I review experimental evidence for the relevance of the fixed mass limit in inclusive processes at high xF. Semi-local duality suggests that inclusive and exclusive processes occur on the same target Fock states. DIS scaling then implies that the Fock states contributing to hard exclusive processes have a large transverse size, i.e., that the hard scattering occurs off a single parton which carries a large fraction of the hadron momentum.
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.
119327590
Semi-exclusive DVCS
We consider Semi-Exclusive Deeply Virtual Compton Scattering, gamma* p \to gamma Y (SECS), where Y is an inclusive state of intermediate mass, \Lambda_QCD<<m_Y<<Q. When the photon is produced with a large transverse momentum k_T \sim m_Y the subprocess is hard and the struck quark fragments independently of the target spectators. Using completeness this allows to express the SECS cross section in terms of ordinary parton distributions. Apart from direct comparisons with data (yet to come) new information on Bloom-Gilman duality may be obtained through comparisons of resonance production via DVCS (gamma* p \to gamma N*) with the SECS scaling distribution in m_Y.
118891192
Rescattering Effects on DIS Parton Distributions
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.
18881983
QCD factorization at fixed Q^2(1-x)
Amplitudes of hard {\it exclusive} processes such as \gamma^*(Q^2) N \to \gamma Y, where Y=N (DVCS) or any other state with a limited mass (M_Y^2 << Q^2), factorize into a hard subprocess amplitude and a target (transition) GPD. The corresponding {\it inclusive} cross section, summed over all states Y of a given (limited) mass, is then given by the discontinuity of a forward multiparton distribution. An application to the Drell-Yan process \pi^+ N \to \gamma^*(x_F,Q^2)+Y allows to explain the observed longitudinal polarization of the virtual photon at high x_F.