121048047
Chiral-odd parton distributions and Drell-Yan processes☆
Abstract We study the twist-two and twist-three chiral-odd parton distributions, h 1 ( x ), h L ( x ) and e ( x ), which appear in the quark density matrix of the nucleon. We explore the relationship between h 1 ( x ) and the spin properties of the nucleon; we unravel the twist structure of h L ( x ) and we emphasize the role of e ( x ) in studying the deep-inelastic structure function E 4 ν N ( x ) and the π N σ-term. We derive sum rules, make model estimates, and show that they all appear in Drell-Yan cross sections with polarized and unpolarized beams.
2998736
Final state interactions and gauge invariant parton distributions
Abstract Parton distributions contain factorizable final state interaction effects originating from the fast-moving struck quark interacting with the target spectators in deeply inelastic scattering. We show that these interactions give rise to gauge invariance of the transverse momentum-dependent parton distributions. As compared to previous analyses, our study demonstrates the existence of extra scaling contributions from transverse components of the gauge potential at the light-cone infinity. They form a transverse gauge link which is indispensable for restoration of the gauge invariance of parton distributions in the light-cone gauge where the gauge potential does not vanish asymptotically. Our finding helps to explain a number of features observed in a model calculation of structure functions in the light-cone gauge.
117193137
Delta -> N gamma* Coulomb quadrupole amplitude in PQCD
We present a leading-order PQCD factorization formula for the helicity-flip Delta-->Ngamma(*) matrix element G(0) (Coulomb quadrupole amplitude C2), taking into account the transverse momenta of the quarks and the contribution from the gluons. In the large Q(2) limit, its scaling behavior acquires a double-logarithmic correction log(2)(Q(2)/Lambda(2)) compared with the standard scaling analysis, due to the contribution from the orbital motion of the small-x partons. Based on this and on the latest JLab experimental results of the C2-M1 ratio R-SM at Q(2)=3-4 GeV2, we make a phenomenological prediction for the latter at higher values of Q(2).
17508397
QCD sum rule calculation for the tensor charge of the nucleon.
The nucleon{close_quote}s tensor charges (isovector {ital g}{sup {ital v}}{sub {ital T}}={delta}{ital u}{minus}{delta}{ital d} and isoscalar {ital g}{sup {ital s}}{sub {ital T}}={delta}{ital u}+{delta}{ital d}) are calculated using the QCD sum rules in the presence of an external tensor field. In addition to the standard quark and gluon condensates, new condensates described by vacuum susceptibilities are induced by the external field. The latter contributions to {ital g}{sup {ital v}}{sub {ital T}} and {ital g}{sup {ital s}}{sub {ital T}} are estimated to be small. After deriving some simplifying formulas, a detailed sum rule analysis yields {ital g}{sup {ital v}}{sub {ital T}}=1.29{plus_minus}0.51 and {ital g}{sup {ital s}}{sub {ital T}}=1.37{plus_minus}0.55, or {delta}{ital u}=1.33{plus_minus}0.53 and {delta}{ital d}=0.04{plus_minus}0.02 at the scale of 1 GeV{sup 2}. {copyright} {ital 1996 The American Physical Society.}
55516651
A Beautiful Spin
Spin is a beautiful concept that plays an ever important role in modern physics. In this talk, I start with a discussion of the origin of spin, and then turn to three themes in which spin has been crucial in subatomic physics: a lab to explore physics beyond the standard model, a tool to measure physical observables that are hard to obtain otherwise, a probe to unravel nonperturbative QCD. I conclude with some remarks on a world without spin.
119403070
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-Yanand Higgs production, which may explain their universality believed to hold to all orders in perturbation theory.
118107909
Status of Excited baryons at BES II
The πN system in J/ψ → NNπ is limited to be pure isospin 1/2 due to isospin conservation. This is a big advantage in studying N* → πN from the J/ψ decays, compared with πN and γN experiments which mix isospin 1/2 and 3/2 for πN system. Based on the 58 million J/ψ data collected at the Beijing Electron Positron Collider,J/ψ → pπ−n and other decay channels are analyzed. In the decay J/ψ → pπ−n, three peaks show up very clearly at 1400 MeV/c2, 1500 MeV/c2 and 1670 MeV/c2 in the πN invariant mass spectrum with additional peak around 2030 MeV/c2 which may be caused by a new N* resonance.
15148506
Baryon Spectroscopy at Beijing Electron Positron Collider
Baryons are the basic building blocks of our world. If we cut any piece of object smaller and smaller,we will ﬁnally reach the nucleons, i.e., the lightest baryons, and we cannot cut them smaller anyfurther. So without mention any theory, we know that the study of baryon structure is at theforefront of exploring microscopic structure of matter. From theoretical point of view, since baryonsrepresent the simplest system in which the three colors of QCD neutralize into colorless objectsand the essential non-Abelian character of QCD is manifest, understanding the baryon structure isabsolutely necessary before we claim that we really understand QCD.Spectroscopy has long proved to be a powerful tool for exploring internal structures and basicinteractions of microscopic world. Ninety years ago detailed studies of atomic spectroscopy resultedin the great discovery of Niels Bohr’s atomic quantum theory [1]. Forty to sixty years later, stilldetailed studies of nuclear spectroscopy resulted in Nobel Prize winning discoveries of nuclear shellmodel [2] and collective motion model [3] by Aage Bohr et al. Comparing with the atomic andnuclear spectroscopy at those times, our present baryon spectroscopy is still in its infancy [4].Many fundamental issues in baryon spectroscopy are still not well understood [5]. The possibilityof new, as yet unappreciated, symmetries could be addressed with accumulation of more data.The new symmetries may not have obvious relation with QCD, just like nuclear shell model andcollective motion model.Joining the new eﬀort on studying the excited nucleons, N