The full spin structure of quarks in the nucleon (original) (raw)
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Spin-dependent parton distributions in polarized deep inelastic lepton nucleon scattering
Zeitschrift f�r Physik C Particles and Fields, 1988
We analyze the recently measured first moment FP(Q 2) of the structure function gpl(x,Q 2) obtained in deep inelastic scattering of polarized electrons from polarized protons. It is shown that the recent experimental result _F'P(( Q2 > ~ 10 GeV 2) ,-~ 0.113 implies a polarized strange quark sea whose total polarization As(p 2) ~_-0.22 is comparable to Au(/~ 2) -0.74 and Ad(# 2) _ -0.50 already at a typically hadronic scale # = 0(1 GeV). Most remarkably, the total polarization due to quark distributions du(~t 2) + Ad(# 2) + As(# 2) practically vanishes which implies that the spin of the proton is carried by the gluons, A G(#2), and/or the angular momentum of the partons. This surprising conjecture can be experimentally tested with heavy quark production in longitudinally polarized lepton-nucleon scattering. In particular the (real) photon-gluon fusion process 79 ~ Q Q provides a rather unique measure of A G(x, Q2).
Quark initial state interaction in deep inelastic scattering and the Drell-Yan process
Physical Review D, 2005
We pursue a phenomenological study of higher twist effects in high energy processes by taking into account the off-shellness (virtuality) of partons bound in the nucleon. The effect of parton off-shellness in deep inelastic ep → eX scattering (DIS) and the Drell-Yan process (pp → llX) is examined. Assuming factorization and a singleparameter Breit-Wigner form for the parton spectral function, we develop a model to calculate the corresponding off-shell cross sections. Allowing for a finite parton width ≈ 100 MeV, we reproduce the data of both DIS and the triple differential Drell-Yan cross section without an additional K-factor. The results are compared to those from perturbative QCD and the intrinsic-k T approach.
Spin effects in the fragmentation of a transversely polarized quark
Physics Letters B, 2000
An azimuthal dependence of pions produced in polarized Deep Inelastic Scattering, γ * p ↑ → πX, has been recently observed and might be related to the so-called Collins effect. We discuss in details, for a general spin configuration of the nucleon, the kinematics of the process and methods of extracting information on the fragmentation properties of a polarized quark. Assuming that the observed azimuthal dependence is indeed due to Collins effect, we derive a lower bound estimate for the size of the quark analysing power, which turns out to be large.
Physical Review D, 2005
Polarized deep-inelastic scattering data on longitudinally polarized hydrogen and deuterium targets have been used to determine double spin asymmetries of cross sections. Inclusive and semiinclusive asymmetries for the production of positive and negative pions from hydrogen were obtained in a re-analysis of previously published data. Inclusive and semi-inclusive asymmetries for the production of negative and positive pions and kaons were measured on a polarized deuterium target. The separate helicity densities for the up and down quarks and the anti-up, anti-down, and strange sea quarks were computed from these asymmetries in a "leading order" QCD analysis. The polarization of the up-quark is positive and that of the down-quark is negative. All extracted sea quark polarizations are consistent with zero, and the light quark sea helicity densities are flavor symmetric within the experimental uncertainties. First and second moments of the extracted quark helicity densities in the measured range are consistent with fits of inclusive data.
Physical Review D, 2007
We pursue a phenomenological study of higher twist effects in high energy processes by taking into account the off-shellness (virtuality) of partons bound in the nucleon. The effect of parton off-shellness in deep inelastic ep → eX scattering (DIS) and the Drell-Yan process (pp → llX) is examined. Assuming factorization and a singleparameter Breit-Wigner form for the parton spectral function, we develop a model to calculate the corresponding off-shell cross sections. Allowing for a finite parton width ≈ 100 MeV, we reproduce the data of both DIS and the triple differential Drell-Yan cross section without an additional K-factor. The results are compared to those from perturbative QCD and the intrinsic-k T approach.
Quark spin distributions and axial anomaly in polarized deep inelastic scattering
Czechoslovak Journal of Physics, 1999
SECTION 2 ON BEHALF OF THE SPIN MUON ~OLLABORATION \u present a measurement of inclusive and semi-inclusive spin asymmetries from deep inelastic scette ring of polarized muons on polarized protons and r in the range 0.003 < x < 0.7 and Q2 > 1 GeV 2. From these asymmetries we determine the polarized quark distributions of valence quarks and non-stra nge sea quarks at Q2 = 10 GeV 2. The polarized u valence quark distribution is positive and d valence quark distribution is negative. The non-strange sea spin distribution is consistent with zero over the whole measured range of x. We calculate moments of those distributions and, for valence quarks, we find the first moments consistent with values obtained from weak decay constants and the second moments consistent with lattice QCD predictions. We also examine a hypothesis of anomalous contribution to the nucleon spin from colour background field at high x by fitting this hypothesis to the world data on inclusive andsemi.inclusive asymmet ries. I.
Single-spin asymmetries in semi-inclusive deep inelastic scattering and Drell-Yan processes
Physical Review D, 2013
We examine in detail the diagrammatic mechanisms which provide the change of sign between the single transverse spin asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) and in the Drell-Yan process (DY). This asymmetry is known to arise due to the transverse spin dependence of the target proton combined with a T -odd complex phase. Using the discrete symmetry properties of transverse spinors, we show that the required complex phase originates in the denominators of rescattering diagrams and their respective cuts. For simplicity, we work in a model where the proton consists of a valence quark and a scalar diquark. We then show that the phases generated in SIDIS and in DY originate from distinctly different cuts in the amplitudes, which at first appears to obscure the relationship between the single-spin asymmetries in the two processes. Nevertheless, further analysis demonstrates that the contributions of these cuts are identical in the leading-twist Bjorken kinematics considered, resulting in the standard sign-flip relation between the Sivers functions in SIDIS and DY. Physically, this fundamental, but yet untested, prediction occurs because the Sivers effect in the Drell-Yan reaction is modified by the initial-state "lensing" interactions of the annihilating antiquark, in contrast to the final-state lensing which produces the Sivers effect in deep inelastic scattering.
Single spin asymmetries in deep inelastic scattering
Phys Rev D, 1997
We consider possible mechanisms for single spin asymmetries in inclusive deep inelastic scattering processes with unpolarized leptons and transversely polarized nucleons. Tests for the effects of nonzero intrinsic k⊥, for the properties of spin-dependent quark fragmentations and for quark helicity conservation are suggested.