New quark distributions and semi-inclusive electroproduction on polarized nucleons

Yerevan Physics Institute, Alikhanian Brothers St. 2, AM-375036 Yerevan, Armenia
Nuclear Physics B (Impact Factor: 3.93). 05/1995; 441(1):234-256. DOI: 10.1016/0550-3213(95)00098-D
Source: arXiv


The quark-parton model calculation including the effects of intrinsic transverse momentum and of all six twist-two distribution functions of quarks in polarized nucleons is performed. It is demonstrated that new twist-two quark distribution functions and polarized quark fragmentation functions can be investigated in semi-inclusive DIS at leading order in Q2. The general expression for the cross-section of semi-inclusive DIS of polarized leptons on polarized nucleons in terms of structure functions is also discussed.

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    • "[16] [17] [18] [19] [20] [21] [22] [23] [24] for leading twist single hadron production – 1 – with transverse momentum of the produced hadron being much smaller than the hard scattering scale, and the order of Λ QCD , that is Λ 2 QCD < P 2 h⊥ Q 2 . In this kinematic domain the SIDIS cross section can be expressed in terms of structure functions encoding the strong-interaction dynamics of the hadronic sub-process γ * + p → h + X [25] [26] [27] [28], which are given by convolutions of a hard scattering cross section and TMDs. However the extraction of TMDs as a function of the light-cone fraction x and transverse momentum k ⊥ from single and double spin azimuthal asymmetries is hindered by the fact that observables are complicated convolutions in momentum space making the flavor decomposition of the underlying TMDs a model dependent procedure. "
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    ABSTRACT: In this paper we present a new technique for analysis of transverse momentum dependent parton distribution functions, based on the Bessel weighting formalism. The procedure is applied to studies of the double longitudinal spin asymmetry in semi-inclusive deep inelastic scattering using a new dedicated Monte Carlo generator which includes quark intrinsic transverse momentum within the generalized parton model. Using a fully differential cross section for the process, the effect of four momentum conservation is analyzed using various input models for transverse momentum distributions and fragmentation functions. We observe a few percent systematic offset of the Bessel-weighted asymmetry obtained from Monte Carlo extraction compared to input model calculations, which is due to the limitations imposed by the energy and momentum conservation at the given energy/Q 2. We find that the Bessel weighting technique provides a powerful and reliable tool to study the Fourier transform of TMDs with controlled systematics due to experimental acceptances and resolutions with different TMD model inputs.
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    • "The lepton-hadron cross section of SIDIS (l)+N (P, S) → (l)+h(P h )+X can be expressed [4] [8] [20] [21] in the notation of Ref. [8] as dσ dx B dy dψ dz h dφ h |P h⊥ | d|P h⊥ | "
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    ABSTRACT: The concept of weighted asymmetries is revisited for semi-inclusive deep inelastic scattering. We consider the cross section in Fourier space, conjugate to the outgoing hadron's transverse momentum, where convolutions of transverse momentum dependent parton distribution functions and fragmentation functions become simple products. Individual asymmetric terms in the cross section can be projected out by means of a generalized set of weights involving Bessel functions. Advantages of employing these Bessel weights are that they suppress (divergent) contributions from high transverse momentum and that soft factors cancel in (Bessel-) weighted asymmetries. Also, the resulting compact expressions immediately connect to previous work on evolution equations for transverse momentum dependent parton distribution and fragmentation functions and to quantities accessible in lattice QCD. Bessel weighted asymmetries are thus model independent observables that augment the description and our understanding of correlations of spin and momentum in nucleon structure.
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    ABSTRACT: Nukleonen, also Protonen und Neutronen, bestehen aus Quarks und Gluonen, deren Wechselwirkung durch die Quantenchromodynamik (QCD) innerhalb des Standardmodells der Teilchenphysik beschrieben wird. Diese Arbeit nutzt Gitter-QCD zur Berechnung von Quark-Impulsverteilungen im Nukleon. Dabei wird auf Gitterdaten zurückgegriffen, die auf Hochleistungsrechnern erstellt und bereits erfolgreich für die Analyse der räumlichen Quarkverteilung ("Nukleontomographie") eingesetzt wurden. Für die Untersuchung von Transversalimpuls-abhängigen Partonverteilungsfunktionen stellt diese Arbeit ein neuartiges Verfahren, basierend auf nicht-lokalen Operatoren, vor. Die Ergebnisse zeigen u.a. eine sichtbare Verformung der Transversalimpuls-abhängigen Dichte polarisierter Quarks im polarisierten Nukleon. Ein quantitativer Vergleich mit Streuexperimenten erfordert kompliziertere Operatorgeometrien. Erste Schritte in diese Richtung sind vielversprechend.
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