Resummed QCD Power Corrections to Nuclear Shadowing

Abstract

We calculate and resum a perturbative expansion of nuclear enhanced power corrections to the structure functions measured in deeply inelastic scattering of leptons on a nuclear target. Our results for the Bjorken x-, Q 2 -and A-dependence of nuclear shadowing in F A 2 (x, Q 2 ) and the nuclear modifications to F A L (x, Q 2 ), obtained in terms of the QCD factorization approach, are consistent with the existing data. We demonstrate that the low-Q 2 behavior of these data and the measured large longitudinal structure function point to a critical role for the power corrections when compared to other theoretical approaches.PACS numbers: 12.38. Cy; 12.39.St; 24.85.+p; In order to understand the overwhelming data from the Relativistic Heavy Ion Collider (RHIC) and make predictions for the future Electron Ion Collider (EIC) and Large Hadron Collider (LHC) in terms of the successful perturbative QCD factorization approach [1] we need precise information of the nuclear parton distribution functions (nPDFs) φ A f (x, µ 2 ) of flavor f , atomic weight A, momentum fraction x and factorization scale µ. Although the µ-dependence of leading twist nPDFs can be calculated in terms of pQCD evolution equations, the x-and Adependent boundary condition at a scale µ 0 must be fixed from existing measurements, mostly of the structure function F A 2 (x, µ 2 ) in lepton-nucleus deeply inelastic scattering (DIS) [2]. It was pointed out recently [3] that the available fixed-target data contain significant higher twist effects hindering the extraction of the nuclear parton distributions.On the other hand, it has been argued that for physical processes where the effective x is very small and the typical momentum exchange of the collision Q ∼ µ is not large the number of soft partons in a nucleus may saturate [4]. Qualitatively, the unknown boundary of this novel regime in (x, Q) is where the conventional perturbative QCD factorization approach should fail [5].In this Letter we present a pQCD calculation of the resummed power corrections to the DIS nuclear structure functions and demonstrate their importance in extracting nPDFs. From our results we quantitatively identify the characteristic scale of these power corrections ξ 2 ≪ m 2 N , with nucleon mass m N = 0.94 GeV. We conclude that for Q 2 ≥ m 2 N inclusive lepton-nucleus DIS is above the saturation boundary and can be treated systematically in the framework of the pQCD factorization approach with resummed high twist contributions.Under the approximation of one-photon exchange, the lepton-hadron DIS cross section dσ ℓh /dx dQ 2 ∝ L µν W µν (x, Q 2 ), with Bjorken variable x = Q 2 /(2p · q) and virtual photon's invariant mass q 2 = −Q 2 . The leptonic tensor L µν and hadronic tensor W µν are defined in [6]. The hadronic tensor can be expressed in terms of structure functions based on the polarization states of the exchange virtual photon:, where ǫ µν L , ǫ µν T are given in [7]. The transverse and longitudinal structure functions are related to the standard DIS structure functions F 1 ,...

High transverse momentum quarkonium production and dissociation in heavy ion collisions

“…We use the EKS98 modification factor provided in [64]. For x < 0.1, power-suppressed resummed [21,22] coherent final-state scattering of the struck partons leads to suppression in the observed cross sections. These are included in our calculation and modify the momentum fractions of the incident partons in Eq.…”

“…The CNM [18] effects we consider include nuclear shadowing (here implemented as coherent power corrections) and initial state energy loss. These are calculated in the same framework as previously used for light hadrons [19][20][21][22][23][24][25][26] and open heavy flavor [27][28][29]. We also consider transverse momentum broadening [19,[28][29][30] (as a model for the Cronin effect).…”

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