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Nuclear dependence of $R=frac{sigma_L}{sigma_T}$ and Callan-Gross relation in nuclei

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 Publication date 2017
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and research's language is English




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The electromagnetic nuclear structure functions $F_{1A} (x,Q^2)$, $F_{2A} (x,Q^2)$ and $F_{LA} (x,Q^2)$ have been calculated using a microscopic model of nucleus to study the nuclear medium effects on the ratio $R_A(x,Q^2)=frac{sigma_{LA} (x,Q^2)}{sigma_{TA} (x,Q^2)} = frac{F_{LA} (x,Q^2)}{2xF_{1A} (x,Q^2)}$ and the Callan-Gross relation(CGR) in nuclei. The nuclear medium effects due to the Fermi motion, binding energy, nucleon correlations, mesonic contribution and shadowing have been taken into account. The theoretical results for the nuclear dependence of $R_{A} (x,Q^2)$ and its impact on CGR have been presented and compared with the available experimental data on the various nuclear targets. The predictions have been made for $R_{A} (x,Q^2)$ in the kinematic region of $x$ and $Q^2$ for some nuclei relevant for the future experiments to be performed at the JLab.



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233 - A. Bodek , T. Adams , A. Alton 2001
We report on the extraction of R=sigam_L/sigma_T from CCFR neutrino and antineutrino-Iron differential cross sections. R as measured in neutrno scattering is in agreement with $R$ as measured in muon and electron scattering. All data on R for Q2 > 1 GeV2 are in agreement with a NNLO QCD calculation which uses NNLO PDFs and includes target mass effects. We report on the first measurements of R in the low x and Q2 < 1 GeV2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).
173 - U. K. Yang , T. Adams , A. Alton 2001
We report on the extraction of R=sigma_L/sigma_T from CCFR nu_mu-Fe and nubar_mu-Fe differential cross sections. The CCFR differential cross sections do not show the deviations from the QCD expectations that are seen in the CDHSW data at very low and very high x. R as measured in nu_mu scattering is in agreement with R as measured in muon and electron scattering. All data on R for Q^2 > 1 GeV^2 are in agreement with a NNLO QCD calculation which includes target mass effects. We report on the first measurements of R in the low x and Q^2 < 1 GeV^2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).
We report on a detailed study of longitudinal strength in the nucleon resonance region, presenting new results from inclusive electron-proton cross sections measured at Jefferson Lab Hall C in the four-momentum transfer range 0.2 < Q^2 < 5.5 GeV^2. The data have been used to accurately perform 167 Rosenbluth-type longitudinal / transverse separations. The precision R = sigma_L / sigma_T data are presented here, along with the first separate values of the inelastic structure functions F_1 and F_L in this regime. The resonance longitudinal component is found to be significant, both in magnitude and in the existence of defined mass peaks. Additionally, quark-hadron duality is here observed above Q^2 = 1 GeV^2 in the separated structure functions independently.
We study the Callan-Gross ratio $R={rm d}sigma_L/{rm d}sigma_T$ in heavy-quark pair leptoproduction, $lNrightarrow l^{prime}Qbar{Q}X$, as a probe of linearly polarized gluons inside unpolarized proton, where ${rm d}sigma_T$ (${rm d}sigma_L$) is the differential cross section of the $gamma^*Nrightarrow Qbar{Q}X$ process initiated by a transverse (longitudinal) virtual photon. Note first that the maximal value for the quantity $R$ allowed by the photon-gluon fusion with unpolarized gluons is large, about 2. We calculate the contribution of the transverse-momentum dependent gluonic counterpart of the Boer-Mulders function, $h_{1}^{perp g}$, describing the linear polarization of gluons inside unpolarized proton. Our analysis shows that the maximum value of the ratio $R$ depends strongly on the gluon polarization; it varies from 0 to $frac{Q^2}{4m^2}$ depending on $h_{1}^{perp g}$. We conclude that the Callan-Gross ratio in heavy-quark pair leptoproduction is predicted to be large and very sensitive to the contribution of linearly polarized gluons. For this reason, future measurements of the longitudinal and transverse components of the charm and bottom production cross sections at the proposed EIC and LHeC colliders seem to be very promising for determination of the linear polarization of gluons inside unpolarized proton.
62 - U.K. Yang , A. Bodek 1999
We report on the extraction of the higher twist contributions to F_2 and R = sigma_L/sigma_T from the global NLO and NNLO QCD fits to lepton nucleon scattering data over a wide range of Q^2. The NLO fits require both target mass and higher twist contributions at low Q^2. However, in the NNLO analysis, the data are described by the NNLO QCD predictions (with target mass corrections) without the need for any significant contributions from higher twist effects. An estimate of the difference between NLO and NNLO parton distribution functions is obtained.
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