Nucleon Structure Function F2 Research Articles

EXPLICIT MODEL REALIZING PARTON–HADRON DUALITY

We present a model that realizes both resonance-Regge (Veneziano) and parton–hadron (Bloom–Gilman) duality. We first review the features of the Veneziano model and we discuss how parton–hadron duality appears in the Bloom–Gilman model. Then we review limitations of the Veneziano model, namely that the zero-width resonances in the Veneziano model violate unitarity and Mandelstam analyticity. We discuss how such problems are alleviated in models that construct dual amplitudes with Mandelstam analyticity (so-called DAMA models). We then introduce a modified DAMA model, and we discuss its properties. We present a pedagogical model for dual amplitudes and we construct the nucleon structure function F2(x, Q2). We explicitly show that the resulting structure function realizes both Veneziano and Bloom–Gilman duality.

STUDY OF QUARK-HADRON DUALITY BASED ON A CONSTITUENT QUARK MODEL

The recent measurement of quark-hadron duality is shortly discussed by using a simple constituent quark model. Comparing with the moments of the structure functions in the resonance region and in the deep inelastic scattering region, we study the occurances of Bloom-Gilman quark-hadron duality for the nucleon structure function F2 and g1. Local duality is also analyzed.

HARD NON-VACUUM REGGEON IN THE CKMT MODEL

The CKMT model describing the nucleon structure function F2(x,Q2) in the framework of conventional Regge theory with smooth soft-hard pomeron is modified. Smooth soft-hard non-vacuum reggeon dependence on incoming photon virtuality Q2 is introduced. This dependence has the same functional form as the smooth soft-hard functional Q2 dependence for pomeron in original CKMT model. In region of low W2, better agreement with experimental data is observed.

Nucleon Structure Function F2 in the Resonance Region and Quark-Hadron Duality**The project supported by National Natural Science Foundation of China under Grant No. 10075056, Foundations of the Chinese Academy of Sciences (x-37), the Chinese Ministry of Education (B-22), Institute of Theoretical Physics, and the CAS Knowledge Innovation Project No. KJCX2-SW-N02

Based on a simple nonrelativistic constituent quark model, the nucleon structure function F2 in the resonance region is estimated by taking the contributions from low-lying nucleon resonances into account. Calculated results are employed to study quark-hardon duality in the nucleon electron scattering process by comparing them to the scaling behavior from the data in deep inelastic scattering region.

On the behavior of $F_2$ and its logarithmic slopes

It is shown that the CKMT model for the nucleon structure function F2, taken as the initial condition for the NLO evolution equations in perturbative QCD, provides a good description of the HERA data when presented in the form of the logarithmic slopes of F2 vs x and Q2 (Caldwell-plot), in the whole available kinematic ranges. Also the results obtained for the behavior of the gluon component of a nucleon are presented.

Measurements of the nucleon structure function in the range 0.002 < x < 0.17 and 00.2 < Q2 < 8 GeV2 in deuterium, carbon and calcium

Small angle scattering of 280 GeV positive muons by deuterium, carbon and calcium has been measured at scattering angles down to 2 mrad. The nucleon structure function F2 extracted from deuterium does not show a significant x dependence in the measured range of Q2 and its Q2 dependence is linear in logQ2. For calcium, a depletion of F2 is observed at low x by 30% as compared with the values at x = 0.1 where F2(Ca) and F2 (D) are not significantly different. This depletion is attributed to shadowing. The carbon structure function exhibits a similar, but less pronounced, x dependence. Such behaviour is observed to be independent of Q2. The data are consistent with those obtained from other charged lepton experiments both at similar and higher values of x and Q2 and considerably extend the range of the measurements down to the low values of x to be measured in forthcoming experiments at HERA.

Analysis of the electroproduction structure functions in the lowQ 2 region, combining the vector meson dominance and the parton model with possible scaling violation

The nucleon structure functionF 2 is constructed and analysed for low values ofQ 2 using the generalised vector meson dominance representation with the largeQ 2 spectral function calculated from the analytic continuation of the parton model structure function. Various parametrisations of the parton distributions are considered. Possible effects of the largeQ 2 scaling violation on the lowQ 2 part of the structure function are investigated. The magnitude of the total contribution given by this asymptotic part can be as high as 50% of the vector meson contribution in the low-Q 2, low-χ region. The contribution of the valence quarks alone to the structure function at lowQ 2 turns out to be at least as important as the corresponding non-Pomeron Regge-pole-like terms coming from the vector meson part. Increase of the structure function with ν coming from the increase of the quark sea in the limit of small χ implied by QCD turns out to be relatively weak at lowQ 2. Predictions of the model are compared with available experimental data. The photoproduction cross section and the nuclear effects in the structure function are also briefly discussed.

Ultra-high energy neutrino-nucleon and neutrino-electron cross-sections in the standard model, in supersymmetric and superstring models

The neutrino-nucleon cross-section is calculated for energies up to 1015 GeV in the framework of the standard model assuming that the nucleon structure functionF2(x, Q2) goes like ln2(a/x) asx→0. The cross-sections forvμe−(vee−)-interactions rise linearly with energy up toEν∼107 GeV and amount at this energy to ∼10% of the neutrino-nucleon cross-section. The νN-cross-sections with production of supersymmetric particles in the framework of a supersymmetric model with minimal particle content are estimated. Photino-nucleon and photino-electron interactions are considered for masses of the squarks and sleptons in the range of 80–300 GeV. In superstring inspired unified models an estimation is made of the νN-interaction with an exchange of light leptoquarks.

Test of QCD and a measurement of Λ from scaling violations in the nucleon structure function F2( x, Q2)

Scaling violations in the nucleon structure function F 2( x, Q 2) measured with high statistics in deep inelastic scattering of muons on a carbon target are compared to predictions of perturbative QCD. Excellent agreement is observed with numerical solutions of the Altarelli-Parisi evolution equations over the entire x and Q 2 range of data. In a next-to-leading order nonsinglet approximation, the QCD mass scale parameter Λ MS is determined to be 230±20(stat.)±60(syst.) MeV. A singlet to the data favours a soft gluon distribution.

A high statistics measurement of the nucleon structure function F2( x, Q2) from deep inelastic muon-carbon scattering at high Q2

We present results from a high statistics study of the nucleon structure function F 2( x, Q 2) measured in deep inelastic scattering of muons on carbon in the kinematic range 0.25⩽ x⩽0.80 and Q 2⩾25 GeV 2. The analysis is based on 1.5×10 6 reconstructed events recorded at beam energies of 120, 200 and 280 GeV. R= σ L / σ T is found to be independent of x in the range 0.25⩽ x⩽0.07 and 40 GeV 2⩽ Q 2⩽200 GeV 2 with a mean value R=0.015±0.013 ( stat) ±0.026 (syst.).

Ratio of the nucleon structure function F2 for heavy nuclei and free nucleons

An intuitive nuclear wave function is used to show that the so-called European Muon Collaboration Effect can be accounted for by nucleons having a somewhat larger effective size when bound in nuclear matter than when free. In spite of its crudeness, the same model also gives a not unreasonable nucleon structure function F 2( x) for intermediate x-values.