PREPRINTS/PAPERS IN 1997

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SAGA-HE-97-97, DOE/ER/40561-255-INT96-19-01

Violation of the Gottfried sum rule was suggested by the New Muon Collaboration in measuring proton and deuteron $F_2$ structure functions. The finding triggered many theoretical studies on physics mechanisms for explaining the antiquark flavor asymmetry $\bar u-\bar d$ in the nucleon. Various experimental results and proposed theoretical ideas are summarized. Possibility of finding the flavor asymmetry in Drell-Yan experiments is discussed together with other processes, which are sensitive to the $\bar u/\bar d$ asymmetry.

1. Introduction
2. Possible violation of the Gottfried sum rule
2.1 Gottfried sum rule
2.2 Early experimental results
2.3 NMC finding and recent progress
2.4 Small $x$ contribution
2.5 Nuclear correction: shadowing in the deuteron
2.6 Parametrization of antiquark distributions
3 Expectations in perturbative QCD
3.1 Operator product expansion
3.2 Perturbative correction to the Gottfried sum
4 Theoretical ideas for the sum-rule violation
4.1 Lattice QCD
4.2 Pauli exclusion principle
4.3 Mesonic models
4.3.1 Meson-cloud contribution
4.3.2 Chiral models
4.3.3 Anomalous $Q^2$ evolution
4.4 Diquark model
4.5 Isospin symmetry violation
4.6 Flavor asymmetry ubar-dbar in nuclei
4.7 Relation to nucleon spin
4.8 Comment on effects of quark mass and transverse motion
5 Finding the flavor asymmetry ubar-dbar in various processes
5.1 Drell-Yan process
5.1.1 Fermilab-E866 results
5.2 W and Z production
5.3 Quarkonium production at large $x_{_F}$
5.4 Charged hadron production
5.5 Neutrino scattering
5.6 Experiments to find isospin symmetry violation
6 Related topics on antiquark distributions
7 Summary and outlook

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SAGA-HE-117-97

We investigate numerical solution of Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) $Q^2$ evolution equations for longitudinally polarized structure functions.Flavor nonsinglet and singlet equations with next-to-leading-order $\alpha_s$ corrections are studied. A brute-force method is employed. Dividing the variables $x$ and $Q^2$ into small steps, we simply solve the integrodifferential equations. Numerical results indicate that accuracy is better than 1\% in the region $10^{-5}<x<0.8$ if more than two-hundred $Q^2$ steps and more than one-thousand $x$ steps are taken. Our evolution results are compared with polarized experimental data of the spin asymmetry $A_1$ by the SLAC-E130, SLAC-E143, EMC, and SMC collaborations. The comparison indicates that we cannot assume $A_1$ is independent of $Q^2$. We provide a FORTRAN program for the Q$^2$ evolution and devolution of polarized nonsinglet-quark, singlet-quark, $\Delta q_i+\Delta\bar q_i$, and gluon distributions (and corresponding structure functions).

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SAGA-HE-122-97

Chiral-odd structure function h1 is expected to be measured in polarized Drell-Yan process. We calculate two-loop anomalous dimensions for h1 in the minimal subtraction scheme. Dimensional regularization and Feynman gauge are used for calculating the two-loop contributions. Our results are important in studying Q^2 dependence of h1.

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SAGA-HE-118-97

Flavor asymmetry in light antiquark distributions is discussed.
In particular, recent progress on the u-bar/d-bar asymmetry
is explained. Then, we discuss possible future experimental studies.
1. Introduction
2. Present situation
3. Future u-bar/d-bar asymmetry studies
3.1 Drell-Yan process
3.2 Charged-hadron production
3.3 W charge asymmetry
3.4 Deuteron acceleration at HERA

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SAGA-HE-124-97

Because the chiral-odd structure function h_1 will be measured
in the polarized Drell-Yan process, it is important to predict
the behavior of h_1 before the measurement. In order to study
the Q^2 evolution of h_1, we discuss one and two loop anomalous
dimensions which are calculated in the Feynman gauge and minimal
subtraction scheme.

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SAGA-HE-125-97

We investigate numerical solution of the Dokshitzer-Gribov-Lipatov-
Altarelli-Parisi (DGLAP) Q^2 evolution equation for the transversity
distribution Delta_T q or the structure function h_1. The leading-order
(LO) and next-to-leading-order (NLO) evolution equations are studied.
The renormalization scheme is MS or overline{MS} in the NLO case.
Dividing the variables x and Q^2 into small steps, we solve the
integrodifferential equations by the Euler method in the variable Q^2
and by the Simpson method in the variable x. Numerical results indicate
that accuracy is better than 1% in the region 10^{-5}<x< 0.8 if
more than fifty Q^2 steps and more than five hundred x steps are taken.
We provide a FORTRAN program for the Q^2 evolution and devolution of the
transversity distribution Delta_T q or h_1. Using the program, we show the
LO and NLO evolution results of the valence-quark distribution Delta_T u_v
+Delta_T d_v, the singlet distribution sum_i (Delta_T q_i + Delta_T qbar_i),
and the flavor asymmetric distribution Delta_T ubar - Delta_T dbar.They are
also compared with the longitudinal evolution results.

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