arXiv subjects

M. Miyama

Publications and source records attributed to M. Miyama.

24 records · Page 2Linked to original sources

arXiv1996

Q^2 evolution studies of nuclear structure function F_2 at HERA

Q**2 dependence of nuclear structure functions is important for understanding perturbative QCD in nuclear environment. However, current experimental data are not sufficient for studying nuclear dependence in the Q**2 evolution because the data are limited in the small Q**2 region at small x. The future HERA program can study the evolution in the large Q**2 region, and it provides us crucial information on recombination effects and on higher-order alpha_s effects in the nuclear structure functions.

hep-ph↗

arXiv1995

Nuclear dependence of Q^2 evolution in the structure function F_2

$Q^2$ evolution of the structure functions $F_2$ in tin and carbon nuclei is investigated in order to understand recent NMC measurements. $F_2$ is evolved by using leading-order DGLAP, next-to-leading-order DGLAP, and parton-recombination equations. NMC experimental result $\partial [F_2^{Sn}/F_2^C]/ \partial [\ln Q^2]\ne 0$ could be essentially understood by the difference of parton distributions in the tin and carbon nuclei. However, we find an interesting indication that large higher-twist effects on the $Q^2$ evolution could be ruled out. Nuclear dependence of the $Q^2$ evolution could be interesting for further detailed studies. 1. Introduction 2. Q^2 evolution of F_2 in tin and carbon nuclei 3. Conclusions

hep-ph↗

arXiv1995

Numerical solution of $Q^2$ evolution equations in a brute-force method

We investigate numerical solution of $Q^2$ evolution equations for structure functions in the nucleon and in nuclei. (Dokshitzer-Gribov-Lipatov-)Altarelli-Parisi and Mueller-Qiu evolution equations are solved in a brute-force method. Spin-independent flavor-nonsinglet and singlet equations with next-to-leading-order $α_s$ corrections are studied. Dividing the variables $x$ and $Q^2$ into small steps, we simply solve the integrodifferential equations. Numerical results indicate that accuracy is better than 2\% in the region $10^{-4}<x<0.8$ if more than two-hundred $Q^2$ steps and more than one-thousand $x$ steps are taken. The numerical solution is discussed in detail, and evolution results are compared with $Q^2$ dependent data in CDHSW, SLAC, BCDMS, EMC, NMC, Fermilab-E665, ZEUS, and H1 experiments. We provide a FORTRAN program for Q$^2$ evolution (and ``devolution'') of nonsinglet-quark, singlet-quark, $q_i+\bar q_i$, and gluon distributions (and corresponding structure functions) in the nucleon and in nuclei. This is a very useful program for studying spin-independent structure functions.

hep-ph↗

arXiv1995

Nuclear modification in the structure function $F_3$

Nuclear shadowing in the structure function $F_3$ is investigated as a possible test of shadowing models. The $F_3$ shadowing is studied in two different theoretical models: a parton-recombination model with $Q^2$ rescaling and an aligned-jet model. We find that predictions in these models differ completely in the small $x$ region. It suggests that the $F_3$ shadowing could be used for discriminating among different models, which produce similar shadowing behavior in the structure function $F_2$.

hep-ph↗

arXiv1995

Nuclear Shadowing in the Structure Function $F_3(x)$

Nuclear modification of the structure function $F_3$ is investigated. Although it could be estimated in the medium and large $x$ regions from the nuclear structure function $F_2^A$, it is essentially unknown at small $x$. The nuclear structure function $F_3^A$ at small $x$ is investigated in two different theoretical models: a parton-recombination model with $Q^2$ rescaling and an aligned-jet model. We find that these models predict completely different behavior at small $x$: {\it antishadowing} in the first parton model and {\it shadowing} in the aligned-jet model. Therefore, studies of the ratio $F_3^A/F_3^D$ at small $x$ could be useful in discriminating among different models, which produce similar shadowing behavior in the structure function $F_2$. We also estimate currently acceptable nuclear modification of $F_3$ at small $x$ by using $F_2^A/F_2^D$ experimental data and baryon-number conservation.

hep-ph↗

arXiv1994

Numerical Solution of Altarelli-Parisi Equations

We discuss numerical solution of Altarelli-Parisi equations in a Laguerre-polynomial method and in a brute-force method. In the Laguerre method, we get good accuracy by taking about twenty Laguerre polynomials in the flavor-nonsinglet case. Excellent evolution results are obtained in the singlet case by taking only ten Laguerre polynomials. The accuracy becomes slightly worse in the small and large $x$ regions, especially in the nonsinglet case. These problems could be implemented by using the brute-force method; however, running CPU time could be significantly longer than the one in the Laguerre method.

hep-ph↗