ar X iv : h ep - p h / 99 01 33 3 v 2 8 F eb 1 99 9 New Insight into the Photoproduction of D ∗ - meson in QCD

In the framework of the model motivated by perturbative calculations in the fourth O(α 3 s α)-order, the estimates for the γp cross-section of the D *-meson production in the ZEUS experiment are performed. We factorize the hadronization of (c¯ q)-state hardly produced in perturbative QCD, which allows us to take into account the higher twist terms in the powers of 1/p T at p T ∼ m c and to correctly reproduce the c-quark fragmentation dominant at high p T ≫ m c to the given order of α s. We find a good agreement with the experimental data on the photoproduction, if the color-octet (c¯ q)-state is taken into account, which yields O (8) ≈ 0.33 − 0.49 GeV 3. The measurement of the charm production by the ZEUS and H1 collaborations at HERA in the interaction of quazireal photon with the proton [1, 2] rises the problem on the data interpretation in the framework of QCD. The description of process for the heavy quark production in the perturbative QCD (pQCD) is completely justified due to the hardness of partonic subprocesses. At present, there are two types of calculations based on the results in the next-to-leading order over α s , i.e. in O(αα 2 s): for the production of massive and massless quarks, correspondingly [3, 4]. In the both approaches the fragmentation model for the c-quark hadronization into D * was used at p T ≫ m c. It was applied in the following form: d 2 σ D * dzdp T = dˆσ c¯ c (k T , µ) dk T k T = p T z · D c→D * (z, µ) z , (1) where D c→D * (z, µ) is a fragmentation function normalized by a probability of the c-quark fragmentation into the D *-meson, W (c → D *), which is empirically determined from the e + e −-annihilation data [5], where W (c → D *) = 0.22 ± 0.014 ± 0.14, and µ ∼ p T is the factorization scale for the perturbative partonic cross section dˆσ/dk T. It is clear that such the approach does not allow one to describe the experimental data in the region 1