Measurement of D*+- production and the charm contribution to F_2 in deep inelastic scattering at HERA

TL;DR

This study measures D*± production in deep inelastic e+p scattering with ZEUS at HERA, using 1996–1997 data to test NLO pQCD predictions for charm production via boson-gluon fusion. By analyzing two D0 decay channels (K2π and K4π) and employing HVQDIS-based extrapolations with realistic fragmentation, the authors extract the charm contribution F2cc̄ to the proton structure function, observing a strong rise with decreasing x and significant Q^2–dependent scaling violations. The data show overall agreement with NLO QCD when using appropriate charm fragmentation models, providing support for hard-scattering factorization and linking F2cc̄ to the gluon density. The results extend the kinematic reach and improve the precision of previous measurements, highlighting the role of charm in DIS and its connection to the proton’s parton structure.

Abstract

The production of D*+-(2010) mesons in deep inelastic scattering has been measured in the ZEUS detector at HERA using an integrated luminosity of 37 pb^-1. The decay channels D*+ -> D0 pi+(+c.c.), with D0 -> K- pi+ or D0 ->K- pi- pi+ pi+, have been used to identify the D mesons. The e+p cross section for inclusive D*+- production with 1<Q^2<600 GeV^2 and 0.02<y<0.7 is 8.31 +- 0.31(stat.) +0.30-0.50(syst.) nb in the kinematic region 1.5< pT(D*+-)<15 GeV and |eta(D*+-)|<1.5. Differential cross sections are consistent with a next-to-leading-order perturbative-QCD calculation when using charm-fragmentation models which take into account the interaction of the charm quark with the proton remnant. The observed cross section is extrapolated to the full kinematic region in pT(D*+-) and eta(D*+-) in order to determine the charm contribution, F^ccbar_2(x,Q^2), to the proton structure function. The ratio F^ccbar_2/F_2 rises from ~10% at Q^2 ~1.8 GeV^2 to ~30% at Q^2 ~130 GeV^2 for x values in the range 10^-4 to 10-3.

Figures (9)

• Figure 1: Diagram of the boson-gluon-fusion process in $e^+p$ collisions.
• Figure 2:
• Figure 3: A comparison of reconstructed DIS quantities at the detector level for the $K2\pi$ data (points) and for the RAPGAP Monte Carlo simulation (shaded histogram): (a) the scattered positron energy, $E_{e}^{\prime}$, (b) the scattered positron angle, $\theta_{e}^{\prime}$, (c) the hadronic angle, $\gamma_{h}$ and (d) ${\delta}$$\equiv \Sigma_i(E_i - p_{z,i})$.
• Figure 4: A comparison of the reconstructed DIS kinematic distributions at the detector level for the $K2\pi$ data (points) and for the RAPGAP Monte Carlo simulation (shaded histogram): (a) $Q^{2}_{e}$, (b) Bjorken-$x$, $x_{e\Sigma}$ and (c) the total hadronic center-of-mass energy, $W_{e\Sigma}$. The remaining plots show a comparison of the reconstructed $D^{\ast \pm}$-related quantities at the detector level for data and for the RAPGAP Monte Carlo simulation: (d) $p_T(D^{\ast})$, (e) $\eta(D^{\ast})$ and (f) $x(D^{\ast})$.
• Figure 5: Differential cross sections for $D^{\ast \pm}$ production from the $K2\pi$ final state (solid dots) in the ${Q^2}$, $y$, $p_T(D^{\ast})$ and $\eta(D^{\ast})$ kinematic region as functions of (a) $\log_{10}\hbox{${Q^2}$}$, (b) $\log_{10}x$, (c) $W$, (d) $p_T(D^{\ast})$, (e) $\eta(D^{\ast})$ and (f) $x(D^{\ast})$. The inner error bars show the statistical uncertainties while the outer ones show the statistical and systematic uncertainties summed in quadrature. The results from the $K4\pi$ channel (open triangles) are also shown in the $p_T(D^{\ast})$ (d) and $\eta(D^{\ast})$ (e) plots. The data are compared with the NLO QCD calculation as implemented in HVQDIS using the ZEUS NLO pdf's. The open band corresponds to the standard Peterson fragmentation function with the parameter $\epsilon$ = 0.035. For the shaded band, the Peterson fragmentation was replaced by that extracted from RAPGAP (see the text for details). The boundaries of the bands correspond to charm mass variations between 1.3 (upper curve) and 1.5 ${\rm GeV}$ (lower curve). In (a) and (b), the open band is indistinguishable from the shaded band.