Measurement of D^{+} and Lambda_{c}^{+} production in deep inelastic scattering at HERA

TL;DR

This ZEUS study measures open-charm production in deep inelastic $ep$ scattering, focusing on $D^{+}$ and $\Lambda_{c}^{+}$ via $D^{+}\to K^{0}_{S}\pi^{+}$, $\Lambda_{c}^{+}\to pK^{0}_{S}$ and $\Lambda_{c}^{+}\to \Lambda\pi^{+}$ to extend sensitivity to low $p_T$ using strange-hadron final states. It compares $D^{+}$ cross sections to NLO QCD predictions from HVQDIS within the FFNS framework and extracts the fragmentation fraction $f(c\to\Lambda_{c}^{+})$ by combining two decay channels; the analysis also presents differential cross sections in $p_T$, $\eta$, $x$, and $Q^{2}$. The results show general agreement with NLO predictions for shapes and provide the first DIS measurement of $f(c\to\Lambda_{c}^{+})$ at HERA, compatible with previous $\gamma p$ and $e^{+}e^{-}$ results. This work enhances our understanding of charm production mechanisms and charm-quark fragmentation in DIS at low $p_T$.

Abstract

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb^{-1}. The hadronic decay channels D^{+} -> K^{0}_{S} pi^{+}, Lambda_{c}^{+} -> p K^{0}_{S} and Lambda_{c}^{+} -> Lambda pi^{+}, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0 < p_{T}(D^{+}, Lambda_{c}^{+}) < 10 GeV, |eta(D^{+}, Lambda_{c}^{+})| < 1.6, 1.5 < Q^{2} < 1000 GeV^{2} and 0.02 < y < 0.7. Inclusive and differential cross sections for the production of D^{+} mesons are compared to next-to-leading-order QCD predictions. The fraction of c quarks hadronising into Lambda_{c}^{+} baryons is extracted.

Figures (7)

• Figure 1: Mass distributions of the secondary vertex candidates in the (a) $K^{0}_{S}$, (b) $\Lambda$ and (c) $\bar{\Lambda}$ samples. The statistical uncertainties are in general smaller than the point size. For illustration the data have been fitted using the sum of a "modified" Gaussian function Chekanov:2005mm and a linear background.
• Figure 2: The $M(K^{0}_{S}\pi^{+})$ distribution (dots) for $D^{+}$ candidates. The reflection caused by the decay $D_{s}^{+}\to K^{0}_{S}K^{+}$ has been subtracted as described in the text. The solid curve represents a fit to the sum of a Gaussian signal and a background function, while the background contribution alone is given by the dashed curve. The dotted histogram shows the reflection scaled as described in the text with an offset of 680 to position it at the bottom of the figure.
• Figure 3: The $M(K^{0}_{S}\pi^{+})$ distribution (dots) for $D^{+}$ candidates in the region $0 < p_{T}(D^{+}) < 1.5{\,\text{Ge}\text{V}}$. The reflection caused by the decay $D_{s}^{+}\to K^{0}_{S}K^{+}$ has been subtracted as described in the text. The solid curve represents a fit to the sum of a Gaussian signal and a background function, while the background contribution alone is given by the dashed curve.
• Figure 4: The $M(pK^{0}_{S})$ distribution (dots) for $\Lambda_{c}^{+}$ candidates in the region $0 < p_{T}(\Lambda_{c}^{+}) < 6{\,\text{Ge}\text{V}}$. The solid curve represents a fit to the sum of a Gaussian signal and a background function, while the background contribution alone is given by the dashed curve.
• Figure 5: The $M(\Lambda\pi^{+})$ distribution (dots) for $\Lambda_{c}^{+}$ candidates. The solid curve represents a fit to the sum of a Gaussian signal and a background function, while the background contribution alone is given by the dashed curve. The dotted histogram shows the distribution of wrong-charge combinations (see text).