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Inclusive $D^0$ and $D^*\pm$ Production in Deep Inelastic $ep$ Collisions at HERA

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TL;DR

This study reports the first measurements of inclusive $D^0$ and $D^{*\pm}$ production in deep inelastic $ep$ scattering at HERA, using H1 data from 1994. The analysis identifies charm via $D^0\to K^-\pi^+$ and $D^{*+}\to D^0\pi^+_{slow}$ decays, and extracts both integrated and differential cross sections, subsequently deriving a charm production cross section in DIS of $\sigma(ep\to c\bar c X)=(17.4\pm1.6\pm1.7\pm1.4)$ nb and the charm content of the proton structure function $F_2^{c\bar c}$ for $x$ between $8\times10^{-4}$ and $8\times10^{-3}$. The results corroborate boson-gluon fusion as the dominant charm production mechanism in DIS at HERA, constrain the charm-sea contribution to charm production to $\epsilon<0.05$ at 95% CL, and show a significant rise of $F_2^{c\bar c}$ with decreasing $x$, consistent with an increasing gluon density at low $x$. The measured $F_2^{c\bar c}/F_2$ ratio is roughly $0.237$, in line with NLO QCD fits, though the overall charm cross section lies somewhat above some predictions, highlighting sensitivities to the gluon density and charm mass in the theory.

Abstract

First results on inclusive D0 and D* production in deep inelastic $ep$ scattering are reported using data collected by the H1 experiment at HERA in 1994. Differential cross sections are presented for both channels and are found to agree well with QCD predictions based on the boson gluon fusion process. A charm production cross section for 10 GeV$^2\le Q^2\le100$~GeV$^2$ and $0.01\le y\le0.7$ of $σ(ep\to c\barcX) = (17.4 \pm 1.6 \pm 1.7 \pm 1.4)$~nb is derived. A first measurement of the charm contribution F2_charm(x,Q^2) to the proton structure function for Bjorken $x$ between $8\cdot10^{-4}$ and $8\cdot10^{-3}$ is presented. In this kinematic range a ratio F2_charm/F2= 0.237\pm0.021{+0.043\atop-0.039}$ is observed.

Inclusive $D^0$ and $D^*\pm$ Production in Deep Inelastic $ep$ Collisions at HERA

TL;DR

This study reports the first measurements of inclusive and production in deep inelastic scattering at HERA, using H1 data from 1994. The analysis identifies charm via and decays, and extracts both integrated and differential cross sections, subsequently deriving a charm production cross section in DIS of nb and the charm content of the proton structure function for between and . The results corroborate boson-gluon fusion as the dominant charm production mechanism in DIS at HERA, constrain the charm-sea contribution to charm production to at 95% CL, and show a significant rise of with decreasing , consistent with an increasing gluon density at low . The measured ratio is roughly , in line with NLO QCD fits, though the overall charm cross section lies somewhat above some predictions, highlighting sensitivities to the gluon density and charm mass in the theory.

Abstract

First results on inclusive D0 and D* production in deep inelastic scattering are reported using data collected by the H1 experiment at HERA in 1994. Differential cross sections are presented for both channels and are found to agree well with QCD predictions based on the boson gluon fusion process. A charm production cross section for 10 GeV~GeV and of ~nb is derived. A first measurement of the charm contribution F2_charm(x,Q^2) to the proton structure function for Bjorken between and is presented. In this kinematic range a ratio F2_charm/F2= 0.237\pm0.021{+0.043\atop-0.039}$ is observed.

Paper Structure

This paper contains 17 sections, 16 equations, 7 figures, 7 tables.

Table of Contents

  1. Introduction
  2. H1 Detector and Data Sample
  3. Kinematics
  4. Monte Carlo Simulation
  5. Event Selection
  6. Selection of Deep Inelastic Scattering Events
  7. Selection of Charm Events
  8. Selection of $D^{*+}\rightarrow D^0\pi^+_{slow}\rightarrow K^-\pi^+\pi^+_{slow}$ Decays
  9. Selection of $D^0\rightarrow K^-\pi^+$ Decays
  10. Results
  11. Integrated Cross Sections
  12. Experimental Systematic Uncertainties
  13. Model Dependent Uncertainties
  14. Differential Cross Section
  15. Mechanisms of Charm Production in $ep$ Scattering
  16. ...and 2 more sections

Figures (7)

  • Figure 1: Generic Feynman diagrams for deep inelastic $ep$ scattering up to order $\alpha\alpha_s$: (a) $ep$ interaction of the virtual probe ($\gamma,\;Z^0$) with a valence or a sea quark in the proton according to the quark parton model (QPM), (b) corrections to process (a) due to gluon radiation off the struck quark before or after interacting with the probe (QCD Compton scattering, QCDC), and (c) contribution due to boson gluon fusion (BGF).
  • Figure 2: Distribution of (a) the polar angle and (b) the energy of the scattered electron for charm events as observed in the $D^{*+}$ analysis. The background subtracted data is compared with the expectation of the AROMA (histogram) Monte Carlo simulation, normalized to the number of events in the data. Only statistical errors are shown.
  • Figure 3: Distribution of (a) the mass difference $\Delta m$ and (b) the $K^-\pi^+$ mass for DIS events selected as described in the text. The data points in (a) are obtained from the $K^-\pi^+$ mass combinations fulfilling $|m_{K\pi}-m_{D^0}|\le 90$ MeV. The shaded histogram shows the background expectation, which is obtained from the high mass sideband $2.05\;\rm GeV\le {\it m_{K\pi}}\le2.5\;\rm GeV$ normalized to the region $0.160\;\rm GeV\le\Delta{\it m}\le0.180\;\rm GeV$. The data points in (b) are obtained from the candidates in an interval of 2.2 MeV around the nominal $\Delta m$ value expected for the decay $D^{*+}\rightarrow D^0\pi^+$. The shaded histogram shows the background expectation from the region $0.170\;\rm GeV\le\Delta{\it m}\le0.180\;\rm GeV$ normalized by the two body phase space factors according to the $\Delta m$ intervals. The solid lines represent the result of the fits as described in the text.
  • Figure 4: $K^-\pi^+$ mass distribution observed in the inclusive $D^0$ analysis. The solid line is a fit to the data as indicated in the text. The dashed line shows the contribution from the wrong $K-\pi$ assignment to the tracks. The shaded area indicates contributions to the fit due to combinatorial background and reflections while the dashed line describes the mass distribution for the wrong mass assignment to the tracks.
  • Figure 5: Normalized distributions of $1/\sigma\;d\sigma/dp_t(D^0)$ of the $D^0$ mesons from the $D^{*+}$ (full points) and the $D^0$ analysis (open circles) in comparison to the AROMA expectation for $m_c=1.3\;\rm GeV$ (full line) and $m_c=1.7\;\rm GeV$ (dashed line) using the MRSH parameterization of the parton densities in the proton.
  • ...and 2 more figures