Intrinsic Charm at High-Q^2 and HERA Data

Abstract

We compute the predictions of intrinsic charm for deep-inelastic scattering at high-Q^2 and compare to HERA data. With the inclusion of constraints from low-energy data, enhancements beyond the predictions of standard structure functions are very modest, but peaking in the leptoquark mass variable is present near 200 GeV. Ultimately, the ability of HERA to probe the intrinsic charm hypothesis could be very substantial.

Figures (5)

• Figure 1: Predictions for $F_2^{c~{\gamma^\star}}(x)$ at $Q^2=25000\,{\rm GeV}^2$: solid --- SM next-to-leading order prediction using MRS96(R2) mrs96 distribution functions only; dots --- the $n=2$ IC component alone; dot-dashed --- SM plus $n=2$ IC; dashes --- $n=8$ IC only; dash-long-dash --- SM plus $n=8$ IC.
• Figure 2: EMC data for $F_2^c(x)$ at $\overline\nu=168\,{\rm GeV}$ compared to: (i) dotdash --- the extrinsic charm prediction of Ref. hsv; (ii) dots --- the CTEQ3 perturbative prediction; (iii) solid --- EC+IC prediction for $n=2$; (iv) dashes --- EC+IC prediction for $n=8$.
• Figure 3: The $x_F$ distribution for $pp\to \Lambda_c+X$. Data from Ref. lambdacisr is compared to: (i) dotdash --- $gg+q\overline q\to c\overline c$ fusion followed by $c\to\Lambda_c$; (ii) solid --- fusion plus $n=2$ intrinsic charm contributions; (iii) dashes --- fusion plus $n=8$ IC contributions. A $1\%$ probability for the IC component of the proton wave function is used to fix the IC cross section. In all three cases, the overall normalization is fixed by $\sigma(x_F\geq0.5)$.
• Figure 4: Predictions of various models for $[d\sigma/dQ^2]/[d\sigma^{SM}/dQ^2]$ at HERA center-of-mass energy after integrating over $0.1\leq y\leq 0.9$. Results are shown for $e^{\pm}p$ scattering and both neutral current (NC) and charged current (CC) scattering. Curve legend: solid --- $e^+p$ scattering and $n=2$ IC; dotdash --- $e^+p$, $n=8$ IC; dashes --- $e^-p$, $n=2$ IC; dots $e^-p$, $n=8$ IC; dash-dash-dot --- $e^+p$, $\delta u(x)=0.02(1-x)^{0.1}$; dash-dot-dot --- $e^-p$, $\delta u(x)=0.02(1-x)^{0.1}$.
• Figure 5: Predictions for $[d\sigma/dM]/[d\sigma^{SM}/dM]$ at HERA center-of-mass energy after integrating over $y\geq 0.4$. Notation as for Fig. \ref{['rvsqsq']}; the dash-dash-dot curve in the NC window is not shown since it is nearly identical to the dash-dot-dot curve.