Abstract
The forward LHCb acceptance opens interesting possibilities of studying precision Standard Model hard processes in a kinematical region beyond the reach of ATLAS and CMS. In this paper we perform a feasibility study for cross-section measurements of top quark pairs with the LHCb detector, with an analysis of signal and background rates for selected final states, and determine the potential precision achievable at $\sqrt{s} =$ 7 and 14~TeV. We then study the dependence of theoretical uncertainties on the pseudorapidity distribution of top quarks produced in pair production at NLO, and observe that a cross-section measurement at high pseudorapidity has enhanced sensitivity to probe the high-$x$ gluon PDF as compared to measurements in the central-region. Based on simulated pseudodata, the impact of a 14~TeV cross-section measurement on the gluon PDF and charge asymmetry is quantified.
Highlights
There have been large efforts in the QCD community to improve the precision of top quark pair production predictions
We study the dependence of theoretical uncertainties on the pseudorapidity distribution of top quarks produced in pair production at NLO, and observe that a crosssection measurement at high pseudorapidity has enhanced sensitivity to probe the high-x gluon PDF as compared to measurements in the central-region
A recent study of the impact of these uncertainties on the inclusive cross-section at next-to-nextto-leading order (NNLO)+next-to-next-to-leading log (NNLL) accuracy can be found in ref. [10], where it is observed that such a measurement, with minimal scale uncertainties, has the potential to strongly constrain the gluon PDF
Summary
Given the promising signal yield and observability at 14 and 7 TeV, we study the theoretical uncertainties on the signal at the parton level within the LHCb acceptance. The pseudotop differential cross-section with respect to pseudorapidity is shown in figure 5 for 7 and 14 TeV, the blue uncertainty band is due to scale variation as previously described. The enhanced sensitivity of measurements at high pseudorapidity can be seen by comparing the relative uncertainties for the inclusive and differential LHCb cross-sections. This comparison is done by taking the ratio of their relative uncertainties, δXratio δXLHCb δXN LO. Summary of cross-section and theoretical uncertainties within the LHCb fiducial region at s = 7 (left) and 14 TeV (right), plotted with respect to each PDF collaborations preferred value for αs(MZ). The inner and outer error bars correspond to the scale and total uncertainties respectively
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