Parton Distribution Function sensitivity studies using electroweak processes at LHCb

TL;DR

The paper evaluates how LHCb's forward-rapidity, low-$p_T$ muon triggers enable Drell–Yan–related electroweak measurements that probe PDFs down to $x\sim2\times10^{-6}$ and $Q^2$ near 10 GeV$^2$. It implements two PDF-fitting frameworks—Hessian eigenvector and neural-network replica ensembles (NNPDF)—to quantify potential PDF constraints from W, Z, and low-mass Drell–Yan data. Results indicate substantial reductions in gluon, sea, and valence uncertainties (up to ~70% in some $x$ regions) with 1 fb$^{-1}$, especially from the low-mass Drell–Yan channel and combined W/Z rapidity fits. This demonstrates LHCb's capability to significantly complement central-detector PDF determinations in poorly constrained kinematic regimes.

Abstract

We describe parton density function sensitivity studies, using muon final states produced through the Drell-Yan process via W, Z or $γ^*$ down to a Q^2 of 10 GeV^2. This makes use of LHCb's unique ability to trigger on low transverse momentum objects. Due to the forward acceptance of LHCb, x values down to 2 10^{-6} can be probed, where with just 100 pb-1 of data, the gluon PDF can improved up to 70%.

Figures (2)

• Figure 1: Percentage uncertainty on production cross-section of electroweak boson as function of rapidity
• Figure 2: Ratio between PDF uncertainties before and after adding $1~fb^{-1}$ of LHCb data for different distributions as a function of x