Charm jets as a probe for strangeness at the future Electron-Ion Collider

We explore the feasibility of the measurement of charm-jet cross sections in charged-current deep-inelastic scattering at the future Electron-Ion Collider. This channel provides clean sensitivity to the strangeness content of the nucleon in the high-$x$ region. We estimate charm-jet tagging performance with parametrized detector simulations. We show the expected sensitivity to various scenarios for strange parton distribution functions. We argue that this measurement will be key to future QCD global analyses, so it should inform EIC detector designs and luminosity requirements.

Figure 1

Leading-order diagram for the production of final-state charm in charged-current electron-proton DIS.

Figure 2

The kinematics (momentum, $p$, and polar angle, $\theta$, with respect to the direction of the hadron beam) of generated charm jets in CC DIS with $Q^2>100{\mathrm{GeV}}^2$. The jets are clustered with the anti-$k_{\mathrm{T}}$ algorithm with $R=1.0$.

Figure 3

Inclusive and charm-jet production in charged-current DIS at generator level. The jets are reconstructed with the anti-$k_{\mathrm{T}}$ algorithm with $R=1.0$.

Figure 4

Missing transverse energy ($E_T^{\mathrm{miss}}$) response matrix for charged-current DIS events. The missing energy is reconstructed using delphes particle-flow objects.

Figure 5

Bin survival probability obtained using the Jacquet-Blondel method in charged-current DIS events.

Figure 6

Signed impact parameter significance, ${\mathrm{sIP}}_{3\mathrm{D}}$, probability distribution for light and charm jets.

Figure 7

A pair of event displays of a single CC DIS event simulated with pythia8 and reconstructed with delphes. A reconstructed jet is represented as a yellow cone; blue bars are hadronic calorimeter energy deposits, and red bars are electromagnetic calorimeter energy deposits. Tracks are indicated by blue lines; the yellow-highlighted tracks originate from a displaced decay vertex. The zoomed-in view (bottom) shows these tracks and vertices.

Figure 8

Jet tagging efficiency for light and charm jets as a function of the jet $p_{\mathrm{T}}$. The high-impact parameter track-counting approach is used to obtain these results.

Figure 9

To gauge the event-level sensitivity of charm-jet production, we perform simulations with two extreme inputs for the behavior of the strangeness suppression ratio, $R_s$, as defined in Eq. (1), taken from the recent CT18 NNLO global PDF analysis [48]. The upper panel corresponds to a Lagrange multiplier (LM) scan over values of $R_s$ at high $x=0.1$ in the primary CT18 baseline fit, while the lower panel was obtained for the alternative CT18Z fit, which included the ATLAS 7 TeV $W/Z$ data (ATL7ZW) [57], in addition to a number of other modifications. In both panels, the PDF scale is the factorization scale, $Q=\mu =1.5\mathrm{GeV}$.

Figure 10

(a) For a selection of PDFs, we display the strange-quark PDF, $x^{1.5}s(x,Q)$, at $Q=10\mathrm{GeV}$. The region between our Rs-High [enhanced strangeness] (dashed red) and Rs-Low [suppressed strangeness] (dot-dashed red) PDF curves is shaded to highlight this region. The PDF curves are identified in Table 2. (b) Same as (a), but with the PDF uncertainties indicated with shaded bands bounded by dotted lines.

Figure 11

(a) For a selection of PDFs, we display the strange-quark $R_s(x,Q)$ ratio at $Q=10\mathrm{GeV}$. The region between our Rs-High [enhanced strangeness] (dashed red) and Rs-Low [suppressed strangeness] (dot-dashed red) PDF curves is shaded to highlight this region. The PDF curves are identified in Table 2. (b) Same as (a), but with the PDF uncertainties indicated with shaded bands bounded by dotted lines.

Figure 12

We compare three cases: (a) Rs-Low NNLO with suppressed strangeness. (b) Rs-High NNLO with enhanced strangeness. (c) CT18A NNLO with intermediate strangeness. Our baseline is the Rs-Low (suppressed strangeness), and the gray band indicates the expected statistical error on the reconstructed and tagged charm jet $p_T$ (top), Bjorken $x$ (middle), and reconstructed $x_{JB}$ (bottom) spectrum with $100{\mathrm{fb}}^{-1}$ of data. The points indicate the difference in expected yields $(1+\mathrm{\Delta }N/N)$ for the enhanced (Rs-High) and intermediate (CT18A) strangeness cases relative to the suppressed (Rs-Low) case.