Title: Measurement of $W^\pm$ cross-section ratio in $pp$ collisions at RHIC
PAs: J. Nam, M. Posik, and B. Surrow
Intended Journal: PRD
Paper Draft:
Overleaf (up-to-date)
Analysis Note:
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Abstract:
We report measurements of $W^\pm \rightarrow e^\pm\nu$ production cross sections and their ratio in unpolarized $pp$ collisions at a center-of-mass energy of $\sqrt{s} = 510\gev$.
The measurement was performed within the fiducial region defined by the charged-lepton pseudorapidity $-1 < \eta_e < 1.5$, and transverse energy $25 \;\mathrm{GeV} < E_{\mathrm{T},e} < 50 \;\mathrm{GeV}$.
The cross-section ratio, $\sigma^\mathrm{fid}(W^+ \rightarrow e^+\nu) / \sigma^\mathrm{fid}(W^- \rightarrow e^-\nu)$ and differential cross sections, $d\sigma(W^\pm \rightarrow e^pm\nu)/d\eta_e$, are sensitive to the unpolarized sea quark ratio, $\bar{d}/\bar{u}$, and are measured as a function of the leptonic pseudorapidity within the studied region.
The results are based on $pp$ collision data collected with the STAR detector at RHIC in 2017, which correspond to an integrated luminosity of $340\;\mathrm{pb}^{-1}$, and found to be consistent with previous STAR publications.
Perturbative predictions at $\mathcal{O}(\alpha_s^1)$ accuracy based on the ResBos2 framework with the latest global fit results, supplemented with next-to-leading-log corrections and resummation, are compared to the combined STAR data.
While the predicted cross-section ratio describes the data well, the predictions for the differential cross sections overestimate the measurements by approximately $2 \sigma$.
Conclusion:
The $W^\pm \rightarrow e\nu$ cross sections and their ratio have been measured with RHIC $pp \sqrt{s} = 510 GeV$ collision data collected at STAR in 2017, corresponding to an integrated luminosity of $340 \unit{pb}^{-1}$.
The measurements were performed as a function of the leptonic pseudorapidity $\eta_{e}$ within the kinematic region defined by leptononic pseudorapidity $-1.0 <\eta < 1.5$ and transverse energy $25 \unit{GeV} < E_{T,e} < 50 \unit{GeV}$.
The resulting cross sections and ratio are consistent with previous STAR publications.
These measurements provide independent constraints for the non-perturbative SU(2) $\bar{d}/\bar{u}$ asymmetry at a higher momentum scale ($\sim M_W$), complementary to existing $pp/pd$ Drell-Yan data, and a low-$\sqrt{s}$ and high-$x$ ($\sim 0.2$) reference for LHC $W/Z$ programs.
Perturbative calculations at NLO+NLL accuracy with latest PDF sets implemented in the ResBos2 framework [PLACEHOLDER] have been compared to the data.
The prediction with the NNPDF4.0 PDF set~\cite{NNPDF:2021njg} that includes the latest SeaQuest data~\cite{SeaQuest:2021zxb} in the global fit shows an improvement over the previous NNPDF3.1~\cite{NNPDF:2017mvq} in describing the $W^+/W^-$ cross section ratio observed at STAR.
However, all calculations overestimated the differential cross sections $d\sigma(W^\pm \rightarrow e\nu)/d\eta_e$ throughout the studied $\eta_e$ range.
Relevant Presentations
Preliminary request of W+/W- cross section: TBD
Preliminary request of W+/W- cross section ratio: link
List of Figures:
Figure 1: Signal and background description (Barrel)
Figure 2: Signal and Background description (W+, Barrel, eta binned)
Figure 3: Signal and Background description (W-, Barrel, eta binned)
Figure 4: Charge mis-identification correction (Barrel)
Figure 5: Charge mis-identification correction (Barrel, eta binned)
Figure 6: Signal and Background description and charge correction (Endcap)
Figure 7: Efficiency and Efficiency ratio
Figure 8: Systematic Uncertainties
Figure 9: Differential cross sections
Figure 10: Cross-section ratio
Code:
/star/u/jaenam/W2017
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