xchu's blog

Intended journal: PLB

First round review from PLB:
response to referee1
response to referee2
paper with difference shown diff0403
paper paper0403

Submitted to arXiv and PLB on 8/28/2023:
PLB, Ref. No. PLB-D-23-01267
arXiv:2023.15496

Paper draft:
before GPC
v1, v2, v3 (Fig2 not updated)

during GPC
v3.1 (Fig2 updated)
v4
v5
v6
v7

Collaboration Review
v8
v8_Diff
v9
v10

Analysis note:
before GPC
v1, v2, v3
during GPC
v4
v5
Collaboration Review
v6
v7

Abstract:

The differential cross section for $Z^{0}$ production, measured as a function of the boson's transverse momentum ($p_{\mathrm{T}}$), provides important constraints on the evolution of the transverse momentum dependent parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the $Z^{0}$ is sensitive to one of the polarized TMDs, the Sivers function, which is predicted to have the opposite sign in $p+p$ $\rightarrow W/Z+ X$ from that which enters in semi-inclusive deep inelastic scattering. In this Letter, the STAR Collaboration reports the first measurement of the $Z^{0}/\gamma^{*}$ differential cross section as a function of its \pT in $p$$+$$p$ collisions at a center-of-mass energy of 510 GeV, together with the $Z^{0}/\gamma^{*}$ total cross section. We also report the measurement of $Z^{0}/\gamma^{*}$ TSSA in transversely polarized $p$$+$$p$ collisions at 510 GeV.

Conclusion:

(1) The measured Z^{0} p_{T} spectrum provides important constraints on the evolution of the TMDs, together with the results of Drell-Yan, semi-inclusive deep inelastic scattering, and other $Z^{0}$ data from the collider experiments at Tevatron and LHC.

(2) The measured TSSA of $Z^{0}$ is 0.056 $\pm$ 0.081 (statistic uncertainty) $\pm$ 0.050 (systematic uncertainty), the uncertainty is dominated by the statistics. It is challenging to test the sign change for the Sivers function with current STAR data.

Figures:

Figure1: The reconstructed invariant mass distribution of e^{+}e^{-} pairs, together with the invariant mass distribution of like sign e^{+}e^{+} and e^{-}e^{-} pairs.

Figure2: The measured p_{T} spectrum of Z^{0}. The systematic uncertainties come from detector efficiency correction, varying p_T cut of the lepton (varying from 25 GeV/c to 24 GeV/c and 26 GeV/c), varying gain of BEMC (run11-13: gain +- 5%, run17: gain +- 3%), and like sign charge background (e^{+}e^{+} and e^{-}e^{-} pairs). The theoretical calculations of Next-next-leading logarithmic accuracy (NNLL) are from Regensburg group (JHEP 06(2019) 028). The Next-next-next-leading logarithmic accuracy calculations (NNNLL) are from Pavia group based on the paper (JHEP10(2022)127), this is the newest version from Pavia+MAP22.

Figure3: Comparison of the total Z0 cross section measured in this analysis and the previous STAR data, as well as the results from other experiments. The older STAR results Phys. Rev. D 85 (2012) 092010, Phys. Rev. D 103 (1) (2021) 012001, and higher energy results from the LHC are shown as well. The vertical bars indicate the total uncertainties from combining statistical and systematic ones. In the small panel, the previous and current STAR results are shown within a shorter range of collision energies.

Figure4: The measured transverse single spin asymmetry of Z^{0}. The systematic uncertainties come from like sign charge background (e^{+}e^{+} and e^{-}e^{-} pairs). The Next-next-next-leading logarithmic accuracy calculations (NNNLL) are from PRL 126 112002 (2021). The Next-leading logarithmic accuracy calculations (NLL) are from Pavia group (arXiv:2004.14278).