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$\cos 2 φ$ asymmetries in unpolarized semi-inclusive DIS

Bing Zhang, Zhun Lu, Bo-Qiang Ma, Ivan Schmidt

TL;DR

The paper investigates the $\cos 2\phi$ asymmetry in unpolarized SIDIS as a probe of the Boer–Mulders function $h_1^{\perp}$ and the Collins fragmentation function $H_1^{\perp}$. It combines Boer–Mulders extractions from unpolarized Drell–Yan data (E866/NuSea) with Collins parameterizations to predict SIDIS asymmetries, accounting for both the Cahn effect and the BM–Collins mechanism, and explores two BM sign scenarios. Predictions for ZEUS, JLab, and HERMES show that charged-pion asymmetries are typically small when charges are summed but can be sizable and charge-dependent when analyzed separately, especially for $\pi^-$; this motivates separate $\pi^+$ and $\pi^-$ measurements to better constrain the underlying TMDs. The study also contrasts two BM sets to illustrate how upcoming Drell–Yan and SIDIS data can distinguish between them and refine our understanding of transverse spin-momentum correlations in hadrons.

Abstract

We use the Boer-Mulders functions parameterized from unpolarized $p+D$ Drell-Yan data by the FNAL E866/NuSea Collaboration combined with recently extracted Collins functions to calculate the $\cos 2 φ$ asymmetries in unpolarized semi-inclusive deeply inelastic scattering (SIDIS) processes both for ZEUS at Hadron Electron Ring Accelerator (HERA) and Jefferson Lab experiments (JLab), and to compare our results with their data. We also give predictions for the $\cos 2 φ$ asymmetries of SIDIS in the kinematical regime of HERMES Collaboration, and the forthcoming JLab experiments. We predict that the $\cos 2 φ$ asymmetries of semi-inclusive $π^-$ production are somewhat larger than that of $π^+$ production. We suggest to measure these two processes separately, which will provide more detail information on the Boer-Mulders functions as well as on the Collins functions.

$\cos 2 φ$ asymmetries in unpolarized semi-inclusive DIS

TL;DR

The paper investigates the asymmetry in unpolarized SIDIS as a probe of the Boer–Mulders function and the Collins fragmentation function . It combines Boer–Mulders extractions from unpolarized Drell–Yan data (E866/NuSea) with Collins parameterizations to predict SIDIS asymmetries, accounting for both the Cahn effect and the BM–Collins mechanism, and explores two BM sign scenarios. Predictions for ZEUS, JLab, and HERMES show that charged-pion asymmetries are typically small when charges are summed but can be sizable and charge-dependent when analyzed separately, especially for ; this motivates separate and measurements to better constrain the underlying TMDs. The study also contrasts two BM sets to illustrate how upcoming Drell–Yan and SIDIS data can distinguish between them and refine our understanding of transverse spin-momentum correlations in hadrons.

Abstract

We use the Boer-Mulders functions parameterized from unpolarized Drell-Yan data by the FNAL E866/NuSea Collaboration combined with recently extracted Collins functions to calculate the asymmetries in unpolarized semi-inclusive deeply inelastic scattering (SIDIS) processes both for ZEUS at Hadron Electron Ring Accelerator (HERA) and Jefferson Lab experiments (JLab), and to compare our results with their data. We also give predictions for the asymmetries of SIDIS in the kinematical regime of HERMES Collaboration, and the forthcoming JLab experiments. We predict that the asymmetries of semi-inclusive production are somewhat larger than that of production. We suggest to measure these two processes separately, which will provide more detail information on the Boer-Mulders functions as well as on the Collins functions.

Paper Structure

This paper contains 5 sections, 25 equations, 18 figures, 1 table.

Table of Contents

  1. Introduction
  2. The $\cos 2 \phi$ asymmetry in unpolarized SIDIS
  3. Sets of the boer-mulders and collins functions used in our calculation
  4. Results and predictions
  5. Conclusion

Figures (18)

  • Figure 1: Lepton and hadron planes in semi-inclusive deep inelastic scattering.
  • Figure 2: The $P_T$-dependent $\cos 2 \phi$ asymmetries for unpolarized $p+p$ and $p+D$ Drell-Yan processes of the FNAL E866/NuSea Collaboration. The left part is taken of Set I , and the right part is taken of Set II.
  • Figure 3: The $E_{T,min}^{HCM}$-dependent $\cos 2 \phi$ asymmetries at ZEUS with pseudorapidity $-5 < \eta^{HCM} \leq -2.5$, $-2.5 < \eta^{HCM} \leq -1$ and $-1 < \eta^{HCM} \leq 0$. The left column is from Boer-Mulders functions of Set I with $0.2 \leq \omega \leq 0.5$, the right column is from Boer-Mulders functions of Set II with $0.5 \leq \omega \leq 0.8$.
  • Figure 4: The $\eta^{HCM}$-dependent $\cos 2 \phi$ asymmetries at ZEUS. The left column is from Boer-Mulders functions of Set I with $0.2 \leq \omega \leq 0.5$, the right column is from Boer-Mulders functions of Set II with $0.5 \leq \omega \leq 0.8$.
  • Figure 5: The $P_c$-dependent $\cos 2 \phi$ asymmetries at the earlier ZEUS experiment. Data are from Ref. zeus2000. The left column is from Boer-Mulders functions of Set I with $0.2 \leq \omega \leq 0.5$, the right column is from Boer-Mulders functions of Set II with $0.5 \leq \omega \leq 0.8$.
  • ...and 13 more figures