Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Single transverse spin asymmetry of dilepton production near $Z^0$ pole

Zhong-Bo Kang, Jian-Wei Qiu

TL;DR

This work investigates single transverse spin asymmetries in inclusive dilepton production within a TMD-factorization framework, incorporating contributions from $\gamma^*$, $Z^0$, and their interference. By using the latest SIDIS-derived Sivers functions and a Gaussian TMD model, it predicts a negative $A_N$ at low invariant mass $Q$ and a positive, sizable $A_N$ near the $Z^0$ pole, with about 10% asymmetry achievable for a broad $Q$ range around $M_Z$ in central to near-forward rapidities. The results provide a complementary test of time-reversal modified universality of Sivers functions and the validity of TMD factorization, with strong implications for upcoming RHIC measurements. They also highlight the importance of flavor-dependent weighting and channel dominance in shaping SSAs across different hard scales.

Abstract

Using the latest quark Sivers functions extracted from the global analysis of available data on single transverse spin asymmetry (SSA), we calculate the SSA of Drell-Yan inclusive production of lepton pairs of invariant mass $Q$ at both $4<Q<9$ GeV and $Q\sim M_Z$ in $p^\uparrow p$ collisions at RHIC energies. We find that the features of the asymmetry $A_N$ for $Q\sim M_Z$ are significantly different from that when $4<Q<9$ GeV. The $A_N$ near $Z^0$ pole is positive and sizable in the central rapidity region while the $A_N$ at low $Q$ is negative and only sizable in the forward rapidity region. We show that the size of $A_N$ is sufficiently large for a wide range of $Q$ around the $Z^0$ pole, and even with the lepton pair's invariant mass integrated from Q=70 GeV to 110 GeV, the $A_N$ is still close to 10 percent for the central and near forward rapidity region. We argue that the SSAs of Drell-Yan inclusive dilepton production at low $Q$ and that near the $Z^0$ pole provide complementary information for testing the time-reversal modified universality (the sign change) of the Sivers functions.

Single transverse spin asymmetry of dilepton production near $Z^0$ pole

TL;DR

This work investigates single transverse spin asymmetries in inclusive dilepton production within a TMD-factorization framework, incorporating contributions from , , and their interference. By using the latest SIDIS-derived Sivers functions and a Gaussian TMD model, it predicts a negative at low invariant mass and a positive, sizable near the pole, with about 10% asymmetry achievable for a broad range around in central to near-forward rapidities. The results provide a complementary test of time-reversal modified universality of Sivers functions and the validity of TMD factorization, with strong implications for upcoming RHIC measurements. They also highlight the importance of flavor-dependent weighting and channel dominance in shaping SSAs across different hard scales.

Abstract

Using the latest quark Sivers functions extracted from the global analysis of available data on single transverse spin asymmetry (SSA), we calculate the SSA of Drell-Yan inclusive production of lepton pairs of invariant mass at both GeV and in collisions at RHIC energies. We find that the features of the asymmetry for are significantly different from that when GeV. The near pole is positive and sizable in the central rapidity region while the at low is negative and only sizable in the forward rapidity region. We show that the size of is sufficiently large for a wide range of around the pole, and even with the lepton pair's invariant mass integrated from Q=70 GeV to 110 GeV, the is still close to 10 percent for the central and near forward rapidity region. We argue that the SSAs of Drell-Yan inclusive dilepton production at low and that near the pole provide complementary information for testing the time-reversal modified universality (the sign change) of the Sivers functions.

Paper Structure

This paper contains 4 sections, 14 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Single transverse spin asymmetry of dilepton production
  3. Phenomenology
  4. Conclusion

Figures (3)

  • Figure 1: SSA of lepton pair production as a function of the pair's rapidity $y$ (left) and invariant mass $Q$ (right) at $\sqrt{s}=200$ GeV (solid lines) and $\sqrt{s}=500$ GeV (dashed lines). We have integrated the pair's transverse momentum from 0 to 1 GeV.
  • Figure 2: SSA of lepton pair production at $Z^0$ pole $Q=M_Z$ as a function of the pair's transverse momentum $q_T$ (left) and rapidity $y$ at $\sqrt{s}=500$ GeV.
  • Figure 3: Left: SSA of lepton pair production as a function of the pair's invariant mass $Q$. Right: SSA of lepton pair accumulated around $Z^0$ pole as a function of rapidity $y$.