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

TL;DR

This paper calculates the single transverse spin asymmetry (SSA) in dilepton production near the Z^0 pole using recent Sivers functions, revealing distinct asymmetry features at different invariant mass ranges and proposing tests for Sivers function universality.

Contribution

It provides the first detailed prediction of SSA behavior near the Z^0 pole, highlighting differences from lower mass regions and suggesting experimental tests for Sivers function universality.

Findings

SSA near Z^0 pole is positive and sizable in central rapidity.

SSA at low Q is negative and prominent in forward rapidity.

Integrated SSA around Z^0 mass range remains close to 10%.

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.