Transversity signals at COMPASS

TL;DR

This paper reports preliminary results from the COMPASS experiment on measuring transverse spin asymmetries in semi-inclusive DIS, providing insights into the nucleon spin structure and hadron production mechanisms.

Contribution

It presents the first comprehensive analysis of Collins and Sivers asymmetries using the full data set collected with transversely polarized targets at COMPASS.

Findings

Observation of non-zero Collins asymmetries.

Measurement of Sivers asymmetries indicating parton orbital angular momentum.

First results on transverse spin asymmetry in hadron pair production.

Abstract

COMPASS is a fixed target experiment at the CERN SPS, with a rich physics program focused on nucleon spin structure and on hadron spectroscopy. One of the main goals of the spin program is the measurement of the transverse spin distribution function $\Delta_T q(x)$ in semi-inclusive DIS off transversely polarized nucleons. For this purpose approximately 20% of the running time in the years 2002 to 2004 with the longitudinally polarized muon beam of 160 GeV and with $^6$LiD polarized target was used to collect data with the target polarized transversely with respect to the beam direction. The 2002 data have been already analysed and published. We present here the preliminary results from the full statistics for the Collins and Sivers single hadron asymmetries and for the transverse spin asymmetry in hadron pair production.