Forward jet-like event spin-dependent properties in polarized p+p collisions at $\sqrt{s}$=200 GeV

TL;DR

This paper reports on measurements of spin-dependent asymmetries in forward jet-like events from polarized proton collisions at 200 GeV, aiming to understand the origins of forward asymmetries beyond inclusive pion production.

Contribution

It introduces the use of electromagnetic calorimeter cluster responses to study jet-like events and their spin asymmetries, providing new insights into forward proton spin structure.

Findings

Preliminary measurements of transverse single spin asymmetries in jet-like events.

Use of calorimeter clustering to approximate forward jets.

Data collected with polarized protons at 200 GeV with 60% polarization.

Abstract

The STAR collaboration has reported precision measurements on the transverse single spin asymmetries for the production of forward $\pi^0$ mesons from polarized proton collisions at $\sqrt{s} =\,$200 GeV. To disentangle the contributions to forward asymmetries, one has to look beyond inclusive $\pi^0$ production to the production of forward jets or direct photons. Present forward detector capabilities are not well matched to the complete reconstruction of forward jets, but do have sufficient acceptance for "jet-like" events. "Jet-like" events are the clustered response of an electromagnetic calorimeter that is primarily sensitive to incident photons, electrons and positrons. During the RHIC running in the year 2006, STAR with the Forward Pion Detector (FPD++) in place collected 6.8 pb$^{-1}$ of data with an average polarization of 60%. FPD++ was a modular detector prototype of the Forward Meson Spectrometer (FMS) that consisted of two detectors placed symmetrically with respect to the beam line at a distance of 7.4 m from the interaction point. Readout of the FPD++ was triggered when the sum of energies in the central module of the calorimeter used for $\pi^0$ measurements was larger than a threshold. This trigger minimizes the bias for "jet-like" events, making it appropriate to disentangling contributions to the forward transverse spin asymmetries. We report on the status of the analysis.