This is the wiki for the W and Z analyses using the Barrel Electromagnetic Calorimter (BEMC) at STAR.
The goal of the analyses is to measure a cross section and single helicity asymmetry, A_L.

Introduction

Single spin asymmetries in W and Z production can be used to probe the spin structure of the proton.

  1. Detector

STAR detector at RHIC is used to reconstruct charge and neutral EM particles from pp collisions at sqrt of 500 GeV.

  1. Signal

Pythia event generator is used to produce pp events yielding W-bosons. An example of W-event which decay to electron and neutrino is shown on the plot below. Requirement has been imposed on this event to deposit at least 20 GeV of ET in EMC in single cluster located at phi [80,100] deg and pseudo-rapidity [-0.8,+0.8]

  1. Backgrounds

Most common type of result of collision of 2 protons is a pair of jets. Below you can see and example of such QCD background event passing the same criterium of depositing at least 20 GeV ET in localized cluster.
Below are example of STAR response to W-event (left) and QCD-event (right)
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