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.
- Detector
[STAR] detector at [RHIC] is used to reconstruct charge and neutral EM particles from pp collisions at sqrt of 500 GeV.
- 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]
[[Image:Picture_7.png]]
10 similar W-events are in this PDF [[Media:Pyt500Weve.pdf]] (13 MB)
==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.
[[Image:EMC_ET-20_GeV.png]]
10 similar QCD-events are in this PDF [[Media:Pyt500QCDeve.pdf]](13 MB)
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