Initial performance of the PHENIX Hadron Blind Detector at RHIC

The PHENIX Hadron Blind Detector (HBD) was successfully operated during the 2009 high energy polarized proton run at RHIC. This was the first data taking run after the detector was rebuilt following its first commissioning run in 2007. The detector was operated for several months under actual beam conditions and showed greatly improved performance over the commissioning run. Results are given on the operation of the detector, determination and calibration of the gain using scintillation light produced by charged particles in CF₄, stability of the CsI photocathodes, the ability to identify single and double electrons using the signal from Cherenkov light, and the level of sensitivity of the detector to charged hadrons. A description is also given on the methods used to reconstruct the detector that led to its improved performance.