[Jlab-seminars] Today's Physics Seminar: Eroc Pooser; The GlueX Start Counter \& Beam Asymmetry $\Sigma$ in single $\pi^{0}$ Photoproduction

[Stephanie Tysor]

*Physics Seminar*

*Eric Pooser*

**

*Florida International University, Miami, FL***

/The GlueX Start Counter \& Beam Asymmetry $\Sigma$ in single $\pi^{0}$ 
Photoproduction/

//

*Abstract:*

The GlueX experiment aims to study meson photoproduction while utilizing 
the coherent bremsstrahlung technique to produce a 9 GeV linearly 
polarized photon beam incident on a liquid $\mathrm{H_{2}}$ target. A 
Start Counter detector was fabricated to properly identify the 
accelerator electron beam buckets and to provide accurate timing 
information. The Start Counter detector was designed to operate at 
photon intensities of up to $\mathrm{10^{8}\gamma/s}$ in the coherent 
peak and provides a timing resolution $\mathrm{\sim 300\ ps}$ so as to 
provide successful identification of the electron beam buckets to within 
99\% accuracy. Furthermore, the Start Counter detector provides 
excellent solid angle coverage, $\sim 90 \%\ \mathrm{of}\ 4 \pi\ 
\mathrm{hermeticity}$, and a high degree of segmentation for background 
rejection.  It consists of a cylindrical array of 30 scintillators with 
pointed ends that bend towards the beam at the downstream end. Magnetic 
field insensitive silicon photomultiplier detectors were selected as the 
readout system.

An initial measurement of the beam asymmetry $\Sigma$ in the exclusive 
reaction $\vec{\gamma}p \rightarrow \pi^{0}p$, where $\pi^{0} 
  \rightarrow \gamma \gamma$ has been carried out utilizing the GlueX 
spectrometer during the Spring 2015 commissioning run.  The tagged 
photon energies ranged from $2.5 \leq E_{\gamma} \leq 3.0\ \mathrm{GeV}$ 
in the coherent peak.  These measurements were then compared to the 
world data set and show remarkable agreement with only two hours of 
physics production running.

*Monday, March 14, 2016*

*10:00 am*

*CEBAF Center A110*

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