Photon Tagging in the Hall D Beamline James McIntyre University of Connecticut 13 May GlueX Graduate Student Workshop Newport News, VA

Outline How we tag photons Photon production Tagger Microscope – Components – Construction 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 2

Our interest is in determining the energy of the photons which produce an event in the target. The energy of an electron that produced (via bremsstrahlung) a photon of interest is measured so that the counterpart photon can be “tagged” with a correct energy. Things to consider: – Not all photons produced will create a usable event in the target. – Not all electrons will produce a photon. – Need a way to limit & filter accidental tags and noise from the data stream. Limiting – Occurs due to our design choices. Filtering – Statistically process the data stream. 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 3 Tagging

Photon Production As the electrons pass through the 20 µm diamond radiator photons can be produced via bremsstrahlung. The angle of deflection off the beamline varies. 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 4

Distance between the Tagger Microscope and Target is ~ 300 feet. Over such a large distance even small angles of deflection become considerable. 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 5 Hall D Beamline

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 6 ~97 Ft41 Ft~161 Ft~91 Ft Location of TargetLocation of Tagger Microscope Hall D Beamline e - Beam

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 7 e - Beam Tagger Magnet Tagger Area Photon Beam e - Beam

We can use the deflection to our advantage. – Use collimator to filter out photons that have large angles. – Use Scintillating Fibers (SciFi) size to our advantage. The electron which produced a photon with a large angle will also have a larger angle. Based on Monte Carlo simulations SciFi length and cross- sectional area was selected to provide optimum filtering of incoming electrons (along with other considerations). – 2 mm square multi-clad fibers – 2 cm long 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 8 Tagging

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 9 Tagging

Scintillating Fibers – Fast Green Scintillator (BCF – 20) – Decay time 2.7 ns Other faster fibers were considered but not chosen due to problems such as shadow signal after event, etc. Waveguide – BCF-98 – ~23 inches long per channel 13 May 2010 GlueX Graduate Student Workshop Newport News, VA 10 Fiber Selection

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 11 Prototype of Tagger Microscope

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 12 Parallel Railing System Parallel Railing Unit

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 13 Ability to adjust bundle angle to permit alignment with electron beam. Step motors permit 3-point adjustment of railing height & angle (remotely).

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 14 Bundle Support Unit (aka Pop-Sickle Stick) 5x5 Bundle will mount on it via epoxy. Permits adjustment of bundle angle. Nuts on the underside of the rails will secure unit in place. Parallel Railing Unit

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 15 Fiber Array (Full Scale) Full Scale Tagger Microscope Fiber Array 500 Fibers 20 – 5x5 Fiber Bundles Note: Prototype will only have a single bundle (25 fibers) of which only 20 channels will be utilized. 5 horizontal rows Allow for proper alignment to the incoming beam by using all channels, then secure all except one row during the test runs. Provides longer operational lifetime, since radiation damaged fibers can be shifted via the step motors (instead of being changed out) to keep running using another viable row. 100 vertical rows Determines the amount of curvature of the electron due to the Tagger Magnet, therefore allowing us to calculate its energy and thus know the energy of the counterpart photon created during bremsstrahlung. End on view. The electrons would be going into the page.

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 16 Gluing Station Allows for close alignment of the two fibers Permits fine adjustment of the gap between the fibers Al construction allows for quicker curing on a heat plate Gap Adjustment Screw

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 17 Polishing: End-Mill to paper sanded Sanded fibers (400 grit) Straight edge when sanded (in contrast to the rounding shown above) Prep for Gluing (Old vs. New)

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 18 Glued Fiber

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 19 Painting Fibers Glued fiber joint showing light transmission. Air Gun used to paint the individual fibers after gluing.

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 20 Bundle of Fibers Glued fiber bundles (3x3 practice bundles) Foreground: Trial bundle with painted individual fibers. BC-600 epoxy was used. Background: Unpainted trial bundle using Elmer’ Glue. Tin Foil

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 21 Splicing Fibers MSU Splicing Unit Most promising way to connect SciFi to Waveguides As strong as a single fiber Quick production (once setup correctly) Uses a high intensity lamp to heat the fiber to the melting point and fuse them Was made for round fibers Need ferrule for square fibers to maintain shape during slicing Use of MSU Splicing Unit courtesy of Ron Richards

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 22 Digital Control Board Backplane Board Amplifier Board Electronics Backplane is secured to the top plate via six 6-32 machine screws. A Sponge Gasket provides a light seal for the penetration of the electronics. Not pictured – Card Guides and Chimney

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 23 Electronics Card Guide Backplane Board Chimney Waveguide SiPM Amplifier Board 96 Pin Euro Connector Amp Board Guard Amplifier Board Guard & Guides/Chimney Amp Board Guard protects SiPMs by preventing rubbing with the waveguides and other components. Card Guides/Chimney provide for alignment with respect to the waveguides, both vertical and horizontal. Designed to allow for ease of fiber mounting and removal.

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 24 Electronics Amp Board Guard SiPM Leveling strip

13 May 2010 GlueX Graduate Student Workshop Newport News, VA 25 Summary Measuring electron energy via deflection in a magnetic field Tagging photons Components of the Tagger Microscope