April 15, 2008 Calorimetry

Connection

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Reference Documents

1. Previous minutes: March 21, 2008 Calorimetry
2. Schedule, Tracker and Drawings (gluex pass)
3. Schedule

Tentative Agenda

1. Review Options for Working Group Meeting Time
2. Calibration Update / Discussion (Athens)
   • Goals for calibration
   • Deployment in various subsystems
3. FCAL Update
   • A few plots that show typical FADC response and time resolution that migh be achieved (Mihajlo)
4. BCAL Update
   • Reanalysis of timing resolution from cosmics (Media:talk080415.pdf) - Andrei/Irina
5. SiPM gain non-uniformities and energy resolution [1] (Richard)
6. SiPMs
   • Phone conference yesterday. Divided shipments of 1 mm2 A20HD and A35HD and 3 mm2 A20HD units shipped to UofR and JLab. 3mm2 A35HD units delayed by 4-6 weeks. Testing to be conducted upon receipt:
   • UR tests
     1. IV curves
     2. Scanning SiPMs for uniformity. Current illumination is 1mm diameter, but improving setup to 0.25 mm diameter to allow for finer scans.
     3. Use coupling to fiber array to measure light yield and normalized to the number of photoelectrons. [Array is about 2x1.8x25 cm3. On one side the fibers are flared out and coupled to a Winston Cone guide.
   • JLab tests, use optical setup using LEDs
     1. IV curve
     2. Linearity of response
     3. Relative gain
     4. Dark rate
     5. Timing characteristics. [Notes from George: timing response of newer glass arrays show rise times of about 10 ns, and contained in a 70-75]
     6. Later, not in initial tests: temperature dependence of units.
7. Fiber Specifications
   • Response of Kuraray and St. Gobain to the request to JLab sources sought / do we need more samples?
   • Summary of fiber spectra analysis (Alex) [2]
   • How to specify a) Fiber color/spectrum and b) light output
   • JLab Tests (Carl)
8. Review of Action Item Tracker
   • Fabrication plan and QA /visit to Alberta?
9. Any other business

Minutes

Online: Elton, Elke, Tim, Richard, Zisis, Matt, Alex, Christina, Carl

1. Review Options for Working Group Meeting Time
   • Decided to have the meetings on Mondays at 10:30 am every two weeks. We will start next week April 21.
2. Calibration Update / Discussion (Athens)
   • Received materials from CERN to setup tests. Two setups will be prepared. The first consists of a laser feeding a 10x10x10 cm3 scintillator viewed by 10 clear fibers. The second setup will be similar to the first, but use a LED as a source instead of a laser. The fibers are 4 m long. Initial goals will be to measure the intensity of light and uniformity of light coming out of each fiber. Expect results in the next couple of weeks.
3. FCAL Update (Matt gave an update on activities at IU)
   • Mihajlo is studying the timing resolution that can be obtained from digitized pmt pulses. It was noted at the last meeting that the pulses had a slow rise time. This has been traced to running the pmts at too low a voltage and possibly unsynchronized clocks on the single-cell FADCs they are using. Both issues are being addressed.
   • The option for constructing a plastic cellular wall is being prototyped by John. So far a module with a single pmt has been completed but is very promising. Will scale up to 4 pmts and larger prototypes to check deformation as holes are drilled. Eventually plan a circular prototype with 68 channels.
   • Tim suggested that recommendations from plastic vendors could be useful as many different materials are available.
4. SiPM gain non-uniformities and energy resolution [3] (Richard)
   • Richard gave a summary of his work to determine the sensitivity of the Bcal resolution in response to non-uniform gain across light sensors.
   • Derived an analytical model for an ideal calorimeter which gives only a statistical term to the resolution and no floor term. Updates to the model include non-uniform response across the sensitive face which introduces a floor term to the resolution. Two extreme examples were given: the first matches the bcaL output directly to the sensor and non-uniform gain directly translates into resolution degradation. If the light is mixed in the light guide before detection, this situation leads to no degradation in resolution.
   • Richard suggested that the mixing of light in the light guides be measured so that its behavior could be used in the model to predict the effect on resolution. Zisis said they would look into this, which could be done experimentally or in simulation. Matt commented that simulation would give a conservative prediction because perfect optical surfaces never mix the light as much as real detectors.
5. BCAL Update
   • Reanalysis of timing resolution from cosmics ( Analysis of Cosmic-Ray Time Information ) - Andrei/Irina
   • Zisis summarized the work of Andrei (out sick) and Irina. They have reanalyzed the cosmic-ray data from the beam test and after a careful analysis show that they get the same resolution function as derived by Blake for electron showers. This analysis was done for the XP2020, similar analysis for the Burle 8575 yield significantly worse resolution. Speculation is that they were old tubes that might have degraded over time.
   • Fabrication plan and QA /visit to Alberta? No communication with Alberta has been made. Elke was not able to meet with Jim during the DIS conference.
6. SiPMs
   • Phone conference yesterday. Divided shipments of 1 mm2 A20HD and A35HD and 3 mm2 A20HD units shipped to UofR and JLab. 3mm2 A35HD units delayed by 4-6 weeks. Testing to be conducted upon receipt both at UofR and JLab.
7. Fiber Specifications
   • Summary of fiber spectra analysis (Alex) [4] General conclusion from the studies by Alex (in agreement with Carl's measurements) is that the response of the SiPM which is quite uniform over wavelength results in very similar response between blue and green fibers. The attenuation length measurements for the recent samples of St. Gobain and Kuraray fibers are confusing: The St. Gobain fibers yield attenuation lengths that are much shorter than previous samples (~1.2 m instead of >2.5m) and the Kuraray fibers yield attenuation lengths far in excess of the manufacturer specifications (>3.5 m).
   • Carl brought up the suggestion of obtaining some standard samples of fibers with test results from both St. Gobain and Kuraray so that we can normalize our light output measurements to their tests.
   • The consensus is that the response to a source (e.g. 90Sr) is the only method for absolute measurement of the light output and we should be prepared for these measurements.