Latest revision as of 15:55, 23 July 2009

Prelude

• Two gases are used: 70/30 and 90/10 Ar/CO2
• Two fADC clock settings are used: 125 and 200 MHz

• Drift time spectra (DCOG method is used):

90/10 Ar/CO2 drift time spectra.

70/30 Ar/CO2 drift time spectra.

• Red line is fit to get absolute minimal drift time
  • Best tracking results if extracted minimal drift time + 1 time sample

• Samples per rising edge - 2 extra samples 125 -> 200 MHz

Samples/rising edge - 70/30 Ar/CO2 - 125~MHz clock.

Samples/rising edge - 70/30 Ar/CO2 - 200~MHz clock.

• Time-2-distance relation:
  • GARFIELD is used. To get best resolutions out of it:
    • 68/32 Ar/CO2 is put in GARFIELD for 70/30 gas
    • 89/11 Ar/CO2 is put in GARFIELD for 90/10 gas
    • +-6% CO2 can give 100~ns difference

Resolutions

• Difference in gases - blue line is a model prediction:

Resolutions (in um) as a function of distance to the wire (in mm) for 70/30.

Resolutions (in um) as a function of distance to the wire (in mm) for 90/10.

• 90/10 worse because shorter drift times.
• Model contains:
  • Timing resolution (0.75 length of time sample)
  • accuracy
  • diffusion (Garfield)

• Table with resolutions for straw 7 and different clock settings:
  • high: with hit removed from tracking
  • low: with hit included

• The difference between high and low is largest for 1-3 mm driftdistances but overall the difference is not that big.
• Gas mixture has a big impact
• We might not have a big enough lever arm:

Drawing of the end plate of the small prototype.

GARFIELD - DATA

Below 70/30 gas mixture ch 7: left MC, right data

Resolutions as a function of drift distance (MC).

Resolutions as a function of drift distance (data).

To do

• There is a full simulation of the chamber and results are on there way
• We are testing 80/20 gas right now
• We want to test the same gas mixture as FDC uses
• We also want to try and add ethane
• Try different timing algorithms
• Find a way to extract the timing resolution directly