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Status of the TOF Detector

Status of the TOF Detector. Matthew Jones. Purdue University. Signals are generally smaller now than they were when we installed the PMT’s How do we know? How big is this effect? How does it affect performance? Do we understand why? What are we going to do about it?

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Status of the TOF Detector

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  1. Status of the TOF Detector Matthew Jones Purdue University • Signals are generally smaller now than they were when we installed the PMT’s • How do we know? • How big is this effect? • How does it affect performance? • Do we understand why? • What are we going to do about it? • This talk should provide some answers to these questions. April 6, 2006

  2. Mean of ADC response distribution Average over 432 channels Changes to gate width ADC for 1 MIP 20% loss over ~1 year Attenuation length approximately constant?

  3. A Closer Look at PMT Response • Recent validation suggests degraded performance in recent data (CDF Note 8169): Some effects could be correlated with higher occupancy in more recent data.

  4. A Closer Look at PMT Response • A more detailed analysis of individual PMT response can quantify this • Main approach (CDF Note 7693): • Measure amount of scintillator a track must traverse to produce enough light to fire the discriminator • Define minimal length for minimum ionizing particle • Measure this as a function of z • Sensitive to gain loss in each PMT separately • Somewhat sensitive to changes in attenuation length • Unbiased, unlike the ADC readout

  5. Minimal path length study • Channel 5: one that ages gracefully. L=171x1030 cm-2s-1 L=135x1030 L=137x1030 L= 69x1030 Minimal luminosity dependence

  6. Minimal path length study • Channel 221 (other end of same bar) shows significant change: Far end Near end

  7. Effect on Efficiency for MIPs • Require enough light to fire discriminators on both ends of the bar: Feb 2002 Dec 2005

  8. Loss of Efficiency • That was probably somewhat pessimistic (not all tracks are MIP’s) • Nevertheless, the loss of efficiency is real and probably significant • Slow protons ionize more: enhanced proton fraction in more recent data? • Tracks that do produce hits will have smaller pulses now than in 2002 – does the calibration handle this adequately?

  9. Resolution from low momentum pions

  10. What’s wrong with the PMT’s? • Several parameters are somewhat correlated... They can change dramatically and unpredictably in a magnetic field. • Strongest correlation seems to be with HV: More gain loss Interesting... But this does not imply causality. Less gain loss

  11. Bad Bad Good Good Good Gain loss vs PMT serial number • Assumes that serial numbers correlate to manufacturing date (probably reasonable). Received PMT’s from Hamamatsu in 6 batches.

  12. Correlation with Timing Resolution Timing resolution at z=0 from 2002 data • Suggests that all PMT’s were about the same initially.

  13. Correlation with Timing Resolution • Appears to be some correlation with loss of gain observed in path length analysis. Timing resolution at z=0 from 2005 data

  14. Possible Courses of Action • Here are some options: • Do nothing and suffer efficiency loss and degraded timing resolution • Turn up the HV: might accelerate the aging? Or maybe it wouldn’t... • Replace PMT’s? Probably too many need to be replaced to make an impact. • Attach amplifiers between ends of cable and front end electronics? • We are discussing these to form a consensus on how best to proceed.

  15. Summary • Definite loss of response since early 2002 • Developed more quickly in 2005 • Probably due to higher integrated luminosity • Probably having some impact on physics • Dominant effect is associated with PMT’s • Several ways to proceed – good chance we can recover performance and run through the rest of Run-II.

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