Tped shifting and the crab
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TPed Shifting and the Crab. Curtis Lansdell University of Maryland. History. Timing calibration of outriggers Examined outrigger TChi distributions for wandering of pedestals with time and temperature Studied day/night and seasonal variation – how does the TChi peak change?

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TPed Shifting and the Crab

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Tped shifting and the crab

TPed Shifting and the Crab

Curtis Lansdell

University of Maryland

Milagro Collaboration Meeting


History

History

  • Timing calibration of outriggers

    • Examined outrigger TChi distributions for wandering of pedestals with time and temperature

    • Studied day/night and seasonal variation – how does the TChi peak change?

  • Found out that some PMTs have poor TChi distributions and decided to try shifting hit times to see if better distributions could be produced

  • Applied TPed shift method to Crab RAW data files and examined skymaps

  • Found good angular resolution for hard cut events


Day night differences

Day/Night Differences

  • Fit TChi peak to Gaussian for day and night data

    • From Dec. 19, 2004

  • Get difference in fits’ mean positions and plot

    • Small differences seen, but typically < 0.2ns


Summer winter differences

Summer/Winter Differences

  • Fit TChi peak to Gaussian for day and night data

    • From May 19 and Dec. 19, 2004

  • Get difference in fits’ mean positions and plot

    • Here, showing only day differences

    • Worse statistics because May data from SAV file (probably should have used Crab RAW)

    • Even with worse statistics, there does seem to be larger variations (> 0.5ns)


Timing problem

original

ns

Timing Problem

  • Can temperature effect be removed?

  • Examining TChi distributions show that timing can be off by large amounts (by as much as ~60ns in some cases)

  • Shifting hit times can fix this


Fixing the time pedestals offline

after shift

ns

Fixing the Time Pedestals (offline)

  • Measured hit time = difference between the pedestal time and the TDC time

  • TChi = difference between shower front fit time and the measured hit time

  • If the TChi peak is at positive time, the hits were usually early, else hits were late

  • First reconstruction of events, find TChi peak times

  • Store fit peak times in text files

  • Reconstruct events again with adjusted hit time


Apply tped shifts to the crab

Apply TPed Shifts to the Crab

  • Reconstructed same period of Crab data as done before January 2005 collaboration meeting

    • September 2003 to October 2004 – 416 solar days

    • Unlike previous reconstruction, only AS and OR PMTs used in fits

    • TPed shifting was applied

  • Created skymaps

    • 2 hour maps summed up – total integration duration of 100 days


Previous crab results

Previous Crab Results

  • AS+MU+OR used in fit

  • 12 parameter MARS models used (see January 2005 collaboration meeting talk)


Tped shifted crab results

TPed Shifted Crab Results

  • AS+OR used in fit

  • See memo (to be posted) “Timing Pedestal Shifting and the Crab” for full table of the cuts examined (various nFit and x2 cuts)

  • Same MARS cuts give higher signal to background and significance

    • Q-factor increase of 1.3 just from new reconstruction


Finding the optimal binsize

Finding the Optimal Binsize

  • Looked for largest significance in hard cut events

    • nFit>150, x2>6, x2cx>6 (x2cx=nb2/cxPE)

    • marsOn>0, marsOff>0 was used by accident…

    • Made smoothed maps in square bins from 0.4° on a side to 1.3°

  • 0.6°x0.6° or 0.7°x0.7° square bin size seems optimal

    • Angular resolution is 0.25° for 0.7° square bin


Radial distribution

Radial Distribution

  • Plot radial excess distribution using unsmoothed maps from Crab coordinates

    • Normalized to ring area

  • Gaussian fit centered at the Crab gives angular resolution of 0.33±0.06°

  • Gaussian fit centered at the maximal significance (5.26σ) bin gives 0.32±0.06°


Summary

Summary

  • Removal of muon layer PMTs from fit and addition of TPed shifting appears to give better angular resolution for hard cut events

    • Scanning bin sizes gives 0.25° angular resolution which corresponds to a 0.7°x0.7° optimal square bin size (S/B = 39%)

    • Radial distribution fit at the Crab bin gives 0.33±0.06° angular resolution

    • Maximal S/B = 44% is seen for a 0.5°x0.5° square bin size

  • Currently reconstructing the same Crab data a third time with only AS+OR PMTs in the fit and no TPed shifting to see exactly what effect the shifts have – memo will be submitted after examining the no-TPed shift results and running on current reconstruction without MARS cuts

  • How do we put TPed shifting online?

    • Create TPed shift files once per run number

      • corresponds to basically once per day – this should be plenty because largest variations on timing come from seasonal temperature changes

    • Use TPed shift files when creating REC files

  • Will also create AS only reconstruction of the Crab data to see what effect the outriggers have (not for memo)


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