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TPed Shifting and the Crab

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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  1. TPed Shifting and the Crab Curtis Lansdell University of Maryland Milagro Collaboration Meeting

  2. 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

  3. 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

  4. 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)

  5. 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

  6. 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

  7. 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

  8. Previous Crab Results • AS+MU+OR used in fit • 12 parameter MARS models used (see January 2005 collaboration meeting talk)

  9. 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

  10. 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

  11. 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°

  12. 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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