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Breaking the 4 micron barrier

Breaking the 4 micron barrier. Can it be done? . Paula: Work contributed here from Alessandra, Justin, Marina, JC, Veerle , Jan, Richard, Xavi , Ryan ++…. What is the optimal Timepix resolution?. 21-04-2010 – we broke the 5 m m barrier Veerle achieved 4.6 m m resolution at the DUT

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Breaking the 4 micron barrier

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  1. Breaking the 4 micron barrier • Can it be done? Paula: Work contributed here from Alessandra, Justin, Marina, JC, Veerle, Jan, Richard, Xavi, Ryan ++…. LHCb Upgrade Meeting Paula Collins

  2. What is the optimal Timepix resolution? • 21-04-2010 – we broke the 5 mm barrier • Veerle achieved 4.6 mm resolution at the DUT • http://indico.cern.ch/getFile.py/access?contribID=1&resId=0&materialId=slides&confId=83480 • Since then we reduced this number to 4.2 mm • More hard work on the alignment • Cut on the telescope clusters • Maximum cut on ADC • Or, use Zhou cluster cleaning

  3. Last thing to try • Pixel calibration • Overall offset • Individual pixel calibrations LHCb Upgrade Meeting Paula Collins

  4. Calibration of DUT now nicely under control (see talk of Marina) Testpulse scan data show a perfect fit to the “surrogate function” (see http://aladdin.utef.cvut.cz/ofat/Methods/TimePixCalibration) These plots are for the DUT with threshold ~ 1500 e, ikrum 5 Typical fit values: a=0.207, b=31.04, c=133.9, d=30.1 The translation 46.8 electrons per mV applies The testpulse offset is ~ 35 mV (has already been taken into account in these plots) JC has provided detailed fits to all the data and to all 65000 pixels Many thanks to XaviLlopart for acquiring the data for us LHCb Upgrade Meeting Paula Collins

  5. To first order the TOT response introduces an offset in the data and skews the eta distribution • Starting from a perfect detector, with perfect charge sharing and a threshold of 1500, no noise, no landau fluctuations, no reality… • The black curve shows what would be expected for perfect reconstruction • The red curve shows the effect of the imperfect TOT response • To a first order estimate the TOT response will add ~4 micron in quadrature to the resolution Track impact point Cluster reconstructed position LHCb Upgrade Meeting Paula Collins

  6. Try applying calibration to data to see what happens to the resolution Choose run 512 (the optimum angle so far) Landaus after Landaus before The correction seems to be doing the right thing! (This study is being done in detail by Syracuse) BUT – the residuals in the DUT degrade from 4.8 to 6.1 micron!!! LHCb Upgrade Meeting Paula Collins

  7. Looking in detail at the eta distributions Before TOT calibration After TOT calibration It can be seen that the issue is that before correction the effects of the eta distribution and the TOT offset have combined to produce a curve that is already “quite good”. Simply applying the TOT calibration is not enough – the eta distribution has to be redone aswell. (Many thanks to Jan, JC, and Marina for invaluable insights.) LHCb Upgrade Meeting Paula Collins

  8. Final results LHCb Upgrade Meeting Paula Collins

  9. Conclusions (Preliminary) • This is still all very fresh! These results could still be wrong… • It seems that at the optimal angle including all known effects brings us an extra 0.1 mm in precision • At perpendicular angle the same exercise does not bring an improvement. • Applying an individual calibration to all 65536 pixels does not seem to help (but may remove a few outliers) • So… did we break the 4 mm barrier? No.. We are at 4.1 mm! But we can still cheat…. LHCb Upgrade Meeting Paula Collins

  10. Just for fun…. • Cut on the ADC in the DUT itself (= remove delta rays) Residual of 4.4 mm Subtracting track contribution gives a DUT resolution of 3.8 mm (for a 40% efficiency) Not a serious measurement, but it shows that our telescope is still discriminating at this level LHCb Upgrade Meeting Paula Collins

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