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New Measurements of Lorentz Angle in Silicon Strip Detectors

This study presents new measurements of the Lorentz angle in irradiated silicon strip detectors. The researchers used CMS sensors to measure at higher bias voltages and achieved better sensitivity. They also measured the Lorentz angle in highly irradiated sensors and compared the results with CMS data. The study proposes a new parametrization of the Lorentz angle model.

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New Measurements of Lorentz Angle in Silicon Strip Detectors

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  1. New Measurements of Lorentz angle in (irradiated) silicon-strip-detectors Wim de Boer, Alexander Dierlamm, Andreas Sabellek, Mike Schmanau, Michael Schneider RD09 conference Florence, 2009

  2. What is new? • Measured real CMS ministrip sensors (instead of ministrips from HERA-B, which had smaller pitch) CMS sensors allowed to measure to much higher bias voltages, use 500 um for better sensitivity • Measured RD50 n-in-p sensors to get much better Lorentz angle measurements for electrons • Measure Lorentz angle in highly irradiation sensors

  3. Outline • Experimental Setup • Sensors • New parametrization of Lorentz angle model • Results • Comparison with CMS data • Lorentz angle over fluence • Summary

  4. Experimental Setup (1)

  5. Experimental Setup (2) • Sensor with readout-chip PreMux (=APV w.o. Pipeline) on hybrid • Hybrid mounted on structure for magnet • Optical fibers for laser • red laser for best signal • infrared laser for MIP-like signal

  6. Experimental Setup (3)

  7. Experimental Setup - Magnet • Magnet lab of ITP at Forschungszentrum Karlsruhe • Measurements of lorentz shift up to 8T

  8. Sensors • Measurement of depletion voltage by finding the knee in the 1/C2 over U plot • Irradiated at Karlsruhe Kompaktzyklotron with 25 MeV protons • Hardnessfactor 1.85

  9. Signals of unirradiated sensors Electrons with F=0 n/cm2 at 127K and Ubias=40 V Signal in mV Strip number

  10. Lorentz-shift of unirradiated sensors

  11. Parametrization of Lorentz angle model An Algorithm for calculating the Lorentz angle in silicon detectors.V. Bartsch, W. de Boer, J. Bol, A. Dierlamm, E. Grigoriev, F. Hauler , S. Heising, L. Jungermann. Nucl.Instrum.Meth.A497:389-396,2003. e-Print: physics/0204078 tanL=evB/eE=v/E B=rHµB evxB eE rH=Hall factor, depends on scattering mechanism mobility New fit of the 4 parameters: • shaping exponent b • temperature exponents electrons holes

  12. New: Parametrization of hall scattering factor standard value valid for small B fields • Parabolic dependence of hall scattering factor on electric field • Good description of data • A constant rH seems not appropriate (1.1 expected for small fields (i.e. small Lorentz angles, implying little curvature between scatterings)

  13. Results (1) holes CMS sensor (p-in-n) NEW OLD Fit deviations at high E-fields holes Fit

  14. Results (2) electrons n-in-p (float zone) deviations at low temp. Fit electrons Fit NEW OLD deviations at low temp.

  15. Lorentz angle from cluster width in CMS

  16. Comparison with previous results

  17. Lorentz angle versus fluence 40 V electrons 300 V 500 V holes 1000 V 1000V 1000V • Strong dependence of Lorentz angle on fluence? • Change of sign at high fluences for electrons?? Non uniform E inside thin depletion zone?

  18. Summary • New Lorentz measurements for holes with real mini-CMS sensors (100 orientation, previous partially 111) • Slight changes, but still incompatible with CMS • minimal cluster width method • Since Lorentz angle varies with fluence, in situ measure- ment by analog read out is needed for SLHC. • Completely new parametrization for detectors with • electron drift • Strange change in sign of Lorentz shift of electrons at high fluences??

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