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Particle incident angle study with Mimosa 17

Particle incident angle study with Mimosa 17. C.Dritsa, J.Baudot. Outline Motivation Digitiser Analysis Summary. 11 th CBM collaboration meeting GSI Darmstadt. Motivation. Open charm feasibility studies are of major importance for CBM

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Particle incident angle study with Mimosa 17

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  1. Particle incident angle study with Mimosa 17 C.Dritsa, J.Baudot • Outline • Motivation • Digitiser • Analysis • Summary 11th CBM collaboration meeting GSI Darmstadt

  2. Motivation Open charm feasibility studies are of major importance for CBM The MVD is the key detector for open charm measurements. Transport (GEANT) Background & Signal Generation Geometry (thickness, stations’ position) Simulate detector’s response For MVD: gaussian smearing The actual model using gaussian smearing is not adapted for studying event pile-up and delta electrons. Can this model be improved ? The implementation of a more realistic MAPS response ( digitisation model ) will allow us studying the impact of the above points especially on the open charm reconstruction. This work is under progress at IPHC, Strasbourg.

  3. Simplistic illustration of the digitisation model No Electric Field: θ Electrons are diffusing sensitive volume • Digitisation model for non depleted detector (MAPS detector): • Particle trajectory divided in segments inside the sensitive volume. • Energy deposited in each segment is translated into charge. • Charge spread in the sensitive volume within a definedcone. • Advantage of digitiser: possibility to study particles with inclined tracks. • Need to adapt the model’s parameters in order to reproduce experimental data.

  4. Beam Test MIMOSA 17 MAPS response to tracks with large incident angle was not studied in detail yet. • Beam test performed in November 2007 at CERN with a 120 GeV pion beam. • The chip under test was a MIMOSA 17 : • 30 μm pitch - 14μm epi

  5. Top view of the setup DUT θ: 080! Reference plane: MIMOSA 17 Reference plane: MIMOSA 17 Analysis steps • The two external planes (reference planes) are used for track reconstruction. • The middle plane is the Detector Under Test (DUT): the tracks extrapolated in the DUT are matched with the hit located closest to the reconstructed track position. • Measurements were taken for several angles: • θ: 0°, 15°, 30°, 45°, 60°, 75° and 80°

  6. How is the cluster shape affected when track is inclined ? t L Charge collected in each pixel L L: length of the particle trajectory in the epitaxial layer t: epitaxial layer thickness θ: angle of incidence with respect to the vertical  

  7. 0° 15° 30° 45° 60° 75° 80° Average Cluster Shape • 7x7 cluster • Each square represents one pixel • Color scale normalised Differences in the average cluster shape are obvious for large angles (>60o)

  8. 0° 15° 30° 45° 60° 80°

  9. Charge collected (electrons) Collected charge

  10. Signal to Noise Ratio on seed • For small angles (<30o) the SNR is almost constant • For bigger angles (>60o) the SNR varies significantly

  11. Residuals V σ of the distribution of track-hit distance. U

  12. V Can the inclination of the track be derived from cluster properties? Comparison of properties of average clusters for two angles: 0° 80° U • The number of significant pixels (above given threshold) is higher for 80° than for 0°. • The aspect ratio is different. Allow to identify and suppress hits from delta electrons?

  13. V cluster width Can the inclination of the track be derived from cluster properties? 80° v=u U cluster width • 0° • 80° V cluster width Width defined by :

  14. Summary and results Motivation Implement MAPS digitiser. Study MAPS response to inclined tracks. • Beam test (pions, 120GeV) on inclined tracks up to 80° was performed. • For small angles (<30o) the SNR of the seed, the charge of the seed and the charge of the full cluster are constant. • For large angles (>60o) the SNR of the seed , the charge of the seed and the charge of the full cluster increase significantly. • The residuals along the V direction (along the rotation axis) remain constant but the residuals along the U direction increase (up to 4 times for 80 degrees, but algorithm not optimised) • It seems possible to identify hits created from tracks with large incident angle. Investigate possible applications of this identification. • Next steps: • Implementation of the digitiser • Perform simulation study to evaluate the fraction of particles with large incident angle.

  15. Can the inclination of the track using information from the cluster be derived ?

  16. V U

  17. 80 degrees 0 degrees 1 Digital 3 CoG 3x3 5 CoG 5x5 7 Eta 4var 9 Eta 3x3 11 Eta 2x2 13 Eta 5x5 Residuals 7x7 cluster: Different methods Residuals (μm) The residuals obtained from eta 3x3 are the best even for 80 degrees rotation

  18. Charge on seed MIMOSA 17 ( 14microns epi )

  19. Charge 49 pixels MIMOSA 17 ( 14microns epi )

  20. Noise on seed MIMOSA 17 ( 14microns epi )

  21. What about charge collection efficiency at large angles? Charge on 49 pixels (Qtot) if CCE is const and clustering is correct: Error bars correspond to 1o error in defining the rotation angle ~10% With a 10% precision CCE can be approximated as constant wrt the particle incident angle

  22. Residuals 7x7 cluster 80 degrees 0 degrees μm μm

  23. 0 15 30 45 60 75 80

  24. Mean Cluster Form (3D) 0 15 30 • 7x7 cluster • Each square represents one pixel • Color scale normalised 45 60 75 80

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