Difference: NSWPublicResults (16 vs. 17)

Revision 172015-05-22 - KonstantinosNtekas

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META TOPICPARENT name="AtlasResults"
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Fig. 2: Integrated charge for one APV channel for a single event
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Fig. 1: Integrated charge for one APV channel for a single event
 Typical integrated charge from one MicroMegas strip readout with the APV25 hybrid cards (through the Scalable Readout System) operated at 40 MHz with 27 samples. A fit with a Fermi-Dirac function with an additional baseline is performed to determine
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Fig. 2: Efficiency map
2D hit reconstruction in a Tmm chamber during a high statistics run. For this study the chamber was kept perpendicular to the beam axis. The hit position in both X and Y readouts is calculated using the centroid method and only events with a single cluster per readout (perpendicular tracks) are used. The inefficient spots appearing every 2.5 mm, corresponding to the pillar structure supporting the mesh of the chamber, are visible. Four different representations of the same plot are shown.
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Fig. 3: Efficiency map
2D hit reconstruction in a Tmm chamber during a high statistics run. For this study the chamber was kept perpendicular to the beam axis. The hit position in both X and Y readouts is calculated using the centroid method and only events with a single cluster per readout (perpendicular tracks) are used. The inefficient spots appearing every 2.5 mm, corresponding to the pillar structure supporting the mesh of the chamber, are visible. Four different representations of the same plot are shown.
 The measurements were performed with a Tmm type MM bulk resistive chamber operated with an amplification voltage of HVamp = 540 V. The data were acquired during PS/T9 with a 10 GeV/c π+/p beam.

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Fig. 2: Efficiency map
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Fig. 4: Efficiency map
 Hit reconstruction efficiency as a function of the extrapolated reference track hit position for a 2D readout chamber of Tmm type. The reference track is reconstructed from 3 Tmm chambers and is then extrapolated to the fourth Tmm under study. Left column corresponds to X and right column corresponds to Y.

The first row shows the efficiency for an irradiated area 20 mm wide. The efficiency dips 15% appearing every 2.5 mm correspond to the pillar structure supporting the mesh. The second row focuses only on selected areas on the Y readout of the chamber which are around the pillar region (bands 500μm). The effect of the pillars is more severe in these regions reaching local efficiency dips of the order of 40%. By scanning only the region in between the pillars the efficiency is uniform along the readout channels and a high efficiency is measured for both layers (above 98%). The Y readout shows higher efficiency owing to the fact that it is right below the resistive strips and thus it accumulates more charge than the X layer.

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Fig. 2: Efficiency map
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Fig. 5: Efficiency map
  Hit reconstruction efficiency as a function of the extrapolated reference track hit for 2 small T type bulk resistive MM chambers namely TQF, T2. The reference track is reconstructed from 4 Tmm chambers and is then extrapolated to the chamber under study. The two plots on the left correspond to data acquried with the chambers perpendicular to the beam axis while for the two right plots the chambers were inclined by 30 degrees. In both cases the centroid method is used for the reconstruction of the hits. The efficiency dips (5%) appearing every 5 and 2.5 mm respectively correspond to the pillar structure supporting the mesh. The pitch between the pillars and their size are different for the two chambers under study as it is evident from the plots. The TQF chamber has 500 μm wide pillars with a pitch of 5 mm while the T2 pillars are $300μm wide with a pitch of 2.5 mm. In the case of the inclined chambers the particles traverse the chambers under an angle inducing signal in larger number of strips compared to the 0 degrees case. In this case the efficiency is expected to be unaffected by the pillars as it is shown on the two plots corresponding to the 30 degrees case (above 99%).
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Fig. 7: Effect of the pillars on the hit reconstruction
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Fig. 6: Effect of the pillars on the hit reconstruction
 Apart from the efficiency the pillar structure affects also the hit reconstruction intriducing a bias in the hits reconstructed in their region. This effect (bias) is studied using a set of three Tmm chambers to reconstruct a reference track which is then extrapolated to a fourth Tmm chamber. Chambers are kept perpendicular to the beam and the hit in each chamber is reconstructed using the centroid method. In the top plot, the residuals between the hit reconstructed in the chamber under study and the reference tracks are plotted versus the reconstructed hit position. In the bottom plot the reconstructed 2-D hit position in the same chamber is plotted. The position of the pillars is clearly visible in the bottom plot and the observed bias in the reconstructed hit position can be associasated with the position of the pillars comapring the two plots. The bias is evident in each pillar region with a maximum value 150μm.

The measurements were performed with Tmm type MM bulk resistive chambers operated with an amplification voltage HVamp = 540 V. The data were acquired during PS/T9 with a 6 GeV/c π+/p$ beam.

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Fig. 4: Spatial resolution of precision coordinate of Tmm/Tmb chambers
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Fig. 7: Spatial resolution of precision coordinate of Tmm/Tmb chambers
  Residual distributions from the hit position difference between a Tmm and a Tmb chamber, divided by √2 (assuming similar resolution for both chambers sice the effect of the different pillar pattern is negligible), featuring a 2D readout. The left plot corresponds to the residuals of the X readouts while the right one shows the Y hit residuals. For this measurement the chambers were kept perpendicular to the beam and the hit reconstruction was done using the centroid method selecting single cluster events in both chambers. A similar performance, in terms of spatial resolution, for X and Y readouts is observed.
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Fig. 6: Spatial resolution of the T chambers
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Fig. 8: Spatial resolution of the T chambers
 Residual distributions from the hit position difference between two T type MM chambers (T2,T4) , divided by √2. For this measurement the chambers were kept perpendicular to the beam and the hit reconstruction was done using the centroid method selecting single cluster events in both chambers.

σcore corresponds to the width of the core gaussian while σweight is the weighted average of the two gaussians

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Fig. 4: Spatial resolution of precision coordinate of the MMSW
The MMSW is the Micromegas Quadruplet Prototype. Residuals between the first and the second layer of the MMSW, both with strips
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Fig. 9: Spatial resolution of precision coordinate of the MMSW
The MMSW is the Micromegas Quadruplet Prototype. Residuals between the first and the second layer of the MMSW, both with strips
 measuring the precision coordinate, divided by √2 (assuming similar resolution for both layers).

σcore corresponds to the width of the core gaussian while σweight is the weighted average of the two gaussians

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Fig. 4: Spatial resolution of precision coordinate of the MMSW
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Fig. 10: Spatial resolution of precision coordinate of the MMSW
 Left: Residuals between the second and the combination of the two stereo readout layers. Right: Residuals between the first and the combination of the two stereo readout layers. The residuals are divided by √1.5 (assuming similar resolution for all 3 layers) because the second hit is reconstructed by combining the two stereo layers (T.Alexopoulos et al., ATL-MUON-INT-2014-005}).\
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Fig. 5: Spatial resolution of second coordinate of the MMSW
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Fig. 11: Spatial resolution of second coordinate of the MMSW
 Left : Residual distributions from the hit position difference between the 2nd coordinate hit, reconstructed using the stereo readout 3 and 4 layers of MMSW, with a 2nd coordinate hit reconstructed in one reference chamber at a distance 20 cm from the first plane of the MMSW. Both chambers wee perpendicular to the beam axis and the hit per layer is reconstructed using the centroid method. Right : MC simulation of the ratio between the resolution of the 2nd hit reconstructed combining two stereo layers with the precision coordinate resolution of each stereo layer as a function of the stereo angle value (T.Alexopoulos et al., ATL-MUON-INT-2014-005). For a stereo angle of 1.5 degrees, as in the MMSW case, we expect this ratio to be 27 which is in good agreement with our measurement.
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Fig. 5: μTPC refinement - Angular Dsitributions
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Fig. 12: μTPC refinement - Angular Dsitributions
  Angular distributions reconstructed with a T type MM chamber with the μTPC method for four different chamber inclination angles with respect to the beam axis (10, 20, 30, 40 degrees). The long tails correspond to badly reconstructed tracks because of wrong timing determination or owing to clusters with small number of strips. The mean reconstructed angle is estimated by fitting a gaussian on the peak of the distribution. The angular resolution (width of the gaussian) improves with increasing the incidence angle of the track owing to the fact that there is a larger number of points (strips) to be used for the reconstruction of the track.
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Fig. 5: μTPC refinement - Angle Reconstruction and Spatial Resolution
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Fig. 13: μTPC refinement - Angle Reconstruction and Spatial Resolution
  Left: Comparison of the mean reconstructed angle for different chamber inclination angles with respect to the beam axis before (blue markers) and after (red markers) the refinement of the μTPC method. When the μTPC method is corrected for the effect of the capacitive coupling between neighboring strips and the charge position assignment in the edges of the cluster a significant reduction in the observed mean reconstructed angle bias is observed. The remaining bias is attributed to the remaining effect of the capacitive coupling between the middle strips of the cluster.
Right: Comparison of the spatial resolution measured for different chamber inclination angles with respect to the beam axis (blue markers) and after (red markers) the refinement of the μTPC method. The refinement of the μTPC method results in a siginficant improvement in the measured spatial resolution (especially for the 10, 20 degrees case). The residual distributions that are used for the extraction of the resolution are fitted with a double gaussian to take into account also the tails. For the resolution plot shown here the resolution is defined as the σ of the core gaussian.
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Fig. 10: Spatial resolution of a single Micromegas chamber vs incident angle
Spatial resolution using the charge centroid method (blue triangles), the μTPC method (full red circles) and the combination of the two (black open circles) as a function of the particle incident angle. The resolution is obtained from the residual distribution of the hit position difference between two Micromegas chambers separated by a small distance.
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Fig. 14: Spatial resolution of a single Micromegas chamber vs incident angle
Spatial resolution using the charge centroid method (blue triangles), the μTPC method (full red circles) and the combination of the two (black open circles) as a function of the particle incident angle. The resolution is obtained from the residual distribution of the hit position difference between two Micromegas chambers separated by a small distance.
 

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