ALFA OVERLAP DETECTOR STUDY (NOT UP TO DATE)

The Prototype Overlap Detector (OD) built for the test beam consists of 2 sets of 2 planes each composed of 30 fibres on the left side and 30 fibres on the right side. The upstream planes are referred as OD2 and the downstream planes as OD1.

RECONSTRUCTION OF THE DISTANCE BETWEEN OD2 & OD1

Reconstruction with 2 planes per OD

• Runs used: 10394 - 10408
• HV = 950V, DAC = 70V
• Total number of events per run: 50k or 100k
• Selected events must have one and only one hit in each of the 4 layers.
  

Reconstruction with 1 plane per OD

• Runs used: 10394 - 10408
• HV = 950V, DAC = 70V
• Total number of events per run: 50k or 100k
• Selected events must have one and only one hit in each of the 2 layers.
• The reconstruction with 1 layer / OD should give the same result as with 2 layers / OD. However we find different results. We think it comes from the high number of channels fired for a single event, it can reach as many as 60 channels (all the active channels) and it is greater than 10 channels for many events. The selection of tracks with 1 layer instead of 2 layers is therefore worsened by the fact that we have a higher probabitlity to randomly select unexisting tracks for a given event.
  

HIT MULTIPLICITY & SELECTION EFFICIENCY

Position scan at 950V

• Runs used: 10394 - 10408
• HV = 950V, DAC = 70V
• Total number of events per run: 50k or 100k
• Position scan between the runs
• From run #10401, the number of hits in OD1 increases. It might be due to collective effects.
  

Typical distributions of hits before (left) and after (right) this increase are shown at the bottom.

Threshold scan at 950V

• Runs used: 10357 - 10368
• HV = 950V, DAC = 40V to 70V
• Total number of events per run: 50k
• Relative position of 1 set of plane and the other is constant
• multiplicity_950V_DAC_scan.jpg:
  

Threshold scan at 1000V

• Runs used: 10379 - 10384
• HV = 950V, DAC = 20V to 30V
• Total number of events per run: 50k
• Relative position of 1 set of plane and the other differs by 1.6mm for the same DAC values
• multiplicity_1000V.jpg:
  

HV scan at DAC = 70V

• Runs used: 10379 - 10384
• HV = 850 - 950V, DAC = 70V
• Total number of events per run: 50k

Multiplicity in every layer & selection efficiency for each OD

Multiplicity in both ODs & selection efficiency in the full detector (4 hits, single hit per layer)

Probability of hitting an expected fibre in the next layer

CROSS TALK

Cross talk at level of the fibres...

Cross talk at level of the MAPMT...

*Position scan:

*HV scan:

NOISE

A look at the unconnected channels

• Runs used: 10367 - 10358
• HV = 950V, DAC = 40 - 70V
• Number of events: 50k

Number of hits per channel for layers 15 (in the beam) and layer 16 (out of the beam)

• A. # of hits on fibres in the beam ~1800 3.6 %
• B. # of hits on channels unconnected in the beam ~200 0.4 %
• C. # of hits on fibres out of the beam ~200 0.4 %
• D. # of hits on channels unconnected out of the beam ~20 0.04 %

Number of hits per channel for the 4 complete PMTs

Ratio of hits from channels not connected to fibres and channels connected to fibres

• Runs used: 10357 - 10368
• HV = 950V, DAC =40 - 70V
• Number of events per run: 50k
  

Ratio of hits from channels connected to fibres and hits on the trigger

• Runs used: 10357 - 10368
• HV = 950V, DAC =40 - 70V
• Number of events per run: 50k
  

Ratio of hits from channels not connected to fibres and hits on the trigger

• Runs used: 10357 - 10368
• HV = 950V, DAC =40 - 70V
• Number of events per run: 50k
  

-- AlessandroMapelli - 28 Feb 2007