Aras Papadelis. NIKHEF 1 Aras Papadelis B-physics meeting 15/ Results from the Nov2004 VELO test beam (and what followed…)

Aras Papadelis. NIKHEF 2 Outline ● VELO reminder ● Test beam of Nov 2004 ● Pulse shape and S/N measurements ● Cluster efficiency ● Charge sharing problems ● Resolution ● X-talk measurements with CERN data ● X-talk measurements at NIKHEF (last week+this week)

Aras Papadelis. NIKHEF 3 VELO- the LHCb Vertex Locator detector ● Silicon strip (n-on-n detector ● 2048 strips/sensor * 4 sensors/ station * 21 stations in detector Beetle chip Radiation hard, FE chip (developed at NIKHEF/Heidelberg) Analog readout at 40 MHz + digital part for pile up veto. 0.9  s readout time for L strips connected to each chip  16 chips per hybrid  1344 chips in VELO (64 in PU) ~8 cm

Aras Papadelis. NIKHEF 4 Test beam at CERN, November 2004 ● 3-15 Nov. 2004, X7 area ● 120 GeV pions ● Telescope of prototype VELO sensors (72° instead of 182°) ● Tested: – R and Phi detectors of thickness 200 and 300  m – 16-chip hybrids, mixtures of: B1.3, B1.4 and B1.5 – Full analogue chain ! (up to ADC input) – Test sensors perpendicular and at various angles – bias scans of Beetle chip and sensor.

Aras Papadelis. NIKHEF 5 Telescope and sensors in TB BEAM

Aras Papadelis. NIKHEF 6 “LHCb-like” read out chain Beetle  Hybrid  Kapton interconnects  repeater boards  60 m cabel  ADC  Storage on disk

Aras Papadelis. NIKHEF 7 “LHCb-like” read out chain Beetle  Hybrid  Kapton interconnects  repeater boards  60 m cabel  ADC  Storage on disk

Aras Papadelis. NIKHEF 8 ● Three different versions(flavours) of Beetle chips tested(1.3/1.4/1.5). Is the pulse shape and S/N sensitive to which chip is used? Pulse shape and Signal/Noise comparison Pulse shapes are similar for Beetle flavours, Beetle 1.5 has higher S/N without increasing the overspill (requirement < 30%). Good! B1.5 S/N between 16.3 – 17.1 for 300  m thick sensor, depending on sensor region. (Minimum requirement by trigger is 14)

Aras Papadelis. NIKHEF 9 Cluster efficiency (Doris Eckstein) ● Cluster efficiency = how often can a cluster be matched to a telescope track in the sensor (residual < 500  m). ● Depends on S/N threshold, if it’s too low we’ll see very high efficiency (but a lot of noise clusters are accepted) and if it’s too tight efficiency drops but less noise clusters are accepted. S/N Noise Signal > 99.5 %

Aras Papadelis. NIKHEF 10 Charge sharing issues To increase resolution in the detector, charge sharing between strips is used. – Telescope used to determine where tracks traverse sensor. – By comparing how much charge was collected in the strips left and right of the track, Q L and Q R, the determination of position of the cluster becomes more accurate. – Without charge sharing, the resolution becomes “digital”, i.e. accuracy limited by distance between strips (either the particle passed through the left or the right strip volume) QLQL QRQR Pitch  m

Aras Papadelis. NIKHEF 11 Problems with CS discovered! (Paula, Doris) Good charge sharing should look like this: But the problem is that it looks more like this: This will deteriorate the resolution. Telescope R300 detector   track pos

Aras Papadelis. NIKHEF 12 Resolution (Doris E, Paula C, Juan P, David P) ● The resolution is defined as width of distribution of residuals between cluster and associated track. ● Angled tracks (more realistic) have better resolution due to more charge sharing. ● R300: Resolution goes from 10  m(small radii) to 25  m (large radii) ● Phi300: ~ 15  m resolution Increasing radius  R300 – perp tracks Phi300

Aras Papadelis. NIKHEF 13 X-talk enters the stage ● Test beam analysis showed large xtalk effects in data. ● Xtalk deteriorates resolution of cluster. ● A digital filter (FIR) was implemented in software  Go out and measure xtalk! ● Test pulse data were taken with same analogue readout chain as test beam. Method: ● Two channels per Beetle port were pulsed. One even and one odd. ● Beetle port = Read out of the total 128 channels is divided into 4 ports with 32 channels on each port.  8 channels pulsed per chip. B1.3/B1.4/B1.5 chips included in analysis. Look at signal in adjacent channels.

Aras Papadelis. NIKHEF 14 Xtalk (Aras P, Jeremie B) RAW ADC/ CHANNEL To get xtalk, compare mean ADC value in pulsed channel with adjacent channels.

Aras Papadelis. NIKHEF 15 Considerably more xtalk in testbeam setup than expected from previous lab measurements in Heidelberg. Hard to see patterns in xtalk. Not only did it seem to depend on odd/even channel, but also on Beetle port (only for xtalk to previous channel, not to next ch) on which chip was read out. on which TDC cut was used. Different kinds of xtalk… (direct and differential) Xtalk issues

Aras Papadelis. NIKHEF 16 Considerably more xtalk in testbeam setup than expected from previous lab measurements. Hard to see patterns in xtalk. Not only did it seem to depend on odd/even channel, but also on which Beetle link was read out (only for xtalk to previous channel, not to next ch) on which chip was read out. on which TDC cut was used. Different kinds of xtalk… (direct and differential) Xtalk issues Signal in central ch (Signal in ch-1)*10

Aras Papadelis. NIKHEF 17 Considerably more xtalk in testbeam setup than expected from previous lab measurements. Hard to see patterns in xtalk. Not only did it seem to depend on odd/even channel, but also on which Beetle link was read out (only for xtalk to previous channel, not to next ch) on which chip was read out. on which TDC cut was used. Different kinds of xtalk. (direct and differential) Xtalk issues Signal in central ch (Signal in ch-1)*10

Aras Papadelis. NIKHEF 18 Something wrong with the B1.5? Heidelberg scope measurement: CERN data Big discrepancy with old measurements. Main conclusion: The analogue readout chain introduces a lot of xtalk! The difference between B1.4 and B1.5 became a worry!

Aras Papadelis. NIKHEF 19 Latest developments ● New scope measurements conducted last week at NIKHEF gave us some answers. CERN data NIKHEF Beetle analogue xtalk levels are ~2%. The “rest” can be attributed to the analogue link in the test beam setup. B1.5 does not xtalk more than B1.4. All tested chips give same values. Nice and consistent!

Aras Papadelis. NIKHEF 20 Summary ● The test beam in Nov2004 was a success from an “operational point of view”. ● Many interesting results came from it: – Less charge sharing in new PR04 sensors than expected – not completely understood. – Worse resolution than expected. Example: TDR: 3.6  m resolution for 100 mrad track at fine pitch Preliminary results presented at LHCb week indicate ~10  m. – “LHCb-like” analogue readout chain introduced lots of xtalk in the system. Subject to much study lately. – Excellent cluster finding efficiency! – The Beetle 1.5 is performing well! Gives high S/N. RnD phase is over, VELO is entering production phase…