Occupancies at High
Luminosity
M. Needham
CERN
Outline
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Introduction
T and TT occupancies @ 2 * 1032
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signal B
Numbers @ 2 * 1033
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Further studies:
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Reduced readout gate
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Increased IT size
Velo
Talk is about occupancies --> equally important is momentum resolution
Amount of material in detector should not increase significantly
Introduction
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Why do occupancies matter ?
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Combinatorics in pattern recognition
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Stereo wires overlap 0.1 * wirelength/pitch
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In 2012 computing power will be infinite --> less problem than now
'Pile-up' effects in Silicon
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High occupancies complicate common mode correction
Merged clusters from adjacent tracks
'Pile-up' effects in OT
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25 ns analogue deadtime + 75 ns digital deadtime (single hit mode)
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Deadtime ---> inefficiency
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Correct straw hit, wrong time --> spoil resolution
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Long straws: 2.4 m in length
Introduction
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Note long track ghost rates dominated by wrong combinations of good T and Velo segments
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Reducing OT occupancies will not help so much..
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To gain need to add more information to the track
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More field in Velo and TT region
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More planes in TT (good for Ks finding as well)
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Extra station in T region just after magnet
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Be cleverer
OT Times
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3213 times per event (6 % avg occ)
Event Spill 68.7 %
|---> Primary 43.4 %
|---> Secondary 25.1 %
|---> Unknown 0.2 %
Noise 1.4 % (as expected)
Crosstalk 5 % (input)
Spillover 24.9 %
/Prev/ 10.4 %
/PrevPrev/ + /NextNext 5.8 %
/Next 8.7 %
20 % occ
OT Occupancy
Avg occ: 6 %:
● cf DC'04 4.3 %
● 2005-092 5.1 % (75 ns/after pulses)
● 15 % increase since then (beam-pipe supports)
● Max occ
● Top 9.5 %
● Corner 10.6 %
● Side 9.7 %
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10 -20 % due to steep 100 MeV secondaries and curling tracks
IT
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418 clusters per event
Event Spill 92.6 %
|---> Primary 55.5 %
|---> Secondary 36.9 %
|---> Unknown 0.2
Noise 1.2 %
Spillover 6.2 %
# Clusters/event
/Prev/ 6.1 %
/PrevPrev/ 0.1 %
Beampipe supports
Station
T/B
max
avg
1
0.7
0.57
2
0.6
0.52
3
0.55
0.46
L/R
max
3.3
2.5
1.9
avg
1.4
1.1
0.9
TT Strip Occupancies
TT Clusters
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460 clusters per event:
Event Spill 87 %
|---> Primary 60 %
|---> Secondary 21.8 %
|---> Unknown 0.2
Noise 1 %
Spillover 12 %
/Prev/ 11.2 %
/PrevPrev/ 0.8 %
# Clusters/event
Lessons
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Secondaries from dead material contribute significantly
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Important to minimize material --- especially in beam-pipe and supports
Detector thickness important
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Steep secondaries, curling tracks in OT give hotspots
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Above 400 mrad track hits more than one straw in a layer
Occupancy falls off quite slowly as a function of x
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Hotspots with occupancy of 50 % or more
Cross shape covers most important area for least cost
In the OT we have a 75 ns readout gate
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With good t0 calibration only 60 ns is needed --> reduce occupancy
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If you know y can reduce gate + occupancy
High Lumi
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2 Files of 500 minimum bias events
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At 2 * 1032 occupancy in min bias ~ factor 2 less than B events
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Difference should be less at higher lumi
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Luminosity of 2 * 1033
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Digitize with Boole v12r10
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Re-use each event at least twice for spillover
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End up with 500 digitized events
@ 2x1033 cm-2 s-1
91 particles in acceptance
6.8 collisions/crossing
@ 2x1032 cm-2 s-1
18 particles in acceptance
1.4 collisions/crossing
CPU Time (sec @ 2.8 GHz)
228
CPU Time (sec @ 2.8 GHz)
Size (MB/event)
1.6
Size (MB/event)
35
0.33
OT @ High Lumi
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12730 times per event = 25 % average occupancy
T1
T2
T3
Top
32
33.
35
Corner
36.6
37.1
38
occ T1 versus x
Side
36.1
34.8
34.8
# times/event
Event Spill 0.314328
|---> Primary 0.197037
|---> Secondary 0.116134
|---> Unknown 0.00115752
Noise 0.0606978
Spillover 0.624974
/Next/ 0.259446
/Prev/ 0.229452
/PrevPrev/ + NextNext 0.136076
IT @ High Lumi
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1077 clusters per event
Av
1.4
1.2
1.1
T1
T2
T3
T/B
Max
1.8
1.6
1.1
occ versus channel
L/R
Av Max
3.2 8.4
2.7 6.2
2.2 5.1
Event Spill 0.741616
|---> Primary 0.452786
|---> Secondary 0.287733
|---> Unknown 0.00109718
Noise 0.00456532
Spillover 0.253819
/Prev/ 0.249618
/PrevPrev/ 0.00420084
0.16 hits /mm/crossing 0 < y < 11 cm
Side
T/B
TT @ High Lumi
TT @ High Lumi
Cluster Classification:
Event Spill 0.553049
|---> Primary 0.408668
|---> Secondary 0.143206
|---> Unknown 0.00117613
Noise 0.00287896
Spillover 0.444072
/Prev/ 0.415119
/PrevPrev/ 0.0289523
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1400 clusters per event
# clusters per event
50 ns Gate in OT
Reducing OT readout gate to 50 ns , reduce occupancy by factor 0.7
● 17 % average occupancy
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T1
T2
T3
Top
23
33.5
35
Corner
26
26
27
Side
26
25
25
Increased IT size
Work with the MC we have
● Put hack in the OT digitization to kill last xxx cm of the wire
● Look at values of 5, 10, 15, 20 cm
● Assume Silicon wafer ~ 10 cm high
● From plot below you can generate occupancies in any OT geometry you like
● With a little thought
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Some example layouts on next pages
Increased IT size
2 sensor ladders everywhere
OT acceptance
3 sensor ladders everywhere
Higher occupancy in 'IT side'
● Increased height
● More spillover
● Rough estimate:
● 10 % occupancy nearest beampipe
● (8.4 % with 2 sensor ladders)
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Increased IT size
2 - 3 – 2 layout
OT acceptance
3 - 4 – 3 layout
4 sensor ladders not ideal
● Need 500 micron thickness
● TT like spillover
● Occupancy 11.5 % nearest beampipe
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Increased IT size
2-3 -2 out to 150 cm
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Minimize Silicon coverage to where needed
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13 m2 of Silicon
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248 k channels with 200 micron pitch
2 (centre)– 2/2(side)
IT 4 sensor ladders readout from two sides
● More material
● But can use 410 micron thick ladders
● IT occupancy up to 5.2 %
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Increased IT size
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Clear advantage of 50 ns readout gate
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What to do in side sectors not so clear..
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3 sensor ladders with 100 micron pitch nearest beampipe ?
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Faster front-end ?
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4 sensor readout from two sides ?
In OT 'at best' can expect occupancies of 18 – 22 % in hottest areas
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Assuming 50 ns readout window
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Exact value depends on the layout
Note:
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Estimates a little rough in places
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Still can gain by reducing dead material in the detector
Velo
@ 2 * 10 32
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1160 clusters per event
● 6.4 % spillover
@ 2 * 10 33
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3106 clusters per event
● 26.6 % spillover
1.8 % average cluster occupancy
2.8 % average strip occupancy
Flux: hits/cm2/crossing
(ie without spillover)
up to 9/cm2
# clusters/event
Summary
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First studies of occupancies @ 2 * 10 33 made
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In IT/TT occupancies up to 10 %
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Velo average strip occupancies of 3 %
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Fraction of spillover clusters is sizeable
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All Silicon detectors gain if spillover can be reduced
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'Faster' front-end ?
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OT with current layout have occupancies up to 20 %
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Win by:
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Reducing the readout gate (factor 0.7)
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Increasing the IT size
For reasonable IT layouts can get occupancy of 18 – 22 % in hottest OT area