Risultati preliminari
del test beam
21/6/2002
Tommaso Boccali
1
Outline
•I risultati sono quelli presentati la settimana scorsa nella CMS
Week, non ho nessun update da allora
•Le due analisi sono state realizzate dai due gruppi
•TT6: italiani Bari-Firenze-Perugia-Pisa
•Rob: R.Bainbridge e R.Chierici
•Tutte le trasparenze sono rubate da quei talk...
S. My, D. Giordano (INFN Bari), V. Ciulli, S. Paoletti (INFN Firenze),
L. Servoli, C. Zucchetti (INFN Perugia), G. Bagliesi, T. Boccali J. Bernardini,
M. D'Alfonso, R. Dell'Orso, S. Dutta, S. Gennai, A. Giassi, F. Palla, F. Rinaldi,
A. Rizzi, P.G.Verdini (INFN Pisa)
Rob Bainbridge
Roberto Chierici
Imperial College
21/6/2002
Tommaso Boccali
CERN
2
Aims of PSI beam test

Measurement of HIP rate




Direct measurement of induced deadtime


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Simulation (Mika) predicts comparable rates at PSI and X5
X5 rate: ~4  10-4 per plane per pion
Verify the rates in an environment more CMS-like
Trigger trains and APV25 multi-mode operation allow full recovery to be
observed. Detailed picture of the APV recovery.
(C.f. X5, when only “average” deadtime measurement possible - 300 ns)
HIP rate / deadtime measurements with reduced RINV


Laboratory measurements showed reduction in HIP rate and deadtime for
reduced RINV (100   50 )
Verify this by equipping different APVs with different resistors
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Experimental set-up

2 boxes containing 3 TIB, 3 TEC and 6 TOB (nonirradiated) modules



Beam:
APV25 was operated in peak mode throughout beam test
A range of RINV were used (50, 75, 100 )

300 MeV pions (+/-)
72 MeV protons
20 ns bunch structure
Detectors:
TIB: pitch~120 m, thickness~300 m
TEC: pitch~200 m (variable), thickness~500 m
TOB: pitch~180 m, thickness~500 m
PM3
PM1
PM2
TIB1, TIB2, TIB3, TEC1, TEC2, TEC3, TOB1, TOB2, TOB3, TOB4, TOB5, TOB6
100,
50,
100, 100, 100, 100,
50,
50,
75,
100,
50,
100
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Operating modes

Normal trigger mode (for HIP rate measurement)
 1 frame per trigger per APV
 identify HIP events through characteristic APV
behaviour (saturated baseline, large signals)
 calculate the probability of a HIP event per trigger per plane per incident 

Multi trigger mode (for deadtime measurement)
 3 frames per trigger per APV (triggers are spaced by 75 ns)
the first trigger is followed by 9 forced trigger
X 10
 identify HIP events in the frame train
 follow the APV behaviour in time (10x3x25ns=750ns)
 Full picture of APV recovery
 Direct deadtime measurement on an event-by-event basis possible
APV25 always operated in peak mode
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Physics program
300 MeV - beam
I~15 kHz, with pre-filter
I~300 kHz, with and without pre-filter
I~1.2 MHz, with pre-filter
300 MeV + beam
I~25 kHz, with pre-filter, with and without APV25
operated in inverting mode
72 MeV p beam
Deadtime measurement: multi-trigger mode
300 MeV - beam
pre-filter and backward veto
300 MeV + beam
pre-filter and backward veto
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Beam profile
Problems in the first TIB module
Different pitches and geometric
characteristics!
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Some examples
of HIP events…
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Identifying HIP events

CM sensitive to hardware settings
Positions of baseline and FED dynamic
range define maximum CM shift
CMMAX = peds – d0

CMMAX



Define CMRATIO = CMABS / CMMAX
 allows comparison between APVs
Distributions grouped according to
detector and resistor type
CM peak due to HIP events only



Pre-filter used before all triggers
 do not observe dead APV25s
c.f. X5: more pronounced peak, due
to HIP events and dead APV25s
Select HIP events with
CMRATIO  -0.8 -and S>200 counts21/6/2002
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HIP rate measurement
Integral distribution of CM, normalised to
number of good triggers, planes and incident
pions (at 90 degrees !)
Preliminary HIP rates:
TIB 50 
(2.3±0.1)
TIB 100
(3.7±0.1)
TEC (100)
(6.2±0.1)
TOB ~50
(5.5±0.1)
TOB 75
(5.8±0.2)
TOB 100
(6.2±0.1)
10-4
10-4
10-4
10-4
10-4
10-4
 clear factor between 300 m and 500 m
 confirmation of the reduction of HIP rate
with smaller Rinv
HIP cut
Linear behaviour with
thickness
- runs - 1/2 stat. -
Runs with + give similar results
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Deadtime measurement
Profile histos of the average CM vs
time grouped according to modules
and resistors
 X5 (+lab) results confirmed with
much higher accuracy
 chips with lower resistors recover
first
 “reasonable” CM value restored
after ~300 ns
Work to do in order to find the
“true” dead-time value
21/6/2002
overshoot (>400 ns)
recovery time (~250 ns)
dead-time (<~100 ns)
Tommaso Boccali
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Example of APV25 recovery
HIP happens ! (t=0 s)
400 ADC counts
The chip is dead
Recovery starts (t~100 ns)
is the chip really alive again?
The typical CM slope when recovering
is clearly visible
375
325
575
ns
175
125
25
150
100
625
300
475
350
550
200
600
500
750 ns
400
450
425
50
275
525
ns
225
250
ns
Nominal baseline
Overshooting now (t~400 ns)
Hit strips sort of “frozen” to original
ADC values (peak mode!)
microseconds to perfect recovery?
Digital zero
100 ADC counts
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Interpretation
The induced cluster reconstruction inefficiency induced by dead-time is, per unit
traversed length (300 MeV ):
p ( E  E0 )TOB  x  deadtim e
hit
 128  occ. 


x
x
500m
25ns
~4
~5x10-4/500 m
weighted local occupancy
pessimistic estimates for low luminosity:
TIB, TOB ~1 (Tommaso)
 Inefficiency induced at low luminosity (worst case, assuming dead-time=4 BX)
TIB ~ 1x10-3, TOB ~ 2x10-3 (factor 3/5)
another factor 5 to be assumed for high luminosity  0.5-1% inefficiency regime
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DAQ problems: scan of some bad event ...
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CM distributions after event filtering TOB:
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How do we define the hip rate ?
Depending on apv settings, common
mode saturates at different values
ped-d0 = 116
TOB1
ped-d0 = 58
Two (?) effects:
TOB
"saturation due to finite dynamic range
"saturation of apv pre-ampl or apv
ped-d0 = 122
inverter
TOB
ped-d0 = 100
TOB
vpsp pedestal
negative dynamic-range
ped-d0 = 121
TOB
ped-d0 = 107
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TOB
First test: select events with low rms
Use the rms of truncated raw signal distribution: when the apv is
saturated, the raw signal is forced to the digital 0 value, giving
very low rms values.
CM < -80.
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Alternative approach: relate the HIP rate to a physical
cross section

ds
dE
P(E>Ecut) = P(CM<CMcut)
p

Assumption: for the same E all the CM baselines go down by the same
amount. Then:
=P(CM < CMcut) ~ P(E>Ecut)
=all modules with the same thickness have the same rate
This assumption may be broken if:
=different Rinv imply different CM shifts for same E
=apv pre-ampls are not the same and saturate at different values
=? ....
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Rates as function of CM cuts
Hip rates assuming one track per event
(could scale up by 20-30% because of bad DAQ events)
warning: hip events involving more than one module are multi-counted !
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Preliminary results on dead/recovery
time
RUNS analysed:
0040290-0040295
HIP selected by
RMS<1
Time
50 Ohm
100
Ohm
Dead
~ 50 ns
~ 100
ns
Recovery ~ 300 ns ~ 400
ns
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Cluster width
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Conclusioni?
Nessuna in realta’, I numeri definitivi saranno dati alla tracker week
Comunque:
•Hip rate dell’ ordine di 2-6 x 10-4 e scalano come atteso fra 300
um e 500 um.
•Non e’ chiarissimo quanto I 50 Ohm su Rinv migliori le cose. In
laboratorio il miglioramento era piu’ forte
•Abbiamo anche dei dati non analizzati senza inverter. L’Hip rate
dovrebbe essere esattamente zero; da studiare quanto sia
fattibile…
•Recovery time: ancora problemi di definizione, dovendo dare un
numero direi 4-10 bunch crossings
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Conclusioni?
•Impatto dei protoni, l’HIP rate dovuto a ionizzazione da parte
di protoni da < 100 MeV dovrebbe essere alto (per fortuna
abbiamo il campo magnetico!)
•Recovery time: cosa possiamo fare nel recovery time, quando
la baseline e’ storta? E’ possibile pensare/implementare nel FED
qualcosa di piu’ furbo dell’ attuale. Calcolare il common mode
su 32 invece che su 128 strip per esempio potrebbe gia’ aiutare
parecchio….
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Conclusioni?
Dead time: Roberto da’
2 x 10-3 con soli 4 bunch crossings per il recovery a bassa
luminosita’
… non voglio commentare questo numero, vorrei solo dire che un
fattore 5 di incertezza per vari motivi non puo’ essere escluso!
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Tommaso Boccali
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