Preliminary results from
test beam data
Roberto Chierici
- CERN
On behalf of the CMS tracker collaboration
Aim and experimental setup
 Event reconstruction
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Module performance
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S/N, stability, cluster characteristics
Latency scans
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Pedestal, common mode and noise evaluation
Cluster finding
Peak and deconvolution modes: features and observations
Efficiencies and delay curves
Conclusions (still preliminary)
Experimental setup
25-Oct-2001/3-Nov-2001
25 ns bunch spacing
120 GeV , 
Pitch=183 m
w/p~0.25
Sensor width=500 m
V=300 V
100 mrad
Non irradiated TOB modules
Almost final DAQ setup
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Event Reconstruction
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Rough pedestal ped0 (n0 events)
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Refined pedestals and first common mode noise (n1 events)
 <ADCi>, ADC in time removing strips with pol×(ADCi-ped0)>threshold
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CMN=<ADCi-pedi> over strips; pedi= <ADCi-CMN> in time
ni2= <ADCi-pedi-CMN>2 in time
Loop over events
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CMN0=<ADCi-pedi> over strips
Noise determination and better pedestals/CMN (n2 events)
 Exclude those strips for which pol×(ADCi-pedi)>KADC
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<ADCi> in time
Remove bad events, determine noisy/dead strips
Recalculate CMN; update pedestals and noise after n0+n1+n2 events
Cluster finding
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si=ADCi-pedi-CMNi consider only those for which si/ni>2
Good clusters if nstrip>0, Scl1/Ncl1>5
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Pedestals
Module 1
Module 2
Module 4
Module 5
 deconvolution
Module 3
Module 6
Module 2
APV 1
APV 2
APV 3
APV 4
Plots from G. Pásztor
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Noise
Noise < 3 ADC counts
Very stable in
space and time
Module #2: noise for two
different updating windows
N depends upon
the updating
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Corrected data
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si=ADCi-pedi-CMNi (CMN~0.3noise)
pedestal runs tell us we correctly estimate our noise
 deviation of a factor 2 only outside 4 region
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Pedestal run
=1.04
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Cluster characteristics
Module #2
S/Ncluster~20
APV 1
APV 2
APV 3
APV 4
Unexpectedly large number of strips per cluster !
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Confirmed by different analyses (Pisa)
Effect not present in July 2000 beam test
(but very different settings)
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From Pisa group
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Latency scans
Runs in deconvolution mode
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Detectors 1-2-5-6 kept at optimal latency value
Latency scans for detectors 3-4
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Preliminary 1D tracking
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Excellent way for studying delay curves and efficiency
Use 15k muons for alignment of modules (fits to residuals)
Modules 3-5 (4-6) aligned with respect to 1 (2)
Look for coincident clusters in modules 1-5 (2-6) and build a “track” :)
Look what happens around the intercept (10 strips) in modules 3 and 4
Averaging over events
Runs in peak mode
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Scans of all APVs.
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Alignment procedure as above
Tracking gives worse performance: use the highest strip in module
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Delay curves
q in  10 strips from the
intercepts in modules 3,4
 no cluster finding
dependence
deconvolution
Non-ideal APV parameters
(VFS=70, Isha=90)
 asymmetry
 too efficient 25 ns off peak
 undershoots
undershoot...
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Amplitudes in time
Deconvolution
Peak
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Strips in cluster
Peak
Mode
Symmetric charge sharing (Y)
CAC
Cb
Cint
Cb
Cint
q
L
Q
C
q
R
preampl.
Cb
shaper
Asymmetric diffusion (X)
q1
q2
latency
Diffusive component ~ 20% of the total
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Delay curves per strip (peak)
|L-R|/(L+R+T)<0.2
Test beam data
 ‘faster’ curve for adjacent strips
 signal propagating on 2 closest strips
X-checked by lab calibration
 very similar peak ratios
(L. Mirabito)
Cal. channel
1
2
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Delay curve per strip (deco)
Reasonable shape of the hit strip
 deconvolution nicely tuned
|L-R|/(L+R+T)<0.2
Different output for the neighboring:
 result of the different pulse shape
(input to the deco not anymore a CRRC 50 ns)
 deconvolution enhances q1/q0
Possible explanation given by the
behaviour of the amplifier as R at
high frequency:
 +Cint=h.p. filter to adjacent strips
=delay curve
 The shape is expected to be APV
parameter dependent !
Consequences for the tracker:
 position resolution
 cluster reconstruction
 two track separation
 data volume
 studies going on...
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Delay (ns)
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Cluster finding efficiency
~99.5%
Still too efficient at 25 ns
 better tuning of APV parameters
Excellent efficiency at 75 ns (mod. 3)
 not too sensitive to the position of the maximum
 cluster finding much more efficient than charge
integral
Cluster finding cuts to be optimized…
 efficiency curve can be adjusted
 the efficiency ‘plateau’ can be considerably
smaller
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Response function
Charge sharing
Diffusive regions
The response function can be determined
by assuming a uniform beam intensity
over the strip:
 diffusion region
 position resolution
(work is going on…)
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Conclusions
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The 25 Oct - 3 Nov test beam on 25 ns beam was a success
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Several configurations tried
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latency scans in peak and deconvolution
latency scans with different APV parameters
special triggers
Preliminary results very interesting
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6 TOB modules tested on a 25 ns beam with the next-to-final DAQ setup
excellent quality of the collected data
S/N of clusters ~ 20 (deco, non irradiated detectors), noise as expected
work going on for optimizing delay curves. Excellent track efficiency
CintAPV at high frequency may cause undesired features (not dramatic)
A lot of things to do...
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Huge amount of data (340 GB on castor) to analyze
optimize/distribute common tools for data analysis
further investigations + lab tests to be continued
 Everyone very welcome to join !
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Further info
Module #2
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Two events
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Zero suppressed info
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Module tilting visible
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Deconvolution...
RC(2)
CR-RC(1)
deconvolution
2=100 ns
2=50 ns
2=25 ns
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DAQ setup
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Shape vs amplitude
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Pulse height ratios are stable for different input amplitudes.
Amplitude
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Diffusion and sharing
Deconvolution
Peak
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Some (nice) picture...
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Charge asymmetry in time
Deconvolution
Peak
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Charge sharing in time
Deconvolution
Peak
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Aim
Experimental setup (hardware and software)
Event reconstruction
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Module performance
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S/N and stability
Cluster characteristics
Latency scans
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Pedestal and common mode
Noise evaluation
Cluster finding
Peak and deconvolution mode: features
Efficiency and delay curves per strip
New observations
Resolution curve
Conclusions (preliminary!)
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From Pisa group
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7 entries per track
From Pisa group
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Special runs
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Trigger changed from 1001 to 0011
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another way to study efficiency off peak
<n>~1.86
<n>~1.55
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2nd cluster
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Further crosschecks (Pisa)
July 2000
November 2001
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S/N in cluster
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Pisa results
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