The heavy ionising particles in CMS tracker
description
Transcript of The heavy ionising particles in CMS tracker
Vertex 2002Kailua-Kona
The heavy ionising particles in CMS tracker
Hip effect description.
The PSI beam test.
Measurements of hip rate and induced dead time.
Impact on Cms tracker performances.
Benjamin TROCME (IPN Lyon) on behalf of CMS collaboration
Vertex 2002Kailua-Kona
Test beam
Lhc
The Cms all silicon tracker: ~16k modules with ~75k read out
chips(Apv). 128 strips/Apv, 4 or 6 Apvs per module.
Inelastic hadronic interactions generate hips: Up to 1000 mips signal in a 500m Si
detector. Well known effect, whose rate is predicted
by theory of energy deposition in silicon.
Impact on Apv first observed in 120GeV test beam at Cern in october 01.
CMS tracker and hip: introduction
Vertex 2002Kailua-Kona
The hips and their effects on Apvs
Inverter supply common to 128 strips:
In case of hip: sharing of the current ''consumed'' by few hit strips.
Hip topology:
High signal shared between few strips.
Downward saturated baseline in the remaining strips of the apv.
Apv may remain saturated during ~100-700 ns
1 128Strips
0 0 nsns25 25 nsns50 50 nsns75 75 nsns100 100 nsns125 125 nsns150 150 nsns175 175 nsns200 200 nsns225 225 nsns250 250 nsns275 275 nsns300 300 nsns325 325 nsns350 350 nsns375 375 nsns400 400 nsns425 425 nsns450 450 nsns475 475 nsns500 500 nsns525 525 nsns550 550 nsns575 575 nsns600 600 nsns625 625 nsns650 650 nsns
PedestalPedestal
100
300
Raw
dat
a(A
DC
)
Digital zeroDigital zero
Vertex 2002Kailua-Kona
The PSI test beam
Goal:estimate hip rate and induced Apv deadtime.
12 modules of different thicknesses and with different Rinv
.
Two trigger modes:
(PM1+PM2)1 data read out:hip rate estimate.
(PM1+PM2+!PM3) (enriched hips sample)30 data read out spaced by 25ns: Apv recovery following.
PM1 / PM2
300MeV pions(+/-)
20ns bunched beam
PM1 / PM2 PM3
Vertex 2002Kailua-Kona
The PSI test beam (cont’d)
For the first time, use of Xdaq framework:
Stable with high performances.
Efficient online monitoring.
Quasi online analysis with Orca (C++ reconstruction framework).
Outer barrel module
Endcap module
Beam profile S/N~20
Vertex 2002Kailua-Kona
CMNPedestal
Hip caracterisation
Basic method:
Common Mode Noise:event by event Apv noise.
Because of limited digitizer dynamic:
CMN > -CMN0.
An Apv is said ''hipped'' if: CMN/CMN0 < -0.8
A 2nd method makes use of baseline flatness:
An Apv is said ''hipped'' if:Rms(Raw data)<1
Not considered here but leads to similar results.
Warning:all numbers are preliminary.
Hip
CMN/CMN0
Vertex 2002Kailua-Kona
Hip rate measurement
Distribution normalised to number of good trigger,incident pions.
Hip rate increases with:
Thickness.
Rinv (100 by default).
Rinv() Thickness(m) Hip rate(x0.001)Inner barrel 50 320 0.23 +/- 0.01Inner barrel 100 320 0.37 +/- 0.01Endcap 100 500 0.62 +/- 0.01Outer barrel 50 500 0.55 +/- 0.01Outer barrel 75 500 0.58 +/- 0.02Outer barrel 100 500 0.62 +/- 0.01
Thickness:320m
Thickness:500m
Cut on CMN/CMN0
Hip
rat
e
Vertex 2002Kailua-Kona
Induced dead time estimate
Principle:
Use of data sample with 30 consecutive readouts. Only 6 detectors considered (500m thick).
Looks for a hipped Apv in a detector.
In following samples,looks for tracks intercepting hipped Apv.
Compute tracking efficiency
Normalise it by regular efficiency (i.e non hipped Apv).
Vertex 2002Kailua-Kona
Induced dead time estimate(cont'd)
Average Apv dead time:
track.
x t = 165ns
00 00 00 00 00 00 00Time t(ns)
tr
acki
ng
00 00 00 00 00 00 00
tr
acki
ng
Corrected
Not corrected
Vertex 2002Kailua-Kona
Impact on physic
Hip effect included in Cms full simulation:
2 input parameters:hip rate and induced dead time .
Simple simulation:when a hip occured,all apv data are lost during At high luminosity:1.6 (0.2) equivalent hadron per bunch crossings in
first (last) layer of silicon.
Track angle with detector is taken into account.
Pessimistic parameters choice:
Parameters Measured Chosen(x 0.001) 0.3-0.6 1
(ns) 165 165
Vertex 2002Kailua-Kona
Impact on physic(cont'd)
High P tracks (>1Gev) from B jets:
Impact on HLT performances:
Inefficiency-Layer 1 Inefficiency-Layer 9No Hip 0.004 +/- 0.001 0.001 +/- 0.001
With hip 0.012 +/- 0.001 0.003 +/- 0.001
B tagging Double jet taggingNo Hip 26% 40%
With hip 25% 39%
Vertex 2002Kailua-Kona
Conclusion
Due to the presence of an inverter supply common to 128 strips,the Apv chip can be disabled by heavy ionising particle.
The occurrence of such events and the induced deadtime has been studied during a dedicated testbeam.
Preliminary studies showed a very limited impact on physic performance.