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.