1 The CMS tracker 6 th international conference on hyperons, charm and beauty hadrons Chicago, June...

1http://cern.ch/Martin.Weber

The CMS tracker

6th international conference on hyperons, charm and beauty

hadronsChicago, June 28 – July 3

Martin Weber, CERN, for the CMS collaboration


Contents

● What you can not expect

– Physics data

● LHC starts 1st April 2007

– Final physics analysis

● The Physics TDR (technical design report) will be ready late 2005

● What you can expect

– A description of our detector,

– it's tracking performance,

– vertexing techniques,

– b-tagging methods


The tracker in CMS

`

Compact: 1/8 ATLAS m3

covered in this talkHadronic calorimeter

Electromagnetic calorimeter

Solenoid: 4T @ 4KMuon: physics!

Silicon strip trackerPixel


Tracker Overview

5.4 m

Endcaps (TEC)

2.4

m

Inner Barrel & Disks (TIB & TID)

PixelsOuter Barrel (TOB)

• 198 m2 of Si strip sensors• 1 m2 of pixel sensors• volume: 24.4 m3

• running temperature: –10oC• dry atmosphere for years


Overview of Pixel system

barrel layers●low lumi: r=4cm, 7cm●high lumi: r=4.4cm 7.3cm, 10.2cm●1200 modules●η< 2.4 (collision centered)●η< 2.2 (collision 1σ displaced)

endcap disks●r=6cm...15cm●700 modules●rotate endcap petals by 20o for lorentz angle

● b-physics (CP, Bs oscill., rare B-decays) needs vertex finding!

general layout●active area ~ 1m2

●dimensions: 100 cm x 30 cm●40*106 channels●pixel size: 100 µm (rφ) x 150 µm (z)

1m

hit resolution●electron drift●lorentz angle (23o) -> charge sharing●resolution: 10 µm (rφ) x 15 µm (z)


Pixel technology

readout chip●determines pixel size!●25 µm IBM DMILL process●pixel size:100 µm x 150 µm●1280 k transistors●used in barrel and endcap

module layout●silicon baseplate●readout chip●silicon sensor●High Density Interconnect card●capton/voltage driver chips●capton cablesreadout chip

sensorsensor

bump bonding


Silicon strip tracker

blue = double sided (ds)red = single sided (ss)

Endcap9 disks, 7 rings (1..4 thin)

Inner disk3 disks, 3 rings (thin)

Outer barrel6 layers of 500 µm sensorshigh resistivity, p-on-n

Inner barrel●4 layers of 320 µm sensors●low resistivity, p-on-n


Silicon strip trackerModules and superstructures

CF frame

pitch adapter

hybrid conn.readout hybrid●4 or 6 APV à 128 channel●192x25ns analog pipel.●0,25 µm CMOS technol.●capton flex circuit●ceramic stabiliser

kapton bias

●sensor●10cm length●80..200 µm pitch●512 or 768 strips●STM / HPK

TEC

TOB

TIB

TOB rod

TEC petal


Tracker performance

single µ single πjets, fake rate < 1%

momentum resolutionη<1.751-10 GeV: <2%100 GeV: <3%

10-2

10-1

radi

atio

n le

ngth

η


Vertex finding: A foreword

● Everything shown here is being constantly enhanced...

● Vertex finding relies on good track identification

– Kalman filter, Gaussian sum filter, Deterministic annealing...

– Our software framework allows the user to choose the algorithm!

● Need to separate hard event from background

– 1 out of <17> events in high luminosity (L=1034 cm-2/s) phase...

– primary vertex: 3 pixel hits are enough (algorithms: histo/divisive)

– secondary vertex: least squares, trimmed, adaptive, gaussian sum, d0-phi (CDF)

minimization problemfind from n tracks and the beam constraint a vertex position that is „most probable“

by minimizing a distance function F

knowing the full track covariance matrix C

example!


Vertex finding example:Adaptive vertex fitter

● Least squares fit with

F = Σi=1N wi ri ri = (x-xi )T Ci

-1 (x-xi )

● Trimmed: wi = 0, 1 (Tracks are „cut off“)

● Adaptive:wi = { 1+exp[ (ri

2 - r2cutoff ) /2T]}-1

– T is high at the beginning, reduced each step

– far tracks are downweighted

– avoids local minima

wi

ri2

r2cutoff

“T”slope

ResidualsAdaptiveLinear


b-tagging

● b-tagging

– impact parameter, secondary vertex finding, soft lepton tag

example!

σ(d0) [μm]

pT = 1, 10 , 100 GeV/c

η = -ln tan(θ/2)

d/σ(d) > 3


b-tag: track counting method

mistagging rate for u-jets10-2

b-ta

g ef

fici

ency

10-3

72 %, η < 0.7

η

b-ta

g ef

fici

ency

comparison to other methodstrack countjet probabilitysecondary vertexmore or less same ε !

track count method●two tracks, d/σ(d) > 3●two or three pixel hits●depending on η


End of presentation...

Questions?


Radiation levels

Radiation level(charged hadrons)Pixel: 4 107 h/cm2/sInner: 4 106 h/cm2/sOuter: 4 105 h/cm2/s

Demanding goals!

OccupancyPixel: 10-4

Inner: 10-2

Outer: 10-2


readout chip (ROC) final assembled barrel module

base plate, ROC, sensor

layout●300 micron silicon sensors●3 layer HDI interconnect card●pixel size 100µmx150µm ●due to 0.25 µm IBM DMILL ROC●ROC 1280k Transistors

Detailed pixel technology


Modules and Superstructures: Outer Barrel

688 rods: 6 or 12 modules

5550 modules: 2 sensors

2 wheels


Modules and Superstructures: Inner Barrel

16 shells2 units

3800 modules: 1 sensor

6 Tracker Inner Disk


Modules and Superstructures: Endcap

3800 modules: 1..2 sensor

288 petals 18 wheels

two endcaps


Hybrid production history

Cracks near connector spotted on assembled TOB modules, second week of September 2003: about 900 hybrids lost

Problem solved by the introduction of a rigidifierProduction restarted in November 2003

Bonding quality problems observed in January 2004About 1’000 hybrids rejected

Problem solved with re-optimized bonding parameters, and production restarted

Production started in Spring of 2003


The via problem

Hole in the glue

Copper marginaly deposited

This is due to the Picture.

CKK

G

CS

Ni

a bad via

a good via The circuit is made with 2 plates of kapton (K) with 18 microns layers of copper on each side (CK). These 2 plates are glued together (G). The via is drilled using a laser beam, which is focused and defocused when it goes through the kapton, copperor glue. And after this drilling about 15 microns of copper is deposited (CS), and a thin layer of Nickel (Ni) – see the different color – is also chemically deposited. What is observed is an “overetching” of the glue layer due to a different behaviour under the laser beam and (to a lesser extend) at the plasma cleaning stage.

TOB hybrid


week 19 20 21 22 23 24 25 26 27 28 29 30 31CMS week Tracker week

Distribution and shipping QTC standard QTC (PI, PG, VIE, KA) re-testsPQC standard PQC (FI, ST, VIE)p-irradiation in Karlsruhe 8 sensors 8 modulesModule construction/ tests 100 modules 100 modulesLongtime tests sensors longtime tests in Vienna and StrasbourgCurrent fluctuation tests Wx in VIE OBx in IC OBx in VIE

Status of silicon sensors

•Thin sensors: HPK / Japan•all are already delivered, very good quality

•Thick sensors: STM, Italy•we have observed quality issues in the past•7000 sensor subcontracted to HPK•we never officially qualified STM sensors•now we start qualification of 1000 sensors

we are here today

optical inspection

IV-curves vaccum tests flatband voltage

we take the decision here


ECAL crystals: status

● ECAL crystals are produced in Bogoroditsk (Russia) by BCTP

● Company had cash flow problems

– running at loss

– power cut -> no oven, no crystals

– price has been raised

● Alternative: Apititi, China

– awaiting evaluation of crystals

● First priority: ECAL barrel in 2007

– endcap staged until end of year?

● review situation for October...

raw crystals

cut & polished

APDs


Tracker Alignment

Internal alignment (rays 2,3,4): 100 m measurement of Si-module relative positions (for track pattern recognition) 10 m monitoring of Si-module positions stability (for track parameter reconstruction)

External alignment (rays 1): 100 m measurement of TK position w.r.t. MS 20 rad measurement of TK orientation w.r.t. gravityboth for joint TK+MS track fit

offline reconstruction not yet available!


Primary vertex finder

Simple algorithm using pixel detector

1. Match hit pairs from 1st two layers (barrel & endcaps) in R- and z-R 2. Valid pairs are matched with hit in 3rd layer track candidates

3. Establish primary vertex candidates where 3 tracks cross the z-axis4. Identify most likely “signal” vertex from pT and number of tracks5. Erase tracks not pointing to signal vertex PV finding efficiency


vertex finding / b-tagging

•Least-squares, trimmed, adaptive and Gaussian sum vertex fitting methods have been implemented for CMS

• The adaptive vertex fitting method seems very promising

PVR, b-jets 100 GeV, || < 1.4Secondary verticesPurity 55%

Btag eff 65%

Mistag rateu-jets = 1%

52%

40%


Vertex finding

(d0) = f(pT,)• pT = 1 GeV/c: 0.1 0.2 mm• high pT: 10 20 m

= -ln tan(/2)


Physics example: Bs -> J/Ψ Φ

ℓ+

ℓ-

K+

K-

p p

angular distributions depend on ΔΓs , φs , Δms

Bs -> J/Ψ ΦJ/Ψ -> l+ l-

Φ ->K+ K-

Measurement of CKM η parameterφs= - 2λ2η ≈ 0.03(weak Bs / Bs mixing angle)

Bs

σ=22.4 MeV/c2σ=2.2 MeV/c2σ=46.5 MeV/c2 φJ/ψ

HLT le

vel


Bs: more information

8380083800

Events/ 10fbEvents/ 10fb-1-1

14.5 Hz14.5 Hz

L2 Rate L2 Rate

<1.7Hz<1.7Hz8.7%8.7%13.7%13.7%16.5%16.5%

L3 RateL3 RateL3 L3 L2 L2 L1 L1

strip length●10 cm (inner layer, one sensor)●20 cm (outer layer, two sensors)

strip pitch●80 .. 200 µm ●depending on location


High level trigger

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