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The LHCb Tracking System. Jeroen van Hunen

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(1)

Jeroen van Hunen

(2)

The LHCb Experiment

LHCb at Point 8 : a lot of activity!

LHCb : a B-physics experiment that is

being constructed for :

Precision measurements of the

CP-violation parameters

Rare B-decays

The CP parameters and rare

decays are sensitive to physics

beyond the standard Model

(3)
(4)

The LHCb Tracking System

(5)

LHCb Tracking

VELO

seeds

Long track (forward)

Long track (matched)

T seeds

Upstream track

Downstream track

T track

VELO track

T tracks

useful for RICH2 pattern recognition

Long tracks

highest quality for physics (good IP & p resolution)

Downstream tracks

needed for efficient K

S

finding (good p resolution)

Upstream tracks

lower p, worse p resolution, but useful for RICH1 pattern recognition

(6)

The VErtex LOcator (VELO)

VErtex LOcator (VELO) vacuum tank at LHCb (P8)

Front end : Beetle (0.25

μ

m CMOS)

Pitch Adapter

Carbon fiber

substrate with

laminated kapton

circuit

Cooling block

Al foil of 300

μ

m to separate primary (beam)

and secondary vacuum

(7)

The VErtex LOcator (VELO)

• n

+

in n-bulk sensors

• second metal layer for signal routing

• 2048 micro strips per sensor

• 40 – 100

μ

m pitch

• 300

μ

m thick

• 21 tracking stations in total (4 half

discs per station, 2φ

and 2R)

• Radiation environment:

- R= 8mm : 1.3×10

14

neq/cm

2

/year

- R= 42mm : 5×10

12

neq/cm

2

/year

The modules need to be replaced after

3 - 4 years.

R-sensor

φ

-sensor

(8)

The Trigger Tracker

TT = Station before the magnet. Used in

the trigger for momentum estimate.

(small field between magnet and velo)

80 half modules in

production, several

are fully completed

and tested.

- Silicon sensors : 9.4*9.6 cm

2

, 500μm thick

- Long modules of 14 sensors, with max 4

sensors per front-end (Beetle) ⇒

55pF

- Long Kapton cables : front-end ⇔

sensors

(9)

The Outer and Inner Tracker

Outer Tracker :

Straw Tubes

=5mm

Inner Tracker

cm

OT occupancy:

Average = 4.5%

Hottest region = 9%

IT occupancy,

hottest region :

2.3%

Beam Pipe

Inner Tracker :

Silicon micro strip

198

μ

m pitch

(10)

The Outer Tracker

• 3 stations (T1 – T3) with 4 layers of

straws (0

o

,-5

o

,5

o

,0

o

) each.

• Drift gas : Ar(0.7)/C0

2

(0.3). Drift

time is 45ns for 2.5mm.

• The straws are 2.4 meter long

• Wire is W/Au.

All modules have been produced,

installation at P8 in June/July this year

ASDBLR

OTIS

(11)

The Inner Tracker

• 3 stations (T1 – T3) with 4 detector boxes

per station.

• 4 Silicon layers per box, 28 modules ( with

one or two sensors each)

• 336 modules in total : 60 built and tested

Beetle (0.25

μ

m

CMOS

) front-end

One of the three IT stations

Alumina Pitch adapter

with Au strips

Silicon sensor: p

in n-bulk,

198

μ

m pitch, 420

μ

m and

300

μ

m thick, 7.8

×

11cm

2

.

1mm thick Carbon

sandwich (2

×

2

uni-directional carbon

with Airex)

25

μ

m kapton

isolation

Kapton hybrid

(12)
(13)

The Expected Tracking Performance

Long tracks

• Typically 38 measurements per track

• Efficiency > 95% for p > 12GeV

• Ghost rate < 7% for p > 12GeV

• For twice the event multiplicity the

efficiency drops by 4% and ghost rate

increases by 7%

(14)

The Expected Tracking Performance

Momentum resolution

IP resolution

1/p

t

distribution for B tracks

p distribution for B tracks

(15)

The Expected Tracking Performance

B

s

K

+/-π

+/-K

+

K

-D

s

PV

τ

B-meson decay time

B-meson decay time error

σ

τ

(fs)

•Typical error on

τ

= 37 fs

•Average error on

τ

= 51 fs

•B

s

mass resolution=14 MeV

•Decay time resolution=37 fs

This excellent decay time

resolution is needed to

resolve the fast

oscillations.

0 s 0 s

B

B

(16)

Conclusions

Construction of the LHCb tracking system well advanced

Vertex Locator: 8 ‘pre-series’ modules produced (need 84 half modules)

Trigger Tracker: 80 half modules in production (need 128)

Outer Tracker: All modules produced

Inner Tracker: 100 modules produced & 60 are fully tested (need 336)

Expected performance : tracking efficiency > 95% while the ghost rate remains

below 7% (for p>12 GeV)

B-meson decay time resolution is 37fs

Looking forward to real data!

References

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