The BTeV Pixel Detector and Trigger System

Simon Kwan

Fermilab

P.O. Box 500, Batavia, IL 60510, USA

BEACH2002, June 29, 2002

Vancouver, Canada

The BTeV Spectrometer

Pixel Vertex DetectorReasons for Pixel Detector:•Superior signal to noise•Excellent spatial resolution -- 5-10 microns depending on angle, etc•Very Low occupancy•Very fast •Radiation hard

Special features:•It is used directly in the Level 1 trigger•Pulse height is measured on every channel with a 3 bit FADC•It is inside a dipole and gives a crude standalone momentum

Hybrid Silicon pixel devices

• Independent development and optimizations of readout chip and sensor

• n+ pixels on n-type substrates: inter-pixel insulation technology under investigation

• Bump-bonding of flipped chip: 2 technologies being considered: Indium (In) and solder (SnPb)

0.25 m rad-hard FPIX2 chip

Comparing to other Pixel Detectors

Experiment

Property

ALICE

Pb-Pb

Collider

ATLAS

p-p

Collider

CMS

p-p

Collider

BTeV

p-pbar

Collider

Pixel Size

50 x 425

50 x 400

150 x 150

50 x 400

Min. distance

to beam

40 mm 43 mm (B)

101 mm

41 mm

70 mm

6 mm

Number of

Pixels

16 x 106 140 x 106 56 x 106 22 x 106

Total Active

Area

0.26 m2 2.2 m2 1.1 m2

0.60 m2

Material Xo

per plane

1.4 % 1.80 %

1.62 %

1.65 %

2.3 %

1.2%

Special Features 50 tracks/cm2 4 bit TOT

ADC

Low luminosity

inner layer

Level 1 Trig

3 bit ADC

Luminosity at FermiLab detectors 2x1032 cm-2 sec-1

Luminosity at LHC detectors 1x1034 cm-2 sec-1

BTeV Radiation Background(L=2·1032 cm-2 s-1), charged hadrons

Pixels, Z = (55 – 60) cm

Pixel Readout Chip

FPIX2

•Reat out rate: 132 ns crossing time

•Greater output bandwidth to easily readout all hit data and provide to trigger

•R&D started in 1997

•Two generations of prototype chips(FPIX0 & FPIX1) have been designed& tested, with & without sensors,including a beam test (1999) inwhich resolution <9was demonstrated.

•New “deep submicron” radiationhard design (FPIX2):Three test chipdesigns have been produced & tested.(radiation hardness tested, no changeafter 2x 1015proton/cm2)Each with increasing complexity.

A pixel

Test outputs

Readout

Irradiation Results: Pixel ROC

Silicon Sensor R&D:Vdep vs Fluence

High density flex circuit development

•15 HDI delivered from CERN; only 4 without defects•Preliminary performance assessment very satisfactory design validation•We need to do more extensive tests and find commercial vendor for large scale production

Built 10% Model

The Pixel Detector (2-D Side View)

Physics Performance of Pixel DetectorDistribution in L/ of Reconstructed Bs

Primary-secondary vertex separationMinus generated. = 138

proper (reconstructed) - proper (generated)= 46 fs

Mean = 44

The BTeV Level I Vertex Trigger

• Key Points– This is made possible by a vertex detector with

excellent spatial resolution, fast readout, low occupancy, and 3-d space points.

– A heavily pipelined and parallel processing architecture using inexpensive processing nodes optimized for specific tasks ~ 3000 processors (DSPs).

– Sufficient memory (~1 Terabyte) to buffer the event data while calculations are carried out.

The trigger will reconstruct every beam crossing and look for TOPOLOGICAL evidence of a B decaying downstream of the primary vertex. Runs at 7.6 MHz!

• Generate Level-1 accept if “detached” tracks in the BTeV pixel detector satisfy:

2

2.0

25.02

b

mb

pT

(GeV/c)2

cm

L1 vertex trigger algorithmExecute Trigger

b

p p

B-meson

L1 trigger efficiencies

Process Eff. (%) Monte Carlo

Minimum bias 1 BTeVGeant

Bs D+sK- 74 BTeVGeant

B0 D*+- 64 BTeVGeant

B0 00 56 BTeVGeant

B0 J/s 50 BTeVGeant

Bs J/*0 68 MCFast

B- D0- 70 MCFast

B- Ks- 27 MCFast

B0 2-body modes 63 MCFast

()

Level 2 Trigger

• Start with the Level 1 tracks from the ``triggering collision” within the crossing.

• Search for pixel hits along these tracks.

• Refit the tracks using a Kalman Filter. Resultant momenta are improved to about 5-10%.

• Resultant event must satisfy one of the two following criteria:

– A secondary vertex must be present or

– The collection of tracks must satisfy a minimum pT cut.

• The combined L1 and L2 rejection is 1000-1.

• Overall Efficiency is roughly 50% for most B decays of interest.

Summary

• Great progress has been achieved in the design of the sensor, front end electronics and module structure of the BTeV pixel detector

• We are making rapid progress towards a full system design that satisfies all the BTeV requirements

• This vertex system will be the key element of the Trigger algorithm that will enable efficient collection of a variety of beauty decays & provide a superb tool to challenge the Standard Model