Transcript Document

The LHCb VErtex LOcator
Tracking, Vertexing and Triggering
in a
harsh radiation environment
Doris Eckstein, CERN
May 29, 2003
9th Pisa meeting on advanced detectors
Doris Eckstein
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The LHCb Experiment
•Dedicated to the study of CP violation in the B system
•LHC: -pp collisions @ 14TeV
-full spectrum of B hadrons ( B , Bd,0 s, c , baryons )
-high intensity:
L  2x10 32 cm-2s-1 with σbb  500 μb
O (1012 ) bb pairs per year
•LHCb: -single arm spectrometer
-15-300mrad angular acceptance
-recently optimised to minimise
material
Vertex
Locator
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The requirements for the VELO
•Reconstruction of pp interaction vertex
wide spread of interaction region in z (sz=5.3cm)
Interaction
many stations around z=0
region
•Reconstruction of b-hadron decay vertex
short track extrapolation distances
measure at smallest radii
minimal multiple scattering
minimise material between interaction and
first measured point
~1m
•VELO is the tracker before the LHCb magnet
Angular coverage of full downstream detector
angular range
21 Silicon stations allowing to measure at least 3 hits/track
2 R- and 2 F-measuring sensors per station
overlap (acceptance, alignment)
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The VELO Design
Mechanical design as consequence of these criteria
•VELO sensors as close as possible to beam
no beam pipe, sensors ~7mm away from beam
•Injection: larger aperture required
retraction by 30mm
•Protect sensors against RF pickup from
the LHC beam
•Protect the LHC Vacuum from possible
outgasing of detector modules
•Place sensors in a secondary
vacuum: Roman pots
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Secondary Vacuum – RF Foil
outer corrugations
•Made from 250mm thick Al
•Inner corrugations :
Minimal material before the first
sensor is hit
•Outer corrugations:
allow for overlap of detector halves
for full azimuthal coverage and for
alignment
•Prototyping at NIKHEF
method: Hotgas Forming
full size foil
vacuum tight and stiff
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F sensors
R sensors
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inner corrugations
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More requirements for the VELO
•Rejection of multiple interactions in L0
Trigger
additional VETO stations upstream of
interaction point
•Fast stand-alone tracking and vertexing for
L1 Trigger
motivates R-and F-measuring sensors
•Design allows to optimise resolution vs.
number of channels
May 29, 2003
•Baseline design of sensors:
•Active area 8mm to 42 mm
•R measuring sensors:
division into 45o sectors
• F measuring sensors:
inner/outer region
•increasing pitch from inner towards outer
radii
•2nd metal layer to route signal to chips
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Second Level Vertex Trigger
•Forward flight direction of B: Rz impact parameter
First step: 2D
-build Triplets of clusters in R sensors
-form tracks in Rz
-fill z-vertex histogram
-preselect large impact parameter
tracks in Rz
-match to m
Second step: 3D
-preselected (5-10) 2D tracks
-add information from F sensors for
3D reconstruction
-match to L0 and TT
Example: 2D tracks in 45o
z-vertex histogram
sz~70mm
May 29, 2003
xy-vertex
sx,y~30mm
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Optimisation of VELO sensor design
•L1 Trigger: speed, number of ghost tracks
sector division
New 45o
•Clustering/tracking efficiency: Signal to Noise
strip length
Old 90o
200mm sensor
•Different strip pitches
•Does impact parameter
resolution suffer?
max. 5%
Resolution (mm)
•Options of design studied
(keeping constant number of
strips)
• design chosen with gradual
increase of pitch (40mm
to 103mm)
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9th Pisa meeting on advanced detectors
Doris Eckstein
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Even more requirements for the VELO
This detector has to operate in an extreme radiation environment
Middle
station
•Maximum irradiation per station:
5x1012 to 1.3x1014 neq/cm2/year
•Strongly non-uniform dependence on
R and station (z)
Far
station
•Maintain a good S/N performance
for at least 2 years (replacement)
•Extensive R&D program to select
Sensor and Front-End chip
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9th Pisa meeting on advanced detectors
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Prototype testing in Lab and Test beam
Test beam: CERN SPS (120 GeV p and m)
DELPHI-ds sensor
PR03 sensors
Irradiated/Not irradiated
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Tests of the p-on-n prototype
•Efficiency of cluster reconstruction close to track
•Box size ~ efficiency
•PR02 F-sensor: routing lines in outer region
none in inner region
•More efficient in inner region
•Less efficient in irradiated region
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9th Pisa meeting on advanced detectors
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P-on-n vs n-on-n
•P-on-n:
-Fraction of charge in routing line
reaches 20% in outer region
•Compare efficiency for p-on-n and
n-on-n for different depletion depth
-5% in inner region
•P-on-n efficiency degrades fast
-Detector has undepleted and insulating
layer after irradiation
•N-on-n efficiency ~100% for only 60%
depletion depth
-Expected to be less for n-on-n
Chose n-on-n for VELO
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Front-End chip decision
•Two parallel developments: SCTA_VELO (DMILL) and
Beetle (0.25mm CMOS)
•Features: 128 input channels
40MHz sampling (LHC clock)
•Hybrids equipped with 16 chips tested in test beam
SCTA_VELO
•Decision taken at beginning of this year to use Beetle
•Performance equally good
•Availability, radiation hardness and usage in LHCb
Beetle1.1
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Beetle chip tests
•Currently Beetle1.2 under study
•Test set-up in Lab with one chip reading out a n-on-n 200mm thick
prototype sensor
•Sensor close to final design
•Measure S/N with Sr source
•Prepare for test beam:
Hybrid with 16 Beetle1.2
chips reading out a full
sensor
•MPW submission of improved
Beetle1.3 soon
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Summary & Outlook
•VELO design is close to completion
•Important decisions: finalised sensor design
choice of Front-End chip
•Successfully tested module prototypes consisting
of Sensor, Hybrid and 16 chips
•Plan to have first module end of 2003
•Complete VELO in 2006
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