Description of BTeV detector
Jianchun WangSyracuse University
Representing The BTeV Collaboration
DPF 2000 Aug 9 - 12 , 2000 Columbus, Ohio
DPF 2000 Jianchun (JC) Wang 2
Introduction
BTeV: dedicated beauty and charm experiment at pp collider at Fermilab
Physics goal: mixing, CP violation, rare decays of b- and c- hadronsAccurately determine Standard Model
parametersSearch for physics beyond Standard Model
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Characteristics of b Production at Tevatron
Luminosity (leveled) 21032 cm-2s-1
b cross-section 100 µb# of b’s per 107 sec 41011
b fraction ~ 0.15 %c cross-section >500 µbBunch Spacing 132 nsLuminous region length z = 30 cmLuminous region width
x ~y ~ 50 µmInteractions/crossing <2>
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A Forward Detector at pp Collider
The higher momentum b are at larger
b production angle
b production angle
b production peaks at large angles with large bb correlation
Pseudo-rapidity
BTeV detector covers forward region, 10-300 mrad
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High background ( b/tot ~ 1/500 ), large data rate ( 1kHz ) to be recorded
Detached vertex trigger and background rejection
Deadtimeless trigger and DAQ system
Background from real b event can overwhelm “rare” processes
Excellent particle identification
Radiation hard detector components
Main Challenges
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The C0 Interaction Region
C0 collision Hall( 9 m x 24 m )
C0 Assembly Building
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The BTeV Detector
Pixel Vertex Detector
Dipole Magnet
Magnet Coil
Beam Pipe
Forward tracking
RICH
PbWO4 EM calorimeter
Muon Toroid
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The Pixel Detector
Function: Deliver clean, precise space
points to detached vertex trigger
Provide vertex information for offline analysis
Pixel sensor Eliminate ambiguity problems
with high track density (essential to the detached vertex trigger)
Radiation hard, low noise Easy pattern recognition
Pixels size: 50m 400 m (total 3 107 channels)
Elevation View 10 of 31 Doublet stations
5mm
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Silicon Pixel Detector
FPIX2 Readout Chip3-bit analog readoutNoise ~ 100 e0.25m CMOS process
Pixel sensor Size: 50400 m2
Thickness: 250 m Type: n+np+
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Support and Cooling
Carbon composite structures include integrated cooling tubes ( by ESLI) Shingled surface, allow the multichip assemblies to overlap Movable structure, adjustable distance between the sensor and the beam Light mass material ( ~ 0.9 % X0 includes the detector)
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Pixel Test Beam Results
280 m thick detector bump bonded to custom made electronics chip developed at Fermilab
Excellent resolution ( requirement: 9 m ) Diamond target test, track density higher than BTeV
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Decay Time Resolution
• Decay length (from primary vertex to secondary vertex) <L> = c
= 480 m pB/mB (2700 m at pB = 30 GeV)
• Excellent resolution (L 75 m at pB = 30 GeV)
– Reduces background
– Allows detached vertex trigger
• Smallest error near peak (30GeV) pB (GeV)
L (
cm)
B
PB distribution
Decay length error
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Detached Vertex Trigger
State efficiency(%) State efficiency(%)
B +- 63 Bo K+- 63
Bs DsK 71 Bo J/ Ks 50
B- DoK- 70 Bs J/K* 68
B- Ks- 27 Bo oo
Idea: finds the primary vertex, selects events that have additional tracks miss it
Requirement: at least 2 tracks detached by more than 6 1% minimum bias
Efficiency: (after the other analyses cuts)
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Forward Tracking System
Major functions: Improve P measurement combined with pixel system Reconstruct and measure all parameters for tracks outside the
acceptance of pixel system Project tracks into downstream detectors Provide information for level 2 trigger
Combination of straw-tube chambers and silicon strips (along the beam line, 7 station per arm)
Straw-tube (4mm diameter, x ~ 150 m): small cell for large chamber, no heavy frame near the beam
Silicon strip (100m pitch, x ~ 29 m): near the beam, handle high track density
Momentum resolution ( 0.4% - 0.9% )
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Ring Imaging CHerenkov
Goal: /K/p separation from 3 - 70 GeV/c Radiators: freon, aerogel (~ 4cm thick) Photon detector: hybrid photodiodes (HPD)
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Hybrid Photo Diode
e
Silicon diode
Pins to readout chip
window with aphoto-cathode at -20 kV
Electrostatic acceleration and focusing of a photo-electron on a silicon diode
Large active area ( ~ 80%), hexagonal close packed, no lens system needed
163 channels, manufactured by DEP
Large HV (20kV) but no current draw
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Particle Identification
Rings from Bo+ -High efficiency
with excellent rejection
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The PbWO4 EM Calorimeter
Goal: Reconstruction of (B, etc), identification of electron Excellent resolution, radiation hard
PbWO4 crystal Radiation hard Scintillation is fast, 99% of light emitted < 100 ns Lateral size: 25.425.4 mm2 (front), 2626 mm2 (back) Length 22 cm (25 X0)
Photo-multiplier tube (PMT) readout (no magnetic field)
Projective geometry, covers up to 210 mrad (reduce cost)
Total of 2 11,850 crystals needed
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Expected Resolution
M(GeV)
0 at 10 GeV
M=2.6MeV
E / E
= 0.77%
BK*
22
E %55.0)GeV(E
%6.1
E
22
x 200)GeV(E
3500)m( Excellent Resolution:
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Expected Efficiency
High rate at small radius
resolution and efficiency degrade About 80% efficiency at large radius
BK*
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The Muon Detector
Goals:Muon Identification
Trigger on di-muons in level 1, Provides a method of checking detached vertex triggering efficiency
Design: Two Toroids with three sets of position detectorsToroid: 1 m thick, 1.5 Tesla,
absorb hadron, deflect track
position detectors: 1 between toroids, two downstream
To beam center
B
B
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The Muon Position Detector
Planks of 3/8" diameter stainless steel proportional tubes
Eight overlapping pie shaped octants
Four views (r, u, v, r)
p / p= 19% 0.6% p
r vu
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DAQ Scheme
See Paul Lebrun’s talk7.6MHz crossing rate
2 - 4 kHz
40 KB/event
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The Status of BTeV
BTeV submitted a preliminary technical design report in May of 1999 and a full proposal in May of 2000
BTeV is an approved experiment,
Fermilab E897
More information can be found at
http://www-btev.fnal.gov