event reconstruction in drift chamber of the cmd-3 · young researchers workshop “physics...
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Event Reconstruction in Drift
Chamber of the CMD-3
Anastasia Karavdina
Budker Institute of Nuclear Physics
Novosibirsk, Russia
Young Researchers Workshop
“Physics Challenges in the LHC Era”
Frascati, Italy
14 May 2009
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VEPP-2000
CMD-3
SND
• circumference – 24.38 m• revolution time – 82 nsec• beam current – 0.2 A• beam length – 3.3 cm• energy spread −−−− 6.4××××10−−−−4
• ββββx = ββββz = 4 ÷÷÷÷ 10 cm• L = 1032 cm-2s-1 at 2E=2.0 GeV• L = 1031 cm-2s-1 at 2E=1.0 GeV
-1 per dete10 ctor per ye a0 r Ldt pb∫ �
SND
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Physics program
•Study of hadronic cross-sectionse+e−→2h, 3h, 4h, … h =π, K, η …
•Precision measurements of R=σ(e+e−→hadrons)/σ(e+e−→µ+µ−)
•Study of light vector meson radial excitations: ρ’, ρ’’, ω’, ϕ’…
•Comparison of energy dependence of e+e−→hadrons (I=1)with spectral functions in τ decays to test CVC
•Measurements of nucleon electromagnetic form factors and searchfor resonances
•Measurements of e+e−→hadrons with ISR
NN
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CMD-31. Vacuum Chamber
2. Solenoids of VEPP-2000
3. BGO Calorimeter
4. Drift Chamber
1. Ярмо магнита
2. Соленоиды ВЭПП-2000
3. Калориметр BGO
4. Дрейфовая камера
5. CsI Calorimeter
6. Time-of-Flight System
7. LXe Calorimeter
8. Z-Chamber
9. SC solenoid
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Drift Chamber
• 1218 hexagonal cells (side 9 mm)
• signal wire diameter 15 µm (gold plated W-Re)
• tension 35 g (wire stretch 1.08 mm)
• tension loss due to end cap deflection ±1.8 %
• field wire diameter 100 µm (gold plated Ti)
• tension 120 g (wire stretch 0.6 mm)
• tension loss due to end cap deflection ±20 %
• gas mixture - Ar isobutan (80/20)
Chamber body – carbon fibers:
E ∼∼∼∼2000 kg/mm2, ρ∼ρ∼ρ∼ρ∼1.6 g/cm3
End plates are covered by 30 µm copper foil
Inner surface of the outer shell is covered by
250 µm of PET and copper plated G10
(discharge voltage 100 kV/mm)
Inner shell is wrapped up with 30 µm copper foil
2.1*10-3
0.7*10-3
1*10-2
0.04
2.6*10-3
7.5*10-4
0.077
0.02
0.2
0.7
30
Vacuum chamber (Be)
Inner shell (carbon fibers)
Outer shell (carbon fibers)
End caps (carbon fibers)
Gas mixture
(Ar:isoC4H10(80:20))
Wires
0.015Whole chamber
Matter, X0Thickness,
cm
Construction unit
Material budget
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Track Parameters� In a uniform magnetic field helix describes trajectory of a charged particle :
k — curvature;
φ, θ — angles;
— z-coordinate at point of closest approach of projected circle to the origin of
coordinates;
ρ — impact parameter (distance from track projection on (x,y) to origin of
coordinates)
0Z
y
x
r
z
1/k
θ
ϕρ
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Track Reconstruction
� Reconstruction Chain
,100
dπ
φ π φ< =
Raw data
Electronic Calibration
Add hits
•Seed search (for non-central tracks)
•Histogramming (separately in (k-φ) and (z-θ)
planes)2 1 4 1
4 10 , 4 10k cm k cm− − − −< ⋅ ∆ = ⋅
2, 3.14 10φ π φ −< ∆ = ⋅
20.4 0.4, 6 10θ π θ −< < − ∆ = ⋅
20, 5z z mm< ∆ =
Track parameters
are determined
by LMS
Hits
Track-Candidate
Track
Track Search
Track Fit
0( , , , , )k Zα φ ρ θ
→
=
∑
−+
−=
hits z
hit
i
track
i
t
hit
i
track
itrack
zztt2
2
2
22 ))(())((
σ
α
σ
αχ
rr
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Track Reconstruction� Experiments with cosmic rays without magnetic field
Speed of track reconstruction is 550 Hz
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Offline Calibration� Isochrone � Z-coordinate
Initial estimate t(r,φ) from Garfield
is corrected:
drifttrack rtrtrt ),(),(),( ϕϕϕδ −=
Residuals between measured
z-coordinate and z-coordinate of track
are minimized. Parameters of
calibration are length of wire,
pedestals, gain and input impedances
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Vertex reconstruction
� Reconstruction Chain
Tracks
Vertex Search
Vertex candidate
Vertex Fit
Add tracksVertex
Speed of vertex reconstruction is 950 Hz ( simulation )
Distancebetween vertex candidate and each track < 5 mm
Vertex position is obtained by LSM
LS KKee →−+
π π+ −
R
Z
φ→
−∆ ∆ =
∆
2 1T
V V
tracks
Cχ→ →
−= ∆ ∆∑
T
VC Cα
α α
→ →
→ →
∂ ∆ ∂ ∆ = ∂ ∂
0( , , , , )k Zα φ ρ θ→
=
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Vertex reconstruction� Test on simulation
−+−+ → ππ 22ee √s=1.5 GeV
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Vertex reconstruction
� Моделированиеπ π+ −LS KKee →−+ √s=1.02 ГэВ� Test on simulation
Reconstructed invariant mass
0
2 1
0 0( ( , ) ) ( ( , ) )T
V VV p C V pαχ α α α α
→ → → → → → → →−= − −
0( , , , , )k Zα φ ρ θ→
=
and from track fitting0α→
V→
vertex position, particle momentum in vertexVp→
0Cα
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Results
� Programs for event reconstruction in drift chamber of the CMD-3 detector were developed.
� Offline calibration of isochrones and z-coordinate are implemented� Programs for track reconstruction were used in runs with cosmic
particles without magnetic field (with different voltages, thresholds, electronics modifications)
� Obtained resolution :100 µm (minimum) in (x,y) plane1.6 mm along wires
� Analysis of event reconstruction efficiency with MC
� To implement Kalman filter for reconstruction of low momentum particle tracks
Plan
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Thank you for your attention!
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Cell Efficiency
Cell efficiency vs distance from track to
sense wire was measured
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Track Reconstruction� Simulation of (magnetic field B = 1.5 T, √s=1 GeV)e e µ µ+ − + −→
Efficiency of track finding
Efficiency of track reconstruction is 99.97 %
Reconstructed particle momentum