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

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

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

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

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

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

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

Track Reconstruction� Experiments with cosmic rays without magnetic field

Speed of track reconstruction is 550 Hz

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

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→

=

Vertex reconstruction� Test on simulation

−+−+ → ππ 22ee √s=1.5 GeV

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

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

Thank you for your attention!

Cell Efficiency

Cell efficiency vs distance from track to

sense wire was measured

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