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CLAS12 Drift Chambers
Simulation and Event Reconstruction
Latifa Elouadrhiri
Jefferson Lab
Hall B 12 GeV Upgrade Drift Chamber Review
Jefferson Lab
March 6- 8, 2007
Outline
• CLAS12 Drift Chambers Requirements
• Luminosity Studies:
– Two methods: occupancy estimation, direct track
reconstruction
– Results: comparison of different methods
• Resolution: p, θ, φ
– Two methods: linearized calculations, track simulation and
reconstruction
– Results: comparison of different methods
• Monte Carlo Simulation of Physics Reactions
CLAS12 Drift Chambers Requirements
Goals:
Specifications:
measure virtual photon flux
accurately
dq ~ 1 mrad
dp/p < 1%
select an exclusive reaction;
e.g. only one missing pion
dp < 0.05 GeV/c
dq p < 0.02 GeV/c
sinq df p < 0.02 GeV/c
measure small
cross-sections
L = 1035/cm2/s
layer occupancy < 4%
Tracking efficiency>95%
good acceptance at forward
angles
Df ~ 50% at q=5o
R3
R2
R1
Arrangement of drift
chambers in CLAS12
Background Situation at L=1033cm-2s-1, DT = 150ns
Electrons
Drift ChambersR1
Photons
No Magnetic Field
Background Situation at L=1035cm-2s-1, DT = 150ns
Electrons
Photons
No Magnetic Field
CLAS12 – Single sector (exploded view)
CLAS 12 Solenoid provides
magnetic field for guiding
Møller electrons away from
detectors.
Beamline
equipment
CLAS12 Solenoid Requirements
 Provide magnetic field for charged particle
tracking for CLAS12 in the polar angle range
from 40o to 135o.
 Provide magnetic field for guiding Møller
electrons away from detectors.
 Allow operation of longitudinally polarized
target at magnetic fields of up to 5 Tesla, with
field in-homogeneity of ΔB/B < 10-4 in cylinder
of 5cm x 3cm.
 Provide full coverage in azimuth for tracking.
 Sufficient space for particle identification
through time-of-flight measurements.
CLAS12 Solenoid
 Minimize the stray field at the PMTs of the
Cerenkov Counter
 Minimize the forces created by one magnet on
the other
CLAS12 Solenoid Requirements
CLAS 12 Solenoid provides magnetic field for guiding Møller electrons
away from detectors.
Background Situation at L=1035cm-2s-1, DT = 150ns
Electrons
Photons
No Magnetic Field
Background Situation at L=1035cm-2s-1, DT = 150ns
Electrons
Photons
One Event
with 5 T Magnetic Field
Møller Electrons in 5 Tesla Solenoid Field
Distance from the beam line in (cm)
Low Energy Moeller Electrons
0
20
40
60
80
z(cm)
Møller Electrons in 5 Tesla Solenoid Field
Distance from the beam line in (cm)
Mid-Energy Moeller Electrons
0
20
40
60
80
z(cm)
Møller Electrons in 5 Tesla Solenoid Field
Distance from the beam line in (cm)
High Energy Moeller Electrons
Møller Shield
0
20
40
60
80
z(cm)
Background Situation at L=1035cm-2s-1, DT = 150ns
Electrons
Photons
One Event
with 5T Magnetic Field
Background Situation at L=1035cm-2s-1, DT = 150ns
Electrons
Photons
One Event
Shielding
with 5 T Magnetic Field and Shielding
Background Event Generator
The Event generator code DINREG:
 Monte Carlo nuclear fragmentation event generator,
reproduces multiplicities and spectra of secondary
hadrons and nuclear fragments in electro- and
photonuclear reactions.
 Generates events fully conserving 4-momentum,
baryon number and charge in the reaction.
 Modified to include the electroproduction processes in
the energy range 2 - 10 GeV.
 Has been used extensively at JLab for background
and shielding calculations.
CLAS12 Tracking Efficiency
CLAS12 Tracking Efficiency
High tracking efficiency at L = 1035
CLAS12- DC Geant Simulation
• Geant Simulation:
DC R3
– CLAS12 DC geometry
– magnetic fields
– Møller shield
• Upgrade of the event
reconstruction code
Beamline
Shielding
• Luminosity Studies
– Tracking efficiency
– DC occupancy
• Resolutions
– P, q, f
Solenoid Field
DC R2
DC R1
CLAS12
Y(cm)
TORUS - Magnetic Field
Y
Z
X (cm)
3m
CLAS12
Solenoid-Torus Magnetic Field
Θ = 5o
Solenoid
B(Gauss)
B(Gauss)
Field in TORUS sector mid-plane
15o
10o
Torus
30o
B(Gauss)
20o
B(Gauss)
B(Gauss)
Z(cm)
40o
CLAS12 Single Event Display
Low momentum
track
5 degree
angle particle
Simulations of tracking resolutions
• Use two methods: “MOMRES” and “RECSIS12”
– MOMRES is a calculation of the change to p, q and x due
to multiple scattering at fixed locations and due to finite
spatial resolution
• “linearized approach” - assumes small deviations from
ideal
• applies to “bend plane” variables only
– RECSIS12 is the name of the CLAS tracking program,
upgraded with the correct CLAS12 DC geometry
• “clusters” found, left-right ambiguities in drift cells
resolved locally, track segments from all super-layers
are linked
• final track is fit globally
CLAS12 Momentum Resolution
CLAS12 Angular Resolution
CLAS12 Drift Chambers Resolution: Summary
Momentum Resolution
DP/P
35o
30o
o
25
20o
DQ(mrad)
Angular Resolution
15o
10o
5o
 P resolution < 1%
 q resolution < 1mrad
 X resolution < 200 mm
Dx(mm)
Position Resolution
CLAS12 Missing Mass Resolution
CLAS12
Missing Mass Techniques
ep → eL(pp-)X
K
K*(892)
Summary
• Drift Chamber system design parameters for the
CLAS12 detector are well defined. They were
developed based on:
– extensive detector simulation in realistic background environment
– direct track reconstruction in both solenoid and Torus magnetic fields
– extensive simulation of the physics processes of the 12 GeV science
program
• The current design of the Drift Chambers in combination
of the Torus and solenoid design will allow us to operate
CLAS12 with L ≥ 1035 cm-2s-1 and achieve excellent
resolution in p, q and f.
•
With these capabilities the CLAS12 will be able to carry
out a world-class experimental program in fundamental
nuclear physics.
Summary
 The magnetic configuration for the CLAS12 Detector
are well defined. They were developed based on:
– Extensive simulation of the physics processes of
the 12 GeV science program
– Extensive detailed design and simulation of the
CLAS12 detectors that impact the magnet design
• Optics of the High Threshold Cerenkov
Counter
• Geometry of the Forward Silicon
Detector
• Geometry and design of the Polarized
target
– Extensive background simulations to calculate the
rates and radiation doses on the central detectors
(TOF and SVT) and on the forward detectors
(SVT, HTCC, Drift Chambers) to make sure of the