Latifa ElouadrhiriLatifa ElouadrhiriJefferson LabJefferson Lab

Hall B 12 GeV Upgrade Drift Chamber Review Jefferson Lab

March 6- 8, 2007

CLAS12CLAS12 Drift Chambers Drift Chambers Simulation and Event ReconstructionSimulation and Event Reconstruction

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

Arrangement of drift chambers in CLAS12

Goals: Specifications:

measure virtual photon flux accurately

~ 1 mrad

p/p < 1%

select an exclusive reaction; e.g. only one missing pion

p < 0.05 GeV/c

p < 0.02 GeV/c

sin p < 0.02 GeV/c

measure small

cross-sections

L = 1035/cm2/s

layer occupancy < 4%

Tracking efficiency>95%

good acceptance at forward angles

~ 50% at 5o

CLAS12 Drift Chambers Requirements

R1

R3

R2

Background Situation at L=1033cm-2s-1, T = 150ns

No Magnetic Field

Drift ChambersR1Electrons

Photons

Background Situation at L=1035cm-2s-1, T = 150ns

No Magnetic Field

Electrons

Photons

Beamline equipment

CLAS12 – Single sector (exploded view)CLAS 12 Solenoid provides magnetic field for guiding Møller electrons away from detectors.

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.

Minimize the stray field at the PMTs of the Cerenkov Counter

Minimize the forces created by one magnet on the other

CLAS12

CLAS12 Solenoid

Solenoid Requirements

CLAS 12 Solenoid provides magnetic field for guiding Møller electrons away from detectors.

CLAS12

Background Situation at L=1035cm-2s-1, T = 150ns

No Magnetic Field

Electrons

Photons

Background Situation at L=1035cm-2s-1, T = 150ns

with 5 T Magnetic Field

Electrons

Photons

One Event

Møller Electrons in 5 Tesla Solenoid Field

0 20 40 60 80 z(cm)

Dis

tan

ce f

rom

th

e b

eam

lin

e in

(cm

)

Low Energy Moeller Electrons

0 20 40 60 80 z(cm)

Dis

tan

ce f

rom

th

e b

eam

lin

e in

(cm

)

Møller Electrons in 5 Tesla Solenoid Field Mid-Energy Moeller Electrons

Møller Electrons in 5 Tesla Solenoid Field

0 20 40 60 80 z(cm)

Dis

tan

ce f

rom

th

e b

eam

lin

e in

(cm

)

High Energy Moeller Electrons

Møller Shield

Background Situation at L=1035cm-2s-1, T = 150ns

with 5T Magnetic Field

Electrons

Photons

One Event

Background Situation at L=1035cm-2s-1, T = 150ns

with 5 T Magnetic Field and Shielding

Photons

One Event

Electrons

Photons

One Event

Shielding

Background Event GeneratorThe 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:– CLAS12 DC geometry– magnetic fields– Møller shield

• Upgrade of the event reconstruction code

• Luminosity Studies – Tracking efficiency– DC occupancy

• Resolutions– P, ,

DC R3

DC R2DC R1

Beamline Shielding

Solenoid Field

TORUS - Magnetic FieldCLAS12

3 m

ZY

(cm

)

Y

X (cm)

Solenoid-Torus Magnetic FieldCLAS12Field in TORUS sector mid-plane

Θ = 5o

10o

20o 40o

B(G

auss

)B

(Gau

ss)

B(G

auss

)Torus

Solenoid

30o

15o

B(G

auss

)

B(G

auss

)

Z(cm)

CLAS12 Single Event Display

5 degree angle particle

Low momentumtrack

• Use two methods: “MOMRES” and “RECSIS12”

– MOMRES is a calculation of the change to p, 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

Simulations of tracking resolutions

CLAS12 Momentum Resolution

CLAS12 Angular Resolution

CLAS12 Drift Chambers Resolution: Summary

5o

10o

15o

20o25o

30o

35o

P/P

x

m

m

rad

Momentum Resolution Angular Resolution

Position Resolution

P resolution < 1%

resolution < 1mrad

X resolution < 200 m

CLAS12 Missing Mass Resolution

K*(892)K

CLAS12

ep → e(p-)X

Missing Mass Techniques

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, and

• 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 high luminosity capabilities.