Simulation of a Ring Imaging Cerenkov detector to identify

relativistic heavy ions.

M.Fernández-Ordóñez, J.Benlliure, E.Casarejos, J.Pereira

Universidad de Santiago Compostela

ToF techniques present severe constraints to achieve a velocity resolution 10-3 for large angular ranges.

RICH advantages:High velocity resolution.Large angular aceptance.

RICH disadvantages:Beam intensity loss due to nuclear interactions.Loss in identification resolution due to atomic interactions.

RICH

Motivation:Detailed simulations of the Cerenkov detector to determinethe optimum radiator thickness and radiator nature.

Cerenkov radiation characteristics

Nature Material n Tth

Gas He 1.000035 > 110 GeV/u

Aerogel 1.004 > 9 GeV/u

Aerogel 1.1 1.3 GeV/u

Liquid C6F14 1.28 550 MeV/u

Solid MgF2 1.43 375 MeV/u

Solid SiO2 1.56 280 - 750 MeV/u

2

2 11

nLZ

cdE

dN ph

Frank-Tamm relation:

nC

1cos

nTth

1

Simulation walength range: U-V.

Simulations with the code GEANT 3.21

-Setup geometry.-Particle tracking.-Interactions of heavy-ions with matter:

-Energy loss.-Energy straggling.-Angular straggling.

-Cerenkov radiation:-Dispersion law.-Transmission.-Abortion proccesses.

-Photon Detector:-Quantum efficiency-Granularity.

Velocity determination from the Cerenkov ring radii

1)(

11

21

22

22122

1

nn

nLndR

R

R

N ph

1

E

C

2

2

tan1

tan

8 mm thickness C6F14 radiator.96Ru at 1 GeV/u

Numerical solutionPhoton emission at the middle of the radiator.Mean refractive index.Algorithm accuracy.

R = r.m.s of the data setNph= number of detected photons

Simulated performances of different radiators

96Ru600 MeV/u700 MeV/u for C6F14

2 mm thickness4 mm for C6F14

-The radiators have different ranges.-The required velocity resolution is achieved for ions above Z=15.-The effect of the dispersion law is observed.-The effect of the energy loss in the radiator is also observed.

(2mm)

C6F14 (4 mm)

(2mm)

Simulated performances of different radiators

-The energy loss compensates the photon statistic (radiator thickness).-The dispersion law compenstes the granularity of the photon detector.

96Ru

600 MeV/u

800 MeV/u

96Ru

700 MeV/u

600 MeV/u

2 mm

4 mm

Key experiments: Fission 238U + Pb (600 A MeV)

-Multiple ring events.-Large angular range.-Thick target.

Radius distribution

Atomic interactions for 96Ru

Key Experiments: Fission 238U + Pb (600 A MeV)

Kinetic energy resolution

T=f(v,)

T=f (E, )

Energy range of the fissioning system: -450-600 MeV/u for SiO2.

-Above 550 MeV/u for MgF2

v and are given by Wilkins

Proposed radiator: SiO2 (2 mm)

Key experiments: Spallation 208Pb + p (600 A MeV)

)·3(2

1 22cmcmvmT

From Morrisey

Primary interactionsKinetic energy resolution

Reaction probabilities

Key experiments: Spallation 56Fe + p (600 A MeV)

Reaction probabilities

Primary interactions

Kinetic energy resolution

Key experiments: Fragmentation 132Sn + Pb (600 A MeV)

Primary interactions

Kinetic energy resolution

Reaction probabilities

Key experiments: Spallation 208Pb + p (1000 - 500 A MeV)

-Thin Target.-Large energies: total internal reflexion.

Atomic interactions for 175Re:

Key experiments: Spallation 208Pb + p (1000 - 500 A MeV)

Velocity resolution for SiO2

In total reflexion mode (2 mm).

Proposed radiator: MgF2 (2 mm) or SiO2 (2 mm) in total reflexion.

)·3(2

1 22cmcmvmT

Kinetic energy resolution from:

Conclusions-RICH detectors are better suited than ToF techniques to achieve high accuracyvelocity measurements for large angular ranges. However they induce additionaluncertainty sources: atomic and nuclear interactions Simulation.

-Detailed simulations of the detector: geometry, particle tracking, interactionsof heavy-ions with matter, Cerenkov radiation, transmissions, photon absortion,quantum efficiency and granularity of the photon detector.

-Comprehensive analysis of the performances of different radiators: radiator thicknessand radiator nature.

-Simulation of key experiments:Fission experiments: multiple rings, large angular range, thick targets.

Proposed radiator SiO2 (2 mm)Spallation experiments: large energy range, thin targets.

Proposed radiator MgF2 (2 mm) or SiO2 (2 mm) total reflexion.