SIMULATION OF RECOMBINATION IN XE + TMA FOR DIRECTIONAL DETECTION - - PowerPoint PPT Presentation

SIMULATION OF RECOMBINATION IN XE + TMA FOR DIRECTIONAL DETECTION OF DARK MATTER

Megan Long Azriel Goldschmidt

8.15.14

Simulation Objectives

• Quantify electron-ion recombination in xenon gas in

Garfield++ in a parallel plate drift chamber

• Microphysics simulation – run at NERSC
• Multiple electrons tracked at once as a cloud
• Model how additives like TMA affect recombination
• Investigate possibility of directional detection via columnar

recombination

• Benchmark simulation against experimental results

Dark Matter & Columnar Recombination

When a nuclear recoil is parallel to the electric field, as in Case 1, there will be more electron-ion recombination since the electron passes more ions as it drifts through the chamber.

Current Status

• Gets diffusion and drift velocities correct
• Aren’t seeing several effects that have been observed in

experiment

• Looking for a portion of parameter space in which

directionality is observed

• Run simulations on Carver cluster at the National Energy

Research Scientific Computing Center (NERSC)

• 400,000 hours used to date
• ~100 electrons is maximum can currently simulate at once

Physics of Simulation: Initial Conditions

+y e- drift direction E

Xe+ Xe+

n total e-

e- Xe+ e- Xe+ e- e-

e-s ‘released’ at 10% of Onsager radius at random initial angle and direction parent ion density similar to alpha track: 10nm apart at 10 atm

3D chamber at room temperature Specify: P, E, gas mix, number of e-, angle of e- line w.r.t. E, runtime

Physics of Simulation: Recombination

• After each step made while cycling through electrons and

tracking them using their kinematics, the program checks to see if above recombination conditions have been met.

e- Xe+

Distance to an ion from the electron must be less than either its deBroglie wavelength or the Onsager radius, whichever is smaller Total electron energy must be negative

Current Results: Pure Xenon

Current Results: TMA at 1x ion spacing

Current Results: TMA at 4x ion spacing

Next Steps

• Benchmarking the simulation
• Angular dependence – run more simulations at different angles
• In pure xenon, should see increase in recombination at low fields

based on Bolotnikov

• Zaragoza’s results with gammas & alphas in Xe + TMA
• Possible explanations:
• Need to extend the simulated track to compare with actual length of

alpha track

• TMA energy levels affect recombination near an ion
• Combine gamma ray clusters and sections for whole-track

recombination estimate

• Simulate alpha tracks to use for initial position

Thank you.

Questions?