Detector Design and Data Analysis for Heavy Ion Collision Experiments

Peter, Chan Chak Fai

SURE 2011

Supervisor: Prof Betty Tsang(NSCL, MSU)

National Superconducting Cyclotron Laboratory (NSCL)Michigan State University (MSU)

With Prof Betty Tsang and HiRA group

Background• Symmetry Energy Project (SEP) is one of the current

projects at NSCL.

• Its physics goals include the determination the equation of state of nuclear matter, density dependence of symmetry energy, etc.

• Heavy ion collisions (Ca, Sn, etc.) are studied experimentally and with computer simulations.

• The project is an international collaboration.

Equation of State

Energy in nuclei:

SymmetryEnergy TermImage from http://www.nscl.msu.edu/~tsang/iso_Texas_11.pdf

Detector Design• A Time Projection Chamber (TPC)

is designed to detect pions and charged particles emitted in heavy ion collisions.

• The charged particles produced in heavy ions collision will ionize the gas in the chamber.

• The ionized gas is drifted towards the pad plane by electric and magnetic field.

• The drift time and the position of the ionized gas can be used to generate the tracks of primary charged particles.

• It is designed and made in US and will be installed in RIKEN, Japan.

Image from http://www-rnc.lbl.gov/EOS/

Overall Design

Overall Design

Lid and electronics

Field cage

Enclosure

Voltage step down

Contributions in TPC design

• Use of Computer-Aided Design (CAD) software

• Design modification

• Model construction

• Rotation structure design

• Stress calculations

CAD Software used• Autodesk Inventor, a Computer-Aided Design (CAD) software is used

for the 3D design of TPC.

Design Modification

• Examples of my contributions:

• Changed the color of the cooling rod.

• Added the copper strips on the corners of the field cage.

• Modified the position of the standoff in voltage step down.

• Modified the dimension of the enclosure.

Foam Model Making• The foam model of TPC is made and shipped to Japan to ensure it can

be placed inside the magnet.

• Made together with Jon Barney and Justin Estee.

MSURIKEN

• Not all the ribs are made.

• In addition, the TPC should be able to move down the hallways and doors in NSCL.

• The foam model in Japan (photos from RIKEN)

Rotation Structure Design• The TPC will be assembled upside down since there are wires to be

attached to the bottom of top plate.

• It has to stand on its side to move down the hallways at NSCL.

• One idea is to rotate the TPC around its center of mass:

Stress analysis• The frame structure should be able to support the TPC(~520kg).

• The condition of the TPC on its side sitting on a cart is simulated by inventor.

• Less than 2mm deformation is observed.

• Simulation to rotate the TPC to different orientation is still in progress.

Analysis of Computer Simulated Collision Data

• Simulations are done by Hang Liu using the supercomputer in Austin, Texas

• Improved Quantum Molecular Dynamics Model (ImQMD) is currently used, the results would be compared to transport theory(BUU) and real collision.s

• More than 60000 collision events are generated for each reaction.

• The collision under different initial conditions at different energies and impact parameters are simulated:

• Examples:

- Sn124+Sn124 (sn124s)

- Sn124+Sn112 (sn112m)

- Sn112+Sn124 (sn124m)

- Sn112+Sn112 (sn112s)

Visualization of collisions in computer simulation

Photo from Y.X. Zhang www.imqmd.com/income/zhang1.pdf

Contributions in Data Analysis

• Computation knowledge of Fortran was used• Some observables were analyzed• Neutron-to-proton (n/p) ratio• Tritium-to-helium3 (t/3He) ratio• Ri value

n/p ratio• Example: E70b7x0.7

- beam energy = 70MeV/A

- impact parameter = 7fm

- stiffness of equation of state of nuclear matter (gamma) = 0.7

n/p ratio for e70b7x0.7

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100

Ec.m.(MeV)

n/p

ra

tio sn112m

sn112s

sn124m

sn124s

• After colliding, fragments with lower energy have a higher neutron content, while that with higher energy have a higher proton content.

• The graphs of n/p ratio for other reactions and graphs of double ratio were also plotted.

n/p ratio for e70b7x0.7

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100

Ec.m.(MeV)

n/p

ra

tio sn112m

sn112s

sn124m

sn124s

t/3He ratio• t/3He ratio is interesting because neutron is hard to detect in experiment

and hence the error in experimental value of n/p ratio is high.

• More tritium(t) are produced in lower energy while more 3He are produced in higher energy in general.

t/He3 ratio for e70b7x0.7

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50

Ec.m.(MeV)

t/H

e3

ra

tio sn112m

sn112s

sn124m

sn124s

• The error in this result is larger than that of n/p ratio.

• The count number at high energy is small, which produces a relatively high statistical error.

• More events will be simulated to reduce the error.

t/He3 ratio for e70b7x0.7

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50

Ec.m.(MeV)

t/H

e3

ra

tio sn112m

sn112s

sn124m

sn124s

Ri value

• Ri is the isospin transport ratio, which is a measure of isospin diffusion.

• XAA refers to the neutron-rich system (sn124+sn124), XBB refers to the proton-rich system (sn112+sn112).

• If no diffusion, Ri(XAA) = 1; Ri(XBB) = -1.

• If isospin equilibrium is reached, Ri(XAB) = Ri(XBA) = 0.

• In theory, X is the asymmetry of the fragments.

• Two types of Ri: Ri(n,frag) and Ri(zmax>20)

• In general, the isospin diffuse more at lower beam energy and lower gamma. Current plan is to compare Ri at more beam energies.

• Graphs for comparing different incident energies at fixed impact parameters were made.

• The next step is to compare for different impact parameters.

Value of Ri(n,frag), b7

00.10.20.30.40.50.60.70.80.9

0 0.5 1 1.5 2 2.5

gamma

Ri(

n,f

rag

)

e35(Ri(124+112))

e50(Ri(124+112))

e70(Ri(124+112))

e35(-Ri(112+124))

e50(-Ri(112+124))

e70(-Ri(112+124))

Acknowledgement

• Thanks to Betty Tsang, Bill Lynch, Fei Lu, Rebecca Shane, Jon Barney and Justin Estee for all their help!

• Thanks to Department of Physics, CUHK for the opportunity of SURE!