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A Report on the R&D of the e-Bubble Collaboration. Colin Beal Virginia Polytechnic Institute and State University R.M. Wilson Saint Louis University Advisors Dr. Jeremy Dodd, Dr. Raphael Galea & Dr. Bill Willis Nevis Labs, Columbia University REU 2005. Some Neutrino Physics

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A report on the r d of the e bubble collaboration
A Report on the R&D of the e-Bubble Collaboration

Colin Beal

Virginia Polytechnic Institute and State University

R.M. Wilson

Saint Louis University

Advisors

Dr. Jeremy Dodd, Dr. Raphael Galea & Dr. Bill Willis

Nevis Labs, Columbia University

REU 2005


Outline

Some Neutrino Physics

Some Holes in Neutrino Physics

Goals of the e-Bubble Detector

Physics of the e-Bubble Detector

Test Chamber

Experimental Results

Simulation Results

Outline


A report on the rd of the e bubble collaboration 1329368

Wolfgang Pauli, 1930

Cowan & Reines, 1956

Enrico Fermi

Using reactor source,

“neutrino”

-First experimental evidence of neutrino

(Italian for “little neutral one”)


A report on the rd of the e bubble collaboration 1329368

Neutrinos

Weak interactors by the exchange of the W and Z bosons

http://www-numi.fnal.gov/public/images/standardmodel.gif


A report on the rd of the e bubble collaboration 1329368

p

e-

Neutrinos

W

& Interactions with Matter

n

t

e-

W

e-

e-

Z

e-

n,p

Z

n,p

x


A report on the rd of the e bubble collaboration 1329368

Neutrinos

t

… more interactions

e-

W

Z

e-

e-

e+

e-

W

W

x

e-

e+

e-


A report on the rd of the e bubble collaboration 1329368

Neutrinos

& the Sun


A report on the rd of the e bubble collaboration 1329368

Neutrinos

The Solar flux


A report on the rd of the e bubble collaboration 1329368

Neutrinos

The First Solar Neutrino Detector

Homestake

  • Built at BNL in 1965

  • 615 tons tetrachloroethylene

  • Observed the following solar neutrino reaction…

  • Saw deficit in solar neutrino flux…

http://www.its.caltech.edu/~sciwrite/journal03/A-L2/greissl.html


A report on the rd of the e bubble collaboration 1329368

Neutrinos

The Solar Neutrino Problem

The Solar Standard Model (SSM) is tested…

Super-Kamiokande

  • H2O Cherenkov Detector, 500 metric tons

  • Minimum ~3 MeV neutrinos

  • Detects Cherenkov light from scattered electrons

  • Reported 1/3 expected solar neutrino flux

http://ale.physics.sunysb.edu/nngroup/superk/pic/sk-half-filled.jpg

The missing neutrinos can be compensated for if a model incorporating new physics is taken into account…


A report on the rd of the e bubble collaboration 1329368

Neutrinos

They Oscillate

Assuming that neutrinos do have some mass, and that their masses are a mixture of the neutrino (say ne and nm) flavor eigenstates…

Then the probability that an ne will be detected as an ne a distance L (km) away from its origin is given by…

constant

Energy of Neutrino (eV)

Mass difference


A report on the rd of the e bubble collaboration 1329368

Neutrinos

The Solar Neutrino Solution

Sensitive to electron, muon and tau neutrinos…

SNO

  • D2O Cherenkov Detector, 1000 metric tons

  • Minimum ~3 MeV neutrinos

  • Detects Cherenkov light from scattered electrons

  • Reported expected solar neutrino flux

So what else is there to know?

http://www.pparc.ac.uk/Nw/Press/sudburysalt.asp


A report on the rd of the e bubble collaboration 1329368

Neutrinos

There is so much more…

  • What can we learn from low-energy neutrino experiments? …

  • Most of the Suns power lies at energies well below the threshold of current real-time neutrino detection experiments.

  • Our models tell us that high energy neutrino oscillations (governed by the MSW effect) behaves much differently than low energy neutrino oscillations.

  • Is nuclear fusion the primary source of the Suns energy, or is there something else at work?

  • The neutrino magnetic moment m is much more accessible for measurement at low energies.


A report on the rd of the e bubble collaboration 1329368

e-Bubble

The Objective

To design, build and implement a real-time low-energy neutrino detector* using a cryogenic liquid detection medium.

*The detector will be a tracking detector, i.e. one which utilizes the ionization track of electrons produced in a ne-e scattering event to extract information about the incident particle, in this case, a neutrino.


A report on the rd of the e bubble collaboration 1329368

e-Bubble

Performance Goals

Due to the nature of low-energy neutrinos, we’ll need a detector with the following features…

  • Excellent spatial resolution (sub-mm)

  • Excellent energy resolution

  • Large volume or high event-rate

  • Low background


A report on the rd of the e bubble collaboration 1329368

e-Bubble

Tracking Detector

2-D Detection Plane

Drifting Ionized Electrons

Incident Neutrino

n-e interaction

e-e ionizations


A report on the rd of the e bubble collaboration 1329368

Neutrino-Electron Interaction

Origin of the Electron Track

Bahcall, John H., Rev. Mod. Phys., 59, 2, 1987.


A report on the rd of the e bubble collaboration 1329368

Neutrino-Electron Interaction

  • Cross-Sections

    Magnetic Moment

m


A report on the rd of the e bubble collaboration 1329368

Neutrino-Electron Interaction

  • Cross-Sections

    Weak Interactions


A report on the rd of the e bubble collaboration 1329368

e-Bubble

Tracking Detector


A report on the rd of the e bubble collaboration 1329368

e-Bubble

Information from Tracks

Length of Track

Energy of Neutrino

Total Ionized Charge

Origin of Neutrino

Shape of Track


A report on the rd of the e bubble collaboration 1329368

e-Bubble

The Detector Medium

LNe

LHe

  • T = 27K

  • r = 1.24 g/cm3

  • ~1 metric ton

  • Short tracks ( 700 mm,  300 keV)

  • Pointing only for highest energy npp

  • Self-shielding

  • T = 2K

  • r = 0.125 g/cm3

  • ~5 metric tons

  • Long tracks (1-7 mm, 100-300 keV)

  • Good pointing capability

  • Minimum ionizing (low dE/dx)

  • Pure (long drifts, low internal background)

e-Bubbles


A report on the rd of the e bubble collaboration 1329368

  • Solar npp flux 6.2E10 cm-2s-1

  • Expect ~674 ton-1year-1

LNe

  • T = 27K

  • r = 1.24 g/cm3

  • ~1 metric ton

  • Short tracks ( 700 mm,  300 keV)

  • Pointing only for highest energy npp

  • Self-shielding

  • Minimum ionizing (low dE/dx)

  • Pure (long drifts, low internal background)

e-Bubbles


A report on the rd of the e bubble collaboration 1329368

e-Bubbles

… A Social Metaphor

A Red Sox fan enters Yankee Stadium…

Go home

r

And the “Red Sox Fan”-Bubble phenomenon may be observed…


A report on the rd of the e bubble collaboration 1329368

e-Bubbles

In LNe (or LHe)

  • Equilibrium state of free electrons in Low-Z noble liquids (LHe, LNe)

  • Due to Pauli repulsion between free electron and noble atoms

  • ~1-2 nm diameter

  • Displaces ~50-100 atoms of liquid


A report on the rd of the e bubble collaboration 1329368

e-Bubbles

In LNe (or LHe)

Useful Properties…

Creates large “drag” in liquid

Low mobility

Slow drift velocity in electric field

Small diffusion due to thermal equilibrium


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks

  • Two primary forms of charged particle energy loss…

  • Radiative (Bremsstrahlung)

  • Ionization


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks


A report on the rd of the e bubble collaboration 1329368

LNe

Physics of Ionization Tracks

250 keV Recoil Electron Tracks

150 keV Recoil Electron Tracks

(Single ionizations, parameterized angular distribution)


A report on the rd of the e bubble collaboration 1329368

LNe

Pointing Capability

How well can we determine the origin of the incident neutrino?

  • Angular diffusion of the ionization track

  • Length of ionization track

  • Diffusion over drift in detector


A report on the rd of the e bubble collaboration 1329368

LNe

Pointing Capability


A report on the rd of the e bubble collaboration 1329368

LNe

e-Bubble Drifts

Liquid Surface

Einstein-Nernst Equation

for Thermal Diffusion

s

Path of e-Bubble Drift

Ionization Location


A report on the rd of the e bubble collaboration 1329368

LNe

e-Bubble Drifts

Predicted Mobility…

Drift Velocity…

E = 1000 V/cm

E = 5000 V/cm


A report on the rd of the e bubble collaboration 1329368

LNe

e-Bubble Drifts

Liquid Surface

What happens at the liquid surface?

Why does it matter?


A report on the rd of the e bubble collaboration 1329368

LNe

Trapping e-Bubbles at the Liquid-Vapor Interface

  • Dielectric discontinuity at the interface (el> ev)

  • Potential well just beneath surface

  • e-Bubble has some probability of tunneling through potential barrier in time

Schoepe, W. and G.W. Rayfield, Phys. Rev. A, 7, 6, 1973.


A report on the rd of the e bubble collaboration 1329368

LNe

Trapping e-Bubbles at the Liquid-Vapor Interface

Barrier Height


A report on the rd of the e bubble collaboration 1329368

2-D Detection

Ejecting Charge from Liquid Surface

  • Method needs to be conducive to maintaining resolution (energy and spatial)

  • Local high-field pulsing at surface

  • Photo-emission

Due to their large size, e-Bubbles are highly sensitive to photo-excitation.

Effective, but noisy


A report on the rd of the e bubble collaboration 1329368

2-D Detection

Charge Amplification

Due to low ionized charge, a method of amplification is required…

GEMs

  • High localized fields

  • Charge amplification and light emission (~1000x amplification)


A report on the rd of the e bubble collaboration 1329368

2-D Detection

Charge Amplification

Due to low ionized charge, a method of amplification is required…

GEMs

  • Commercial CCD Cameras to read out light emission

  • Pixelated anode

  • No method for in-liquid detection found effective

Garfield simulation of charge amplification and drifts


A report on the rd of the e bubble collaboration 1329368

In the mean time…

some proof of principle.

  • Experimental verification of LNe physics

  • Simulated LNe drifts

All essential in constructing a large scale detector


Research and results
Research and Results

  • Outline:

    • e-Bubble Test Chamber Setup

    • Experimental Data

    • Computer Simulation Results


Experimental run design
Experimental Run:Design

e-Bubble experiment is set up at Brookhaven National Lab

A cryostat uses liquid

Helium (~4K) and liquid

Nitrogen (~77K) to cool

the test chamber.

Optical windows enable

“first-hand” observation

of the experimental runs


Experimental run test chamber setup
Experimental Run:Test Chamber Setup

Electrons must be “artificially” inserted

into the test chamber

  • Goals:

    • - Test electron sources

    • - Make electron bubble drift measurements


Experimental run electron sources
Experimental Run:Electron Sources

  • Photo-Cathode

  • High Voltage Tip

  • Radioactive Alpha Source


Experimental run drift time
Experimental Run:Drift Time

Experimental

Theoretical

Although the experimental drift time differs from the predicted time by only a few ms, many approximations were used.

…stay tuned

Drift time is 78 ms @ 4 kV/cm

Using µ = 1.6E-3 (cm2/Vs)

Drift time is ~80 ms @ 4 kV/cm


Experimental run mobility
Experimental Run:Mobility

  • Using the predicted drift time equation, mobility was fitted as a free parameter

    1.66E-3 < µ < 1.9E-3

    (cm2/Vs)

  • The derived mobility was consistent with previously determined electron bubble mobility in LNe (Storchak, Brewer and Morris).

Drift time (ms)

E-Field (kV/cm)

Drift time (ms)

E-Field (kV/cm)

C (cm2/V) is a constant to compensate for

omitting the emission and anode regions


Experiment run drift velocity
Experiment Run:Drift Velocity

  • The electron bubble drift velocity can be determined using:

    V=µE

    For µ=1.6E-3 (cm2/Vs) and E=4 kV/cm;

    V = 6.64 cm/s.


Experiment run tip charge emission
Experiment Run:Tip Charge Emission

  • The total charge deposited is calculated using

where; Q is the total charge at the anode (MeV), q is the charge injected by pulse (MeV), A is the measured amplitude (mV), a is the calibrated pulse voltage (mV), ∆T is the measured signal FWHM (ms), and ∆t is the calibrated signal FWHM (ms).

q = 10 MeV, a = 14:6 mV and t = 0:222 ms.


Experiment run mesh transmission
Experiment Run:Mesh Transmission

  • The meshes in the test chamber will stop many electron bubbles.


Experimental run trapping time
Experimental Run:Trapping Time

  • The first attempt at measuring the electron bubble trapping time at the liquid-vapor interface in LNe was inconclusive.


Experiment run conclusions
Experiment Run:Conclusions

  • Photo-Cathode in LNe= Bonk!

  • High Voltage Tip= Success!

  • Drift Time = 76 ms (under a 4 kV/cm drift field)

  • Drift Mobility = 1.66 x 10-3 (cm2/Vs)

  • Drift Velocity = 6.64 cm/s

  • Tip Charge Emission

  • Mesh Transmission


Simulations
Simulations

  • Garfield:

    • Cell Definition

    • Gas Definition

    • Field

    • Drift

    • Signal


Simulations drift time mobility
Simulations:Drift Time; Mobility

76.85 ms

  • Electrons were drifted through the simulated cell by defining mobility=1.9E-3 (µ=1.9E-3 cm2/Vs).

  • Recall the experimental drift time was ~78 ms.

The predicted drift time

is 78. 5 ms (µ=1.9E-3

cm2/Vs)


Simulations diffusion
Simulations:Diffusion

LongDiff = .001, TransDiff=1E-5 (cm/cmdrift)

  • Diffusion (longitudinal and transverse) effects the result of the simulated drifts.

  • Generally, as diffusion increases the observed signal will widen and exhibit a more predominant tail

LongDiff = .001, TransDiff=1 (cm/cmdrift)


Simulations diffusion1
Simulations:Diffusion

  • Diffusion displays a “threshold” characteristic.


Simulations signal
Simulations:Signal

Signal resulting from 80 electron bubble drifts


Simulation conclusions
Simulation:Conclusions

  • Consistent drift time results.

    • Yields accepted electron bubble mobility and velocity

  • Diffusion “threshold” characteristic

  • Simulated signal for direct comparison to experimental data


What now
What now?

  • Little Picture:

    • Trapping Time

    • Gas Bubbles

    • GEM Characteristics

  • Big Picture

    • Finish Research and Design

    • Ramp Up

    • Construction