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Developing a Lithium Doped Glass Detector to Measure the Electric Dipole Moment of Ultra

Cold NeutronsLori Rebenitsch

University of WinnipegJune 17, 2014

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Overview Neutron electric dipole moment (nEDM) Experimental set-up UCN counter

o Requirementso Specifications

Please note that captions appear in top right corner of slides!

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Neutron Electric Dipole Moment

Baryogenesiso Baryon/antibaryon asymmetry in the early universeo Sakharov conditions (Sakharov, 1967)

• Baryon number violation • CP-symmetry violation• Interactions outside of thermal equilibrium

Standard model has small sources of CP-violationo CKM matrix - quarkso Electric dipole moment of fundamental particles

Extensions increase CP-violation Possible EDM in neutrons due to quark structure

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Ultra Cold Neutrons Properties

o < 3mKo ~7m/so Subject to gravityo Polarizable

Find neutron electric dipole moment (nEDM) by finding Larmor frequency

| e-cm for current experimental limit (Harris et. al) | e-cm for new physics | e-cm for CKM in Standard Model | e-cm for

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nEDM Experiment Requirements

o High UCN densityo Stable magnetic shieldso High counting efficiency

Goalo UCN/cycleo Comagnetometer ~10fTo nEDM measurement e-cm in first phase for new physics

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Neutron EDM Facility Graphic of planned facility

proto

ns

UCNdetect

or

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Detector Requirements Handle rates >1.3 MHz for periods of few seconds Reject background

o Gammaso Thermal neutrons

0.05% efficiency stability Normalize UCN density

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Lithium Doped Glass

Based on design from PSI (Ban et. al)

Dual layered scintillating glasso Optically bonded

• Top layer – lithium depleted• Bottom layer – lithium doped

o Capture full scintillation path

Right: Autodesk image of detector. Bottom: Diagram of dual layer glass and how UCN capture and scintillate.

𝐿𝑖+𝑛→𝛼(2.05𝑀𝑒𝑉 )+𝑡(2.73𝑀𝑒𝑉 )❑6

Lithium glass

Lightguides

PMTs

UCN

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Measurement

Visibility of fringes

Statistical uncertainty

Formula for determining

Ramsey resonance

The four points on the graph are used to find the Ramsey resonance frequency.

𝑁𝑢𝑝

𝜔

𝑁𝑢𝑝𝑚𝑎𝑥

𝑁𝑢𝑝𝑚𝑖𝑛

Γ

𝜔𝑟

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High Rates DPP-PSD

o Generates analysis faster than the computer

o Describes signal in few variables in place of full waveform

o Reduces computation load on DAQ DAQ

o Minimal computingo Saves

• PSD• Slow control

Analyzero Separate from DAQo Puts data into TTree

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DPP-PSDLeft: Inverted signal from Am source. Longer events are α’s and short events are γ’s. Right: Waveform with corresponding DPP-PSD gates. The long and short gates collect charge when open.

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Background Rejection

By comparing the PSD variables, gamma background can be removed from data.

Comparison of the gate values for a thermal neutron source, . Note how the gamma background has a strong 1:1 ratio while the neutrons do not.

neutrons

gammas

Comparison of PSD Charge Integration Gates

Short

Inte

gra

tion G

ate

(A

DC

)

Long Integration Gate (ADC)

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Stability of Efficiency

Environmental – long term efficiencyo Glasso Temperature o Tests in progress

Pile-upo Occurs 2-3MHz

between pulseso Pile-up events have

• Higher than average long gate value

• Average short gate value

• Can be flagged and recounted

Top right: Scope example of a double pulse generated from pulser. Bottom right: Rate of pile-up with respect to frequency of double pulse.

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Normalize UCN Density UCN are produced in

cycles Number of UCN vary per

cycle Example to normalize

UCN densityo Utilize volume below cell

for UCN density estimationo Factors

• Volume below cell is ~10x larger

• Volume presents greater probability of pile-up

• Throttle the UCN and/or account for pile-up

detector

analyzer foil

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Future Work Detector in process of being built Stability tests RCNP proposal to take data with UCN spallation

source this fall

University of Winnipeg, University of Manitoba NSERC, CFI

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Thank you