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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

protons

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

Shor

t Int

egra

tion

Gate

(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

16 Thank you