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Development of a New Search for Neutron/Anti-neutron Oscillation at - - PowerPoint PPT Presentation

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Development of a New Search for Neutron/Anti-neutron Oscillation at the European Spallation Source Matthew Frost UTK HEP Seminar April 5, 2017 Why study NNbar? Novel Observation: The spontaneous transmutation of a neutron to an

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Development of a New Search for Neutron/Anti-neutron Oscillation at the European Spallation Source

Matthew Frost UTK HEP Seminar – April 5, 2017

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Why study NNbar?

  • Novel Observation: The spontaneous transmutation of a neutron to an

anti-neutron would be the first experimental observation of Baryon number violation.

  • SUSY and BSM Physics: Reveals new physics that would exist in

constructs beyond the Standard model, setting energy scales for these new physical phenomena. -> Ξ” 𝐢 βˆ’ 𝑀 ; Δ𝐢 = 2

  • Astronomical Observations: Justification of observed matter/anti-matter

imbalance in the universe.

  • Historical Vindication: Ettore Majorana proposed that charge-neutral

fermions were in fact their own anti-particle.

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Neutron Oscillation

  • For a two-level system the probability of oscillation is

For free neutrons, π‘Š β‰ͺ 1, and 𝑒 β‰ͺ 1 yielding π‘„π‘œ~

𝑒 πœπ‘œβˆ’π‘œ 2

, where the oscillation time πœπ‘œβˆ’π‘œ =

ℏ 𝛽

Additional details in Josh Barrow’s March 8 presentation: www.phys.utk.edu/research/hep/seminar-slides/2017-spring/barrow-march08.pdf

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Experimental Figure of Merit

  • Used to optimize experiment design in simulation.

Figure of Merit = Ξ¦ 𝑒2

  • Ξ¦ β†’Total neutrons on detector (scales with source intensity)
  • 𝑒2 β†’Square of Mean Flight Time (scales with wavelength)
  • Sensitivity units are in β€œILL/year”
  • Compared to last observation attempt at ILL in 1990.

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Baseline Experiment Geometry

The proposed NNbar experiment at the European Spallation Source (ESS) entails four main components:

  • A large view of ESS cold neutron moderator systems.
  • An Ellipsoidal super-mirror reflector about 40 meters in length.
  • An ultra-high vacuum tube with magnetic field shielding about 200 meters in length.
  • A 2 meter diameter carbon foil annihilation target surrounded by a particle tracker detection

system.

CTUB

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Baseline Experiment Geometry

This optimization has shown performance gains ~100x beyond the ILL experiment with other simulated cold neutron sources, and thus provides a good configuration to test with other cold source concepts.

  • Super Mirror Reflectivity

m=6

  • Minor Axis

b=2 m

  • Major Axis

c=100 m

  • Start/Stop reflector position

10-50 m

  • Acceptance Angle

Β±5Β°

  • Detector Efficiency

50%

CTUB

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The European Spallation Source

  • A pulsed source of cold (<25meV)

neutrons designed particularly for neutron scattering instrumentation used in studies of advanced materials. (Condensed Matter, Engineering materials, Biological structures)

  • Proposed startup in 2019.

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ESS Experiment Features



5MW, 14Hz, 3.2ms pulse width

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Competitive with other sources.

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Time Averaged brightness comparable to ILL cold source.



Long flight paths are already planned for scattering instrumentation.

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Simulation Sensitivity History

Moderator TDR 2013 LD2 Pancake H2 Baseline FOM/yr 250 550 200

Preliminary investigations of experiment sensitivity with various proposed source designs proved useful in determining whether to pursue development of the experiment at ESS.

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Neutron Beam Phase Space

  • Beam trajectory phase spaces have lower dimensionality and distinct correlations between

those dimensions, and thus are easy to represent via distributions that are developed from a statistically relevant set of MC data.

  • Source design and conceptual development is performed using MCNP
  • MCNP output events are investigated via correlation and histograming
  • Space and trajectory distributions are fit and weighted against the calculated correlation
  • The result is a suitable subroutine that provides events describing the complete phase space
  • In development for high intensity LD2 source to advance experimental sensitivity.

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𝜍(𝑦, 𝑧, 𝑀𝑦, 𝑀𝑧, 𝑀, 𝑒)

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BF2 Moderator Concept

  • The ESS will move forward with

the β€œButterfly” shaped hybrid moderator design for Mark-I of the source moderator/reflector system.

  • This design incorporates elements
  • f both thermal and cold

moderating sources of neutrons for scattering instrumentation.

Be Reflector Enclosure Be Reflector Enclosure Spallation Target Upper BF2 Lower BF2

To Nnbar/HIBEAM Experiment

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Large Beam Port

  • A Large Beam Port was designed

to accommodate high-intensity experiments like NNbar.

  • Equivalent to three traditional

beam ports in horizontal.

  • Allows a view of both the top and

bottom moderator systems.

  • Enables placement of optical

devices closer to the source.

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  • Once the BF2 configuration was finalized, further optimization of the position of

super-mirror reflector was pursued.

  • Due to the spatial distribution of the cold neutron emitting surfaces of the BF2,

the baseline experiment ellipsoid will not be the most effective means by which to transport the cold intensity.

Reflector Geometry for BF2

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Baseline ellipsoid centered on lower cold spot 313 Baseline ellipsoid centered on middle of lower BF2 188 Baseline ellipsoid centered

  • n middle of both BF2

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  • Using a more complex

parameterized lobed reflector model, an optimized geometry specifically tailored to BF2 can be determined

  • β€œClover” reflector
  • z0, zend, m(z)
  • btop, bbottom, ytop, ybottom, xoffset

Quadruple Focusing (Lobed) Ellipse

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btop bbottom ybottom ytop xoffset Cross Section of Clover Reflector

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Segmentation of Reflectors

  • Initial simulations are performed

using an ideal ellipsoid, but this ultimately will prove to be impractical.

  • A method will be developed to

most economically segment the reflector, while minimally impacting the overall sensitivity contribution.

  • Current super-mirror guide

geometries are constructed of many surfaces approximately 50cm in length, and 5-10cm wide

  • Initial results suggest that angular

segmentation near focal points and around beam trajectory has much greater impact on transport as compared to along the axis

  • With modern super-mirror

substrate technologies, a hybrid design can be conceived.

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Segmentation of Reflectors

50 100 150 200 250 300 0.05 0.1 0.15 0.2 0.25 0.3

Inverse Number of Segments Sensitivity Ideal Ellipse (No Segmentation)

  • Initial results suggest that angular

segmentation near focal points and around beam trajectory has much greater impact on transport as compared to along the axis

  • With modern super-mirror

substrate technologies, a hybrid design can be conceived.

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Reflectivity Optimization

  • Cold neutron intensity could be

enhanced with high reflectivity super-mirrors

  • Higher reflectivity increases

cost, and may provide little benefit closer to reflector entrance.

  • Benefit strongly depends on

reflector geometry, and is included in optimization parameter space.

Target Reflector Source

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  • Significant decrease in length, with little

compromise on reflector illumination, yielding a higher overall FOM.

  • Resources can be saved with a smaller

reflector area, however the system is further complicated by suspension of optics and smaller, more complex segmentation

  • First order calculations show a possible

30% increase in sensitivity with nested

  • ptics

Nested Ellipse Geometry

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  • R. Cubitt et al. / Nuclear Instruments and Methods in

Physics Research A 622 (2010) 182–185

Multi-SANS for Neutron Reflection

Model Dependencies:

  • Particle Radius Distribution
  • Scattering amplitudes
  • Absorption probability
  • Bulk Density and Depth
  • Macroscopic determination of free-path lengths
  • Incident Particle Velocity
  • Nano-particle temperature
  • Down/Up inelastic scattering

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Multi-SANS for Neutron Reflection

  • Increase in experiment sensitivity due to
  • Divergence redirection οƒ  More neutrons on specular reflector
  • In-elastic down-scattering οƒ  Longer Free Flight Time
  • If particles are actively cooled

Sub-Thermal Neutron Phase Space Map at R = 2755 mm to be used for further analysis.

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Preliminary Hardware R&D

  • The ESS will startup at low power and slowly ramp to full power as planned over a 2-3 year period.
  • One moderator will be used in the first generation reflector/moderator system
  • HIBEAM provides an opportunity to test experiment concepts applicable to a final NNbar experiment.
  • Novel Optics
  • Annihilation Detector Systems
  • Magnetic Shielding
  • Background investigations
  • Radiological Shielding
  • Other Fundamental Neutron Physics endeavors can be pursed as well.

High Intensity Baryon Extraction And Measurement

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Questions?

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