Status of the miniBETA experiment.

Maciej PerkowskiKU Leuven: prof. N. Severijns WI groupJU Krakow: prof. K. Bodek group

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Outline:

• Physics goals (β spectrum shape)• Fierz term• Weak magnetism

• miniBETA spectrometer

• Measurement of cosmic muons

• Single cell efficiency optimization:o Pure isobutane @300mbar

• Summary/plans for future

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Physics goals:

• Precise measurements of the beta spectrum (looking for the influence of Fierz term and weak magnetism).

• Providing data for groups developing models of electrons traversing through matter (backscattering, transmission through thin foil, …) (e.g. for Geant4).

4β spectrum shape

term Effect

K constant factor

F Fermi function

M Weak magnetism(~We )

L0 finite size of the nucleus

C nucleonic orbitals

R radiative corrections

W0,e energy

p electron momentum

First order approximation

+ corrections :

𝑏′=± 𝛾𝑚𝑊𝑒

ℜ (𝐶𝑇+𝐶𝑇′

𝐶𝐴)

Fierz term

For pure Gammow-Teller transitions:

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miniBETA spectrometer

magnetic field

plastic scintillator-Modular reconfigurable drift chamber -beta source inside-energy from curvature of trajectory in mag. field (~0.01T)-trigger from scintillators (start signal for TDC)-operates with light gas at low pressure (~300mbar)-80 hexagonal cells (10 signal planes with 8 wires)-X-Y space resolution 0.5mm- Z position from charge division

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F

S

FF

F

magnetic field

plastic scintillator

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r = 0 r =

amo

un

t o

f to

tal

plane multiplicity

Single Cell Efficiency (from the binomial distribution): - multiplicity 3 - 48%;

4 - 45%; 5 - 40%

Drift chambers suppose to have SCE≈100% ...

Measurement of cosmic muons

TDC spectrum

size of the cell

TDC (a.u.)

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Single cell efficiency optimization

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Pure isobutane @300mbar (mB module)

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Pure isobutane @300mbar (mB module)

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Pure isobutane @300mbar (FASTER)

𝝐=𝑵

𝑵 𝒕𝒓𝒊𝒈𝛀𝒐𝒗𝒍𝒂𝒑

„ ”

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Pure isobutane @300mbar (FASTER)

𝝐=𝑵

𝑵 𝒕𝒓𝒊𝒈𝛀𝒐𝒗𝒍𝒂𝒑

„ ”

13Pure isobutane@300 mbar

𝝐=𝑵

𝑵 𝒕𝒓𝒊𝒈𝛀𝒐𝒗𝒍𝒂𝒑

FASTER

miniBETA module

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Summary

• miniBETA detector is still in testing phase

• Current status:o ADC range is too small – hardware change in modules

requiredo Artifacts on TDC spectrum (further investigation)o Very low trigger efficiency (tests with 90Sr, new

detectors)o Still not satisfying single cell efficiency (tests with

multiple planes, different gas mixtures)

THANK YOU

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Literature

• N. Severijns, M. Beck and O. Naviliat-Cuncic; “Tests of the standard electroweak model in nuclear beta decay”; Reviews of Modern Physics 78 (2006) 991-1040,

• G. Soti; “Search for a tensor component in the weak interaction Hamiltonian”; PhD thesis, 2013

• F. Sauli (1977) - Principles of operation of multiwire proportional and drift chambers; CERN-77-09,

• W. Blum, W. Riegler, L. Rolandi (4 Oct 2008). Particle detection with drift chambers. Springer. Retrieved 2012-02-28.

• K. Lojek, K. Bodek, M. Kuzniak; “Ultra-thin gas detector for tracking of low energy electrons”; NIM A, vol. 611, 2009

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scatteringtransmission

18The general Hamiltonian(Lee and Yang, 1956)

Ci , C‘í determine the relative amplitude of each interaction

Can be complex 20 parameters describing symmetries C, P and T

Symmetry Condition for violation

P Ci ≠ 0 and C’i ≠ 0

C (ReCi ≠ 0 and ReC’i ≠ 0) or(ImCi ≠ 0 and ImC’i ≠ 0)

T Im(Ci /Cj ) ≠ 0 or Im(C’i /Cj ) ≠ 0

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Fierz interference term.

such term appears in almost every correlation measurement:

For pure Gammow-Teller transitions:

𝐻 𝛽=𝐻 𝛽𝑆𝑀⋅ (1+𝑏′ )

𝛾=√1−𝛼2𝑍 2

𝜌=𝑀𝐺𝑇 𝐶𝐴

𝑀𝐹𝐶𝑉𝑏′=±

𝛾𝑚𝑒

𝐸𝑒

11+𝜌 2 [ℜ (𝐶𝑆+𝐶𝑆

′

𝐶𝑉)+𝜌 2ℜ (𝐶𝑇+𝐶𝑇

′

𝐶𝐴)]

Fermi/Gamow-Teller mixing ratio

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Helium-isobutan 70/30 @300mbar (mB module)

𝜀=𝑁𝐴Ω𝑡

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Helium-isobutan 70/30 @300mbar (mB module)

𝜀=𝑁𝐴Ω𝑡

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Helium-isobutan 70/30 @300mbar (FASTER)

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Helium-isobutan 70/30 @300mbar (FASTER)

𝜀=𝑁𝐴Ω𝑡

𝜖=𝑁

𝑁𝑡𝑟𝑖𝑔Ω𝑜𝑣𝑙𝑎𝑝

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Helium-isobutan 70/30 @300mbar

𝜖=𝑁

𝑁𝑡𝑟𝑖𝑔Ω𝑜𝑣𝑙𝑎𝑝

FASTER

miniBeta module