Study on Spin Precession of Polarized Slow Positrons in Solids

Yang, Jinfeng; Chiba, M.; Hamatsu, R.; Hirose, T.; Irako, Mitsuhiro; Kumita, T.

doi:10.1143/jjap.36.3764

Cited by 8 publications

(7 citation statements)

References 10 publications

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“…[12]. Based on the simulations presented in [12], the net depolarization of the positrons from 68 Ge is 17% and 8% for 22 Na as they stop in the scintillator and aerogel. The polarization of the ortho-positronium formed is (from statistics) simply 2=3 times the average slow positron polarization [6].…”

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confidence: 99%

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Search forCPT-Odd Decays of Positronium

2003

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We have limited a CPT-violating correlation in annihilations of polarized ortho-positronium. We searched for an asymmetry in the triple correlation s-->.(k-->(1)xk-->(2)), where k-->(1) and k-->(2) are the two largest photon momenta, and s--> is the spin of the positronium. Using the Gammasphere array of Compton-suppressed high-purity germanium detectors, we detected 2.65x10(7) events of ortho-Ps annihilation. The amplitude of a CPT-violating asymmetry in the data set is found to be 0.0026+/-0.0031, a factor of 6 smaller than previous experiments.

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confidence: 99%

“…Such effects have been measured and simulated in Ref. [12]. Based on the simulations presented in [12], the net depolarization of the positrons from 68 Ge is 17% and 8% for 22 Na as they stop in the scintillator and aerogel.…”

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confidence: 99%

Search forCPT-Odd Decays of Positronium

2003

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“…The latter is dominated by the effective ortho-positronium polarisation resulting from the evaluation of the spin axis orientation for each event. The effective polarisation is determined by (i) average longitudinal polarisation of positrons from 22 Na (P e þ ¼ β % 0:67), (ii) the amount of polarisation statistically transferred to the formed positronium (2/3), (iii) polarisation loss during positron thermalisation amounting to ~8% 21,50 , and (iv) the geometrical uncertainty of the estimated direction of positron emission, which was reduced to ~9% in the presented setup 46 . The total effective polarisation was estimated to be P ≈ 37.4%.…”

Section: Resultsmentioning

confidence: 99%

Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography

et al. 2021

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Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies in predictions for the electron–positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10−4, with an over threefold improvement on the previous measurement.

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“…This value decreases only by about 8% during the thermalisation process [29,30] and enables to produce ortho-positronium atoms polarized along the direction of the positron emission with the polarization degree of about 41% when using sodium 22 Na [13,31]. The polarization axis varies from event to event, but it can be determined from the known points of the positron emission and positronium annihilation.…”

Section: Experimental Methodsmentioning

confidence: 99%

Studies of discrete symmetries in a purely leptonic system using the Jagiellonian Positron Emission Tomograph

et al. 2016

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Abstract. Discrete symmetries such as parity (P), charge-conjugation (C) and time reversal (T) are of fundamental importance in physics and cosmology. Breaking of charge conjugation symmetry (C) and its combination with parity (CP) constitute necessary conditions for the existence of the asymmetry between matter and antimatter in the observed Universe. The presently known sources of discrete symmetries violations can account for only a tiny fraction of the excess of matter over antimatter. So far CP and T symmetries violations were observed only for systems involving quarks and they were never reported for the purely leptonic objects. In this article we describe briefly an experimental proposal for the test of discrete symmetries in the decays of positronium atom which is made exclusively of leptons. The experiments are conducted by means of the Jagiellonian Positron Emission Tomograph (J-PET) which is constructed from strips of plastic scintillators enabling registration of photons from the positronium annihilation. J-PET tomograph together with the positronium target system enable to measure expectation values for the discrete symmetries odd operators constructed from (i) spin vector of the ortho-positronium atom, (ii) momentum vectors of photons originating from the decay of positronium, and (iii) linear polarization direction of annihilation photons. Linearly polarized positronium will be produced in the highly porous aerogel or polymer targets, exploiting longitudinally polarized positrons emitted by the sodium 22 Na isotope. Information about the polarization vector of orthopositronium will be available on the event by event basis and will be reconstructed from the known position of the positron source and the reconstructed position of the orthopositronium annihilation. In 2016 the first tests and calibration runs are planned, and the data collection with high statistics will commence in the year 2017.

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Study on Spin Precession of Polarized Slow Positrons in Solids

Cited by 8 publications

References 10 publications

Search forCPT-Odd Decays of Positronium

Search forCPT-Odd Decays of Positronium

Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography

Studies of discrete symmetries in a purely leptonic system using the Jagiellonian Positron Emission Tomograph

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