Ratio<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>|</mml:mo><mml:mfrac><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mi>A</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mrow><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mi>V</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mrow></mml:mfrac><mml:mo>|</mml:mo></mml:math>derived from the proton spectrum in free-neutron decay

Stratowa, C.; Dobrozemsky, R.; Weinzierl, P.

doi:10.1103/physrevd.18.3970

Cited by 91 publications

(70 citation statements)

References 17 publications

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“…Examples are the electron-antineutrino correlation coefficient a [6][7][8], the beta asymmetry parameter A [9][10][11][12][13], the neutrino asymmetry parameter B [14,15] (reconstructed from proton and electron momenta), the proton asymmetry parameter C [16], the triple correlation coefficient D [17,18], the Fierz interference term b, and various correlation coefficients involving the electron spin [19,20]. Each coefficient in turn relates to an underlying broken symmetry.…”

Section: Neutron β-Decay Within Priority Area Bmentioning

confidence: 99%

Precision experiments with cold and ultra-cold neutrons

Abele

2016

Hyperfine Interact

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We present selected results from the first round of the Priority Programme SPP 1491. This programme gets funding from the German DFG and the Austrian FWF funding agencies. The aim of this programme is to address basic open questions in particle and astrophysics using a specific tool: the neutron, which allows the search for new physics becoming manifest itself as small deviations from expectations.Keywords Standard model neutron β-decay · The quantum bouncing ball qBOUNCE

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Section: Neutron β-Decay Within Priority Area Bmentioning

confidence: 99%

Precision experiments with cold and ultra-cold neutrons

Abele

2016

Hyperfine Interact

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“…Earlier determinations of a were inferred from the recoil proton's spectral shape, see, e.g., Ref. [32], and were insensitive to the x dependence of a; the newly proposed a experiment [24] would be the first to measure a as a function of x [33]. The Fierz interference term, b [21], which is zero in the SM can thus be bounded as well.…”

mentioning

confidence: 99%

Sharpening Low-Energy, Standard-Model Tests via Correlation Coefficients in NeutronβDecay

Gardner

Zhang

2001

Phys. Rev. Lett.

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The correlation coefficients a, A, and B in neutron β-decay are proportional to the ratio of the axial-vector to vector weak coupling constants, gA/gV , to leading recoil order. With the advent of the next generation of neutron decay experiments, the recoil-order corrections to these expressions become experimentally accessible, admitting a plurality of Standard Model (SM) tests. The measurement of both a and A, e.g., allows one to test the conserved-vector-current (CVC) hypothesis and to search for second-class currents (SCC) independently. The anticipated precision of these measurements suggests that the bounds on CVC violation and SCC from studies of nuclear β-decay can be qualitatively bettered. Departures from SM expectations can be interpreted as evidence for non-V − A currents.Precision nuclear β-decay measurements have played an important role in the rise of the Standard Model (SM), giving strong credence to the conserved-vector-current (CVC) hypothesis, as well as to the absence of secondclass currents (SCC). We show that upcoming neutrondecay experiments can sharpen tests of the CVC hypothesis and of the absence of SCC significantly, eliminating assumptions inherent to the nuclear studies.Searches for CVC violation and SCC in nuclear β-decay experiments have spanned decades of effort. We consider a CVC test originally suggested by GellMann [1]: the strength of the "weak magnetism" term of the nucleon weak current ought be given by the strength of the corresponding electromagnetic M1 transition. The SM test realized from such a comparison constrains a combination of the weak magnetism and induced tensor terms of the nucleon weak current. The induced tensor term is a "second class" current and thus is zero in the SM [2], save for isospin-violating effects engendered by the differing mass and charge of the u and d quarks. In tests of this sort, the CVC hypothesis is tested if SCC are assumed to be zero, or, alternatively, the non-existence of SCC is tested if the CVC hypothesis is assumed to be valid.Historically, the best constraints on the non-existence of SCC and CVC violation are realized in the mass 12 system [3,4]. The CVC hypothesis can be tested through the comparison of the spectral shape correction parameters a ∓ measured in 12 B → 12 C and 12 N → 12 C transitions with the strength of the electromagnetic M1 transition from the analog state of 12 C. This procedure yields a test of the CVC hypothesis at the 10% level [3][4][5]. In order to realize a SCC test, the decays of spin-aligned 12 B and 12 N nuclei are studied. For purely aligned 1 + → 0 + transitions [6], the e ∓ angular distribution for 12 B (−) and 12 N (+) decay is given by [4]where p e and E e are the momentum and energy of the electron (positron), E max e is the endpoint energy, θ is the angle between p e and the spin orientation axis, and A is the nuclear alignment. The difference α − − α + is sensitive to the weak magnetism term as well as to the induced tensor term in the nucleon weak current. Unfortunately, it is also sensitive t...

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“…Determining the a coefficient can be performed by directly measuring the angular distribution of emitted electron and proton in coincidence, in which case the a 0 /(1 + bm e /E e ) scaling can apply (directional method), or via a measurement of the proton energy spectrum. Directly fitting the proton spectrum or using discrete points from the spectrum (spectral fit method) as in Stratowa et al [24] will result in a m = a 0 + x f b, where x f ∼ 0.09 as determined by Monte Carlo. An alternate method of analyzing proton spectral data is an integral analysis, which has the advantage of being much less sensitive to the presence of a Fierz term, as presented in [25].In such analysis one compares the integral rate over a fixed energy range to the total decay rate.…”

Section: B Dependence Of λmentioning

confidence: 99%

Limits on tensor coupling from neutronβdecay

2013

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Limits on the tensor couplings generating a Fierz interference term, b, in mixed Gamow-Teller Fermi decays can be derived by combining data from measurements of angular correlation parameters in neutron decay, the neutron lifetime, and GV = GFV ud as extracted from measurements of the Ft values from the 0 + → 0 + superallowed decays dataset. These limits are derived by comparing the neutron β-decay rate as predicted in the standard model with the measured decay rate while allowing for the existence of beyond the standard model couplings. We analyze limits derived from the electron-neutrino asymmetry, a, or the beta-asymmetry, A, finding that the most stringent limits for CT/CA under the assumption of no right-handed currents is −0.0026 < CT/CA < 0.0024 (95% C.L.) for the two most recent values of A.

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Ratio|gAgV|derived from the proton spectrum in free-neutron decay

Cited by 91 publications

References 17 publications

Precision experiments with cold and ultra-cold neutrons

Precision experiments with cold and ultra-cold neutrons

Sharpening Low-Energy, Standard-Model Tests via Correlation Coefficients in NeutronβDecay

Limits on tensor coupling from neutronβdecay

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