Neutron skin in CsI and low-energy effective weak mixing angle from COHERENT data

Huang, Xu-Run; Chen, Lie-Wen

doi:10.1103/PhysRevD.100.071301

Neutron skin in CsI and low-energy effective weak mixing angle from COHERENT data

Xu-Run Huang (School of Physics and Astronomy and Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai 200240, China) ; Lie-Wen Chen (School of Physics and Astronomy and Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai 200240, China)

Both the neutron skin thickness $Δ R_{n p}$ of atomic nuclei and the low-energy neutrino-nucleon ( $ν N$ ) interactions are of fundamental importance in nuclear and particle physics, astrophysics as well as new physics beyond the standard model (SM) but largely uncertain currently, and the coherent elastic neutrino-nucleus scattering ( $CE ν NS$ ) provides a clean way to extract their information. New physics beyond the SM may cause effectively a shift of the SM weak mixing angle $θ_{W}$ in low-energy $ν N$ interactions, leading to an effective weak mixing angle $θ_{W}^{*}$ . By analyzing the $CE ν NS$ data of the COHERENT experiment, we find that while a one-parameter fit to the COHERENT data by varying $Δ R_{n p}$ produces $Δ R_{n p}^{CsI} ≃ 0.6 8_{- 1.13}^{+ 0.91} fm$ for CsI with an unrealistically large central value by fixing $\sin^{2} θ_{W}^{*}$ at the low-energy SM value of $\sin^{2} θ_{W}^{SM} = 0.23857$ , a two-dimensional fit by varying $Δ R_{n p}$ and $\sin^{2} θ_{W}^{*}$ leads to a strong positive correlation between $Δ R_{n p}$ and $\sin^{2} θ_{W}^{*}$ with significantly smaller central values of $Δ R_{n p}^{CsI} ≃ 0.2 4_{- 2.03}^{+ 2.30} fm$ and $\sin^{2} θ_{W}^{*} = 0.2 1_{- 0.10}^{+ 0.13}$ . Although the uncertainty is too large to claim a determination of $Δ R_{n p}^{CsI}$ and $\sin^{2} θ_{W}^{*}$ , the present study suggests that the multidimensional fit is important in future analyses of high-precision $CE ν NS$ data. The implication of the possible deviation of $\sin^{2} θ_{W}^{*}$ from $\sin^{2} θ_{W}^{SM}$ on new physics beyond the SM is also discussed.

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      "value": "Both the neutron skin thickness <math><mrow><mi>\u0394</mi><msub><mrow><mi>R</mi></mrow><mrow><mi>n</mi><mi>p</mi></mrow></msub></mrow></math> of atomic nuclei and the low-energy neutrino-nucleon (<math><mi>\u03bd</mi><mi>N</mi></math>) interactions are of fundamental importance in nuclear and particle physics, astrophysics as well as new physics beyond the standard model (SM) but largely uncertain currently, and the coherent elastic neutrino-nucleus scattering (<math><mrow><mi>CE</mi><mi>\u03bd</mi><mi>NS</mi></mrow></math>) provides a clean way to extract their information. New physics beyond the SM may cause effectively a shift of the SM weak mixing angle <math><msub><mi>\u03b8</mi><mi>W</mi></msub></math> in low-energy <math><mi>\u03bd</mi><mi>N</mi></math> interactions, leading to an effective weak mixing angle <math><msubsup><mi>\u03b8</mi><mi>W</mi><mo>*</mo></msubsup></math>. By analyzing the <math><mrow><mi>CE</mi><mi>\u03bd</mi><mi>NS</mi></mrow></math> data of the COHERENT experiment, we find that while a one-parameter fit to the COHERENT data by varying <math><mrow><mi>\u0394</mi><msub><mrow><mi>R</mi></mrow><mrow><mi>n</mi><mi>p</mi></mrow></msub></mrow></math> produces <math><mrow><mi>\u0394</mi><msubsup><mrow><mi>R</mi></mrow><mrow><mi>n</mi><mi>p</mi></mrow><mrow><mi>CsI</mi></mrow></msubsup><mo>\u2243</mo><mn>0.6</mn><msubsup><mrow><mn>8</mn></mrow><mrow><mo>\u2212</mo><mn>1.13</mn></mrow><mrow><mo>+</mo><mn>0.91</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>fm</mi></mrow></math> for CsI with an unrealistically large central value by fixing <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup></mrow></math> at the low-energy SM value of <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mi>SM</mi></mrow></msubsup><mo>=</mo><mn>0.23857</mn></mrow></math>, a two-dimensional fit by varying <math><mi>\u0394</mi><msub><mi>R</mi><mrow><mi>n</mi><mi>p</mi></mrow></msub></math> and <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup></mrow></math> leads to a strong positive correlation between <math><mi>\u0394</mi><msub><mi>R</mi><mrow><mi>n</mi><mi>p</mi></mrow></msub></math> and <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup></mrow></math> with significantly smaller central values of <math><mrow><mi>\u0394</mi><msubsup><mrow><mi>R</mi></mrow><mrow><mi>n</mi><mi>p</mi></mrow><mrow><mi>CsI</mi></mrow></msubsup><mo>\u2243</mo><mn>0.2</mn><msubsup><mrow><mn>4</mn></mrow><mrow><mo>\u2212</mo><mn>2.03</mn></mrow><mrow><mo>+</mo><mn>2.30</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>fm</mi></mrow></math> and <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup><mo>=</mo><mn>0.2</mn><msubsup><mrow><mn>1</mn></mrow><mrow><mo>\u2212</mo><mn>0.10</mn></mrow><mrow><mo>+</mo><mn>0.13</mn></mrow></msubsup></mrow></math>. Although the uncertainty is too large to claim a determination of <math><mrow><mi>\u0394</mi><msubsup><mrow><mi>R</mi></mrow><mrow><mi>n</mi><mi>p</mi></mrow><mrow><mi>CsI</mi></mrow></msubsup></mrow></math> and <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup></mrow></math>, the present study suggests that the multidimensional fit is important in future analyses of high-precision <math><mrow><mi>CE</mi><mi>\u03bd</mi><mi>NS</mi></mrow></math> data. The implication of the possible deviation of <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mo>*</mo></mrow></msubsup></mrow></math> from <math><mrow><msup><mrow><mi>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>\u03b8</mi></mrow><mrow><mi>W</mi></mrow><mrow><mi>SM</mi></mrow></msubsup></mrow></math> on new physics beyond the SM is also discussed."
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Published on:: 07 October 2019
Publisher:: APS
Published in:: Physical Review D , Volume 100 (2019)
Issue 7
DOI:: https://doi.org/10.1103/PhysRevD.100.071301
arXiv:: 1902.07625
Copyrights:: Published by the American Physical Society
Licence:: CC-BY-4.0

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