Muon g2 and Δα connection

Alexander Keshavarzi (Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom) ; William J. Marciano (Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA) ; Massimo Passera (INFN Sezione di Padova, Via Francesco Marzolo 8, 35131 Padova, Italy) ; Alberto Sirlin (Department of Physics, New York University, 726 Broadway, New York, New York 10003, USA)

The discrepancy between the Standard Model theory and experimental measurement of the muon magnetic moment anomaly, aμ=(gμ2)/2, is connected to precision electroweak (EW) predictions via their common dependence on hadronic vacuum polarization effects. The same data for the total e+ehadrons cross section, σhad(s), are used as input into dispersion relations to estimate the hadronic vacuum polarization contributions, aμhad,VP, as well as the five-flavor hadronic contribution to the running QED coupling at the Z-pole, Δαhad(5)(MZ2), which enters natural relations and global EW fits. The EW fit prediction of Δαhad(5)(MZ2)=0.02722(41) agrees well with Δαhad(5)(MZ2)=0.02761(11) obtained from the dispersion relation approach, but exhibits a smaller central value suggestive of a larger discrepancy Δaμ=aμexpaμSM than currently expected. Postulating that the Δaμ difference may be due to unforeseen missing σhad(s) contributions, implications for MW, sin2θefflep and MH obtained from global EW fits are investigated. Shifts in σhad(s) needed to bridge Δaμ are found to be excluded above s0.7 GeV at the 95% C.L. Moreover, prospects for Δaμ originating below that energy are deemed improbable given the required increases in the hadronic cross section. Such hypothetical changes to the hadronic data are also found to affect other related observables, such as the electron anomaly, aeSM, the rescaled ratio Re/μ=(mμ/me)2(aehad,LO VP/aμhad,LO VP), and the running of the weak mixing angle at low energies, although the consequences of these are currently less constraining.

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      "title": "Muon <math><mi>g</mi><mo>\u2212</mo><mn>2</mn></math> and <math><mi>\u0394</mi><mi>\u03b1</mi></math> connection"
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  "abstracts": [
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      "source": "APS", 
      "value": "The discrepancy between the Standard Model theory and experimental measurement of the muon magnetic moment anomaly, <math><msub><mi>a</mi><mi>\u03bc</mi></msub><mo>=</mo><mrow><mo>(</mo><msub><mi>g</mi><mi>\u03bc</mi></msub><mo>\u2212</mo><mn>2</mn><mo>)</mo></mrow><mo>/</mo><mn>2</mn></math>, is connected to precision electroweak (EW) predictions via their common dependence on hadronic vacuum polarization effects. The same data for the total <math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>\u2212</mo></mrow></msup><mo>\u2192</mo><mtext>hadrons</mtext></mrow></math> cross section, <math><msub><mi>\u03c3</mi><mrow><mtext>had</mtext></mrow></msub><mo>(</mo><mi>s</mi><mo>)</mo></math>, are used as input into dispersion relations to estimate the hadronic vacuum polarization contributions, <math><msubsup><mi>a</mi><mi>\u03bc</mi><mrow><mtext>had</mtext><mo>,</mo><mi>VP</mi></mrow></msubsup></math>, as well as the five-flavor hadronic contribution to the running QED coupling at the <math><mi>Z</mi></math>-pole, <math><mi>\u0394</mi><msubsup><mi>\u03b1</mi><mrow><mtext>had</mtext></mrow><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></msubsup><mo>(</mo><msubsup><mi>M</mi><mi>Z</mi><mn>2</mn></msubsup><mo>)</mo></math>, which enters natural relations and global EW fits. The EW fit prediction of <math><mi>\u0394</mi><msubsup><mi>\u03b1</mi><mrow><mtext>had</mtext></mrow><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></msubsup><mo>(</mo><msubsup><mi>M</mi><mi>Z</mi><mn>2</mn></msubsup><mo>)</mo><mo>=</mo><mn>0.02722</mn><mo>(</mo><mn>41</mn><mo>)</mo></math> agrees well with <math><mi>\u0394</mi><msubsup><mi>\u03b1</mi><mrow><mtext>had</mtext></mrow><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></msubsup><mo>(</mo><msubsup><mi>M</mi><mi>Z</mi><mn>2</mn></msubsup><mo>)</mo><mo>=</mo><mn>0.02761</mn><mo>(</mo><mn>11</mn><mo>)</mo></math> obtained from the dispersion relation approach, but exhibits a smaller central value suggestive of a larger discrepancy <math><mi>\u0394</mi><msub><mi>a</mi><mi>\u03bc</mi></msub><mo>=</mo><msubsup><mi>a</mi><mi>\u03bc</mi><mi>exp</mi></msubsup><mo>\u2212</mo><msubsup><mi>a</mi><mi>\u03bc</mi><mrow><mi>SM</mi></mrow></msubsup></math> than currently expected. Postulating that the <math><mi>\u0394</mi><msub><mi>a</mi><mi>\u03bc</mi></msub></math> difference may be due to unforeseen missing <math><msub><mi>\u03c3</mi><mrow><mtext>had</mtext></mrow></msub><mo>(</mo><mi>s</mi><mo>)</mo></math> contributions, implications for <math><msub><mi>M</mi><mi>W</mi></msub></math>, <math><msup><mi>sin</mi><mn>2</mn></msup><msubsup><mi>\u03b8</mi><mi>eff</mi><mrow><mi>lep</mi></mrow></msubsup></math> and <math><msub><mi>M</mi><mi>H</mi></msub></math> obtained from global EW fits are investigated. Shifts in <math><msub><mi>\u03c3</mi><mrow><mtext>had</mtext></mrow></msub><mo>(</mo><mi>s</mi><mo>)</mo></math> needed to bridge <math><mi>\u0394</mi><msub><mi>a</mi><mi>\u03bc</mi></msub></math> are found to be excluded above <math><msqrt><mi>s</mi></msqrt><mo>\u2273</mo><mn>0.7</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> at the 95% C.L. Moreover, prospects for <math><mi>\u0394</mi><msub><mi>a</mi><mi>\u03bc</mi></msub></math> originating below that energy are deemed improbable given the required increases in the hadronic cross section. Such hypothetical changes to the hadronic data are also found to affect other related observables, such as the electron anomaly, <math><msubsup><mi>a</mi><mi>e</mi><mtext>SM</mtext></msubsup></math>, the rescaled ratio <math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mi>e</mi><mo>/</mo><mi>\u03bc</mi></mrow></msub><mo>=</mo><mspace></mspace><mo>(</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>\u03bc</mi></mrow></msub><mo>/</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>e</mi></mrow></msub><msup><mrow><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><mo>(</mo><msubsup><mrow><mi>a</mi></mrow><mrow><mi>e</mi></mrow><mrow><mtext>had</mtext><mo>,</mo><mi>LO</mi><mtext> </mtext><mi>VP</mi></mrow></msubsup><mo>/</mo><msubsup><mrow><mi>a</mi></mrow><mrow><mi>\u03bc</mi></mrow><mrow><mtext>had</mtext><mo>,</mo><mi>LO</mi><mtext> </mtext><mi>VP</mi></mrow></msubsup><mo>)</mo></mrow></math>, and the running of the weak mixing angle at low energies, although the consequences of these are currently less constraining."
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Published on:
20 August 2020
Publisher:
APS
Published in:
Physical Review D , Volume 102 (2020)
Issue 3
DOI:
https://doi.org/10.1103/PhysRevD.102.033002
arXiv:
2006.12666
Copyrights:
Published by the American Physical Society
Licence:
CC-BY-4.0

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