In the experiment with the SND at the VEPP-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2000</mn><mtext> </mtext><mtext> </mtext><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collider, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>η</mi><mi>γ</mi></math> cross section is measured in the energy range <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi><mo>=</mo><mn>980</mn><mi>–</mi><mn>1060</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>. The measurement is carried out in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi><mo stretchy="false">→</mo><mn>2</mn><mi>γ</mi></math> decay mode. Data with an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>73</mn><mtext> </mtext><mtext> </mtext><msup><mi>pb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> collected in 2018 and 2024 are used in the analysis. The measured cross section is the most accurate to date and is higher compared to other measurements. From the fit to the cross section data with the vector meson dominance model, the value of the product of the branching fractions <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo stretchy="false">(</mo><mi>ϕ</mi><mo stretchy="false">→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">)</mo><mi>B</mi><mo stretchy="false">(</mo><mi>ϕ</mi><mo stretchy="false">→</mo><mi>η</mi><mi>γ</mi><mo stretchy="false">)</mo></math> has been obtained.

Russia

M.N. Achasov

A.E. Alizzi

A. Yu. Barnyakov

E.V. Bedarev

K.I. Beloborodov

A.V. Berdyugin

A.G. Bogdanchikov

A.A. Botov

D.E. Chistyakov

T.V. Dimova

V.P. Druzhinin

L.V. Kardapoltsev

A.S. Kasaev

A.A. Kattsin

A.G. Kharlamov

I.A. Koop

A.A. Korol

D.P. Kovrizhin

A.S. Kupich

A.P. Kryukov

N.A. Melnikova

N. Yu. Muchnoi

A.E. Obrazovsky

A.A. Oorzhak

E.V. Pakhtusova

I.A. Polomoshnov

K.V. Pugachev

S.A. Rastigeev

Yu. A. Rogovsky

A.I. Senchenko

S.I. Serednyakov

Yu. M. Shatunov

D.A. Shtol

Z.K. Silagadze

K.D. Sungurov

I.K. Surin

Yu. V. Usov

V.N. Zhabin

Yu. M. Zharinov

V.V. Zhulanov

Measurement of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>η</mi><mi>γ</mi></math> cross section near the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi><mo stretchy="false">(</mo><mn>1020</mn><mo stretchy="false">)</mo></math> resonance with the SND detector

We investigate the sensitivity of a future high-luminosity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>−</mo></msup><msup><mi>e</mi><mo>+</mo></msup></math> collider operating at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>250</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-violating and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-conserving anomalous <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>V</mi><mi>V</mi></math> interactions via the Higgsstrahlung process. The effects of new physics are parametrized in the Standard Model effective field theory (SMEFT) framework through six dimension-6 operators modifying the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>V</mi><mi>V</mi></math> vertices. Using polarized beams and exploiting polarization and spin correlation asymmetries reconstructed from Higgs decay products, we perform a comprehensive analysis across the three dominant decay modes, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>W</mi><msup><mi>W</mi><mo>⋆</mo></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><msup><mi>Z</mi><mo>⋆</mo></msup></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi>W</mi><msup><mi>W</mi><mo>⋆</mo></msup></math> channel exhibits the highest sensitivity to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">O</mi><mrow><mi>H</mi><mi>W</mi></mrow></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">O</mi><mrow><mi>H</mi><mover accent="true"><mi>W</mi><mo stretchy="false">˜</mo></mover></mrow></msub></math>, while the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math> mode constrains the remaining operators with high statistical precision. Sensitivity studies incorporating luminosity scaling and systematic uncertainties show that the projected bounds improve significantly with increasing integrated luminosity, but saturate once experimental systematics exceed the few-percent level. These results highlight the crucial role of spin-based observables and beam polarization in achieving subpercent precision on SMEFT coefficients at future lepton colliders.

India

Amir Subba

Subhaditya Bhattacharya

Abhik Sarkar

Probing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-violating Higgs-gauge couplings with Higgsstrahlung at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>−</mo></msup><msup><mi>e</mi><mo>+</mo></msup></math> colliders

Neutrinoless double-beta (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math>) decays provide an excellent probe for determining whether neutrinos are Dirac or Majorana fermions. The short-range matrix elements associated with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>e</mi><mi>e</mi></math> process contribute at leading order in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></math> decay channel <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>n</mi><mi>n</mi><mo stretchy="false">→</mo><mi>p</mi><mi>p</mi><mi>e</mi><mi>e</mi></math> through pion exchange between nucleons. However, current lattice calculations show notable discrepancies in predicting these short-range contributions. To address this issue, we perform a lattice QCD calculation of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>e</mi><mi>e</mi></math> matrix elements using domain wall fermion ensembles at the physical pion mass generated by the RBC/UKQCD Collaboration. To mitigate contamination from around-the-world effects, we develop a new method to reconstruct and subtract them directly from lattice data. We then perform nonperturbative renormalization in the regularization-independent symmetric momentum-subtraction scheme (RI/SMOM), using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>γ</mi><mi>μ</mi></msub><mo>,</mo><msub><mi>γ</mi><mi>μ</mi></msub><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><menclose notation="updiagonalstrike" other="updiag1"><mi>q</mi></menclose><mo>,</mo><menclose notation="updiagonalstrike" other="updiag1"><mi>q</mi></menclose><mo stretchy="false">)</mo></math> projectors. Compared with previous studies, this work reduces the uncertainties in the matrix elements and provides an independent cross-check that helps to reconcile the discrepancies among previous lattice calculations.

United States

United Kingdom

Peter Boyle

CERN

Felix Erben

China

Xu Feng

Jonathan M. Flynn

Nicolas Garron

Taku Izubuchi

Luchang Jin

Rajnandini Mukherjee

J. Tobias Tsang

Xin-Yu Tuo

Lattice calculation of short-range contributions to neutrinoless double-beta decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>e</mi><mi>e</mi></math> at physical pion mass

We discuss the production of <math altimg='si10.svg'><mrow><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math> pairs in <math altimg='si2.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup></mrow></math> collisions, where <italic>D</italic> refers to either <italic>D</italic> 0 or <math altimg='si30.svg'><msup><mi>D</mi><mo>+</mo></msup></math>. The continuum mechanism with the <italic>t</italic>/ <italic>u</italic>-channel vector-meson <italic>D</italic>* exchanges are considered. The results of the calculation depend on the parameter of the off-shell form-factor for the virtual <italic>D</italic>* mesons. The <italic>D</italic>* <italic>D&#947;</italic> coupling constants are found from the <italic>D</italic>*&#8239;&#8594;&#8239; <italic>D&#947;</italic> decays. We find relatively large contribution for the <math altimg='si4.svg'><mrow><msup><mi>D</mi><mn>0</mn></msup><msup><mrow><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow><mn>0</mn></msup></mrow></math> channel and much smaller contribution in the <math altimg='si1.svg'><mrow><msup><mi>D</mi><mo>+</mo></msup><msup><mi>D</mi><mo>&#8722;</mo></msup></mrow></math> channel. In the second case we consider also the <italic>D</italic> &#8239;&#177;&#8239; exchanges. We conclude that the bump at <math altimg='si31.svg'><mrow><msub><mi>M</mi><mrow><msup><mi>D</mi><mn>0</mn></msup><msup><mrow><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow><mn>0</mn></msup></mrow></msub><mo linebreak='goodbreak'>=</mo><mn>3.8</mn></mrow></math> GeV observed by the Belle and BaBar Collaborations has rather continuum origin than it corresponds to the broad resonance <italic>&#967;</italic> <inf><italic>c</italic>0</inf>(3860). We discuss also production of the <italic>&#967;</italic> <inf><italic>c</italic>2</inf>(3930) resonance which is a candidate for the <italic>&#967;</italic> <inf><italic>c</italic>2</inf>(2 <italic>P</italic>) state. This state can decay into both <math altimg='si10.svg'><mrow><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math> channels, however the branching fractions are not well known at present. From a comparison of our model results to the BaBar data we find <math altimg='si32.svg'><mrow><mi>B</mi><mo>(</mo><msub><mi>&#967;</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>3930</mn><mo>)</mo></mrow><mo>&#8594;</mo><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover><mo>)</mo><mo>=</mo><mn>0.58</mn><mo>&#177;</mo><mn>0.13</mn></mrow></math> using the two-photon width <math altimg='si33.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#915;</mi></mstyle><mrow><mi>&#947;</mi><mi>&#947;</mi></mrow></msub><mo linebreak='goodbreak'>=</mo><mn>0.544</mn></mrow></math> keV (obtained for the Buchm&#252;ller-Tye potential) evaluated within the light-front approach (NRQCD limit). Our finding of <math altimg='si34.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#915;</mi></mstyle><mrow><mi>&#947;</mi><mi>&#947;</mi></mrow></msub><mo linebreak='goodbreak'>&#215;</mo><mi>B</mi><mrow><mo>(</mo><msub><mi>&#967;</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>3930</mn><mo>)</mo></mrow><mo>&#8594;</mo><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mn>0.32</mn><mo>&#177;</mo><mn>0.07</mn></mrow></math> keV is close to the Belle and BaBar results. Realistic predictions of the differential distributions in several variables and integrated cross-sections are given for the Belle II kinematics.

Poland

Izabela Babiarz

Piotr Lebiedowicz

Wolfgang Schäfer

Antoni Szczurek

Competition of <italic>&#967;<inf>c</inf></italic>(2 <italic>P</italic>) quarkonia and continuum in <math altimg='si9.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup><mo>&#8594;</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math>

We suggest that the chiral <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><msub><mrow><mi mathvariant="fraktur">e</mi></mrow><mrow><mn>8</mn></mrow></msub><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn></mrow></msub></mrow></math> theory—in many senses the simplest vertex operator algebra—may have Haagerup symmetry <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="script">H</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>i</mi><mo>=</mo><mn>1</mn></math>, 2, 3. Likewise, we suggest that the nonchiral <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>E</mi><mn>8</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub></math> Wess-Zumino-Witten model may have <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="script">H</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>×</mo><msubsup><mrow><mi mathvariant="script">H</mi></mrow><mrow><mi>i</mi></mrow><mrow><mi>op</mi></mrow></msubsup></mrow></math> symmetry, and that gauging the diagonal symmetry gives a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mo>=</mo><mn>8</mn></math> theory with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><mi mathvariant="script">Z</mi></mrow><mo stretchy="false">(</mo><msub><mrow><mi mathvariant="script">H</mi></mrow><mrow><mn>3</mn></mrow></msub><mo stretchy="false">)</mo></mrow></math> symmetry, which is the theory predicted in Evans and Gannon [<a href="http://dx.doi.org/10.1007/s00220-011-1329-3">Commun. Math. Phys. 307, 463 (2011)</a>]. Along the way, we show that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>E</mi><mn>8</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub></math> also has a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>Fib</mi><mo>×</mo><msup><mrow><mi>Fib</mi></mrow><mrow><mi>op</mi></mrow></msup></mrow></math> symmetry, and that gauging the diagonal symmetry gives the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>G</mi><mn>2</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub><mo>×</mo><mo stretchy="false">(</mo><msub><mi>F</mi><mn>4</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub></math> Wess-Zumino-Witten model, explaining the well-known conformal embedding <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>G</mi><mn>2</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub><mo>×</mo><mo stretchy="false">(</mo><msub><mi>F</mi><mn>4</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub><mo>⊂</mo><mo stretchy="false">(</mo><msub><mi>E</mi><mn>8</mn></msub><msub><mo stretchy="false">)</mo><mn>1</mn></msub></math>. Finally, we suggest a relation to theories with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="script">H</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></math> symmetry at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>c</mi><mo>=</mo><mn>2</mn></math>, 6, complimenting the discussion with new modular bootstrap results.

Jan Albert

Japan

Yamato Honda

Justin Kaidi

Yunqin Zheng

Haagerup Symmetry in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><msub><mrow><mi>E</mi></mrow><mrow><mn>8</mn></mrow></msub><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mn>1</mn></mrow></msub></mrow></math>?

In this study, we investigate a scenario based on the effects of the Loop Quantum Gravity (LQG) on the electromagnetic sector of the Standard Model of Fundamental Interactions and Particle Physics (SM). Starting from a post-Maxwellian version of electromagnetism that includes LQG effects, we derive and discuss the influence of LQG parameters on classical quantities such as the components of the stress-tensor. Furthermore, we inspect the propagation of electromagnetic waves and examine the optical properties of the QED vacuum in this scenario. Among these, we contemplate the combined effect of the LQG parameters and a homogeneous background magnetic field on the propagation of electromagnetic waves by considering issues such as group velocities and refractive indices of the QED vacuum, in detail. Finally, with the aid of the previously analyzed LQG-extended photonic dispersion relations, we re-discuss the kinematics of the Compton effect and conclude that an interesting nonlinear profile emerges in the wavelengths of the incoming and deflected photons.

Brazil

P.A.L. Mourão

G.L.L.W. Levy

J.A. Helayël-Neto

Reassessing aspects of LQG-modified dispersion relations of photons * P. A. L. Mourão is support by CAPES. G. L. L. W. L. Levy is support by the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Grant No. E-26/202.437/2024.

The single Higgs production in neutral-current (NC) and charged-current (CC) processes at an electron–proton ($\textit{ep}$) collider is a useful channel to probe new physics effects in the Higgs coupling to vector boson ($\textit{HVV}$). In this context, observables sensitive to non-standard couplings previously studied at leading order require improved theoretical precision through the inclusion of radiative corrections. In this work, we present a fully differential Higgs plus one jet production at next-to-leading-order (NLO) accuracy in QCD for both the NC and CC processes. For the proposed Large Hadron electron Collider (LHeC) configuration, with a 60 GeV electron beam and a 7 TeV proton beam, the total cross sections receive modest corrections with significantly reduced scale uncertainties. We find that in several kinematic distributions which are relevant to the analysis of $\textit{HVV}$ couplings, the NLO K-factors are not flat. Within the Standard Model, the polar angle of the electron (for NC) and the azimuthal angular correlation (for both NC and CC processes) receive maximum corrections in the range of 8-10% in certain bins. We also compute NLO QCD corrections in the presence of non-standard $\textit{HVV}$ interactions. The corrections in the azimuthal angular correlations are similar to the standard model predictions. For the polar angle of the electron, the corrections are sensitive to the nature of the $\textit{HVV}$ coupling.

Biswajit Das

Pramod Sharma

Ambresh Shivaji

NLO QCD effects on angular observables in $$e^-p \rightarrow e^-(\nu _e)Hj$$ in presence of non-standard $\textit{HVV}$ couplings

We present a comprehensive study of Higgs boson production associated with a neutrino pair at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> colliders (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><mi>h</mi><mi>ν</mi><mover accent="true"><mrow><mi>ν</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math>) at next-to-leading-order accuracy in both the standard model and the two-Higgs-doublet model. We show that these new physics effects will be observable in total and differential cross sections when compared with theoretical predictions that include electroweak corrections, even in the Higgs alignment limit. This highlights the potential of precision studies at future <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> colliders for searching new physics.

Germany

Pia Bredt

Tatsuya Banno

Marius Höfer

Syuhei Iguro

Wolfgang Kilian

Belgium

Yang Ma

Jürgen Reuter

Hantian Zhang

Chasing the Two-Higgs-Doublet Model via Electroweak Corrections at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> Colliders

We investigate the potential of single-spin components of the spin-density matrix in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> process at a future FCC-ee for probing heavy new physics parametrized using the Standard Model effective field theory (SMEFT) framework. We consider the full spectrum of spin observables and the complete angular decomposition of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> production process in our study. We find that single-spin measurements generically provide stronger probes of SMEFT Wilson coefficients than measurements where the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> spins are correlated, and that single-spin observables are important for resolving flat directions that can appear in the Wilson-coefficient parameter space.

Haotian Cao

Frank Petriello

Single-spin measurements and heavy new physics in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> process at an FCC-ee

A fermion can be chiral or vectorlike with respect to a given symmetry, depending on its coupling to the corresponding gauge boson. Vectorlike fermions have a distinct property that their left- and right-handed components behave in the same way under the gauge symmetry. In this paper, we investigate an extension of the standard model with an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><mo stretchy="false">)</mo></math> doublet of vectorlike leptons and two complex scalars. The new physics effects on the lepton anomalous magnetic moment, as well as the electron and muon pair production processes at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> colliders are analyzed. Taking into account the updated measurement results of the electron and muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math>, as well as the Large Electron-Positron Collider and the LHC data, the viable parameter space of the model is identified. We also examine the prospect of testing the model using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></math> signals from electron-position annihilation at the Future Circular Collider (FCC-ee). The analysis shows that the FCC-ee will be able to exclude a significant part of the parameter space, pinpointing exiguous viable regions to be tested in the future due to its high precision.

Vietnam

Sang Quang Dinh

Hieu Minh Tran

Vectorlike lepton imprints at lepton <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math> measurements and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> colliders