We study the next-to-leading order (NLO) electroweak (EW) corrections to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> process in a Pb-Pb ultraperipheral collision (UPC). We find that the EW correction <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>δ</mi><msub><mi>σ</mi><mi>EW</mi></msub></math> decreases the total cross section <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>σ</mi></mrow><mrow><mi>NLO</mi></mrow></msub><mo>=</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>LO</mi></mrow></msub><mo>+</mo><mi>δ</mi><msub><mrow><mi>σ</mi></mrow><mrow><mi>EW</mi></mrow></msub></mrow></math> by <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>−</mo><mn>3</mn><mo>%</mo></mrow></math> at Pb-Pb center-of-mass energy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>5.02</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. The weak correction plays a significant role whose contribution is about–4 times that of QED. The CMS and ATLAS Collaborations use the reaction <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math> in Pb-Pb and proton-proton UPCs to constrain tau’s anomalous magnetic moment <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mi>τ</mi></msub></math>. By parametrizing the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>τ</mi><mi>τ</mi></math> vertex with two form factors <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>F</mi><mrow><mn>1</mn><mo>,</mo><mn>2</mn></mrow></msub></math>, the cross section can be written as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>σ</mi><msub><mi>a</mi><mi>τ</mi></msub></msub><mo>=</mo><msub><mi>σ</mi><mi>LO</mi></msub><mo>+</mo><mi>δ</mi><msub><mi>σ</mi><msub><mi>a</mi><mi>τ</mi></msub></msub></math>, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>δ</mi><msub><mi>σ</mi><msub><mi>a</mi><mi>τ</mi></msub></msub></math> is proportional to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mi>τ</mi></msub></math>. The impact of NLO EW corrections on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mi>τ</mi></msub></math> bounds in a Pb-Pb UPC is limited, as the current experimental bounds are loose. We also find that various differential distributions of the two ratios <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">d</mi><msub><mi>σ</mi><mi>NLO</mi></msub><mo>/</mo><mi mathvariant="normal">d</mi><msub><mi>σ</mi><mi>LO</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">d</mi><msub><mi>σ</mi><msub><mi>a</mi><mi>τ</mi></msub></msub><mo>/</mo><mi mathvariant="normal">d</mi><msub><mi>σ</mi><mi>LO</mi></msub></math> have different line shapes. This work is significant to precisely study the interaction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>τ</mi><mi>τ</mi></math> via the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>γ</mi><mo stretchy="false">→</mo><msup><mi>τ</mi><mo>+</mo></msup><msup><mi>τ</mi><mo>−</mo></msup></math> process.

China

Jun Jiang

Peng-Cheng Lu

Zong-Guo Si

Han Zhang

Xin-Yi Zhang

NLO EW corrections to tau pair production via photon fusion in Pb-Pb ultraperipheral collisions

The dineutron as a bound chargeless nucleus of two identical nucleons has been attracting attention for many decades. In addition to the study of the formation of a bound dineutron in the outgoing channel of specific nuclear reactions, cross-section estimates have been gaining interest as research targets. We used a traditional neutron activation technique to irradiate Lu samples followed by measurements of the induced activity with HPGe spectrometer in order to detect gamma-peaks of the 175Lu ( <italic>n</italic>, 2 <italic>n</italic>) 174 gLu reaction product when this reaction channel is not open for incident neutron energies. Based on two measurements of the instrumental gamma-ray spectra of Lu samples we reliably identified the presence of the 174 gLu isotope in the outgoing channel of the 175Lu ( <italic>n</italic>, 2 <italic>n</italic>) 174 gLu nuclear reaction. Also, the cross-section for this nuclear reaction was obtained and to be equal <math altimg='si1.svg'><mrow><mn>33</mn><mo>.</mo><msubsup><mn>5</mn><mrow><mo>&#8722;</mo><mn>6.7</mn></mrow><mrow><mo>+</mo><mn>7.0</mn></mrow></msubsup></mrow></math> mb. For the first time, the dineutron as a nuclearreaction product was indirectly detected via statistically significant observation of the induced activity of 174 gLu with a corresponding cross-section estimate.

Ukraine

Ihor Kadenko

Hungary

Barna Biró

Mihály Braun

András Fenyvesi

Kateryna Okopna

Nadiia Sakhno

Loránd Zakàny

Formation of bound dineutrons in the 175Lu ( <italic>n</italic>, 2 <italic>n</italic>) 174 gLu nuclear reaction and its cross-section

We revisit the proton emitter $^{149}$Lu utilizing the recently developed triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc). By incorporating the microscopic nuclear structure properties from the TRHBc theory into the WKB approximation, we successfully reproduce the measured proton-emission half-life of $^{149}$Lu within experimental uncertainties. A triaxial ground state characterized by (<math><mi>β</mi><mo>=</mo><mn>0.17</mn><mo>,</mo><mi>γ</mi><mo>=</mo><msup><mrow><mn>31</mn></mrow><mrow><mo>∘</mo></mrow></msup></math>) has been clarified for $^{149}$Lu. The inclusion of triaxiality significantly changes nuclear density distributions and potentials, which results in enhanced binding of both the nuclear system and the proton-emitting orbital. As a result, a slightly extended half-life for the proton emission of $^{149}$Lu is achieved after considering triaxial deformation degrees of freedom. The examination of the dependence of the decay width on triaxial deformation parameters highlights the significance of microscopic description of nuclear deformation beyond the proton dripline.

Qi Lu

Kai-Yuan Zhang

Shi-Sheng Zhang

Triaxial shape of the one-proton emitter Lu

One-proton radioactivity in $^{149}$Lu, the latest identified proton emitter, is studied in the Wentzel-Kramers-Brillouin (WKB) approach with the proton-nucleus potential extracted from the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) for the first time. The predicted half-life turns out to be consistent with the experimental measurement within uncertainties and (almost) independent of the density functionals in the DRHBc theory. Such a microscopic self-consistent calculation reveals that $^{149}$Lu is oblately deformed with a quadrupole deformation <math><msub><mrow><mi>β</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>≈</mo><mo>−</mo><mn>0.18</mn></math>, and rules out the possibility of a prolate quadrupole deformation suggested in the nonadiabatic quasiparticle model. We also check the validity of this approach in the description of $^{150,151}$Lu and their isomeric states. The deviations of the predicted half-lives from their experimental counterparts are mostly smaller than those of the theoretical studies without considering deformation effects. Furthermore, we predict $^{148}$Lu to be a more oblately deformed proton-emitter with a longer half-life than that of $^{149}$Lu, which can be checked in the future. Our studies show that the DRHBc + WKB approach provides a new alternative method to evaluate the half-lives of well-deformed proton emitters.

Yang Xiao

Si-Zhe Xu

Ru-You Zheng

Germany

Xiang-Xiang Sun

Li-Sheng Geng

One-proton emission from Lu in the DRHBc+WKB approach

We consider, at order <math> <msubsup> <mi>α</mi> <mi>s</mi> <mn>2</mn> </msubsup> </math> $$ {\alpha}_s^2 $$ in the QCD coupling, top-quark pair production in the continuum at various center-of-mass energies and b-quark pair production at the Z resonance by (un)polarized electron and positron beams. For top quarks we compute the forward-backward asymmetry with respect to the top-quark direction of flight, the associated polar angle distribution, and we analyze the effect of beam polarization on the QCD corrections to the leading-order asymmetry. We calculate also the polarized forward-backward asymmetry. For b-quark production at the Z peak we explore different definitions of A FB. In particular, we analyze b jets defined by the Durham and the flavor-k T clustering algorithms. We compute the inclusive b-jet and two-jet asymmetry with respect to the b-jet direction. For the latter asymmetry the QCD corrections to order <math> <msubsup> <mi>α</mi> <mi>s</mi> <mn>2</mn> </msubsup> </math> $$ {\alpha}_s^2 $$ are small. That predestines it to act as a precision observable.

Werner Bernreuther

Long Chen

Top and bottom quark forward-backward asymmetries at next-to-next-to-leading order QCD in (un)polarized electron positron collisions

A nonzero neutrino mass may be a sign of new physics beyond the standard model (SM). To explain the small neutrino mass, we can extend the SM using right-handed Majorana neutrinos in a low-scale seesaw mechanism, and the CP violation effect can be induced due to the CP phase in the interference of heavy Majorana neutrinos. The existence of heavy Majorana neutrinos may lead to lepton number violation processes, which can be used to search for the signals of heavy Majorana neutrinos. In this paper, we focus on the CP violation effect related to two generations of heavy Majorana neutrinos at   $ 15 $   GeV   $ 15 $   GeV in the pair production of W bosons and rare decays. It is valuable to investigate Majorana neutrino production signals and the related CP violation effects in rare W boson decays at future lepton colliders.

Zhe Wang

Xing-Hua Yang

Search for heavy Majorana neutrinos at future lepton colliders  

Heavy Majorana neutrinos beyond the standard model can simultaneously explain the origin of tiny neutrino masses and matter-antimatter asymmetry in our Universe. The existence of heavy Majorana neutrinos will also lead to lepton number violation and confirm the possibility of rare lepton-number-violating W decays. With contributions from two different Majorana neutrinos, nonzero CP asymmetry may be generated from the rate difference between W decay and its CP-conjugate process. The aim of this study is to investigate the prospects of measuring CP violation in rare W decays via Majorana neutrinos at the LHC. Our calculations show that the induced CP asymmetry is independent of the Majorana neutrino mass for   $ 15 &lt; {m}_{N}^{} &lt; 70\; {{\rm{GeV}}} $  . Such a CP asymmetry, if observed, would in turn provide unambiguous evidence of new physics beyond the standard model.

Measuring Violation in Rare decays at the LHC  

Within the nonrelativistic quantum chromodynamics framework, we make a comprehensive study of the exclusive production of excited charmonium and bottomonium in <math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>γ</mi></mrow><mrow><mo>*</mo></mrow></msup><mo>/</mo><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>→</mo><mo>|</mo><mo>(</mo><mi>Q</mi><mover><mrow><mi>Q</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>)</mo><mo>[</mo><mi>n</mi><mo>]</mo><mo>⟩</mo><mo>+</mo><mi>γ</mi></mrow></math> (<math><mi>Q</mi><mo>=</mo><mi>c</mi></math> or <math><mi>b</mi></math> quarks) at a future <math><mi>Z</mi></math> factory, where the [<math><mi>n</mi></math>] represents the color-singlet <math><mrow><mi>n</mi><msub><mrow><mmultiscripts><mrow><mi>S</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>1</mn></mrow></mmultiscripts></mrow><mrow><mn>0</mn></mrow></msub></mrow></math>, <math><mrow><mi>n</mi><msub><mrow><mmultiscripts><mrow><mi>S</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>3</mn></mrow></mmultiscripts></mrow><mrow><mn>1</mn></mrow></msub></mrow></math>, <math><mrow><mi>n</mi><msub><mrow><mmultiscripts><mrow><mi>P</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>1</mn></mrow></mmultiscripts></mrow><mrow><mn>0</mn></mrow></msub></mrow></math>, and <math><mi>n</mi><msub><mrow><mmultiscripts><mrow><mi>P</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>3</mn></mrow></mmultiscripts></mrow><mrow><mi>J</mi></mrow></msub></math> (<math><mrow><mi>n</mi><mo>=</mo><mn>1</mn></mrow></math>, 2, 3, 4; <math><mrow><mi>J</mi><mo>=</mo><mn>0</mn></mrow></math>, 1, 2) Fock states. The “improved trace technology” is adopted to derive the analytic expressions at the amplitude level, which is useful for calculating the complicated <math><mi>n</mi><mi>P</mi></math>-wave channels. Total cross sections, differential distributions, and uncertainties are discussed in system. According to our study, production rates of heavy quarkonia of high excited Fock states are considerable at a future <math><mi>Z</mi></math> factory. The cross sections of charmonium for <math><mn>2</mn><mi>S</mi></math>-, <math><mn>3</mn><mi>S</mi></math>-, <math><mn>4</mn><mi>S</mi></math>-, <math><mn>1</mn><mi>P</mi></math>-, <math><mn>2</mn><mi>P</mi></math>-, <math><mn>3</mn><mi>P</mi></math>-, and <math><mn>4</mn><mi>P</mi></math>-wave states are about 53.5%, 30.4%, 23.7%, 13.7%, 6.8%, 9.2%, and 9.2% of that of the <math><mn>1</mn><mi>S</mi></math> state, respectively. And cross sections of bottomonium for <math><mn>2</mn><mi>S</mi></math>-, <math><mn>3</mn><mi>S</mi></math>-, <math><mn>4</mn><mi>S</mi></math>-, <math><mn>1</mn><mi>P</mi></math>-, <math><mn>2</mn><mi>P</mi></math>-, <math><mn>3</mn><mi>P</mi></math>-, and <math><mn>4</mn><mi>P</mi></math>-wave states are about 39.3%, 12.3%, 14.3%, 7.1%, 3.1%, 2.7%, and 3.1% of that of the <math><mn>1</mn><mi>S</mi></math> state, respectively. The main uncertainties come from the radial wave functions at the origin and their derivatives at the origin under different potential models. Then, this super <math><mi>Z</mi></math> factory should be a good platform to study the properties of the high excited charmonium and bottomonium states.

Qi-Li Liao

Gu Chen

Production of excited heavy quarkonia in <math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msup><mrow><mi>γ</mi></mrow><mrow><mo>*</mo></mrow></msup><mo>/</mo><msup><mrow><mi>Z</mi></mrow><mrow><mn>0</mn></mrow></msup><mo>→</mo><mo>|</mo><mo>(</mo><mi>Q</mi><mover><mrow><mi>Q</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>)</mo><mo>[</mo><mi>n</mi><mo>]</mo><mo>⟩</mo><mo>+</mo><mi>γ</mi></mrow></math> at super <math><mi>Z</mi></math> factory

The tiny neutrino masses can be explained naturally by extending the standard model with right-handed Majorana neutrinos in a low-scale seesaw mechanism, and the <math><mi>C</mi><mi>P</mi></math> violation effect induced by the Majorana phase is interesting and worth studying at colliders. In this paper, we investigate the prospects for measuring <math><mi>C</mi><mi>P</mi></math> violation in top quark pair production and rare decay via Majorana neutrinos at the LHC. The <math><mi>C</mi><mi>P</mi></math> asymmetry stems from the significant interference of contributions from two different Majorana neutrinos and can be appreciable when the two neutrino masses are nearly degenerate. It is found that in the Majorana neutrino mass range of <math><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>&lt;</mo><msub><mi>m</mi><mi>N</mi></msub><mo>&lt;</mo><mn>80</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, the <math><mi>C</mi><mi>P</mi></math> asymmetry is independent of the Majorana neutrino mass at the LHC. Any possible new observation of <math><mi>C</mi><mi>P</mi></math> violation will be the clear evidence of new physics beyond the standard model.

<math><mi>C</mi><mi>P</mi></math> violation in top quark decay via heavy Majorana neutrinos at the LHC

We study the decay of the SM Higgs boson to a massive charm quark pair at the next-to-next-to-leading order QCD and next-to-leading order electroweak. At the second order of QCD coupling, we consider the exact calculation of flavour-singlet contributions where the Higgs boson couples to the internal top and bottom quark. Helpful information on the running mass effects related to Yukawa coupling may be obtained by analyzing this process. High precision production for   $ h\to c\bar{c}$   within the SM makes it possible to search for new physics that may induce relatively large interactions related to the charm quark. As an example, we evaluate the axion-like particle associate production with a charm quark pair in the Higgs decay and obtain some constraints for the corresponding parameters under some assumptions.

Shi-Yuan Li

Zhen-Yang Li

Precise evaluation of And Axion-like Particle Production  