The possible anomalous New Physics contributions to dipole and weak dipole moments of the tau lepton bring renewed interest in development and revisiting charge-parity violating signatures in tau-pair production in Z-boson decay at energies of the LHC. In this paper, we discuss effects of anomalous contributions to polarisation and spin correlations in the q & strns;q - tau+tau- production processes, with tau decays included. Due to the complex nature of the resulting distributions, Monte Carlo techniques are useful, in particular for event reweighing with studied New Physics phenomena. Extensions of the Standard Model spin amplitudes, within the Improved Born Approximation used for the matrix element, are implemented in the TauSpinner program. This is mainly with tau dipole and weak dipole moments in mind, but is applicable to arbitrary New Physics interactions, provided they can be encapsulated into the Standard Model 2 - 2 structure of matrix element extensions. The implementation allows one also to introduce an arbitrary phase-shift between vector and axial-vector couplings of Z boson to tau leptons, which would have impact on the observed transverse spin correlations. Basic formulas and algorithm principles are presented, together with distributions for the spin-correlation matrix. Numerical examples of impact decays. Information on how to use and configure the TauSpinner program is given in Appendix B.

The spin correlations in the pair of τ leptons produced in high-energy proton-proton collisions are studied. The invariant mass of the τ-lepton pair is chosen close to the Z-boson mass; in these conditions, Z-boson exchange gives the dominant contribution to the Drell-Yan mechanism. The interaction of Z bosons with τ leptons, in addition to the Standard Model couplings, can include weak anomalous magnetic and electric dipole moments (or form factors) of the τ lepton. The dependence of elements of the pp spin-correlation matrix on the weak anomalous moments is determined for various regions of the rapidity of the τ-lepton pair. Based on this calculation, we construct a semirealistic observable built on the momenta of pions in the τ∓→π∓ντ and τ±→ρ±ντ→π±π0ντ decay channels, and we show that this observable can be sensitive to the weak anomalous dipole moments. Published by the American Physical Society 2025

The possible anomalous New Physics contributions to dipole and weak dipole moments of the τ lepton bring renewed interest in development and revisiting charge-parity violating signatures in τ-pair production in Z-boson decay at energies of the LHC. In this paper, we discuss effects of anomalous contributions to polarisation and spin correlations in the q̅ q → τ^+ τ^- production processes, with τ decays included. Because of the complex nature of the resulting distributions, Monte Carlo techniques are useful, in particular of event reweighing with studied New Physics phenomena. Extensions of the Standard Model spin amplitudes, within Improved Born Approximation used for matrix element, are implemented in the TauSpinner program. This is mainly with τ dipole and weak dipole moments in mind, but is applicable to arbitrary New Physics interactions, provided they can be encapsulated into the Standard Model 2 → 2 structure of matrix element extensions. Implementation allows one also to introduce arbitrary phase-shift between vector and axial-vector couplings of Z boson to τ leptons, which would have impact on observed transverse spin correlations. Basic formulas and algorithm principles are presented, together with distributions for spin correlation matrix. Numerical examples of impact on experimental signatures are shown in case of τ^±→ ρ^± ν_τ→ π^± π^0 ν_τ decays. Information on how to use and configure the TauSpinner program is given in Appendix.

The possible anomalous New Physics contributions to the electric and magnetic dipole moments of the \(\tau \) lepton have brought renewed interest in development of new charge-parity violating signatures in the \(\tau \)-pair production at Belle II energies, and also at higher energies of the LHC and the FCC. In this paper, we discuss the effects of anomalous contributions to the cross section and spin correlations in the \(\gamma \gamma \to \tau ^-\tau ^+\) production processes, with \(\tau \) decays included. Such processes have been observed in the \(pp\) and PbPb collisions at CERN LHC experiments. Due to the complex nature of the resulting distributions, Monte Carlo techniques are useful, in particular for event reweighting with studied New Physics phenomena. For the \(\gamma \gamma \) processes, extensions of the Standard Model amplitudes are implemented in the TauSpinner program. This is mainly with the electric and magnetic dipole moments in mind, however the algorithm can easily be extended to other New Physics interactions, provided they can be encapsulated into the similar form-factors in the Standard Model structure of matrix elements. Basic formulas and algorithm principles are presented, and numerical examples are provided for illustration. Information on how to use the program is given in Appendix of the paper. Published by the Jagiellonian University2025authors

The possible anomalous New Physics contributions to the electric and magnetic dipole moments of the tau lepton have brought renewed interest in development of new charge-parity violating signatures in the tau-pair production at Belle II energies, and also at higher energies of the LHC and the FCC. In this paper, we discuss the effects of anomalous contributions to the cross section and spin correlations in the gamma gamma -> tau-tau+ production processes, with tau decays included. Such processes have been observed in the pp and PbPb collisions at CERN LHC experiments. Due to the complex nature of the resulting distributions, Monte Carlo techniques are useful, in particular for event reweighting with studied New Physics phenomena. For the gamma gamma processes, extensions of the Standard Model amplitudes are implemented in the TauSpinner program. This is mainly with the electric and magnetic dipole moments in mind, however the algorithm can easily be extended to other New Physics interactions, provided they can be encapsulated into the similar form-factors in the Standard Model structure of matrix elements. Basic formulas and algorithm principles are presented, and numerical examples are provided for illustration. Information on how to use the program is given in Appendix of the paper.

The consecutive steps of H to tau tau cascade can be useful for the measurement of Higgs couplings and parity. The analysis methos of ATLAS and CMS Collaborations was to fit a one-dimensional distribution of the phi* angle, phi*, which is sensitive to transverse spin correlations and, hence, to the CP mixing angle, phi^CP. Machine Learning techniques (ML) offer opportunities to manage complex multidimensional signatures. The 4-momenta of the tau decay products can be used as input to the machine learning and to predict the CP-sensitive pseudo-observables and/or provide discrimination between different CP hypotheses. We show that the classification or regression methods can be used to train an ML model to predict the spin weight sensitive to the CP state of the decaying Higgs boson, parameters of the functional form of the spin weight, or the most preferred CP mixing angle of the analysed sample. The one-dimensional distribution of the predicted spin weight or the most preferred CP mixing angle of the experimental data can be examined further, with the statistical methods, to derive the measurement of the CP mixing state of the Higgs signal events. This paper extends our previous studies, with more details for the features and how proposed pseudo-observables can be used in the measurement.

Anomalous contributions to the electric and magnetic dipole moments of the $\tau$ lepton from new physics scenarios have brought renewed interest in the development of new charge-parity violating signatures in $\tau$ pair production at Belle II energies, and also at higher energies of the Large Hadron Collider and the Future Circular Collider. In this paper, we discuss the effects of spin correlations, including transverse degrees of freedom, in the $\tau$ pair production and decay. These studies include calculating analytical formulas, obtaining numerical results, and building semi-realistic observables sensitive to the transverse spin correlations induced by the dipole moments of the $\tau$ lepton. The effects of such anomalous contributions to the dipole moments are introduced on top of precision simulations of $e^-e^+ \to \tau^-\tau^+$, $q\bar{q} \to \tau^-\tau^+$ and $\gamma\gamma \to \tau^-\tau^+$ processes, involving multi-body final states. Respective extensions of the Standard Model amplitudes and the reweighting algorithms are implemented into the {\tt KKMC} Monte Carlo, which is used to simulate $\tau$ pair production in $e^-e^+$ collisions, and the {\tt TauSpinner} program, which is used to reweight events with $\tau$ pair produced in $pp$ collisions.

A bstract A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35 . 6 fb −1 collected at $$ \sqrt{s}=13 $$ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕ γ and ρ γ of 4 . 8 × 10 −4 and 8 . 8 × 10 −4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0 . 9 × 10 −6 and 25 × 10 −6 for ϕ γ and ρ γ, respectively.

A search for leptoquarks decaying into the bτ final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1 at √(s) = 13 TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95

Matching and comparing the measurements of past and future experiments call for consistency checks of electroweak (EW) calculations used for their interpretation. On the other hand, new calculation schemes of the field theory can be beneficial for precision, even if they may obscure comparisons with earlier results. Over the years, concepts of Improved Born, Effective Born, as well as of effective couplings, in particular of $$\sin ^2\theta _W^{{\textit{eff}}}$$ mixing angle for EW interactions, have evolved. In our discussion, we use four versions of DIZET EW library for phenomenology of practically all HEP accelerator experiments over the last 30 years. We rely on the codes published and archived with the KKMC Monte Carlo program for $$e^+e^- \rightarrow f {\bar{f}} n(\gamma )$$ and available for the TauSpinner as well. TauSpinner re-weighs generated events for introduction of EW effects. To this end, DIZET is first invoked, and its results are stored in data file and later used. Documentation of TauSpinner upgrade, to version 2.1.0, and that of its new arrangement for semi-automated benchmark plots are provided. In our paper, focus is placed on the numerical results, on the different approximations introduced in Improved Born to obtain Effective Born, which is simpler for applications of strong or QED processes in pp or $$e^+e^-$$ colliders. The $$\tau $$ lepton polarization $$P_{\tau }$$ , forward–backward asymmetry $$A_{{\textit{FB}}}$$ and parton-level total cross section $$\sigma ^{{\textit{tot}}}$$ are used to monitor the size of EW effects and effective $$\sin ^2\theta _W^{{\textit{eff}}}$$ picture limitations for precision physics. Collected results include: (i) Effective Born approximations and $$\sin ^2\theta _W^{{\textit{eff}}}$$ , (ii) differences between versions of EW libraries and (iii) parametric uncertainties due to, for example, $$m_t$$ or $$\Delta \alpha _h^{(5)}(s)$$ . These results can be considered as benchmarks and also allow to evaluate the adequacy of Effective Born with respect to Improved Born. Definitions are addressed too.

The consecutive steps of cascade decay initiated by H to tau tau can be useful for the measurement of Higgs couplings and in particular of the Higgs boson parity. In the previous papers we have found, that multi-dimensional signatures of the tau^pm to pi^pm pi^0 nu and tau^pm to 3pi^pm nu decays can be used to distinguish between scalar and pseudoscalar Higgs state. The Machine Learning techniques (ML) of binary classification, offered break-through opportunities to manage such complex multidimensional signatures. The classification between two possible CP states: scalar and pseudoscalar, is now extended to the measurement of the hypothetical mixing angle of Higgs boson parity states. The functional dependence of H to tau tau matrix element on the mixing angle is predicted by theory. The potential to determine preferred mixing angle of the Higgs boson events sample including $\tau$-decays is studied using Deep Neural Network. The problem is adressed as classification or regression with the aim to determine the per-event: a) probability distribution (spin weight) of the mixing angle; b) parameters of the functional form of the spin weight; c) the most preferred mixing angle. Performance of methods are evaluated and compared. Numerical results are collected.

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.

The first measurement of longitudinal decorrelations of harmonic flow amplitudes v_{n} for n=2-4 in Xe+Xe collisions at sqrt[s_{NN}]=5.44  TeV is obtained using 3  μb^{-1} of data with the ATLAS detector at the LHC. The decorrelation signal for v_{3} and v_{4} is found to be nearly independent of collision centrality and transverse momentum (p_{T}) requirements on final-state particles, but for v_{2} a strong centrality and p_{T} dependence is seen. When compared with the results from Pb+Pb collisions at sqrt[s_{NN}]=5.02  TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v_{2}, but smaller for v_{3}. Current hydrodynamic models reproduce the ratios of the v_{n} measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions.

Results on $\phi$ meson production in inelastic p+p collisions at CERN SPS energies are presented. They are derived from data collected by the NA61/SHINE fixed target experiment, by means of invariant mass spectra fits in the $\phi \to K^+K^-$ decay channel. They include the first ever measured double differential spectra of $\phi$ mesons as a function of rapidity $y$ and transverse momentum $p_T$ for proton beam momenta of 80 GeV/c and 158 GeV/c, as well as single differential spectra of $y$ or $p_T$ for beam momentum of 40 GeV/c. The corresponding total $\phi$ yields per inelastic p+p event are obtained. These results are compared with existing data on $\phi$ meson production in p+p collisions. The comparison shows consistency but superior accuracy of the present measurements. The emission of $\phi$ mesons in p+p reactions is confronted with that occurring in Pb+Pb collisions, and the experimental results are compared with model predictions. It appears that none of the considered models can properly describe all the experimental observables.

The NA61/SHINE experiment at the CERN SPS is performing a uniqe study of the phase diagram of strongly interacting matter by varying collision energy and nuclear mass number of colliding nuclei. In central Pb+Pb collisions the NA49 experiment found structures in the energy dependence of several observables in the CERN SPS energy range that had been predicted for the transition to a deconfined phase. New measurements of NA61/SHINE find intriguing similarities in p+p interactions for which no deconfinement transition is expected at SPS energies. Possible implications will be discussed.

Matching and comparing measurements of past and future experiments calls for consistency checks of calculations used for their interpretation. New schemes of the field theory may optimize precision, but obscure comparisons with earlier results. Over years concepts of Improved Born, Effective Born, effective couplings, and sin^2theta_W^eff mixing angle for electroweak interactions, have evolved. We use four DIZET electroweak library versions; of today and of the last 30 years, wich were used for phenomenology of practically all HEP accelerator experiments. Versions differ by incremented with time updates of corrections. We rely on the codes archived with the KKMC Monte Carlo program for e^+e^- to f bar f n(gamma). Versions became recently available for the TauSpinner reweighting of simulated and stored events. Documentation of TauSpinner upgrade, to version 2.1.0, and of its arrangement for semi-automated electroweak (EW) effects benchmark plots are provided. Details which can be used to complete simulated sample with EW effects, are given. Focus is placed on numerical results and on approximations introduced in Improved Born to obtain Effective Born, to match with QCD corrections. The tau lepton polarization P_tau, forward backward asymmetry A_FB and parton level cross section sigma^tot are used to monitor electroweak effects and effective sin^2theta_W^eff limitations. Results include: (i) feasibility of Effective Born approximation and sin^2theta_W^eff, (ii) differences between versions of electroweak libraries and (iii) parametric ambiguities due to e.g. m_t or Delta alpha_h^(5)(s). Example results allow to evaluate adequacy of Effective Born with respect to Improved Born.

The measurement of $$K^{*}(892)^0$$ resonance production via its $$K^{+}\pi ^{-}$$ decay mode in inelastic p+p collisions at beam momentum 158 $$\text{ Ge }\text{ V }\!/\!c$$ ($$\sqrt{s_{NN}}=17.3$$ $$\text{ Ge }\text{ V }$$) is presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the $$K^{*}(892)^0$$ signal and double-differential transverse momentum and rapidity spectra were obtained. The full phase-space mean multiplicity of $$K^{*}(892)^0$$ mesons was found to be $$(78.44 \pm 0.38 \mathrm {(stat)} \pm 6.0 \mathrm {(sys)) \cdot 10^{-3}}$$. The NA61/SHINEresults are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data from p+p and nucleus–nucleus collisions.

Abstract The measurement of $$K^{*}(892)^0$$ K∗(892)0 resonance production via its $$K^{+}\pi ^{-}$$ K+π- decay mode in inelastic p+p collisions at beam momentum 158 $$\text{ Ge }\text{ V }\!/\!c$$ GeV/c ($$\sqrt{s_{NN}}=17.3$$ sNN=17.3 $$\text{ Ge }\text{ V }$$ GeV ) is presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the $$K^{*}(892)^0$$ K∗(892)0 signal and double-differential transverse momentum and rapidity spectra were obtained. The full phase-space mean multiplicity of $$K^{*}(892)^0$$ K∗(892)0 mesons was found to be $$(78.44 \pm 0.38 \mathrm {(stat)} \pm 6.0 \mathrm {(sys)) \cdot 10^{-3}}$$ (78.44±0.38(stat)±6.0(sys))·10-3 . The NA61/SHINEresults are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data from p+p and nucleus–nucleus collisions.

The measurement of K^*(892)^0 resonance production via its K^+π ^- decay mode in inelastic p+p collisions at beam momentum 158 Ge V /c ( √(s_NN)=17.3 Ge V ) is presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the K^*(892)^0 signal and double-differential transverse momentum and rapidity spectra were obtained. The full phase-space mean multiplicity of K^*(892)^0 mesons was found to be (78.44 ± 0.38 (stat)± 6.0 (sys)) · 10^-3 . The NA61/SHINEresults are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data from p+p and nucleus–nucleus collisions.