arXiv subjects

Andrzej Kupsc

Publications and source records attributed to Andrzej Kupsc.

15 recordsLinked to original sources

arXiv2026

Hyperon non-leptonic decays in relativistic Chiral Perturbation Theory with resonances

Motivated by recent experimental advances in the corresponding measurements, non-leptonic hyperon decays are calculated, for the first time in a relativistic manner, in Chiral Perturbation Theory at next-to-leading order (NLO). On the one hand, relativistic loop corrections are computed explicitly based on the ground-state octet and decuplet fields. On the other hand, the NLO weak-transition low-energy constants are estimated by resonance saturation, inspired by the non-relativistic tree-level computation of Ref. [1]. In particular, the $1/2^-$ and the (excited) $1/2^+$ resonance octets are utilized. The remaining unknown parameters are fitted to the decay amplitudes. A good combined fit to both $s$- and $p$-wave amplitudes is achieved with the caveat of not being very tightly constrained. The role of the resonances is found to be crucial. Consequences for further investigations and open questions are addressed.

hep-ph↗

arXiv2025

CP violation studies at Super Tau-Charm Facility

Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($τ$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $τ$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.

hep-ex↗

arXiv2025

Tests of CP symmetry in entangled hyperon anti-hyperon pairs at BESIII

Decays of charmonium into hyperon and antihyperon pairs provide a pristine laboratory for exploring hyperon properties, such as their polarization and decay parameters, and for conducting tests of fundamental symmetries. This brief review highlights the significant progress made in precise tests of CP symmetry at BESIII using entangled hyperon-antihyperon pairs, including $Λ\barΛ$, $Σ\barΣ$, $Ξ\barΞ$ and $Λ\barΣ$, selected from the high statistics of $J/ψ$ and $ψ(3686)$ events produced in $e^+e^-$ annihilations. These recent findings have sparked renewed interest in both theoretical and experimental aspects of hyperon physics, but there is still much room for improvement to reach the Standard Model expectations. To address this challenge, the prospects for future investigations on CP asymmetry at next-generation experiments are discussed.

hep-ex↗

arXiv2025

How to determine nucleon polarization at existing collider experiments?

We propose a novel approach to measure spin polarization of nucleons produced in electron--positron collisions. Using existing tracking devices and supporting structure material, general-purpose spectrometers can be utilized as a large-acceptance polarimeter without hardware upgrade. With the proposed approach, the spin polarization of nucleons can be revealed, providing a complementary and accurate description of the final-state particles. This could have far-reaching implications, such as enabling the complete determination of the time-like electromagnetic form factors of nucleons.

hep-ph↗

arXiv2023

Semileptonic decays of spin-entangled baryon-antibaryon pairs

A modular representation for the semileptonic decays of baryons originating from spin polarized and correlated baryon-antibaryon pairs is derived. The complete spin information of the decaying baryon is propagated to the daughter baryon via a real-valued matrix. It allows to obtain joint differential distributions in sequential processes involving the semileptonic decay in a straightforward way. The formalism is suitable for extraction of the semileptonic formfactors in experiments where strange-baryon-antibaryon pairs are produced in electron-positron annihilation or in charmonia decays. We give examples such as the complete angular distributions in the $e^+e^-\to Λ\barΛ$ process, where $Λ\to pe^-\barν_e$ and $\barΛ\to\bar{p}π^+$. The formalism can also be used to describe the distributions in semileptonic decays of charm and bottom baryons. Using the same principles, the modules to describe electromagnetic and neutral current weak baryon decay processes involving a charged lepton-antilepton pair can be obtained. As an example, we provide the decay matrix for the Dalitz transition between two spin-1/2 baryons.

hep-ph↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2022

First Simultaneous K$^-$p $\rightarrow (Σ^0/Λ) \, π^0$ Cross Sections Measurements at 98 MeV/c

We report the first simultaneous and independent measurements of the K$^{-}$p $\rightarrow Σ^0 \, π^{0}$ and K$^{-}$p $\rightarrow Λ\, π^{0}$ cross sections around 100 MeV/c kaon momentum. The kaon beam delivered by the DA$Φ$NE collider was exploited to detect K$^-$ absorptions on Hydrogen atoms, populating the gas mixture of the KLOE drift chamber. The precision of the measurements ($σ_{K^- p \rightarrow Σ^0 π^0} = 42.8 \pm 1.5 (stat.) ^{+2.4}_{-2.0}(syst.) \ \mathrm{mb}$ and $σ_{K^- p \rightarrow Λπ^0} = 31.0 \pm 0.5 (stat.) ^{+1.2}_{-1.2}(syst.) \ \mathrm{mb}\,$) is the highest yet obtained in the low kaon momentum regime.

nucl-ex↗

arXiv2022

Study of CP violation in hyperon decays at Super Charm-Tau Factories with a polarized electron beam

Non-leptonic two-body weak decays of baryons are an important tool to probe the combined charge-conjugation--parity symmetry (CP) violation. We explain why the decays of strange baryons provide complementary information to the decays of kaons. A model-independent parameterization of the non-leptonic decays of the $Λ$- and $Ξ$-baryons is reviewed, and the amplitudes are updated according to the latest experimental input. We demonstrate the potential of performing precision tests in strange baryon decays at the next generation electron-positron $J/ψ$ factories with luminosity of $10^{35}$ cm$^{-2}$s$^{-1}$. The copious production of spin-entangled hyperon-antihyperon pairs via the $J/ψ$ resonance allows for a direct comparison of the baryon and antibaryon decay properties. Using analytic approximations and numerical calculations, we study the quantitative impact of spin correlations and polarization in such CP tests. We show that by using a longitudinally-polarized electron beam, the statistical precision of the CP tests can be significantly improved compared to the experiments without polarized beams. Furthermore, we map out further directions for possible improvements, like analysis of incompletely reconstructed events or a combination of the isospin related processes. Altogether, these methods are promising for the observation of a statistically significant CP-violation signal with a strength corresponding to the standard model predictions. Our conclusions should encourage more detailed feasibility studies, including optimisation of the measurement methods and studies of systematic effects. Finally, our results call for an update of the theory predictions with increased precision.

hep-ph↗

arXiv2021

What can we learn about light-meson interactions at electron-positron colliders?

Precision studies at electron-positron colliders with center-of-mass energies in the charm-tau region and below have strongly contributed to our understanding of light-meson interactions at low energies. We focus on the processes involving two or three light mesons with invariant masses below nucleon-antinucleon threshold. A prominent role is given to the interactions of the nine lightest pseudoscalar mesons (pions, kaons, $η$, and $η'$) and the two narrow neutral isoscalar vector mesons $ω$ and $ϕ$. Experimental methods used to produce the mesons are reviewed as well as theory tools to extract properties of the meson-meson interactions. Examples of recent results from the DA$Φ$NE, BEPCII, and VEPP-2000 colliders are presented. In the outlook we briefly discuss prospects for further studies at future super-charm-tau factories.

hep-ph↗

arXiv2019

CP symmetry tests in the cascade-anticascade decay of charmonium

We analyze joint angular distributions of a charmonium decay to the $Ξ\barΞ$ pair using the $Ξ\toΛπ\to pπ^-π$ weak decay chain for the cascade and the charge conjugated mode for the anticascade. The decays allow a direct comparison of the baryon and antibaryon decay properties and a sensitive test of CP symmetry in the strange baryon sector. We show that all involved decay parameters can be determined separately in vector and (pseudo)scalar charmonia decays into $Ξ\barΞ$ due to the spin correlations between the weak decay chains. Contrary to the recently measured $e^+e^-\to J/ψ\to Λ\barΛ$ process, the transverse polarization of the cascade is not needed and has almost no impact on the uncertainties of the decay parameters.

hep-ph↗

arXiv2018

An overview of $η$ and $η^{\prime}$ decays at BESIII

The world's largest sample of 1.31 billion $J/ψ$ events accumulated at the BESIII detector, provides a unique opportunity to investigate $η$ and $η^\prime$ physics via two body $J/ψ$ radiative or hadronic decays. For many $η^\prime$ decay channels the low background data samples are up to three orders of magnitude larger than collected in any previous experiment. Here we review the most significant results on $η$ and $η^\prime$ obtained at BESIII so far. The analyses range from detailed studies of the common decays dynamics, observations of new radiative and Dalitz decays, and search for rare/forbidden decays with sensitivity up to $\cal{B}\sim 10^{-5}$. Finally, prospects of the forthcoming runs at $J/ψ$ peak for the $η$ and $η^\prime$ physics are discussed.

hep-ex↗

arXiv2017

Hadronic structure functions in the $e^+ e^- \rightarrow \barΛ Λ$ reaction

Cross-section distributions are calculated for the reaction $e^+ e^- \rightarrow J/ψ\rightarrow \barΛ(\rightarrow \bar{p}π^+) Λ(\rightarrow pπ^-)$, and related annihilation reactions mediated by vector mesons. The hyperon-decay distributions depend on a number of structure functions that are bilinear in the, possibly complex, psionic form factors $G_M^ψ$ and $G_E^ψ$ of the Lambda hyperon. The relative size and relative phase of these form factors can be uniquely determined from the unpolarized joint-decay distributions of the Lambda and anti-Lambda hyperons. Also the decay-asymmetry parameters of Lambda and anti-Lambda hyperons can be determined.

hep-ph↗

arXiv2014

Reaction pp -> pp πππas a background for hadronic decays of the eta-prime meson

Isospin violating hadronic decays of the ηand η' mesons into 3πmesons are driven by a term in the QCD Lagrangian proportional to the mass difference of the d and u quarks. The source giving large yield of the mesons for such decay studies are pp interactions close to the respective kinematical thresholds. The most important physics background for η,η'\toπππis coming from direct three pion production reactions. In case of the ηmeson the background for the decays is relatively low (approx 10%). The purpose of this article is to provide an estimate of the direct pion production background for the η'\to 3πdecays. Using the inclusive data from COSY-11 experiment we have extracted differential cross section for the pp\to pp-multipion production reactions with the invariant mass of the pions equal to the η' meson mass and estimated an upper limit for the signal to background ratio for studies of the η'\toπ^+π^-π^0 decay.

hep-ex↗

arXiv2011

Tests of the fundamental symmetries in eta meson decays

Patterns of chiral symmetry violation and tests of the conservation of the fundamental C, P and CP symmetries are key physics issues in studies of the pi0, eta and eta' meson decays. These tests include searches for rare or forbidden decays and searches for asymmetries among the decay products in the not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0 (CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta' meson decays are carried out at four European accelerator research facilities: KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY (Jülich), Crystal Barrel at ELSA (Bonn).

hep-ph↗

arXiv2007

What is interesting in eta and eta' Meson Decays?

An introduction to the physics of eta and eta' meson decays is given. A historical account of the discovery of the mesons is presented. It is followed by an overview and classification of the common decay modes and the relevance of the mesons for modern hadron and particle physics. In more detail the hadronic decay modes are discussed and in particular some interesting features of the eta-> 3pi0 decay are presented. The last section briefly reviews and compares reactions used to produce the eta and eta' mesons for the studies of their decays.

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