arXiv subjects

Milena Piotrowska

Publications and source records attributed to Milena Piotrowska.

17 recordsLinked to original sources

arXiv2026

Isospin-symmetry violation -- kaons and beyond (ISO-BREAK 25: summary and outlook)

This report summarizes the presentations and discussions during the ISO-BREAK 25 Workshop ``Isospin symmetry violation: kaons and beyond'', which was held at Jan Kochanowski University in Kielce on October 23-25, 2025. We address the current status of the isospin-symmetry breaking discovered by NA61/SHINE in nucleus-nucleus collisions at the CERN SPS, its confirmation by other experiments and studies in \ee and deep inelastic scattering. In addition, we discuss the theoretical status as well as we outline experimental and theoretical priorities towards understanding this currently unexplained phenomenon.

nucl-ex↗

arXiv2025

The weak decay constant of positronium

The positronium, as the lightest purely leptonic bound state, provides an ideal testing ground for a quantum field--theoretical (QFT) description of composite systems. While its electromagnetic annihilation is well understood as the dominant decay channel, the weak interaction sector of positronium is strongly suppressed. In this work, we extend the composite QFT framework previously developed for the two--photon decay and introduce the concept of a weak decay constant for para--positronium. This constant, defined in analogy with those of pseudoscalar mesons, quantifies the coupling of the positronium field to the weak axial current and serves as a measure of its internal structure in the electroweak domain. Its numerical value $ f_{P} \simeq \frac{m_{e}}{2\sqrt{\pi}} \alpha^{3/2} = 89.8593~\mathrm{eV} $ is, as expected, small. Nevertheless, the resulting expression and a related comparison to quarkonium systems allow us to determine the vertex function linking the positronium to its own constituents.

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arXiv2025

Two-exponential decay of Acridine Orange

In this work, we experimentally study the fluorescence decay of Acridine Orange at late times, in order to test whether a late-time power-law behaviour emerges, a feature expected to be very small but consistent with quantum mechanical and quantum field theoretical predictions. Using two distinct photon detectors, we find that the data are well described by a sum of two exponential functions with lifetimes $\tau_1 = 1.7331 \pm 0.001$ ns and $\tau_2 = 5.948 \pm 0.012$ ns, in agreement with values reported in the literature. While no deviation from the exponential decay law is observed, this study serves as a reliable test for the experimental setup and enables a precise determination of the sample lifetimes.

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arXiv2025

Quantum Late-Time Decay and Channel Dependence

Quantum mechanics predicts deviations from exponential decay at short and long times, yet experimental evidence is limited. We report a power-law tail after $\sim$10 lifetimes in two fluorescent compounds (erythrosine~B and eosine Y), confirmed by two detectors probing distinct bands but yielding different power coefficients. The data match a divergent but normalizable spectral density, and theory predicts oscillations as a future test. A novel and general result is that in multichannel QM (and QFT) decay, the lifetime is universal, but the late-time deviations are channel- (or band-) dependent, a feature consistent with our data.

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arXiv2024

Two-photon decay of para-positronium within a composite approach

The decay of the para-positronium into two photons is studied in the framework of a composite Quantum Field Theoretical approach. This amounts to the evaluation of the electron-positron dressing together with the Weinberg compositeness condition for the positronium and the triangle-shaped diagram with virtual electrons circulating in it, leading to the two-photon final state. An important role is played by the positronium-electron-positron vertex, which is linked to the wave function of the para-positronium. We show how possible choices for the vertex function affect the $\gamma \gamma$ decay rate. Outlooks to other decay channels and to other positronia are presented.

hep-ph↗

arXiv2023

A QFT scalar toy model analogous to positronium and pion decays

In the framework of a scalar QFT, we evaluate the decay of an initial massive state into two massless particles through a triangle-shaped diagram in which virtual fields propagate. Under certain conditions, the decaying state can be seen as a bound state, thus it is analogous to the neutral pion (quark-antiquark pair) and to the positronium (electron-positron pair), which decay into two photons. While the pion is a relativistic composite object, the positronium is a non-relativistic compound close to threshold. We exam similarities and differences between these two types of bound states.

hep-ph↗

arXiv2023

Is $f_2(1950)$ the tensor glueball?

Glueballs remain an experimentally undiscovered expectation of QCD. Lattice QCD (As well as other theoretical approaches) predicts a spectrum of glueballs, with the tensor ($J^{PC}=2^{++}$) glueball being the second lightest, behind the scalar glueball. Here, using a chiral hadronic model, we compute decay ratios of the tensor glueball into various meson decay channels. We find the tensor glueball to primarily decay into two vector mesons, dominated by $\rho \rho $ and $K^*K^*$ channels. These results are compared to experimental data of decay rates of isoscalar tensor mesons. Based on this comparison, we make statements on the eligibility of these mesons as potential tensor glueball candidates: the resonance $f_2(1950)$ turns out to be, at present, the best match as being predominantly a tensor glueball.

hep-ph↗

arXiv2022

From well-known tensor mesons to yet unknown axial-tensor mesons

While the ground-state tensor ($J^{PC}=2^{++}$) mesons $a_{2}(1320)$, $K_{2}^{\ast}(1430)$, $f_{2}(1270)$, and $f_{2}^{\prime}(1525)$ are well known experimentally and form an almost ideal nonet of quark-antiquark states, their chiral partners, the ground-states axial-tensor ($J^{PC}=2^{--}$) mesons are poorly settled: only the kaonic member $K_2(1820)$ of the nonet has been experimentally found, whereas the isovector state $ρ_2$ and two isoscalar states $ω_2$ and $ϕ_2$ are still missing. Here, we study masses, strong, and radiative decays of tensor and axial-tensor mesons within a chiral model that links them: the established tensor mesons are used to test the model and to determine its parameters, and subsequently various predictions for their chiral partners, the axial-tensor mesons, are obtained. The results are compared to current lattice QCD outcomes as well as to other theoretical approaches and show that the ground-state axial-tensor mesons are expected to be quite broad, the vector-pseudoscalar mode being the most prominent decay mode followed by the tensor-pseudoscalar one. Nonetheless, their experimental finding seems to be possible in ongoing and/or future experiments.

hep-ph↗

arXiv2021

Study of conventional and non-conventional scalar and vector mesons

Enormous progress in physics enriched our knowledge about the particles which build matter. Among them there are mesons, to which this thesis is entirely devoted. The overwhelming majority of mesons is made of `conventional' $q\bar{q}$ pairs, but nowadays there is mounting evidence for `non-conventional' mesons, such as tetraquarks, glueballs, hybrids, and molecules. The main aim of this thesis is to understand the nature of some scalar and vector mesonic states which still remain puzzling. In this thesis we investigate two nonets of $q\bar{q}$ excited vector mesons. Within an effective QFT model we evaluate various decay channels of these states and compare the results with experimental data from PDG. Moreover, we make predictions for a not-yet observed $s\bar{s}$ state in $1$ $^3D_1$ nonet. Some non-conventional mesons can be understood by the mechanism of dynamical generation. We show that the inclusion of a single conventional $q\bar{q}$ seed in the relativistic QFT Lagrangian may cause the appearance of an additional associated state as a dynamically generated companion pole. Along this line, we show that light scalar kaon $K^*_0(700)$ emerges as a companion pole of the $q\bar{q}$ meson $K_0^*(1430)$. Moreover, we show that the enigmatic resonance $X(3872)$ in the charmonium sector can be interpreted as the (virtual) companion pole of the $c\bar{c}$ state $χ_{c1}(2P)$. Then, we study the $c\bar{c}$ meson $ψ(4040)$. We show that an additional companion pole appears on the complex plane. At first sight one may identify it with the enhancement $Y(4008)$ observed by the Belle Collaboration. A detailed analysis reveals that different mechanism is responsible for the creation of $Y(4008)$. Hence, the bump associated with $Y(4008)$ should not be interpreted as an independent resonance, but rather as a manifestation of the strong coupling of $ψ(4040)$ to the $D^*D$ channel.

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arXiv2020

Study of some (non-)conventional mesons in the framework of effective models

The main aim of our study is to understand the nature of some conventional and non-conventional mesonic states by applying effective QFT models. We start from the relativistic Lagrangians containing a unique $q\bar{q}$ seed state which is strongly coupled to the low-masses decay products of the original state. We find out that some states may appear as a dynamically generated companion poles of the heavier $q\bar{q}$ mesons. In particular we show that $K^*_0(700)$ is a companion pole of the well-known $K^*_0(1430)$ resonance, $X(3872)$ emerges as a (virtual) companion pole of $χ_{c1}(2P)$, and the puzzling $Y(4008)$ is not a real state, but a spurious enhancement which appears when studying the state $ψ(4040)$.

hep-ph↗

arXiv2019

$X(3872)$ as virtual companion pole of the charm-anticharm state $χ_{c1}(2P)$

We study the spectral function of the axial-vector charmonium state $χ_{c1}(2P)$ coupled to $DD^{\ast}$ mesons, by employing a quantum field theoretical approach: a pronounced enhancement close to the $D^{0}% D^{\ast0}$ threshold, to be identified with the $X(3872)$, emerges. In the complex plane we find two poles: a pole for the broad seed state $χ_{c1}(2P)$, and -- in the easiest scenario -- a virtual pole for the $X(3872)$. Thus, our approach describes both the seed state and the dynamically generated $X(3872)$ simultaneously. In particular, it explains the most prominent, both molecular-like and quarkonium-like, features of the $X(3872)$: its very small width (the decay into $D^{0}D^{\ast0}$ is predicted to be about 0.5 MeV), the enhanced radiative decay into $ψ(2S)γ$ w.r.t. $ψ(1S)γ$, and the isospin breaking decay into $J/ψρ$ (thanks to $DD^{\ast}$ loops mediating this decay channel). At the same time, we aim to determine the pole position and the properties of the charmonium seed state: quite interestingly, even if a pole is always present, it is possible that there is no peak corresponding to this state in the spectral function, thus potentially explaining why the corresponding resonance could not yet be seen in experiments.

hep-ph↗

arXiv2018

A study of the vector meson $\mathbf{ψ(4040)}$

We investigate the well-known $c\bar{c}$ vector state $ψ(4040)$ in the framework of a quantum field theoretical model. In particular, we study its spectral function and search for the pole(s) in the complex plane. Quite interestingly, the spectral function has a non-standard shape and two poles are present. The role of the meson-meson quantum loops (in particular $DD^*$ ones) is crucial and could also explain the not yet confirmed state $Y(4008)$.

hep-ph↗

arXiv2018

Can the $ψ(4040)$ explain the peak associated with $Y(4008)$?

We study the well-known resonance $ψ(4040)$, corresponding to a $3^{3}S_{1}$ charm-anticharm vector state $ψ(3S)$, within a QFT approach, in which the decay channels into $DD$, $D^{\ast}D$, $D^{\ast}D^{\ast}$, $D_{s}D_{s}$ and $D_{s}^{\ast}D_{s}$ are considered. The spectral function shows sizable deviations from a Breit-Wigner shape (an enhancement, mostly generated by $DD^{\ast}$ loops, occurs); moreover, besides the $c\bar{c}$ pole of $ψ(4040)$, a second dynamically generated broad pole at $4$ GeV emerges. Naively, it is tempting to identify this new pole with the unconfirmed state $Y(4008).$ Yet, this state was not seen in the reaction $e^{+}e^{-}\rightarrowψ(4040)\rightarrow DD^{\ast}$, but in processes with $π^{+}π^{-}J/ψ$ in the final state. A detailed study shows a related but different mechanism: a broad peak at $4$ GeV in the process $e^{+}e^{-}\rightarrowψ(4040)\rightarrow DD^{\ast }\rightarrowπ^{+}π^{-}J/ψ$ appears when $DD^{\ast}$ loops are considered. Its existence in this reaction is not necessarily connected to the existence of a dynamically generated pole, but the underlying mechanism - the strong coupling of $c\bar{c}$ to \ $DD^{\ast}$ loops - can generate both of them. Thus, the controversial state $Y(4008)$ may not be a genuine resonance, but a peak generated by the $ψ(4040)$ and $D^{\ast}D$ loops with $π^{+}π^{-}J/ψ$ in the final state.

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arXiv2017

A study of the excited radial vector meson $ρ$

We study the strong and radiative decays of the radial excitation of the $ρ$ meson, with quantum numbers $n$ $^{2S+1}L_{J}=2$ $^{3}S_{1},$ $I=1$, and denoted as $ρ_{E}$, by making use of an effective model. We test different masses: $1.45$ GeV, corresponding to well known assignment $ρ_{E}\equivρ(1450)$ state; $1.25$ GeV for the assignment $ρ_{E}\equivρ(1250)$ (a resonance whose existence has not yet been confirmed), and $1.35$ GeV, which lies just in the middle between them in order to study the dependence of the results on the mass. The decay widths for different decay processes and two branching ratios of the radially excited meson $ρ_{E}$ were determined and compared to the experimental data reported in the Particle Data Group.

hep-ph↗

arXiv2017

Excited vector mesons: phenomenology and predictions for a yet unknown vector $s\bar{s}$ state with a mass of about 1.93 GeV

The firm understanding of standard quark-antiquark states (including excited states) is necessary to search for non-conventional mesons with the same quantum numbers. In this work, we study the phenomenology of two nonets of excited vector mesons, which predominantly correspond to radially excited vector mesons with quantum numbers $n$ $^{2S+1}L_{J}=2$ $^{3}S_{1}$ and to orbitally excited vector mesons with quantum numbers $n$~ $^{2S+1}L_{J}=1$ $^{3}D_{1}$. We evaluate the decays of these mesons into two pseudoscalar mesons and into a pseudoscalar and a ground-state vector meson by making use of a relativistic quantum field theoretical model based on flavor symmetry. Moreover, we also study the radiative decays into a photon and a pseudoscalar meson by using vector meson dominance. We compare our results to the PDG and comment on open issues concerning the corresponding measured resonances. Within our approach, we are also able to make predictions for a not-yet discovered $s\bar{s}$ state in the $n$ $^{2S+1}L_{J}=1$ $^{3}D_{1}$ nonet, which has a mass of about 1.93 GeV. This resonance can be searched in the upcoming GlueX and CLAS12 experiments which take place at the Jefferson Lab.

hep-ph↗

arXiv2017

Signatures of $α$ clustering in ultra-relativistic collisions with light nuclei

We explore possible observable signatures of $α$ clustering of light nuclei in ultra-relativistic nuclear collisions involving ${}^{7,9}$Be, ${}^{12}$C, and ${}^{16}$O. The clustering leads to specific spatial correlations of the nucleon distributions in the ground state, which are manifest in the earliest stage of the ultra-high energy reaction. The formed initial state of the fireball is sensitive to these correlations, and the effect influences, after the collective evolution of the system, the hadron production in the final stage. Specifically, we study effects on the harmonic flow in collisions of light clustered nuclei with a heavy target (${}^{208}$Pb), showing that measures of the elliptic flow are sensitive to clusterization in ${}^{7,9}$Be, whereas triangular flow is sensitive to clusterization in ${}^{12}$C and ${}^{16}$O. Specific predictions are made for model collisions at the CERN SPS energies. In another exploratory development we also examine the proton-beryllium collisions, where the $3/2^-$ ground state of ${}^{7,9}$Be nucleus is polarized by an external magnetic field. Clusterization leads to multiplicity distributions of participant nucleons which depend on the orientation of the polarization with respect to the collision axis, as well as on the magnetic number of the state. The obtained effects on multiplicities reach a factor of a few for collisions with a large number of participant nucleons.

nucl-th↗

arXiv2017

Strong and radiative decays of excited vector mesons and predictions for a new $ϕ(1930)$ resonance

We study the phenomenology of two nonets of excited vector mesons, $\{ρ(1450)$, $K^{\ast}(1410)$, $ω(1420)$, $ϕ(1680)\}$ and $\{ρ(1700),$ $K^{\ast}(1680),ω(1650),$ $ϕ(???)\},$ which (roughly) correspond to radially excited $2^{3}S_{1}$ and to orbitally excited $1^{3}D_{1}$ vector mesons. We evaluate the strong and radiative decays of these mesons into pseudoscalar and ground-state vector mesons by using an effective relativistic QFT model based on flavour symmetry. We compare decay widths and branching ratios with various experimental results listed in the PDG. An overall agreement of theory with experiment reinforces the standard quark-antiquark assignment of the resonances mentioned above. Predictions for not yet measured quantities are also made. In particular, we shall also make predictions for the not-yet discovered $s\bar{s}$ state of the $1^{3}D_{1}$ nonet, denoted as $ϕ(???)$. Its mass can be estimated to be about $1930$ MeV, hence we shall call this putative state $ϕ(1930).$ Its main decays are into $KK^{\ast}(892)$ (about $200$ MeV) and $KK$ (about $100$ MeV). Since this state couples also to $γη,$ it can be searched in the near future in the photoproduction-based experiments GlueX and CLAS12 at Jefferson Lab.

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