arXiv subjects

V. K. Magas

Publications and source records attributed to V. K. Magas.

At least 19 recordsLinked to original sources

arXiv2026

Comprehensive study of hidden charm pentaquarks with an improved unitarization method

This work investigates dynamically generated hidden-charm baryon resonances arising from meson-baryon interactions. Using the local hidden gauge formalism, we model the interaction via t-channel vector meson exchange and unitarize the amplitude using the Bethe-Salpeter equation. To address regularization issues, we propose a novel ``hybrid loop function'' scheme that eliminates the unphysical poles -- common artifacts in cutoff or dimensional regularization -- while keeping the predictions of physical states. Consequently, the model successfully reproduces six experimentally known hidden-charm pentaquarks as well as earlier theoretical results, and predicts new states in the S=-1, I=1 sector.

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arXiv2025

Double strangeness pentaquarks and other exotic hadrons in the $Ξ_b \to Ξ J/Ψ ϕ$ decay

We study the possibility that four $Ξ$ resonances $(Ξ(1620)$, $Ξ(1690)$, $Ξ(1820)$, $Ξ(1950))$ could correspond to pentaquark states, in the form of meson-baryon bound systems. We also explore the possible existence of doubly strange pentaquarks with hidden charm $(P_{css})$ and find two candidates structured in a similar form, at energies of $4493~{\rm MeV}$ and $4630~{\rm MeV}$. The meson-baryon interaction is built from t-channel meson exchange processes which are evaluated using effective Lagrangians. Moreover we analyse the $Ξ_b\toΞ~J/ψ~ϕ$ decay process, which permits exploring the existence of the heavy double strange pentaquark, as well as other exotic hadrons, in the three different two-body invariant mass spectra of the emitted particles. In the $J/ψϕ$ mass spectrum, we analyse the nature of the $X(4140)$ and $X(4160)$ resonances. In the $J/ψΞ$ invariant mass spectrum, we study the signal produced by the doubly strange pentaquark, where we conclude that it has a good chance to be detected in this reaction if its mass is around $4580-4680~{\rm MeV}$. Finally, in the $ϕΞ$ spectrum we study the likelihood to detect the $Ξ(2500)$ state.

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arXiv2023

Generalized Effective String Rope Model for the initial stages of Ultra-Relativistic Heavy Ion Collisions

We present a Generalized Effective String Rope Model (GESRM) for the description of the initial state of relativistic heavy ion collisions. We start from the Effective String Rope Model (ESRM) and take into account fluctuations in the initial state following the Glauber Monte Carlo approach. Results from symmetric Au+Au collisions at different impact parameters and asymmetric A+Au head on collisions are presented at RHIC energies. The produced initial state is used as an initial condition for further hydrodynamical calculations.

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arXiv2023

Double strangeness molecular-type pentaquarks from coupled channel dynamics

The existence of pentaquarks with strangeness content zero and one are major discoveries of the latest years in hadron physics. Most of these states can be understood as hadronic molecules and were predicted prior to their discovery within a model based on unitarized meson-baryon amplitudes obtained from vector meson exchange interactions. Contrary to earlier statements, we show this model to also predict the existence of pentaquarks with double strangeness, at about 4500 MeV and 4600 MeV, which are generated in a very specific and unique mechanism, via an attraction induced by a strong coupling between the two heaviest meson-baryon states.

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arXiv2023

The $Ξ(1620)$ and $Ξ(1690)$ molecular states from $S=-2$ meson-baryon interaction up to next-to-leading order

We have studied the meson-baryon interaction in the neutral $S=-2$ sector using an extended Unitarized Chiral Perturbation Theory, which takes into account not only the leading Weinberg-Tomozawa term (as all the previous studies in $S=-2$ sector), but also the Born terms and next-to-leading order contribution. Based on the SU(3) symmetry of the chiral Lagrangian we took most of the model parameters from the BCN model \cite{Feijoo:2018den}, where these were fitted to a large amount of experimental data in the neutral $S=-1$ sector. We have shown that our approach is able to generate dynamically both $Ξ(1620)$ and $Ξ(1690)$ states in very reasonable agreement with the data, and can naturally explain the puzzle with the decay branching ratios of $Ξ(1690)$. Our results clearly illustrate the reliability of chiral models implementing unitarization in coupled channels and the importance of considering Born and NLO contributions for precise calculations.

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arXiv2017

An Initial State with Shear in Peripheral Heavy Ion Collisions

In the present work we propose a new initial state model for hydrodynamic simulation of relativistic heavy ion collisions based on Bjorken-like solution applied streak by streak in the transverse plane. Previous fluid dynamical calculations in Cartesian coordinates with an initial state based on a streak by streak Yang-Mills field led for peripheral higher energy collisions to large angular momentum, initial shear flow and significant local vorticity. Recent experiments verified the existence of this vorticity via the resulting polarization of emitted $Λ$ and $\barΛ$ particles. At the same time parton cascade models indicated the existence of more compact initial state configurations, which we are going to simulate in our approach. The proposed model satisfies all the conservation laws including conservation of a strong initial angular momentum which is present in non-central collisions. As a consequence of this large initial angular momentum we observe the rotation of the whole system as well as the fluid shear in the initial state, which leads to large flow vorticity. Another advantage of the proposed model is that the initial state can be given in both [t,x,y,z] and $[τ, x, y, η]$ coordinates, and thus can be tested by all 3+1D hydrodynamical codes which exist in the field.

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arXiv2016

The chiral S=-1 meson-baryon interaction with new constrains on the NLO contributions

We present a study of the $S=-1$ meson-baryon interaction, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the model have been fitted to a large set of experimental scattering data in different two-body channels, to threshold branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hidrogen. In contrast to other groups, we have taken into consideration the $K^- p\to K^+Ξ^-, K^0Ξ^0$ reaction data, since we found in a previous work to be especially sensitive to the NLO parameters of the chiral Lagrangian. In the present work we also include the Born terms, which usually have very little effect, and find them to be non-negligible in the $K^- p\to KΞ$ channels, correspondingly causing significant modifications to the NLO parameters. We furthermore show that the importance of the Born terms becomes more visible in the isospin projected amplitudes of the $K^-p \to KΞ$ reactions. The measurement of processes that filter single isospin components, like the $K^0_L p \to K^+ Ξ^0$ reaction that could be measured at the proposed secondary $K^0_L$ beam at Jlab, would put valuable constraints on the chiral models describing the meson-baryon interaction in the $S=-1$ sector.

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arXiv2016

A hidden-charm $S=-1$ pentaquark from the decay of $Λ_b$ into $J/ψηΛ$

The hidden charm pentaquark state $P_c(4450)$ observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness $S=-1$ sector. In this work we argue that a hidden-charm strange pentaquark could be seen from the decay of the $Λ_b$, just as in the case of the non-strange $P_c(4450)$, but looking into the $J/ψηΛ$ decay mode and forming the invariant mass spectrum of $J/ψΛ$ pairs. In the model presented here, which assumes a standard weak decay topology and incorporates the hadronization process and final state interaction effects, we find the $J/ψηΛ$ final states to be populated with similar strength as the $J/ψK^- p$ states employed for the observation of the non-strange pentaquark. This makes the $Λ_ b \to J/ψηΛ$ decay to be an interesting process to observe a possible strange partner of the $P_c(4450)$ . We study the dependence of the $J/ψΛ$ mass spectra on various model ingredients and on the unknown properties of the strange pentaquark.

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arXiv2016

Workshop on Physics with Neutral Kaon Beam at JLab (KL2016) Mini-Proceedings

The KL2016 Workshop is following the Letter of Intent LoI12-15-001 "Physics Opportunities with Secondary KL beam at JLab" submitted to PAC43 with the main focus on the physics of excited hyperons produced by the Kaon beam on unpolarized and polarized targets with GlueX setup in Hall D. Such studies will broaden a physics program of hadron spectroscopy extending it to the strange sector. The Workshop was organized to get a feedback from the community to strengthen physics motivation of the LoI and prepare a full proposal. Further details about the Workshop can be found on the web page of the conference: http://www.jlab.org/conferences/kl2016/index.html .

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arXiv2015

The $Λ_b \to J/ψ~ K ~ Ξ$ decay and the higher order chiral terms of the meson baryon interaction

We study the weak decay of the $Λ_b$ into $ J/ψ~ K ~ Ξ$ and $J/ψ~ η~ Λ$ states, and relate these processes to the $Λ_b \to J/ψ~ \bar K ~N$ decay mode. The elementary weak transition at the quark level proceeds via the creation of a $J/ψ$ meson and an excited $sud$ system with $I=0$, which upon hadronization leads to $\bar K N$ or $ηΛ$ pairs. These states undergo final state interaction in coupled channels and produce a final meson-baryon pair. The $K Ξ$ state only occurs via rescattering, hence making the $Λ_b \to J/ψ~ K ~ Ξ$ process very sensitive to the details of the meson-baryon interaction in strangeness $S=-1$ and isospin $I=0$. We show that the corresponding invariant mass distribution is dominated by the next-to-leading order terms of the chiral interaction. The $I=0$ selectivity of this decay, and its large sensitivity to the higher order terms, makes its measurement very useful and complementary to the $K^- p \to K Ξ$ cross section data. The rates of the $Λ_b \to J/ψ~ K ~ Ξ$ and $Λ_b \to J/ψ~ η~ Λ$ invariant mass distributions are sizable compared to those of the $Λ_b \to J/ψ~ \bar K ~N$ decay, which is measured experimentally, thus, we provide arguments for an experimental determination of these decay modes that will help us understand better the chiral dynamics at higher energies.

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arXiv2015

The $\bar{K} N \rightarrow K Ξ$ reaction in coupled channel chiral models up to next-to-leading order

The meson-baryon interaction in s-wave in the strangeness S=-1 sector has been studied, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to the $\bar{K} N \rightarrow K Ξ$ reaction, which is particularly sensitive to the NLO terms. With the aim of improving the model in the $KΞ$ production channels, effects of the high spin hyperon resonances $Σ(2030)$ and $Σ(2250)$ have been taken into account phenomenologically.

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arXiv2014

The $\bar{K} N \rightarrow K Ξ$ reaction in coupled channel chiral models up to next-to-leading order

We study the meson-baryon interaction in S-wave in the strangeness S=-1 sector using a chiral unitary approach based on a next-to-leading order chiral SU(3) Lagrangian. We fit our model to the large set of experimental data in different two-body channels. We pay particular attention to the $\bar{K} N \rightarrow K Ξ$ reaction, where the effect of the next-to-leading order terms in the Lagrangian are sufficiently large to be observed, since at tree level the cross section of this reaction is zero. For these channels we improve our approach by phenomenologically taking into account effects of the high spin hyperonic resonances.

hep-ph↗

arXiv2013

Effects of the next-to-leading order terms in the chiral SU(3) Lagrangian on the strangeness -1 s-wave meson-baryon interactions

The meson-baryon interactions in s-wave in the strangeness S=-1 sector are studied using a chiral unitarity approach based on the next-to-leading order chiral SU(3) Lagrangian. The model is fitted to the large set of experimental data in different two-body channels. Particular attention is paid to the $Ξ$ hyperon production reaction, $\bar{K} N \rightarrow K Ξ$, where the effect of the next-to-leading order terms in the Lagrangian play a crucial role, since the cross section of this reaction at tree level is zero.

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arXiv2013

Flow Vorticity in Peripheral High Energy Heavy Ion Collisions

The vorticity development is studied in the reaction plane of peripheral relativistic heavy ion reactions where the initial state has substantial angular momentum. The earlier predicted rotation effect and Kelvin Helmholtz Instability, lead to significant initial vorticity and circulation. In low viscosity QGP this vorticity remains still significant at the time of freeze out of the system, even if damping due to the explosive expansion and the dissipation decreases the vorticity and circulation. In the reaction plane the vorticity arises from the initial angular momentum, and it is stronger than in the transverse plane where vorticity is caused by random fluctuations only.

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arXiv2012

New method for measuring longitudinal fuctuations and directed flow in ultrarelativistic heavy ion reactions

It has been shown in recent ALICE@LHC measurements that the odd flow harmonics, in particular a directed flow, v1, occurred to be weak and dominated by random fluctuations. In this work we propose a new method, which makes the measurements more sensitive to the flow patterns showing global collective symmetries. We demonstrate how the longitudinal center of mass rapidity fluctuations can be identified, and then the collective flow analysis can be performed in the event-by-event center of mass frame. Such a method can be very effective in separating the flow patterns originating from random fluctuations, and the flow patterns originating from the global symmetry of the initial state.

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arXiv2012

Explicit Model Realizing Parton-Hadron Duality

We present a model that realizes both resonance-Regge (Veneziano) and parton-hadron (Bloom-Gilman) duality. We first review the features of the Veneziano model and we discuss how parton-hadron duality appears in the Bloom-Gilman model. Then we review limitations of the Veneziano model, namely that the zero-width resonances in the Veneziano model violate unitarity and Mandelstam analyticity. We discuss how such problems are alleviated in models that construct dual amplitudes with Mandelstam analyticity (so-called DAMA models). We then introduce a modified DAMA model, and we discuss its properties. We present a pedagogical model for dual amplitudes and we construct the nucleon structure function F2(x,Q2). We explicitly show that the resulting structure function realizes both Veneziano and Bloom-Gilman duality.

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arXiv2012

Momentum dependence of the phi-meson nuclear transparency

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.

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arXiv2011

Fluid Dynamical Prediction of Changed v1-flow at LHC

Substantial collective flow is observed in collisions between Lead nuclei at LHC as evidenced by the azimuthal correlations in the transverse momentum distributions of the produced particles. Our calculations indicate that the Global v1-flow, which at RHIC peaked at negative rapidities (named as 3rd flow component or anti-flow), now at LHC is going to turn toward forward rapidities (to the same side and direction as the projectile residue). Potentially this can provide a sensitive barometer to estimate the pressure and transport properties of the Quark-Gluon Plasma. Our calculations also take into account the initial state Center of Mass rapidity fluctuations, and demonstrate that these are crucial for v1 simulations. In order to better study the transverse momentum flow dependence we suggest a new "symmetrized" v1S flow component; and we also propose a new method to disentangle Global v1 flow from the contribution generated by the random fluctuations in the initial state. This will enhance the possibilities of studying the collective Global v1 flow both at the STAR Beam Energy Scan program and at LHC.

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