abstract

We present results for the quark mass function in Minkowski space calculated from an interaction kernel that consists of an effective one-gluon-exchange and a constant interaction. We analyze the gauge dependence of our results and compare them in the spacelike region to the available lattice QCD data.

abstract

ALICE is devoted to the study of the properties of the Quark–Gluon Plasma (QGP). This state of matter is created in ultra-relativistic heavy-ion collisions at the LHC. Heavy quarks are considered effective probes of the QGP since, due to their large masses, they are produced in hard-scattering processes and experience the full evolution of the hot and dense medium while interacting with its constituents. The heavy-quark measurements provide insights into processes such as in-medium energy loss and hadronization. Measurements in proton–proton collisions provide the baseline for interpreting heavy-ion collision results and constitute an excellent test of pQCD calculations. In addition, proton–nucleus collisions allow for separating cold nuclear matter effects from those created in heavy-ion collisions due to the deconfined strongly interacting matter. In this contribution, an overview of recent ALICE results for open heavy flavours, quarkonia, and heavy-flavour jets is presented.

abstract

In these proceedings, measurements of angular correlations between hadron pairs in \(pp\) collisions obtained by the ALICE experiment at the LHC are presented and compared with phenomenological predictions. Correlations between particles carrying the same and opposite quantum numbers are studied to understand the hadron production mechanism, and the difference between the same-sign and opposite-sign correlations is used to probe charge-dependent effects in particle production. Correlation measurements dominated by minijet fragmentation agree well with the models, but other results, in particular correlations between baryons and strange hadrons, are not yet understood.

abstract

During the second LHC long shutdown (LS2), the Inner Tracking System (ITS) of ALICE (A Large Ion Collider Experiment) will be replaced by seven layers of CMOS Monolithic Active Pixel Sensors (MAPS). The latest innovations in silicon imaging technology allow for the construction of large, ultra-thin silicon wafers which can further improve the capabilities of the ALICE tracker. The research and development studies towards the construction of a novel vertex detector have started. The detector installation has been proposed for the third LHC long shutdown (LS3) during which the three innermost layers shall be replaced by three cylindrical layers of large curved CMOS wafers. This upgrade (ITS3) will further improve the impact parameter resolution and the tracking efficiency of low momentum particles. The innermost layer will be positioned closer to the interaction point and the material budget will be reduced down to \(0.05\%\,X_0\) per layer. Monte Carlo simulations of a simplified ITS3 geometry within the ITS2 design indicate an improvement in the impact parameter resolution and the tracking efficiency, which are of crucial importance for measurements of heavy-flavour hadrons. This contribution shows the improved performance for the example of the \({\mit \Lambda }_{b}\), for which the significance of its measurement is extracted based on these MC simulations. A significant improvement by almost a factor of three in the low momentum region compared to the ITS2 is observed.

abstract

Massive photon-like particles are predicted in many extensions of the Standard Model as possible portals toward a hidden sector where dark matter is secluded. They are vector bosons mediating the interaction between ordinary and dark matter and can be produced in different processes through a dim mixing to the photon. The PADME experiment searches for a signal of a dark photon \(A^\prime \) in the \(e^+e^-\rightarrow \gamma A^\prime \) reaction in a positron-on-target experiment. For this purpose, the missing mass spectrum is analysed for final states with a single photon, produced in the annihilation of the positron beam of the DA\(\Phi \)NE Beam-Test Facility, at Laboratori Nazionali di Frascati of INFN, on the electrons of a diamond target. By collecting \(10^{13}\) positron-on-target, a sensitivity on the interaction strength down to 0.001 is achievable in the mass region \(M(A^\prime )\lt 23.7\) MeV/\(c^2\). The scientific program of the experiment and its current status are here illustrated.

abstract

The NA62 experiment at CERN was designed to measure the branching ratio of the ultra-rare \(K^+\rightarrow \pi ^+\nu \bar {\nu }\) decay with a decay-in-flight technique. The Standard Model prediction for this branching ratio is very precise and this process is an ideal candidate for the indirect search of New Physics at high-mass scale. NA62 took physics data from 2016 to 2018: the results of the \(K^+\rightarrow \pi ^+\nu \bar {\nu }\) analysis in the 2016+2017 data sets are presented. Moreover, the high-intensity setup, the flexibility of its trigger system, and the hermetic coverage of the experiment make NA62 a useful tool for the search of exotic particles in the MeV–GeV range weakly coupled to the Standard Model, such as heavy neutral leptons and dark photons. The status of these analyses will be reviewed, along with other New Physics studies carried out at NA62, such as the search for lepton flavour and lepton number violating \(K^+\) decays.

abstract

The experimental studies of light kaonic atoms offer the unique opportunity to investigate the kaon–nucleus interaction at threshold, performing experiments equivalent to scattering at vanishing relative energies without the need of an extrapolation. In this framework, the SIDDHARTA-2 experiment is going to perform the first measurement of kaonic deuterium \(2p \rightarrow 1s\) transition, which is fundamental to extract the isospin-dependent antikaon–nucleon scattering lengths. The setup was installed on the DA\(\Phi \)NE collider of LNF-INFN in spring 2019 and is presently in optimization phase. The SIDDHARTA-2 data taking campaign for the kaonic deuterium is planned in 2020–2021.

abstract

The latest years have observed a resurrection of interest in searches for exotic states motivated by precision spectroscopy studies of beauty and charm hadrons providing the observation of many new exotic states. The recent results on spectroscopy of exotic hadrons obtained by the LHCb Collaboration are reviewed. This is, in particular, an observation of \(P_{c}(4312)^{+}\) and two-peak structure of \(P_{c}(4450)^{+}\), observation of \(B_{(s)}^{0} \rightarrow J/\psi p \bar {p}\) decays and an evidence of exotic \(Z_{c}(4100)^{-}\) state.

abstract

All existing experimental evidence of the bound state nature of the \(X(3872)\) relies on considering its decay products with a finite experimental spectral mass resolution which is typically \(\Delta m \ge 2\) MeV and much larger than its alleged binding energy, \(B_X =0.00(18)\) MeV. On the other hand, there is a neat cancellation in the \(1^{++} \) channel for the invariant \(D {\bar D}^*\) mass around the threshold between the continuum and bound state contribution. We discuss the impact of this effect for \(X(3872)\) at finite temperature, in prompt production in \(pp\) collisions data with a finite \(p_{\mathrm {T}}\) or the lineshapes of specific production experiments of exotic states involving triangle singularities.

abstract

After the first predictions in seventies that in dense nuclear matter, for example, in neutron stars there could be a pion condensation phenomenon, it was shown that at least \(s\)-wave pion condensation is unlikely to occur in such a medium in different approaches including NJL model consideration with neutrality and \(\beta \)-equilibrium condition. Then it has been found a condition that can promote this phenomenon in dense baryonic matter. It is chiral imbalance, so now it is interesting if this generation can survive rather strict requirement of electric neutrality and \(\beta \)-equilibrium. In this paper, the generation of pion condensation in dense baryonic matter by chiral imbalance is investigated. It is shown that electric neutrality and \(\beta \)-equilibrium conditions do not spoil this phenomenon and this leads to interesting applications for physics of neutron stars. There are several possible mechanisms of generation of chiral imbalance in dense matter. In a view of latest and forthcoming NICER results and the first observed and possibly new events of neutron star mergers, it is rather interesting to explore how possible chiral imbalance in neutron star can influence and change EOS and, hence, mass–radius relation. It is a first step in that direction.

abstract

We construct a model for quarkyonic matter with an extended version of the excluded volume model to a three-flavor system, as an alternative to obtain a hard–soft behavior of the equation of state inferred from gravitational wave observations and analysis.

abstract

It is shown how high-order cumulants of net-charge distribution in hadronic collisions at the LHC energies can be expressed via lower-order terms under the assumption that particle–antiparticle pairs are produced in the independent local processes. It is argued and tested with the HIJING model that this assumption is typically valid for net-proton fluctuations in the case when no critical behaviour is present in the system. Values estimated in such a way can be considered as baselines for direct measurements of high-order net-charge fluctuations in real data.

abstract

The center vortex model, capable of explaining confinement and chiral symmetry breaking, has been plagued by the lattice equivalent of Gribov copies: different maxima of the gauge functional lead to different predictions of the string tension. It is possible to resolve this problem using center regions, loops evaluating to center elements, as a guide for the gauge fixing procedure. The success of this approach was already shown, but the algorithms came with an arbitrary free parameter. In recent development this parameter has been fixed, even improving the results.

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We present a preliminary computation of potentials between two static quarks in \(n_\mathrm {f}=2\) QCD with \(O(a)\) improved Wilson fermions based on Wilson loops. We explore different smearing choices (HYP, HYP2 and APE) and their effect on the signal-to-noise ratio in the computed static potentials. This is a part of a larger effort concerning, at first, a precise computation of the QCD string breaking parameters and their subsequent utilization for the recent approach based on the Born–Oppenheimer approximation [P. Bicudo et al. , Phys. Rev. D 101, 034503 (2020)] to study quarkonium resonances and bound states.

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We consider the \(\pi \pi \)-scattering problem in the context of the Kadyshevsky equation. In this scheme, we introduce a momentum grid and provide an isospectral definition of the phase shift based on the spectral shift of a Chebyshev angle. We address the problem of the unnatural high momentum tails present in the fitted interactions which reaches energies far beyond the maximal center-of-mass energy of \(\sqrt {s}=1.4\) GeV. It turns out that these tails can be integrated out by using a block-diagonal generator of the SRG.

abstract

Within the AdS/CFT correspondence, for description of the \(\mathcal {N}=4\) super Yang–Mills theory in four dimensions, one needs not only low-energy supergravity on AdS\(_5\) but also the whole infinite tower of massive Kaluza–Klein (KK) states on AdS\(_5\times \)S\(_5\) which appear after the KK compactification on five-dimensional sphere. The latter aspect is usually ignored in phenomenological AdS/QCD models. The emerging massive 5D fields on AdS\(_5\) are dual to higher-dimensional operators in 4D gauge theory, with masses being known polynomial functions of canonical dimensions of these operators. Motivated by this observation, we propose to calculate the spectrum of radially excited hadrons in bottom-up holographic QCD models as spectrum of zero KK modes of massive 5D fields dual to higher dimensional operators in QCD. A relevant physical motivation is suggested. The radial states with growing masses are then enumerated by growing dimensions of interpolating QCD operators. We tested the proposal in the Soft Wall and Hard Wall holographic models in the sector of light mesons. The spectrum of Soft Wall model turns out to be unchanged in the new description. However, in the Hard Wall model, our approach is shown to lead to a much better phenomenological spectrum of vector radial excitations than the traditional description.

abstract

The existence and the location of the critical end point (CEP) between the crossover and the first order part of the chiral phase transition in the phase diagram of strongly interacting matter is a heavily studied area of recent particle physics. The baryon number fluctuations and related quantities such as kurtosis and other susceptibility ratios, that are assumed to be good signatures of CEP, are calculated in an (axial)vector meson extended \((2+1)\) flavor Polyakov linear sigma model (EL\(\sigma \)M) at zero and finite \(\mu _\mathrm {B}\). It is compared with the results of lattice as well as other effective model calculations. Divergence of the kurtosis is found at the critical end point.

abstract

We used the U\((1) \otimes {\mathrm {SO}}(3)_{\mathrm {{rot}}} \subset {\mathrm {U}}(3) \subset {\mathrm {SO}}(6)\) hyperspherical harmonics of I. Salom, V. Dmitrašinović, Nucl. Phys. B 920, 521 (2017). to calculate the energy-spectrum of three nonrelativistic quarks in the (interpolation of the) lattice QCD potential. We show that the first clear difference between the \({\Delta }\), or the Y-string confinement and the lattice QCD potential can be seen only in the third shell of excited states. This is beyond experimental access, even in the light-quark sector. We also briefly discuss the role of relativity.

abstract

The interior of compact stars is usually divided into two major parts, the outer part called crust and the inner part called core. There are several possibilities for the composition of these parts. One is a hybrid star, in which the crust contains nuclear matter, while the inner core contains quark matter. Since at large baryon densities one can work with effective models, and nuclear and quark matter are usually described by different models, some unification of the two parts is needed. We show two different approaches for a composite model, and some recent developments in hybrid star constructions using the extended linear sigma model for modeling the quark matter at the core.

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In this paper, we review our recent work where we determine with precision the parameters of the much debated lightest strange resonance \(\kappa /K_0^*(700)\) using as an input a constrained dispersive data analysis on \(\pi K\rightarrow \pi K\) and \(\pi \pi \rightarrow K\bar K\). For this, we use forward and other sets of partial-wave dispersion relations obtained either from fixed-\(t\) or hyperbolic dispersion relations with different subtractions. Partial-wave hyperbolic dispersion relations are then used to extrapolate to the complex plane and establish in a model-independent way the existence of a pole associated to the \(\kappa /K^*_0(700)\), and to obtain precise values for its mass, width and coupling to \(\pi K\).

abstract

The elaborated Unitary and Analytic models of pseudoscalar meson nonet electromagnetic structure, and to some extent also of nucleons, give more precise theoretical prediction for the hadronic contribution \(\Delta \alpha ^{(5)}_\mathrm {had}(t)\) to the running fine structure constant QED \(\alpha (t)\) in the space-like region, which by the novel approach leads to the following complete SM muon anomalous magnetic moment value \(a^\mathrm {SM}_\mu =(11 659 196.35\pm 4.81)\times 10^{-10}\). This result deviates from the world average experimental value \(a^\mathrm {exp}_\mu \!=\!(11 659 209\!\pm \! 6)\times 10^{-10}\) by \(12.65\pm 7.69\), i.e. 1.6\(\sigma \).

abstract

Utilizing the SU(3) invariant vector–meson–baryon interaction Lagrang-ians, the knowledge of the universal vector–meson coupling constants \(f_V\) and the numerical values of nucleon coupling constant ratios, all unknown hyperon coupling constant ratios in hyperon electromagnetic structure Unitary and Analytic models are predicted.

abstract

The VIP experiment aims to perform high-precision tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the Underground Gran Sasso Laboratories of INFN (Italy). The experimental technique consists in introducing a DC current in a copper conductor, searching for \(K_{\alpha }\) PEP-forbidden atomic transitions when the \(K\) shell is already occupied by two electrons. The results of a preliminary data analysis, corresponding to the first run of the VIP-2 data taking (2016–2017), are presented. The experimental setup in the final configuration is described together with preliminary spectra from the 2019 data-taking campaign.

abstract

The ground-state (lightest) hybrid nonet with exotic quantum numbers \(J^{PC}=1^{-+}\) and the nonet of their chiral partners with \(J^{PC}=1^{+-}\) build a homochiral multiplet involving left- and right-handed currents, which under chiral transformation change just as (axial-)vector mesons. Masses and interactions of hybrids can be obtained in the context of the extended Linear Sigma Model. Here, we concentrate on the decays of hybrids into two pseudoscalar mesons, such as \(\eta \pi \) and \(\eta ^{\prime }\pi \) modes. Indeed, \(\pi _{1}(1400)\rightarrow \pi \eta \) and \(\pi _{1}(1600)\rightarrow \pi \eta ^{\prime }\) have been seen in experiments. Assuming that \(\pi _{1}(1400)\) and \(\pi _{1}(1600)\) correspond to the same state \(\pi _{1}^\mathrm {hyb}\), we show that these decays (and similar ones) follow from a chirally symmetric interaction term that breaks explicitly the axial anomaly. In this respect, these decays would be an additional manifestation of the axial (or chiral) anomaly in the mesonic sector.

abstract

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 \(\chi _{c1}(2P)\), and the puzzling \(Y(4008)\) is not a real state, but a spurious enhancement which appears when studying the state \(\psi (4040)\).

abstract

In this paper, the nonequilibrium correction to the distribution function containing a time- and space-dependent mass is obtained. Given that, fully consistent fluid dynamic equations are formulated. Then, the physics of the bulk viscosity is elaborated for the Boltzmann and Bose–Einstein gases within the relaxation-time approximation. It is found that the parametric form of the ratio \(\zeta /\tau _\mathrm {R}\) for the quantum gas is affected by the infrared cut-off. This may be an indication that the relaxation-time approximation is too crude to obtain a reliable form of bulk viscosity.

abstract

We present a calculation of valence double parton distributions of the pion in the framework of chiral quark models. The result obtained at the low-energy quark model scale is particularly simple, where in the chiral limit a factorized form follows, \(D(x_1,x_2, \vec {q}\,) = \delta (1-x_1-x_2) F(\vec {q}\,)\) with \(x_{1,2}\) standing for the longitudinal momentum fractions of the valence quark and antiquark, and \(\vec {q}\) denotes the relative transverse momentum. For \(\vec {q}=\vec {0}\), the result satisfies the Gaunt–Sterling sum rules. The QCD evolution to higher scales is carried out within the dDGLAP framework. We argue that the ratios of the valence Mellin moments \(\langle x_1^n x_2^m \rangle / \langle x_1^n \rangle \langle x_2^m \rangle \), which do not depend on the dDGLAP evolution, provide particularly convenient measures of the longitudinal correlations between the partons. Such ratios could be probed in future lattice QCD simulations.

abstract

With the reported observation of the Higgs boson at the LHC, the Standard Model of particle physics seems to be complete now as for its particle content. However, several experimental data at low and intermediate energies indicate that there may be two surprises. First, we propose a tentative new boson \(Z_0(57)\), with a mass of about 57 GeV, on the basis of small enhancements we observe in several experiments, using recent data obtained at the LHC as well as much older ones from LEP. If confirmed, we interpret this new particle as a pseudoscalar or scalar partner of a composite \(Z\) vector boson. Secondly, we advocate the existence of a very light spinless boson \(E(38)\), probably a scalar, with a mass of 38 MeV and decaying into two photons. Theoretical arguments and experimental signals supporting such a novel light boson are presented, including a recent direct experimental confirmation at the Joint Institute for Nuclear Research in Dubna.

abstract

Using a recently proposed gauge covariant diagonalization of \(\pi a_1\)-mixing, we show that the low-energy theorem \(F^{\pi }=e f_\pi ^2 F^{3\pi }\) of current algebra, relating the anomalous form factor \(F_{\gamma \to \pi ^+\pi ^0\pi ^-}=F^{3\pi }\) and the anomalous neutral pion form factor \(F_{\pi ^0\to \gamma \gamma }=F^\pi \), is fulfilled in the framework of the Nambu–Jona-Lasinio (NJL) model, solving a long-standing problem encountered in the extension including vector and axial-vector mesons. At the heart of the solution is the presence of a \(\gamma \pi {\bar q} q\) vertex which is absent in the conventional treatment of diagonalization and leads to a deviation from the vector meson dominance (VMD) picture. It contributes to a gauge-invariant anomalous tri-axial (AAA) vertex as a pure surface term.

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We present the analysis of the SM Higgs boson main production channel, \(gg \to H\), and the two photon Higgs decay channel \(H \to \gamma \gamma \) at tree level in order to obtain the differential cross section of \(gg \to H \to \gamma \gamma \) convoluted with the parton distribution functions (PDFs), and reproduce its plot as a function of the diphoton invariant mass distribution \(M_{\gamma \gamma }\). Subsequently, we investigate the applicability of the heavy top-quark approximation in Singlet Higgs boson production and decay, and present a complete next-to-leading order calculation for \(gg \to H \to \gamma \gamma \).

abstract

We review the kinetic-theory-based derivation of relativistic hydrodynamics for polarized systems of particles with spin 1/2. In the case of global equilibrium, we find that the equivalence between the polarization and vorticity is not a necessary condition. With the use of the pseudogauge transformation, we show how to relate the de Groot–van Leeuwen–van Weert expressions forming the basis of our approach with the canonical currents resulting from the Noether theorem.

abstract

We produced a set of gauge configurations generated with a new \(N_{\mathrm {f}}=3+1\) massive renormalization scheme for three degenerate light quarks with a mass that equals the average light-quark mass in nature and a physical charm-quark mass, and a non-perturbatively determined clover coefficient for dynamical Wilson quarks on the lattice. We present the details of the algorithmic setup and tuning procedure of ensembles with three different volumes. We discuss finite volume effects and lattice artifacts, and present physical results for the charmonium spectrum and dimensionless quantities in a first continuum limit study.

abstract

We analyze Sakumichi and Suganuma lattice QCD results for the 3‑quark potential, using hyperspherical three-body coordinates. We show that their data supports neither the Delta, nor the Y-string interpretation, but something in-between. We show that the shape dependence of Sakumichi and Suganuma three-quark potential evaluated at \(\beta =5.8\) differs from the one evaluated at \(\beta =6.0\) by about 2%.