Hybridized tetraquarks

We propose a new interpretation of the neutral and charged X,Z exotic hadron resonances. Hybridized-tetraquarks are neither purely compact tetraquark states nor bound or loosely bound molecules but rather a manifestation of the interplay between the two. While meson molecules need a negative or zero binding energy, its counterpart for h -tetraquarks is required to be positive. The formation mechanism of this new class of hadrons is inspired by that of Feshbach metastable states in atomic physics. The recent claim of an exotic resonance in the View the MathML source channel by the D0 Collaboration and the negative result presented subsequently by the LHCb Collaboration are understood in this scheme, together with a considerable portion of available data on X,Z particles. Considerations on a state with the same quantum numbers as the X(5568) are also made

The Zc(′)→ηcρZ_c^{(\prime)} \to \eta_c \rho decay as a discriminant between tetraquarks and meson molecules

Understanding the nature of the exotic XYZ resonances is one of the open problems in hadronic spectroscopy. Despite the experimental efforts, the structure of these particles still lacks of an accepted theoretical framework. We propose to use the $Z_c^{(\prime)} \to \eta_c \rho$ decays as a possible discriminant between two of the most popular models: the compact tetraquark and the loosely bound meson molecule. We show that the predictions obtained within the two pictures are significantly different and therefore the proposed decay channel might shed some light on the nature of these states.Comment: To be published in the proceedings of CHARM-2015, Detroit, MI, 18-22 May 2015; references added in v

A Decentralized Lifetime Maximization Algorithm for Distributed Applications in Wireless Sensor Networks

We consider the scenario of a Wireless Sensor Networks (WSN) where the nodes are equipped with a programmable middleware that allows for quickly deploying different applications running on top of it so as to follow the changing ambient needs. We then address the problem of finding the optimal deployment of the target applications in terms of network lifetime. We approach the problem considering every possible decomposition of an application's sensing and computing operations into tasks to be assigned to each infrastructure component. The contribution of energy consumption due to the energy cost of each task is then considered into local cost functions in each node, allowing us to evaluate the viability of the deployment solution. The proposed algorithm is based on an iterative and asynchronous local optimization of the task allocations between neighboring nodes that increases the network lifetime. Simulation results show that our framework leads to considerable energy saving with respect to both sink-oriented and cluster-oriented deployment approaches, particularly for networks with high node densities and non-uniform energy consumption or initial battery charge

Exotic Heavy Quarkonium Spectroscopy: A Mini-review

Since nine years experiments have been observing a host of exotic states decaying into heavy quarkonia. The interpretation of most of them still remains uncertain and, in some cases, controversial, notwithstanding a considerable progress has been made on the quality of the experimental information available and a number of ideas and models have been put forward to explain the observations. In this mini-review we will summarize the measurements, with the most recent updates, and list the useful ones yet to be done. We will discuss the problem of the spin of the X, which could hide some major surprise on its interpretation, and review some more phenomenological issues debated in the field.Comment: 14 pages, 2 figures, 5 tables. To appear in Mod. Phys. Lett.

GGI Lectures on Exotic Hadrons

It is well known that M. Gell-Mann, introducing quarks in 1964 to describe the known mesons and baryons, hinted at the existence of further $qq\bar q\bar q$ mesons (tetraquarks) and $qqqq\bar q$ baryons (pentaquarks). In 1977, R. Jaffe proposed a model of the lightest scalar mesons as diquark-antidiquark pairs and A. de Rujula, H. Georgi and S. Glashow coined the term hadron molecules, to describe possible hadrons made by meson-antimeson pairs bound by the familiar nuclear forces, also an overall tetraquark system. The two alternative pictures have been employed to interpret the unexpected hadron discovered by Belle in 2003, the $X(3872)$, confirmed by BaBar and seen in many other High Energy experiments. Since then, a wealth of Exotic Hadrons have been discovered, mesons and baryons that cannot be described by the classical Gell-Mann, $q\bar q$ and $qqq$, configurations, opening a new chapter of Hadron Spectroscopy.Comment: Lectures for the school "Frontiers in Nuclear and Hadronic Physics 2022", held at the Galileo Galilei Institute, Florence (Italy), February 21-25, 202

Exotic hadron spectroscopy

Since the discovery of the X(3872), a decade ago, more than 20 new charmonium-like resonances have been registered. Most of them have features which do no match what expected from standard charmonium theory. A few resonances have been found in the beauty sector too. Some authors just claim that most of the so called XYZ states are not even resonances but kind of effects of kinematical or dynamical origin, due to the intricacies of strong interactions. According to them, data analyses are naïvely describing and fitting as resonances what are indeed the footprints of such complicated effects. On the other hand, the X(3872), for example, is an extremely narrow state, Gamma ~ 1 MeV, and it is very difficult, in our understanding, to imagine how this could be described with some sort of strong rescattering mechanism. We do not know of other clear examples of such phenomena in the field of high-energy physics and in this thesis we will give little space to this kind of interpretations, which we can barely follow. We shall assume instead that what experiments agree to be a resonance is indeed a resonance. Moreover, we find very confusing the approach of mixing the methods proper of nuclear theory to discuss what we learned with the observations of XY Z resonances especially at Tevatron and LHC. It is true that X seems to be an extreme version of deuterium as its mass happens to be fine-tuned on the value of the D0 D0*bar threshold, but one cannot separate this observation from the fact that X is observed at CMS after imposing kinematical transverse momentum cuts as large as pT ~ 15 GeV on hadrons produced. Is there any evidence of a comparable prompt production of deuterium within the same kinematical cuts, in the same experimental conditions? The ALICE experiment could provide in the near future a compelling measurement of this latter rate (and some preliminary estimates described in the text are informative of what the result will be). Some of the XYZ, those happening to be close to some threshold, are interpreted as loosely-bound molecules, regardless of the great difficulties in explaining their production mechanisms in high energy hadron collisions. Some of them are described just as bound hadron molecules, once they happen to be below a close-by open flavor meson threshold. Other ones, even if sensibly above the close-by thresholds, have been interpreted as molecules as well: in those cases subtle mistakes in the experimental analysis of the mass have been advocated. As a result the field of the theoretical description of XYZ states appears as an heterogeneous mixture of ad-hoc explanations, mainly post-dictions and contradictory statements which is rather confusing to the experimental community and probably self-limiting in the direction of making any real progress. It is our belief instead that a more simple and fundamental dynamics is at work in the hadronization of such particles. More quark body-plans occur with respect to usual mesons and baryons: compact tetraquarks. The diquark-antidiquark model in its updated version, to be described in Chapter 7, is just the most simple and economical description (in terms of new states predicted) that we could find and we think that the recent confirmation of Z(4430) + especially, and of some more related charged J^PG = 1++ states, is the smoking gun for the intrinsic validity of this idea. The charged Z(4430) was the most uncomfortable state for the molecular interpretation for at least two reasons: i) it is charged and molecular models have never provided any clear and consistent prediction about charged states; ii) it is far from open charm thresholds. However, if what observed (by Belle first and confirmed very recently by LHCb) is not an “effect” but a real resonance, we should find the way to explain and put it in connection to all other ones. The Z(4430) appears extremely natural in the diquark-antidiquark model, which in general was the only approach strongly suggesting the existence of charged states years before their actual discovery. We think otherwise that open charm/bottom meson thresholds should likely play a role in the formation of XY Z particles. We resort to the Feshbach resonance mechanism, as mediated by some classic studies in atomic physics, to get a model on the nature of this role. The core of our preliminary analysis is the postulated existence of a discrete spectrum of compact tetraquark levels in the fundamental strong interaction Hamiltonian. The occurrence of open charm/beauty meson thresholds in the vicinity of any of these levels might result in an enhanced probability of resonance formation

Study of B → Kππγ decays

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Robust Observation and Control of Complex Networks

The problem of understanding when individual actions of interacting agents display to a coordinated collective behavior has receiving a considerable attention in many research fields. Especially in control engineering, distributed applications in cooperative environments are achieving resounding success, due to the large number of relevant applications, such as formation control, attitude synchronization tasks and cooperative applications in large-scale systems. Although those problems have been extensively studied in Literature, themost of classic approaches use to consider the unrealistic scenario in which networks always consist of identical, linear, time-invariant entities. It’s clear that this assumption strongly approximates the effective behavior of a network. In fact agents can be subjected to parameter uncertainties, unmodeled dynamics or simply characterized by proper nonlinear dynamics. Therefore, motivated by those practical problems, the present Thesis proposes various approaches for dealing with the problem of observation and control in both the framework of multi-agents and complex interconnected systems. The main contributions of this Thesis consist on the development of several algorithms based on concepts of discontinuous slidingmode control. This techniques can be employed for solving in finite-time problems of robust state estimation and consensus-based synchronization in network of heterogenous nonlinear systems subjected to unknown but bounded disturbances and sudden topological changes. Both directed and undirected topologies have been taken into account. It is worth to mention also the extension of the consensus problem to networks of agents governed by a class parabolic partial differential equation, for which, for the first time, a boundary-based robust local interaction protocol has been presented

Flavored tetraquark spectroscopy

The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quark bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons