Browsing by Author "Papa, Alessandro"

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Aspects of phase transitions in gauge theories and spin models on the lattice
(2016-02-26) Cuteri, Francesca; Papa, Alessandro; Fiore, Roberto
The main focus of this thesis are phase transitions both in gauge theories, in particular in Quantum ChromoDynamics (QCD), and in two-dimensional spin models. The approach is numeric, relying on dedicated simulation and analysis softwares, and takes advantage of the possibility to discretize our theories, and describe our models, on a lattice. Three di erent kind of investigations have been carried out, two of them concerning QCD. The thermal decon nement/chiral phase transition in QCD at zero chemical potential has been indeed, indirectly studied, respectively via the characterization of color- eld ux tubes, as footprints for con nement in SU(3) pure gauge theory, and via a study at imaginary chemical potential for the case of full QCD with two degenerate avors of dynamical quarks Nf = 2. In the former case a systematic study of the longitudinal pro le of the chromoelectric eld produced by the strong interaction of a pair of quark and antiquark in the QCD vacuum has been realized, both at zero and nonzero temperature. Measurements have been performed in numerical simulations implementing the appropriate eld-related lattice operator. The characteristic sizes of the ux tubes have been extracted through a tting procedure based on a well known picture for the con nement phenomenon called \dual superconductor model" that traces an analogy between color con nement and superconductivity. Such a picture is found to successfully describe our numerical results for the chromoelectric eld distribution at zero temperature. Taking one step further in the dual analogy, the pro le of the ux tube has been then studied at nite temperature and across the decon nement transition. However, results indicate that the analogy cannot be pushed so far: as the temperature is increased towards and above the decon nement temperature Tc, the amplitude of the eld inside the ux tube gets considerably smaller, while the shape of the ux tube does not vary appreciably at the onset of decon nement. An "evaporation" of ux tubes is observed that has no counterpart in ordinary (type-II) superconductivity and let the tube structure survive the phase transition, consistently with observations in heavy-ion collision experiments. A somewhat di erent analysis about the thermal phase transition in Nf = 2 QCD (where direct studies are prevented either by the well known sign problem or by high numerical costs) can be carried out at imaginary values of chemical potential that are critical for the Roberge-Weiss (RW) phase transition. In particular, the nature of the RW phase transition at the endpoint of the rst order critical RW line has been investigated. It is found to depend on the quark masses in a way that it is a triple rst-order point in the limit of zero (in nite) masses and a second order critical endpoint at intermediate masses. Similar results are relevant for the understanding of the nature of the thermal transition at = 0. Coming to spin models and, to be more speci c, to two-dimensional spin models characterized by non-Abelian symmetry groups U(2) and SU(N) for N = 5; 8, the existence of in nite order (BKT) phase transition has been checked. Such transitions were expected on the basis of analytical computations and have been, indeed, numerically detected in all considered models. By means of nite size scaling analysis it has been also observed that the BKT phase transition that takes place in U(2) models belongs to the universality class of the two-dimensional XY model.
Forward jets at LHC in pQCD
(2012-11-29) Murdaca, Beatrice; Papa, Alessandro; Fiore, Roberto
From semi-hard processes to the unintegrated gluon distribution: a phenomelogical path in the high-energy framework
(Università della Calabria, 2021-04-28) Bolognino, Andrèe Dafne; Cipparrone, Gabriella; Papa, Alessandro
The class of semi-hard reactions represents a promising venue where to enhance our knowledge of strong interactions and deepen the aspects related to this theory in kinematical regimes so far unexplored. In particular, the high energies reached in electron-proton and in proton-proton collisions first at HERA and then at the LHC, allow us to study scattering amplitudes of hard and semi-hard processes in perturbative QCD. The structure of this thesis can be considered twofold. On one hand, the possibility to distinguish those channels where at least two final-state particles are emitted with large separation in rapidity and with an untagged system, permits to test the BFKL dynamics as resummation energy logarithms in the t-channel. Indeed, these inclusive reactions occur in the Regge limit, s jtj, and fixed-order calculations in perturbative QCD miss the effects of energy logarithms, which are so large to compensate the smallness of the strong coupling constant and must be resummed order by order in perturbation theory. The most powerful theoretical tool to provide the resummation of terms proportional to powers of these logarithms is the Balitsky- Fadin-Kuraev-Lipatov (BFKL) approach. In this framework, the hadroproduction of two forward jets with high transverse momenta separated by a large rapidity at the LHC, known as Mueller–Navelet jets process, has been one of the most investigated reactions. With the idea of deepening our understanding of the BFKL formalism, a new channel belonging to the semi-hard processes category is proposed: the inclusive production of a light charged hadron and a jet with high transverse momentum widely separated in rapidity, whose calculation is performed at NLO accuracy. The importance of this process relies in the possibility to probe a complementary region to one analyzed for the Mueller–Navelet jets. Hadrons, indeed, can be tagged at much smaller values of the transverse momentum than jets. It is proved how asymmetric cuts for the transverse momentum (naturally occurring because the final state is featured by objects of different nature) enhance the BFKL effects and how it is possible to discriminate between different parametrizations of fragmentation functions for the hadron in the final state. Additionally, another reaction is proposed: the hadroproduction of heavy-quark pairs well separated in rapidity. On the other hand, also the class of processes featured by the detection of a single forward object in lepton-proton collision can provide us useful ingredients to develop intriguing phenomenological studies. In particular, the exclusive leptoproduction of light vector mesons, r and f, is exhaustively investigated. In this context, the study of helicity-dependent observables allows us to discriminate among several unintegrated gluon distribution models, whose original definition naturally encodes the BFKL-equation evolution dynamics. This kind of parton density allows us to get access to the hadronic structure at small-x.
High-energy resummation in semi-hard processes at the LHC
(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, Alessandro
Semi-hard processes in the large center-of-mass energy limit offer us an exclusive chance to test the dynamics behind strong interactions in kinematical sectors so far unexplored, the high luminosity and the record energies of the LHC providing us with a richness of useful data. In the Regge limit, s jtj, fixed-order calculations in perturbative QCD based on collinear factorisation miss the effect of large energy logarithms, which are so large to compensate the small QCD coupling s and must therefore be accounted for to all perturbative orders. The BFKL approach represents the most powerful tool to perform the resummation to all orders of these large logarithms both in the LLA, which means inclusion of all terms proportional to ( s ln(s))n, and NLA, which means inclusion of all terms proportional to s( s ln(s))n. The inclusive hadroproduction of forward jets with high transverse momenta separated by a large rapidity gap at the LHC, the so-called Mueller–Navelet jets, has been one of the most studied reactions so far. Interesting observables associated to this process are the azimuthal correlation momenta, showing a very good agreement with experimental data at the LHC. However, new BFKL-sensitive observables should be considered in the context of the LHC physics program. With the aim the to further and deeply probe the dynamics of QCD in the Regge limit, we give phenomenological predictions for four distinct semi-hard process. On one hand, we continue the analysis of reactions with two objects identified in the final state (i) by addressing open problems in the Mueller– Navelet sector and (ii) by studying the inclusive dihadron production in the full NLA BKFL accuracy. Hadrons can be detected at the LHC at much smaller values of the transverse momentum than jets, allowing us to explore an additional kinematical range, complementary to the one studied typical of Mueller– Navelet jets. Furthermore, this process permits to constrain not only the parton distribution functions for the initial proton, but also the parton fragmentation functions describing the detected hadron in the final state. On the other hand, we show how inclusive multi-jet production processes allow us to define new, generalised and suitable BFKL observables, where transverse momenta and rapidities of the tagged jets, well separated in rapidity from each other, appear in new combinations. We give the first phenomenological predictions for the inclusive three-jet production, encoding the effects of higher-order BFKL corrections. Then, making use of the same formalism, we present the first complete BFKL analysis for the four-jet production.
High-energy resummation in semi-hard processes at the LHC
(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, Alessandro
Semi-hard processes in the large center-of-mass energy limit offer us an exclusive chance to test the dynamics behind strong interactions in kinematical sectors so far unexplored, the high luminosity and the record energies of the LHC providing us with a richness of useful data. In the Regge limit, s jtj, fixed-order calculations in perturbative QCD based on collinear factorisation miss the effect of large energy logarithms, which are so large to compensate the small QCD coupling s and must therefore be accounted for to all perturbative orders. The BFKL approach represents the most powerful tool to perform the resummation to all orders of these large logarithms both in the LLA, which means inclusion of all terms proportional to ( s ln(s))n, and NLA, which means inclusion of all terms proportional to s( s ln(s))n. The inclusive hadroproduction of forward jets with high transverse momenta separated by a large rapidity gap at the LHC, the so-called Mueller–Navelet jets, has been one of the most studied reactions so far. Interesting observables associated to this process are the azimuthal correlation momenta, showing a very good agreement with experimental data at the LHC. However, new BFKL-sensitive observables should be considered in the context of the LHC physics program. With the aim the to further and deeply probe the dynamics of QCD in the Regge limit, we give phenomenological predictions for four distinct semi-hard process. On one hand, we continue the analysis of reactions with two objects identified in the final state (i) by addressing open problems in the Mueller– Navelet sector and (ii) by studying the inclusive dihadron production in the full NLA BKFL accuracy. Hadrons can be detected at the LHC at much smaller values of the transverse momentum than jets, allowing us to explore an additional kinematical range, complementary to the one studied typical of Mueller– Navelet jets. Furthermore, this process permits to constrain not only the parton distribution functions for the initial proton, but also the parton fragmentation functions describing the detected hadron in the final state. On the other hand, we show how inclusive multi-jet production processes allow us to define new, generalised and suitable BFKL observables, where transverse momenta and rapidities of the tagged jets, well separated in rapidity from each other, appear in new combinations. We give the first phenomenological predictions for the inclusive three-jet production, encoding the effects of higher-order BFKL corrections. Then, making use of the same formalism, we present the first complete BFKL analysis for the four-jet production.
High-energy resummation in semi-hard processes at the LHC
(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, Alessandro
Semi-hard processes in the large center-of-mass energy limit offer us an exclusive chance to test the dynamics behind strong interactions in kinematical sectors so far unexplored, the high luminosity and the record energies of the LHC providing us with a richness of useful data. In the Regge limit, s jtj, fixed-order calculations in perturbative QCD based on collinear factorisation miss the effect of large energy logarithms, which are so large to compensate the small QCD coupling s and must therefore be accounted for to all perturbative orders. The BFKL approach represents the most powerful tool to perform the resummation to all orders of these large logarithms both in the LLA, which means inclusion of all terms proportional to ( s ln(s))n, and NLA, which means inclusion of all terms proportional to s( s ln(s))n. The inclusive hadroproduction of forward jets with high transverse momenta separated by a large rapidity gap at the LHC, the so-called Mueller–Navelet jets, has been one of the most studied reactions so far. Interesting observables associated to this process are the azimuthal correlation momenta, showing a very good agreement with experimental data at the LHC. However, new BFKL-sensitive observables should be considered in the context of the LHC physics program. With the aim the to further and deeply probe the dynamics of QCD in the Regge limit, we give phenomenological predictions for four distinct semi-hard process. On one hand, we continue the analysis of reactions with two objects identified in the final state (i) by addressing open problems in the Mueller– Navelet sector and (ii) by studying the inclusive dihadron production in the full NLA BKFL accuracy. Hadrons can be detected at the LHC at much smaller values of the transverse momentum than jets, allowing us to explore an additional kinematical range, complementary to the one studied typical of Mueller– Navelet jets. Furthermore, this process permits to constrain not only the parton distribution functions for the initial proton, but also the parton fragmentation functions describing the detected hadron in the final state. On the other hand, we show how inclusive multi-jet production processes allow us to define new, generalised and suitable BFKL observables, where transverse momenta and rapidities of the tagged jets, well separated in rapidity from each other, appear in new combinations. We give the first phenomenological predictions for the inclusive three-jet production, encoding the effects of higher-order BFKL corrections. Then, making use of the same formalism, we present the first complete BFKL analysis for the four-jet production.
High-energy resummation in semi-hard processes at the LHC
(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, Alessandro
Semi-hard processes in the large center-of-mass energy limit offer us an exclusive chance to test the dynamics behind strong interactions in kinematical sectors so far unexplored, the high luminosity and the record energies of the LHC providing us with a richness of useful data. In the Regge limit, s jtj, fixed-order calculations in perturbative QCD based on collinear factorisation miss the effect of large energy logarithms, which are so large to compensate the small QCD coupling s and must therefore be accounted for to all perturbative orders. The BFKL approach represents the most powerful tool to perform the resummation to all orders of these large logarithms both in the LLA, which means inclusion of all terms proportional to ( s ln(s))n, and NLA, which means inclusion of all terms proportional to s( s ln(s))n. The inclusive hadroproduction of forward jets with high transverse momenta separated by a large rapidity gap at the LHC, the so-called Mueller–Navelet jets, has been one of the most studied reactions so far. Interesting observables associated to this process are the azimuthal correlation momenta, showing a very good agreement with experimental data at the LHC. However, new BFKL-sensitive observables should be considered in the context of the LHC physics program. With the aim the to further and deeply probe the dynamics of QCD in the Regge limit, we give phenomenological predictions for four distinct semi-hard process. On one hand, we continue the analysis of reactions with two objects identified in the final state (i) by addressing open problems in the Mueller– Navelet sector and (ii) by studying the inclusive dihadron production in the full NLA BKFL accuracy. Hadrons can be detected at the LHC at much smaller values of the transverse momentum than jets, allowing us to explore an additional kinematical range, complementary to the one studied typical of Mueller– Navelet jets. Furthermore, this process permits to constrain not only the parton distribution functions for the initial proton, but also the parton fragmentation functions describing the detected hadron in the final state. On the other hand, we show how inclusive multi-jet production processes allow us to define new, generalised and suitable BFKL observables, where transverse momenta and rapidities of the tagged jets, well separated in rapidity from each other, appear in new combinations. We give the first phenomenological predictions for the inclusive three-jet production, encoding the effects of higher-order BFKL corrections. Then, making use of the same formalism, we present the first complete BFKL analysis for the four-jet production.
High-energy resummation in semi-hard processes at the LHC
(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, Alessandro
Semi-hard processes in the large center-of-mass energy limit offer us an exclusive chance to test the dynamics behind strong interactions in kinematical sectors so far unexplored, the high luminosity and the record energies of the LHC providing us with a richness of useful data. In the Regge limit, s jtj, fixed-order calculations in perturbative QCD based on collinear factorisation miss the effect of large energy logarithms, which are so large to compensate the small QCD coupling s and must therefore be accounted for to all perturbative orders. The BFKL approach represents the most powerful tool to perform the resummation to all orders of these large logarithms both in the LLA, which means inclusion of all terms proportional to ( s ln(s))n, and NLA, which means inclusion of all terms proportional to s( s ln(s))n. The inclusive hadroproduction of forward jets with high transverse momenta separated by a large rapidity gap at the LHC, the so-called Mueller–Navelet jets, has been one of the most studied reactions so far. Interesting observables associated to this process are the azimuthal correlation momenta, showing a very good agreement with experimental data at the LHC. However, new BFKL-sensitive observables should be considered in the context of the LHC physics program. With the aim the to further and deeply probe the dynamics of QCD in the Regge limit, we give phenomenological predictions for four distinct semi-hard process. On one hand, we continue the analysis of reactions with two objects identified in the final state (i) by addressing open problems in the Mueller– Navelet sector and (ii) by studying the inclusive dihadron production in the full NLA BKFL accuracy. Hadrons can be detected at the LHC at much smaller values of the transverse momentum than jets, allowing us to explore an additional kinematical range, complementary to the one studied typical of Mueller– Navelet jets. Furthermore, this process permits to constrain not only the parton distribution functions for the initial proton, but also the parton fragmentation functions describing the detected hadron in the final state. On the other hand, we show how inclusive multi-jet production processes allow us to define new, generalised and suitable BFKL observables, where transverse momenta and rapidities of the tagged jets, well separated in rapidity from each other, appear in new combinations. We give the first phenomenological predictions for the inclusive three-jet production, encoding the effects of higher-order BFKL corrections. Then, making use of the same formalism, we present the first complete BFKL analysis for the four-jet production.
Hunting stabilization effects of the high-energy resummation at the LHC
(Università della Calabria, 2022-03-14) Mohammed, Maher Abdelrahim Mohammed; Cipparrone, Gabriella; Papa, Alessandro
Studying semi-hard processes in the large center-of-mass energy limit gives us an opportunity to further test perturbative QCD in an unexplored kinematical configuration, contributing to a better understanding of the dynamics of strong interactions. For semi-hard reactions in kinematics at large center-of-mass energy ps, the BFKL resummation of energy logarithms comes into play, since large energy logarithms compensate the smallness of QCD coupling as and must therefore be accounted for to all perturbative orders. Tracing the path toward performing precision calculations via BFKL resummation of high-energy logarithms, in this thesis we present phenomenological analyses for distinct inclusive processes, highlighting the recognized problem of instabilities under higher-order corrections and energy-scales variations, that would abort any possibility to investigate semi-hard reactions with high-precision at natural energy-scales. At the same time, we present new reactions that seem to act as fair stabilizers of the highenergy series. First, the inclusive production at the LHC of a charged light hadron and of a jet, featuring a wide separation in rapidity, is presented making use of optimization methods to fix energy-scale. We report some predictions, tailored on the CMS and CASTOR acceptances, for the cross section averaged over the azimuthal angle between the identified jet and hadron and for azimuthal correlations. Then, we propose as a novel probe channel for the manifestation of the BFKL dynamics, the inclusive hadroproduction of a Higgs boson and of a jet, featuring large transverse momenta and well separated in rapidity. We present predictions for azimuthal Higgs-jet correlations and other observables, to be possibly compared with typical experimental analyses at the LHC. Finlay, we propose the inclusive semi-hard production, in proton-proton collisions, of two bottom-flavored hadrons, as well as of a single bottom-flavored hadron accompanied by a light jet, as novel channels for targeting stabilization effects of the high-energy resummation under higher-order corrections. Moreover, we propose the study of double differential distributions in the transverse momenta of the two finalstate particles as a common basis to investigate the interplay of different resummation approaches.
Probing the high-energy dynamics of QCD: selected theoretical and phenomenological studies
(Università della Calabria, 2023-05-04) Fucilla, Michael; Cipparrone, Gabriella; Papa, Alessandro
The center-of-mass energies available at modern accelerators, such as the Large Hadron Collider (LHC), and at future generation accelerators, such as the Electron-Ion Collider (EIC) and Future Circular Collider (FCC), offer us a unique opportunity to investigate hadronic matter under the most extreme conditions ever reached. In particular, we can access the Regge-Gribov (or semi-hard) limit of QCD, characterized by the scale hierarchy s ≫ {Q2} ≫ Λ2 QCD, where √s is the center-of-mass energy, {Q} a set of hard scales characterizing the process and ΛQCD is the QCD mass scale. In this limit, large logarithmic corrections can affect both parton densities and hard scattering cross sections. The Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach represents the established tool to resum to all orders, both in the leading (LLA) and the next-to-leading (NLA) approximation, these large-energy logarithmic contributions. However, it is well known that at very low values of the Bjorken-x, the density of partons, per unit transverse area, in hadronic wavefunctions becomes very large leading to the so-called saturation effects. The evolution of densities is then described by non-linear generalizations of the BFKL equation. Among these, the most general is represented by the Balitsky-JIMWLK hierarchy of equations, which is needed to describe the scattering of a dilute projectile on a dense target, or also the scattering of two dense systems. The dense system condition can be achieved by a very small-x proton, but is more easily achieved for large nuclei. It is clear that a detailed comparison with experimental data requires precision predictions that can only be achieved in the next-to-leading logarithmic approximation or beyond. We face this task from two different perspectives. On the one hand developing analytical calculations that allow to increase the theoretical accuracy that can be reached in predictions, and on the other, by proposing phenomenological analyzes that can be directly tested experimentally. In particular, within the BFKL approach we calculate the full NLO impact factor for the Higgs production. This is the necessary ingredient to study the inclusive forward emissions of a Higgs boson in association with a backward identified jet. We claim that this result should necessarily supplement pure fixed-order calculations entering in the collinear factorization framework, which cannot be able to describe the entire kinematic spectrum in the Higgs-plus-jet channel. The result can be as well used to describe the inclusive hadroproduction of a forward Higgs in the limit of small Bjorken x. Moreover, using the knowledge of already known impact factors we propose a series of new semi-hard reactions that can be used to investigate BFKL dynamics at the LHC. We investigate all observables used so far to study BFKL, including: total cross sections, azimuthal coefficients, azimuthal distributions and pT -differential distributions. In the context of linear evolution, we consider also the problem of extending BFKL beyond the NLLA. To this aim, we compute the Lipatov vertex in QCD with higher ϵ- accuracy, where ϵ = (D − 4)/2. This ingredient enters the BFKL kernel at next-to-NLA (NNLLA) accuracy. In fact, the NNLLA formulation of BFKL requires not only two and three-loop calculations, but also higher ϵ-accuracy of the one-loop results, for instance, in the part of the kernel containing the product of two one-loop Lipatov vertices. Finally, in the saturation framework, and more specifically in the Shockwave approach, we calculate the diffractive double hadron photo- or electroproduction cross sections with full NLL accuracy. These results are usable to detect saturation effects, at both the future EIC or already at LHC, using Ultra Peripheral Collisions.
Study of SU(N) gauge theories on the lattice
(2006) Falcone, Rossella; Papa, Alessandro; Falcone, Giovanni
<> next-to-leading order jet vertex for Mueller-Navelet jets
(2014-11-12) Perri, Amedeo; Papa, Alessandro; Fiore, Roberto