Tesi di Dottorato
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Item 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, AlessandroThe 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.Item High-energy resummation in semi-hard processes at the LHC(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, AlessandroSemi-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.Item High-energy resummation in semi-hard processes at the LHC(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, AlessandroSemi-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.Item High-energy resummation in semi-hard processes at the LHC(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, AlessandroSemi-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.Item High-energy resummation in semi-hard processes at the LHC(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, AlessandroSemi-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.Item High-energy resummation in semi-hard processes at the LHC(2017-06-30) Celiberto, Francesco Giovanni; Carbone, Vincenzo; Papa, AlessandroSemi-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.Item Aspects of phase transitions in gauge theories and spin models on the lattice(2016-02-26) Cuteri, Francesca; Papa, Alessandro; Fiore, RobertoThe 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.Item <> next-to-leading order jet vertex for Mueller-Navelet jets(2014-11-12) Perri, Amedeo; Papa, Alessandro; Fiore, RobertoItem Forward jets at LHC in pQCD(2012-11-29) Murdaca, Beatrice; Papa, Alessandro; Fiore, RobertoItem Study of SU(N) gauge theories on the lattice(2006) Falcone, Rossella; Papa, Alessandro; Falcone, Giovanni