Search

In questo lavoro presento le implementazioni di due processi di produzione di una coppia di bosoni elettrodeboli (EW) dallo scattering di due adroni in due diversi generatori di eventi Monte Carlo all'ordine next-to-next-to-leading (NNLO) nella cromodinamica quantistica (QCD) combinati con la parton shower (PS). Nella prima parte della tesi discuto l'implementazione del processo di produzione di due coppie di leptoni privi di massa con lo stesso sapore e carica opposta dallo scattering protone-protone all'interno del generatore di eventi Monte Carlo Geneva. Dopo aver brevemente introdotto il metodo Geneva, fornisco una descrizione dettagliata di due delle sue funzioni recentemente implementate. Dopo aver passato gli eventi attraverso la parton shower di Pythia8, mostro infine diverse distribuzioni di interesse fenomenologico e le confronto con i dati degli esperimenti ATLAS e CMS al Large Hadron Collider (LHC). Il generatore di eventi Geneva consente di abbinare il calcolo NNLO con la resummazione all'ordine logaritmico next-to-next-to-leading primo (NNLL') della zero-jettiness e quella all'ordine logaritmico next-to-leading (NLL) della one-jettiness. Poiché il contributo della risommazione è differenziale nel solo parametro della N-jettiness, può essere utilizzato per generare eventi soltanto dopo aver fornito la sua dipendenza dall'intero spazio delle fasi di radiazione. Le funzioni utilizzate a questo scopo sono dette funzioni di splitting e devono essere normalizzate in modo da non compromettere l'accuratezza della risommazione. In questo lavoro presento un modo per normalizzarle on the fly, che fornisce una migliore stabilità all'integrazione Monte Carlo. Tuttavia, tale metodo richiede il calcolo analitico di diversi limiti dello spazio delle fasi che dipendono dalle mappe utilizzate per proiettare le configurazioni con N+1 partoni di stato finale su quelle con N partoni di stato finale. Dopo aver descritto tutte le proiezioni attualmente disponibili in Geneva, presento un calcolo dettagliato della normalizzazione delle corrispondenti funzioni di splitting. Successivamente discuto la sottrazione all'ordine next-to-leading (NLO) delle singolarità infrarosse di QCD per qualsiasi processo di produzione di un singoletto di colore. Poiché Geneva richiede l'integrazione Monte Carlo on-the-fly delle ampiezze reali sottratte, mostro un modo per ottimizzare l'efficienza dell'integrazione che può essere particolarmente utile per i processi in cui il calcolo degli elementi di matrice reali è computazionalmente impegnativa. Nella seconda parte della tesi discuto l'implementazione del processo di produzione di una coppia di fotoni da uno scattering protone-protone all'interno del generatore di eventi Monte Carlo Powheg Box + MiNNLOPS. Tale processo richiede un trattamento dedicato poiché è afflitto da divergenze di elettrodinamica quantistica (QED) nel limite in cui qualsiasi fotone diventa collineare a un quark. Dopo aver brevemente introdotto il generatore di eventi Powheg Box e il metodo MiNNLOPS, presento gli strumenti appositamente creati per questo calcolo. Comincio descrivendo una tecnica generale per trattare qualsiasi processo con una sezione d'urto Born divergente nel generatore di eventi Powheg Box senza applicare alcun taglio a livello di generazione. Presento quindi una mappa che impedisce che le configurazioni finite dal punto di vista della QED con un partone di stato finale siano proiettate su configurazioni singolari senza partoni di stato finale. Infine discuto alcune modifiche alla versione originale del metodo MiNNLOPS volte a ridurre l'impatto dei contributi spuri oltre il NNLO. Dopo aver passato gli eventi attraverso la parton shower di Pythia8, concludo mostrando diverse distribuzioni di interesse fenomenologico e confrontandole con i dati di LHC più recenti dall'esperimento ATLAS. In this work, I present the implementations of two processes of electroweak (EW) boson pair production from hadronic scattering within two different Monte Carlo event generators at next-to-next-to-leading order (NNLO) in quantum chromodynamics (QCD) combined with parton showers (PS). In the first part of the work, I discuss the implementation of the process of production of two same-flavor opposite-charge pairs of massless leptons from proton-proton scattering within the Geneva Monte Carlo event generator. After briefly introducing the Geneva method, I provide a detailed description of two of its newly-implemented features. After passing the events through the Pythia8 parton shower, I finally show several distributions of phenomenological interest and compare them with the data from the ATLAS and CMS experiments at the Large Hadron Collider (LHC). The Geneva event generator provides a framework for matching the NNLO calculation with the next-to-next-to-leading logarithmic prime (NNLL') resummation of the zero-jettiness and next-to-leading logarithmic (NLL) resummation of the one-jettiness. Since the contribution from the resummation is only differential in the N-jettiness parameter, it can be used for generating events only after providing its dependence on the full radiation phase space. The functions used for this purpose are called splitting functions and must be normalized so as not to spoil the accuracy of the resummation. In this work, I present a way of normalizing them on the fly, which provides better stability to the Monte Carlo integration. However, such a method requires the analytic computation of several phase-space boundaries, which depend on the mappings used for projecting the configurations with N+1 final-state partons onto those with N final-state partons. After describing all the mappings currently available in Geneva, I present a detailed calculation of the normalization of the corresponding splitting functions. I then discuss the next-to-leading order (NLO) subtraction of the infrared QCD singularities for any process of production of a color singlet. Since Geneva requires the on-the-fly Monte Carlo integration of the subtracted real amplitudes, I show a way to optimize the efficiency of the integration, which can be particularly useful for processes where the evaluation of the real matrix elements is computationally demanding. In the second part of the work, I discuss the implementation of the process of production of a photon pair from a proton-proton scattering within the Powheg Box + MiNNLOPS Monte Carlo event generator. Such a process requires a dedicated treatment since it is plagued by quantum electrodynamics (QED) divergences in the limit where any photons become collinear to a quark. After briefly introducing the Powheg Box event generator and the MiNNLOPS method, I present the dedicated tools devised for this calculation. I begin by describing a generic way to deal with any process with a divergent Born cross section in the Powheg Box event generator without applying any generation-level cuts. I then present a mapping that prevents QED-finite configurations with one final-state parton from being projected to singular configurations with no final-state partons. Finally, I discuss several modifications to the original version of the MiNNLOPS method aimed at reducing the size of spurious contributions beyond NNLO. After passing the events through the Pythia8 parton shower, I conclude by showing several distributions of phenomenological interest and comparing them with the most recent LHC data from the ATLAS experiment.

Resonance production in proton–proton collisions at$$\sqrt{s} = 7$$s=7TeV and 13 TeV have been investigated using a Pythia 8 event generator within the framework of microscopic processes including color reconnection and rope hadronization. Specifically, the observable effects of different modes of color reconnections on the ratio of yields of mesonic and baryonic resonances with respect to their stable counterpart have been explored as a function of mean charged particle multiplicity. A suppression in the ratio is observed as a function of the mean number of charged particles for mesonic resonances. The$$\phi /\mathrm {K}$$ϕ/Kand$${\phi /\pi }$$ϕ/πratios show an enhancement for high-multiplicity events due to enhanced production of strange quarks via the microscopic process of rope hadronization in the partonic phase. The mechanism of the hadronization of color ropes together with the quark–gluon plasma (QCD)-based color reconnection of partons predicted an enhancement in the ratio for baryonic resonances to non-resonance baryons having similar quark content. The yield ratios of resonances are found to be independent of the collision energy and strongly dependent on event activity.

The co-design problem of 2-D event generators and sliding mode controller (SMC) is studied in this article for the discrete-time 2-D Roesser model to reduce the communication usage between the plant and the controller. First, by resorting to the 2-D reaching law conditions, the event-based 2-D SMC schemes are proposed and a kind of horizonal/vertical independent event generator is designed. Then, the stability of the sliding-mode dynamics is analyzed and a nonlinear matrix inequality condition associated with the horizontal/vertical sliding matrices is obtained. In order to solve the derived nonlinear matrix inequality condition without introducing conservatism, a binary genetic algorithm (GA) is applied by considering a multiobjective optimization problem, which reflects the tradeoff between the convergence of the sliding-mode dynamics and the scheduling performance of the designed horizontal/vertical event generators. Finally, a simulation example is exploited to demonstrate the effectiveness of the proposed co-design approach with GA.

The tracking problem of the fractional-order nonlinear systems is assessed by extending new event-triggered control designs. The considered dynamics are accompanied by the uncertain strict-feedback form, unknown actuator faults and unknown disturbances. By using the neural networks and the fault compensation method, two adaptive fault compensation event-triggered schemes are designed. Unlike the available control designs, two static and dynamic event-triggered strategies are proposed for the nonlinear fractional-order systems, in a sense that the minimum/average time-interval between two successive events can be prolonged in the dynamic event-triggered approach. Besides, it is proven that the Zeno phenomenon is strictly avoided. Finally, the simulation results prove the effectiveness of the presented control methods.

Soft-drop grooming of hadron-collision final states has the potential to significantly reduce the impact of non-perturbative corrections, and in particular the underlying-event contribution. This eventually will enable a more direct comparison of accurate perturbative predictions with experimental measurements. In this study we consider soft-drop groomed dijet event shapes. We derive general results needed to perform the resummation of suitable event-shape variables to next-to-leading logarithmic (NLL) accuracy matched to exact next-to-leading order (NLO) QCD matrix elements. We compile predictions for the transverse-thrust shape accurate to NLO+NLL' using the implementation of the CAESAR formalism in the Sherpa event generator framework. We complement this by state-of-the-art parton- and hadron-level predictions based on NLO QCD matrix elements matched with parton showers. We explore the potential to mitigate non-perturbative corrections for particle-level and track-based measurements of transverse thrust by considering a wide range of soft-drop parameters. We find that soft-drop grooming indeed is very efficient in removing the underlying event. This motivates future experimental measurements to be compared to precise QCD predictions and employed to constrain non-perturbative models in Monte-Carlo simulations., 50 pages, 21 figures, extended discussion, version accepted for publication in JHEP

The anisotropic collective flow is one of the important observables sensitive to the transport properties of strongly interacting matter created in relativistic heavy-ion collisions. The performance of the multi-purpose detector (MPD) at NICA collider for elliptic flow measurements of identified charged pions, protons, $$K_{s}^{0}$$ and $$\Lambda $$ particles is studied with Monte Carlo simulations using collisions of Au + Au ions employing the UrQMD event generator. Different methods for flow measurements: event plane and direct cumulants are used to investigate the contribution of non-flow correlations and flow fluctuations.

We have calculated the unpolarized dihadron fragmentation functions (uDiFFs) of pions and kaons using the nonlocal chiral-quark model (NLChQM) and evolved our results to the transferred momentum scale Q$^2$=4$\mathrm{GeV}^2$ by the QCD evolution equations. These uDiFFs have also been computed in the Nambu--Jona-Lasinio-jet (NJL-jet) model for the sake of comparison. We find that there is substantial difference between the results of these two models. Furthermore, the DiFFs of $u\to \pi^{+}\pi^{-}$ and $g\to \pi^{+}\pi^{-}$ at $Q^2=109\,\mathrm{GeV}^2$ in these two models are presented in comparison with the parametrizations fitted by the Monte Carlo event generator JETSET., Comment: 13 pages, 9 Figs, this article supersedes arXiv:1304.0525

Recent observations of QGP-like conditions in high-multiplicity pp collisions from ALICE experiment at the LHC warrant an introspection whether to use pp collisions as a baseline measurement to characterize heavy-ion collisions for the possible formation of a Quark-Gluon Plasma. A double differential study of the particle spectra and thermodynamics of the produced system as a function of charged-particle multiplicity and transverse spherocity in pp collisions would shed light on the underlying event dynamics. Transverse spherocity, one of the event shape observables, allows to separate the events in terms of jetty and isotropic events. We analyse the identified particle transverse momentum ( p T ) spectra as a function of charged-particle multiplicity and transverse spherocity using Tsallis nonextensive statistics and Boltzmann-Gibbs Blast-Wave (BGBW) model in pp collisions at s = 13 TeV using PYTHIA8 event generator. The extracted parameters such as temperature ( T ), radial flow ( β ), and nonextensive parameter ( q ) are shown as a function of charged-particle multiplicity for different spherocity classes. We observe that the isotropic events approach thermal equilibrium while the jetty ones remain far from equilibrium. We argue that, while studying the QGP-like conditions in small systems, one should separate the isotropic events from the spherocity-integrated events, as the production dynamics are different.

Highly reliable Monte-Carlo event generators and detector simulation programs are important for the precision measurement in the high energy physics. Huge amounts of computing resources are required to produce a sufficient number of simulated events. Moreover, simulation parameters have to be fine-tuned to reproduce situations in the high energy particle interactions which is not trivial in some phase spaces in physics interests. In this paper, we suggest a new method based on the Wasserstein Generative Adversarial Network (WGAN) that can learn the probability distribution of the real data. Our method is capable of event generation at a very short computing time compared to the traditional MC generators. The trained WGAN is able to reproduce the shape of the real data with high fidelity., Comment: To appear in Journal of the Korean Physical Society

The event-shape and multiplicity dependence of the chemical freeze-out temperature (Tch), freeze-out radius (R), and strangeness saturation factor (&gamma, s) are obtained by studying the particle yields from the PYTHIA8 Monte Carlo event generator in proton-proton (pp) collisions at the centre-of-mass s = 13 TeV. Spherocity is one of the transverse event-shape techniques to distinguish jetty and isotropic events in high-energy collisions and helps in looking into various observables in a more differential manner. In this study, spherocity classes are divided into three categories, namely (i) spherocity integrated, (ii) isotropic, and (iii) jetty. The chemical freeze-out parameters are extracted using a statistical thermal model as a function of the spherocity class and charged particle multiplicity in the canonical, strangeness canonical, and grand canonical ensembles. A clear observation of the multiplicity and spherocity class dependence of Tch, R, and &gamma, s is observed. A final state multiplicity, Nch&ge, 30 in the forward multiplicity acceptance of the ALICE detector appears to be a thermodynamic limit, where the freeze-out parameters become almost independent of the ensembles. This study plays an important role in understanding the particle production mechanism in high-multiplicity pp collisions at the Large Hadron Collider (LHC) energies in view of a finite hadronic phase lifetime in small systems.

In this article, a new event-triggered $H_{i}/H_{\infty }$ optimization fault detection (FD) scheme is proposed for linear discrete time systems. A linear discrete time system with varying sampling periods is first presented to describe the dynamics of an event-triggered system. Based on this, an observer-based fault detection filter (FDF) is constructed as an event-triggered residual generator so that the generated residual signal is completely decoupled from the event-triggered transmission error. The design of event-triggered FDF is formulated as a multiobjective optimization problem denoted by $H_{i}/H_{\infty }$ and an optimal solution can be obtained by recursive calculation of Riccati equations. In addition, an event-triggered residual evaluation strategy is also presented. Comparing with the existing event-triggered FD schemes, the major contribution of this article is to decouple the residual signals from the event-triggered transmission errors completely and, consequently, the FD performance can be improved significantly. Moreover, an optimal tradeoff between the robustness of residual to unknown input and the sensitivity of residual to fault is achieved in the sense of $H_{i}/H_{\infty }$ optimization, while the design of FDF and event generator can be carried out independently. To demonstrate the effectiveness of the proposed method, a vehicle lateral dynamic system is used as a simulation example.

In this article, a framework for hadronic rescattering in the general-purpose Pythia event generator is introduced. The starting point is the recently presented space-time picture of the hadronization process. It is now extended with a tracing of the subsequent motion of the primary hadrons, including both subsequent scattering processes among them and decays of them. The major new component is cross-section parameterizations for a range of possible hadron-hadron combinations, applicable from threshold energies upwards. The production dynamics in these collisions has also been extended to cope with different kinds of low-energy processes. The properties of the model are studied, and some first comparisons with LHC pp data are presented. Whereas it turns out that approximately half of all final particles participated in rescatterings, the net effects in pp events are still rather limited, and only striking in a few distributions. The new code opens up for several future studies, however, such as effects in pA and AA collisions., 61 pages, 24 figures, 10 tables

The Compressed Baryonic Matter experiment (CBM) at FAIR aims to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures using collisions of heavy ions at center-of-mass energies of a few GeV per nucleon. Anisotropic transverse flow is among the key observables to study the properties of matter created in such collisions. The CBM performance for anisotropic flow measurements is studied with Monte-Carlo simulations using collisions of gold ions at lab momentum of 10A GeV/c employing UrQMD event generator. Different combinations of PSD module groups are used to investigate the possible systematic biases in flow measurement and to study the effects of detector azimuthal non-uniformity. The resulting performance of the CBM for flow measurements is demonstrated for directed flow of charged pions as a function of rapidity and transverse momentum.

Fixed target experiments have an unique possibility to measure centrality of colliding systems by hadronic calorimeters on the beam line. This is usually achieved by the detection of all forward nucleon spectators and accomplishes fluctuation and correlation measures with lower biases than in collider experiments. However, hadronic calorimeters have much lower resolution than multiplicity detectors that introduces additional volume fluctuation to the measures. In this work, we present the first attempt to increase the resolution capacity of the spectator detector by implementing a convolutional neural network to the modular structure of the Projectile Spectator Calorimeter of the NA61/SHINE experiment. The data were generated in the framework of SHIELD Monte-Carlo event generator with detector response simulated with GEANT4 for the collisions of the lightest available system (7Be + 9Be) and for the highest beam momentum (150A GeV/c). Two ways of determination centrality—by a number of forward spectators and by forward energy – are considered. In comparison with the classical centrality selection method, the neural net shows a significant increase of centrality selection accuracy after implementation.

The search for new interactions and particles in high-energy collider physics relies on precise background predictions. This has led to many advances in combining precise fixed-order cross-section calculations with detailed event generator simulations. In recent years, fixed-order QCD calculations of inclusive cross sections at N3LO precision have emerged, followed by an impressive progress at producing differential results. Once differential results become publicly available, it would be prudent to embed these into event generators to allow the community to leverage these advances. This note offers some concrete thoughts on ME+PS matching at third order in QCD. As a method for testing these thoughts, a toy calculation of $e^+e^-\rightarrow u \bar u$ at $\mathcal{O}(\alpha_s^3)$ is constructed, and combined with an event generator through unitary matching. The toy implementation may serve also as blueprint for high-precision QCD predictions at future lepton colliders. As a byproduct of the N3LO matching formula, a new NNLO+PS formula for processes with "additional" jets is obtained., Comment: 19 pages main text + detailed appendices

Recently, the ATLAS data of isolated three-photon production showed that the next-to-leading order (NLO) collinear factorization is not enough to describe experimental data. Therefore, one needs to calculate the cross section beyond the NLO, and as showed later, these data can be well described by the NNLO calculation within the collinear factorization framework. However, it is shown that the $$k_t$$ k t -factorization can be quite successful in describing exclusive and high energy collision processes, henceforth we decided to calculate isolated three-photon production within this framework. In this work we use the Martin, Ryskin, and Watt unintegrated parton distribution functions (MRW UPDFs) at LO and NLO levels, in addition to parton branching (PB) UPDFs in order to calculate cross section which we utilize the KATIE parton level event generator. It will be shown that in contrast to collinear factorization, the $$k_t$$ k t -factorization can describe quiet well the three-photon production ATLAS data. Interestingly our results using the NLO-MRW and PB UPDFs can cover the data within their uncertainty bands, similar to the NNLO collinear results.

In the present paper, we check and study the validity of the KATIE parton level event generator by calculating the inclusive electron-proton (ep) dijet and the proton-proton (pp) Drell-Yan electron-pair production’s differential cross sections in the kt- and collinear factorization frameworks. The Martin-Ryskin-Watt (MRW) unintegrated parton distribution functions (UPDFs) are used as the input UPDFs. The results are compared with those of ZEUS ep inclusive dijet and ATLAS p-p Drell-Yan electron-pair productions, experimental data. The KATIE parton level event generator can directly calculate the cross sections in the kt-factorization framework. It was noticed by van Hameren, the author of KATIE, that the lab to the Breit transformation in this generator was not correctly implemented, so the produced output did not cover the ep ZEUS experimental data in which the mentioned transformation is applied. The author of the code fixed the bug by implementing the correct transformation in the KATIE parton event generator. Then, we could appropriately produce the ep inclusive dijet differential cross section, in comparison with those of ZEUS data. It is also shown that the Martin-Ryskin-Watt at the next-to-leading order level, with the angular ordering constraint, can successfully predict the ATLAS p-p Drell-Yan data. Finally, as it is expected, we conclude that the kt factorization is an appropriate tool for the small longitudinal parton momenta and high center of mass energies, with respect to the collinear one.

In this work, the $p\ensuremath{-}p(\overline{p})$ Drell-Yan lepton pair production (DY) differential cross sections at hadron colliders, such as LHC and TEVATRON, are studied in the ${k}_{t}$-factorization framework. In order to take into account the transverse momenta of incoming partons, we use the unintegrated parton distribution functions of Kimber et al. (KMR) and Martin et al. (MRW) in the leading order (LO), and next-to-leading-order (NLO) levels with the input MMHT2014 PDF libraries. Based on the different off shell partonic matrix elements, we analyze the behaviors of DY differential cross sections with respect to the invariant mass, the transverse momentum and the rapidity as well as the specific angular correlation between the produced leptons. The numerical results are compared with the experimental data, in different energies, which are reported by various collaborations, such as CDF, CMS, ATLAS, and LHCb. It is shown that the NLO-MRW and KMR schemes predict closer results to the data compared to the LO-MRW, since we do not have fragmentation. It is demonstrated that while the ${q}^{*}+{\overline{q}}^{*}\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}/Z+g\ensuremath{\rightarrow}{l}^{+}+{l}^{\ensuremath{-}}+g$ subprocess has a negligible contribution, it has a sizable effect in the low dilepton transverse momentum. In agreement with the NNLO, perturbative quantum chromodynamics (pQCD), report (pythia, sherpa, etc.) by including the higher-order perturbative contributions the better results are archived. On the other hand as the scale of energy increases, for the LHC energies, the Compton subprocess, i.e., ${q}^{*}+{g}^{*}\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}/Z\ensuremath{\rightarrow}{l}^{+}+{l}^{\ensuremath{-}}+q$, has the largest contribution to the differential cross section in the most intervals of some observables, as is expected. The variation of the differential cross section with respect to the various variables such as the invariant mass, the center of mass energy, etc. are discussed. In order to validate our results, we also consider the strong ordering constraint and the KaTie parton-level event generator.

We identify accelerator and beam conditions at the Electron-Ion Collider (EIC) that need to be included in physics and detector simulations. For our studies, we implement accelerator and beam effects in the Pythia 8 Monte Carlo event generator and examine their influence on the measurements in the central and far-forward regions of the detector. In our analysis, we demonstrate that the accelerator and beam effects can be also studied accurately by modifying the Monte Carlo input to detector simulations, without having to implement the effects directly in the event generators.

In a recent article we presented a model for hadronic rescattering, and some results were shown for pp collisions at LHC energies. In order to extend the studies to pA and AA collisions, the Angantyr model for heavy-ion collisions is taken as the starting point. Both these models are implemented within the general-purpose Monte Carlo event generator Pythia, which makes the matching reasonably straightforward, and allows for detailed studies of the full space--time evolution. The rescattering rate is significantly higher than in pp, especially for central AA collisions, where the typical primary hadron rescatters several times. We study the impact of rescattering on a number of distributions, such as pT and eta spectra, and the space--time evolution of the whole collision process. Notably rescattering is shown to give a significant contribution to elliptic flow in XeXe and PbPb, and to give a nontrivial impact on charm production., 38 pages, 16 figures