1,721,121 research outputs found
Misura della sezione d'urto di produzione Wgg in collisioni pp a 13 TeV e limiti agli accoppiamenti anomali quartici all'esperimento CMS
No full textL'importanza dello studio della produzione di un bosone W in associazione a due fotoni in collisioni protone-protone è molteplice. La misura della sezione d'urto costituisce un test di precisione del modello standard essendo sensibile all'interazione reciproca dei bosoni elettrodeboli. Lo stato finale della collisione è anche uno dei possibili fondi nelle ricerche di nuove particelle che possono mediare l'interazione a più bosoni e merita quindi di essere studiato in dettaglio. Il processo può inoltre essere interpretato nell'ottica delle teorie di campo effettive dato che è sensibile alla presenza di accoppiamenti anomali quartici ed è in grado di verificare la presenza di effetti che vanno oltre il modello standard. Dato che la produzione Wgg è un processo raro, è necessario analizzare un campione di dati con elevata statistica.
I limiti agli accoppiamenti anomali quartici nell'ambito delle teorie di campo effettive sono stati studiati dalle collaborazioni CMS e ATLAS sfruttando diversi stati finali con più di un bosone. Lo studio del processo Wgg è stato effettuato sia da CMS che da ATLAS con dati raccolti ad un'energia del centro di massa pari a 8 TeV corrispondenti ad una luminosità integrata di 19 fb-1. Il fattore limitante nella misura della sezione d'urto per queste due analisi è la limitata statistica. Per questo motivo, la misura descritta in questo lavoro è stata effettuata usando dati raccolti dall'esperimento CMS nel Run 2 di LHC ad un'energia del centro di massa pari a 13 TeV corrispondenti a 137 fb-1. In questo modo, le incertezze collegate alla statistica possono essere notevolmente ridotte.
Per questa analisi, sono stati considerati solo gli stati finali con un elettrone o un muone risultante dal decadimento della W. La selezione degli eventi è stata studiata in dettaglio e sono state applicate tutte le necessarie correzioni alle simulazioni Monte Carlo in modo da migliorare il loro accordo con i dati. I fondi principali alla misura sono l'errata ricostruzione di un getto come un fotone e di un elettrone come un fotone. Questi due casi sono stati studiati in dettaglio tramite un approccio basato sull'utilizzo di dati in regioni di controllo. Il contributo degli altri fondi minoritari è stato valutato tramite le simulazioni Monte Carlo. Per la misura della sezione d'urto sono stati tenuti in considerazione gli effetti delle sistematiche legate alla ricostruzione degli oggetti, ai fattori di correzione e alle metodologie utilizzate.
La sezione d'urto è stata misurata nello spazio delle fasi fiduciale per il decadimento del bosone W in un elettrone o in un muone; è stata inoltre calcolata la combinazione dei due risultati.
La presenza degli accoppiamenti anomali quartici può essere testata generando eventi Monte Carlo che tengano in considerazione i contributi di effetti che vanno oltre il modello standard. Confrontando queste distribuzioni con quelle ottenute per i dati è possibile verificare la presenza degli accoppiamenti anomali o determinare nuovi limiti per la loro intensità. Un campione specifico di eventi simulati è stato prodotto precisamente a questo scopo. I risultati ottenuti mostrano un notevole miglioramento rispetto alle precedenti analisi del processo Wgg e sono paragonabili agli altri risultati ottenuti recentemente per processi a molti bosoni a CMS e ATLAS. Nessuna delle misure effettuate indica una deviazione dal comportamento previsto dal modello standard.The importance of the study of the Wgg production in proton-proton collisions is manifold. The measurement of the production cross section constitutes a precision test of the Standard Model since it is sensitive to the self-interaction of electroweak bosons. This final state is also one of the possible background sources in the searches for new particles that can mediate multi-boson interactions and hence deserves to be studied in detail. Moreover, the process can be interpreted in the framework of the Effective Field Theories as it is sensitive to the presence of anomalous gauge couplings and can probe the presence of effects that are beyond the Standard Model. Being the Wgg production a rare process, a dataset with high integrated luminosity is needed.
The limits on the anomalous quartic gauge couplings in the framework of the Effective Field Theories have been studied in many different multi-boson final states at CMS and ATLAS. The study of the Wgg final state has been performed both by the CMS and ATLAS collaborations at a centre of mass energy of 8 TeV with a dataset corresponding to an integrated luminosity of 19 fb-1. The limiting factor on the measurement of the process cross section in these two analyses was the low statistics. For this reason, this measurement is performed using data collected by the CMS experiment during the whole Run 2 of LHC at a centre of mass energy of 13 TeV, corresponding to approximately 137 fb-1. In this way, the uncertainty connected to the statistics can be substantially reduced and competitive limits on the values of the anomalous couplings are expected to be achievable.
For this analysis, only the electron and muon final states of the W decay have been taken into account. The event selection has been studied and all the required corrections to the Monte Carlo simulations needed to improve their agreement with data have been applied. The main background contributions to the Wgg final state, which are the misidentification of jets as photons and the misidentification of electrons as photons, have been studied in detail by developing a data-driven approach. The data-driven approach gives a better prediction for these processes when compared to the Monte Carlo simulations. The contribution of the other, subleading, background sources has been evaluated with Monte Carlo simulations. The final measurement for the cross section has been performed by taking into account many possible systematic uncertainties on the object reconstruction, on the correction factors and on the methods implemented and used.
The cross sections and the signal strengths have been evaluated in the fiducial phase space in the electron and muon decay channels of the W boson. The combination of the two has also been computed.
The presence of anomalous gauge couplings can be tested by generating Monte Carlo events where contributions linked to beyond the Standard Model effects are taken into account. The comparison of these new simulations with the distributions obtained from data can probe the presence of anomalous couplings or set new limits on their strength. For this reason, dedicated simulation samples have been studied and events have been produced. The results that have been obtained show a great improvement if compared to previous Wgg analyses and are competitive with more recent results obtained by other multi-boson analyses both at CMS and ATLAS. None of the measurements suggests a deviation from the Standard Model prediction
Multiboson measurements with Run 2 data at CMS
No full textProcesses with more than one boson in the final state are interesting because they can provide information on different aspects of Electro-Weak High Energy Physics. The non-abelian structure of the theory can be tested through the measurement of the strength of the couplings, while possible deviations from the theoretical prediction can hint to new physics effects. Some of the most recent results obtained by the CMS collaboration exploiting the data collected between 2016 and 2018 are presented in this note. The very high statistics that has been recorded, close to 140 fb−1 , opens the path to the precision study of processes that were not accessible until now
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
US PRESIDENTIAL ELECTORAL CAMPAIGN: THE Role of Polling in Primary Elections
No full textThe analysis presented in the following dissertation investigates the importance of considering the level of decisiveness in pre-electoral early polls, when it comes to primary electoral forecasting. In light of the current electoral campaign for the presidential nomination in the United States, an experiment was conducted at the North Carolina State University in order to test hypotheses related to the accuracy of pre-electoral surveys. The core of the analysis regarded one single poll conducted over a five days' period in November 2015. A specific question set was included in the survey questionnaire in order to improve the understanding of people's decision during the pre-electoral period. The results have clearly supported the idea that previsions based on early-polls are little predictive of the final outcomes, if done as average mainstream media outlets usually do. Moreover, the analysis offers important case studies regarding the specific matter of early primary polls, and gives an understandable view of how the process functions in the field of electoral forecasting.The analysis presented in the following dissertation investigates the importance of considering the level of decisiveness in pre-electoral early polls, when it comes to primary electoral forecasting. In light of the current electoral campaign for the presidential nomination in the United States, an experiment was conducted at the North Carolina State University in order to test hypotheses related to the accuracy of pre-electoral surveys. The core of the analysis regarded one single poll conducted over a five days' period in November 2015. A specific question set was included in the survey questionnaire in order to improve the understanding of people's decision during the pre-electoral period. The results have clearly supported the idea that previsions based on early-polls are little predictive of the final outcomes, if done as average mainstream media outlets usually do. Moreover, the analysis offers important case studies regarding the specific matter of early primary polls, and gives an understandable view of how the process functions in the field of electoral forecasting
Measurement of the charge asymmetry in events in CMS
No full textThe Standard Model (SM) of particle physics is the most general theory to describe the fundamental constituents and interactions of matter. However, precision meas- urements are needed to further test the consistency of the model or to highlight discrepancies between the theoretical predictions and the experimental results that could lead to new physics. In order to achieve this task, uncertainties connected to the modelling and simulation of the physical event must be studied. One of the main uncertainties in the simulation of a high energy proton-proton collision (such as those studied at the Large Hadron Collider) is due to the choice of the parton distribution functions (PDF). The W boson charge asymmetry is a quantity that is sensitive to the PDF set used in the Monte Carlo events generation. A precise measurement of this quantity can then discriminate between which are the best sets of PDF to be used in a future experiment and hence reduce the uncertainties on the measured quantities. In this work, data collected from the Compact Muon Solenoid experiment at CERN √ in 2012 at a centre of momentum energy of s = 8TeV are analysed alongside Monte Carlo simulations. The determination of the W boson charge asymmetry is performed exploiting events where a W boson is produced at parton level and de- cays into an electron-neutrino pair or a muon-neutrino pair. The result obtained from the experimental data is compared to Monte Carlo datasets obtained with different PDF sets. In the first chapter, a brief introduction to the Standard Model is presented with particular attention to the weak interaction. Parton distribution functions are then described from both the theoretical and the experimental point of view. The W bo- son charge asymmetry is introduced, alongside possible future high energy physics measurements. The second chapter describes the Large Hadron Collider and the Compact Muon Solenoid experiment. A detailed description of the main detectors and of the trigger system of CMS is presented alongside future physics goals. In the following chapter, the algorithms exploited to reconstruct physical objects are presented. A detailed description of reconstruction and identification for electrons and muons is reported. Reconstruction techniques for particle jets and for missing transverse energy are also illustrated. In the last chapter, the measurement of the W boson charge asymmetry is presen- ted. After the study of the selection cuts, the analysis of the background contributions to the electron sample is presented, with special attention to the determination of the Quantum Chromo-Dynamics background. Charge reconstruction efficiencies and overall reconstruction efficiencies are studied. The charge asymmetry is computed for both the electron and the muon samples separately. Finally, the comparison between the asymmetry obtained from the data and the one obtained from the Monte Carlo with different PDF sets is presented
Measurement of the production cross section in pp collisions at 13 TeV with full Run2 data and limits on anomalous quartic gauge couplings
No full text
- …
