1,721,129 research outputs found
Search for the Higgs boson decaying into two muons with the CMS experiment
No full textThe Higgs boson was discovered at the CERN LHC by both the ATLAS and CMS collaborations with a mass near 125 GeV in 2012. The measurement of the Higgs boson properties has been one of the main targets of LHC experiments since the discovery. In order to probe the mechanism giving mass to fermions and bosons, the Higgs boson couplings have to be measured. The Standard Model Higgs couplings can be extracted by measuring Higgs boson production and decay rates. Therefore a lot of effort has been done to observe every single experimentally accessible decay in various production modes in the last few years. The bosonic decay modes of the Higgs in gamma gamma, ZZ, and WW have been established using data collected until 2012 (LHC Run 1) while the data collected in 2016 and 2017 allowed to measure the decays to the third generation fermions. The decay of the Higgs boson into tautau has been observed using 2016 data and it confirmed the coupling of the Higgs with leptons. The decay of the Higgs boson into bb has been observed in 2018, hence establishing the coupling with down-type quark. The ttH production mode has also been observed, thus probing directly the coupling to up-type quarks. So far, the Higgs boson couplings have been observed only with the third generation of fermions, thus, the next step would be the search for decays into the second generation. Among those, the Higgs decay into c-quark pairs is the one with the higher event rate. Probing the Standard Model expected event rate is notwithstanding impossible at the LHC because of the large amount of irreducible background and because of the low mass resolution in the dijet final state. Instead, the Higgs boson decay into muons has smaller rates but it also has a clean final state that can be reconstructed with high efficiency and excellent mass resolution, thanks to the CMS tracking and muon systems. However, since the branching fraction B(H→mu mu) is very small (2x104) and the LHC produces abundant backgrounds, an observation of this decay has not been reached yet and upper limits only have been set. My work took part in the most recent search for the Higgs boson decaying to two muons performed by the CMS collaboration. The analysis uses the full proton-proton collision data collected by the CMS experiment at \sqrt{s}=13 TeV during Run 2, corresponding to an integrated luminosity of 137.4 fb-1. The search of the Higgs boson to muon decay targets each of the four main Higgs production channels at the LHC. The four searches use orthogonal data and their results are combined in a single measurement. My work has been dedicated to the improvement of the search in the vector boson fusion (VBF) production mode. In this work, we demonstrate that the VBF channel is the most sensitive among the four H→mu mu searches. The VBF dedicated analysis is based on the fit of a multivariate discriminator, in contrast with the other three dedicated Higgs searches where the fit is performed on the dimuon mass distribution. Moreover, the background estimation is completely based on Monte-Carlo simulations. These two aspects make the strategy to be very similar to the one adopted by two important CMS measurements: the measurement of electroweak production of two jets in association with a Z boson, and the measurement of the Higgs boson decaying into b-quark pairs. Machine learning is a fundamental tool to improve the sensitivity of this search. Two different machine learning techniques are tested for the H→ mu mu search: boosted decision tree (BDT) and deep neural network (DNN). The performance of the two algorithms are compared and the results are extracted from the algorithm that separates better the signal from the background on simulated data. The Higgs boson signal strength is extracted among several regions with a simultaneous maximum likelihood fit and the results are computed for a Standard Model Higgs boson with a mass of 125.38 GeV. In the VBF channel, an excess of events is observed with a strength of 1.36+0.69-0.61, defined as the ratio between the expected and the observed event rate sigmaobs(pp→H→mu mu)/sigmaSM(pp→H→mu mu). The observed excess of events corresponds to a signal significance of 2.4 standard deviations above the background-only hypothesis. The excess of events observed from the combination of the four dedicated searches corresponds to a signal significance of 3.0 standard deviations and it constitutes the evidence of the Higgs boson decay into muons. The results obtained with the data collected at 13 TeV are combined with the ones obtained during Run 1 at the center of mass energies of 7 and 8 TeV. The final combination improves the results of about 1%, resulting in a signal strength of 1.19+0.40-0.30(stat)+0.15-0.14(syst). The thesis is structured as follows. The Standard Model and the Higgs mechanism are introduced in chapter 1. Moreover, the most important measurements of the Higgs boson properties are summarized in that chapter. In chapter 2 the experimental apparatus is described. Firstly, the LHC machine is introduced, then the CMS experiment and the various subdetectors are presented. The algorithms used by CMS to reconstruct physics objects are introduced in chapter 3. In particular, lepton reconstruction and identification are described in the first half of the chapter, while the second half is dedicated to jets. Chapter 4 introduces the search for H with CMS Run 2 data. An overview of the entire analysis is given and the dedicated searches in the ggH, VH, and ttH channels are summarized. The VBF analysis that I have carried out is described in detail in chapter 5. Finally, chapter 6 presents the results of the VBF dedicated search and the results obtained from the combination with the other three dedicated searches and with the data collected during Run 1
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Differential measurement of bb pair production with the CMS experiment at the LHC
No full textSeveral high-mass particles decay into b-quarks. Top quarks always do so, while the Higgs boson is expected to decay into b-quarks more than into any other particles. Distinguishing b-quarks from the QCD background helps to identify the decays of these particles.
At the CERN Large Hadron Collider (LHC) b-quarks are abundantly produced by strong interactions in pp collisions. The hadroproduction of bb̄ pairs is measured to have a large cross section (of the order of 1 mb). In heavy particles studies, the bb̄ pairs produced by QCD cause large backgrounds in wide regions of the phase space. The predictions of those backgrounds have theoretical limits because QCD is a non-perturbative theory and has very large errors in regions where b-quarks are produced with a small angle between them.
The aim of this thesis is the measurement of the momenta and directions of b-quarks in events in which there is one bb̄ pair. There are several variables of the bb̄ pair system that can provide information about non-perturbative bb̄ production. It has been chosen to provide a measurement of the event distribution in the angular distance between the B hadrons and in the transverse momentum (pT) of the bb̄ pair system.
When the b-quarks are produced with small angular separation they are reconstructed as a single jet because the typical angular dimension of a jet is ∆R = 0.4. Identifying the presence of b-quarks using the B hadron decay secondary vertices gives the possibility to detect events where b-quarks are produced at small angular separation. However, it is not possible to measure the transverse momentum of the b-quark from the charged particles contributing to the B hadron vertex since they carry only a fraction of the energy of the quarks.
The energy is measured by merging the information of secondary vertices and jets. The vertices are used as seeds for the construction of the jets and with a new clustering procedure it is possible to assign the jet energy to the two vertices also when b-quarks are produced with a small angular separation.
Several jet triggers have been used in this analysis in order to measure the cross section as a function of the pT of the bb̄ pair in a large pT range. ZeroBias data are also used to cover the very small pT region.
An unfolding procedure with D’Agostini method has been used to remove detector effects from the measured distributions.
The study has been carried out on 2.7/fb of proton-proton collisions recorded by CMS at a centre of mass energy of 13 TeV during 2015. The results of this analysis show that measurements and prediction are compatible in the perturbative region while less agreement is present in the non-perturbative region
TOOCAN cloud mask
No full text<p>This dataset comprises a high cloud mask derived from the TOOCAN dataset (Fiolleau et al., 2020) within the region spanning from 0N to 9.6N latitude and 140E to 149.6E longitude. The TOOCAN dataset offers calibrated infra-red brightness temperatures across the entire tropical band in the period 2012-2016.<br>
The images have 0.04° spatial resolution and 30 minute temporal frequency.</p>
<p>Fiolleau, T., R. Roca, S. Cloché, D. Bouniol, P. Raberanto, 2020: Homogenization of geostationary infrared imager channels for cold cloud studies using Megha-Tropiques/ScaRaB. IEEE Trans. Geosci. Remote Sens., vol 58, no. 9, pp. 6609-6622. doi: 10.1109/TGRS.2020.2978171</p>
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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