Measurement of the double polarization observable E for the photoproduction of π0π+/−\pi^{0} \pi^{+/-} pairs off deuteron and dButanol targets

The binding of nucleons to nuclei and the formation of quarks to nucleons or other hadrons, is governed by the strong interaction. Quantum Chromodynamics (QCD), is well established as a theory of strong interaction and has a characteristic property that the coupling constant decreases as a function of the momentum transfer (energy). In high-energy regime, quarks and gluons behave as free particles and interact only weakly; here the coupling constant is small. Thus perturbative QCD at high energies can deal with the interations of quarks and gluons. However, at lower energies, the quarks interact strongly and virtual gluons can produce gluon-gluon pairs. Due to the large coupling constant here, perturbative calculations of QCD are meaningless and fail to explain the confinement. To verify QCD models at low energies, study of nucleon excitation spectrum is of particular interest. However, over the past years comparison of the model predictions with the experimentally observed states have shown a large discrepancy in number and ordering of the levels. Many more states have been predicted than they have been actually experimentally observed. This issue is known as the problem of missing resonances. This mismatch can either originate from the effective degrees of freedom of the models or due to the experimental bias. In the beginning of hadron spectroscopy, results were obtained from pion-nucleon scattering experiments mostly. However, since the intermediate nucleon resonance depends on the production mechanism, mostly resonances which couple to the $\pi N$ have been observed so far. To compensate this, in the last decades those results have been supplemented with data of unpolarized cross sections obtained from photoproduction of mesons at various acceleration facilities. Nevertheless, the problem of missing resonances persists because of the many broadly overlapping resonances. Therefore, current experiments focus more on the measurement of single and double polarization observables, which may improve the situation. Observables are actually model-independent and sensitive to interference terms that can enhance the weakly contributing suppressed resonances. Photoproduction of $\pi^0\pi^{\pm}$-pairs from quasi-free nucleon bound in the deuterons has been investigated in view of the helicity dependence of these two reactions. While measurements with a liquid deuterium target were used to extract the unpolarized cross sections, along with that a deuterated longitudinally polarized solid butanol target together with a circularly polarized photon beam helped in calculating the observable E. With these results the spin-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ corresponding to the anti-parallel and parallel spin configurations of the photon beam and target nucleon have been derived. The measurements were done at the Mainz MAMI accelerator facility with tagged photon beams produced by bremsstrahlung process for, a longitudinally polarized 1.5 GeV electron beam. The reaction products from the three different target types (deuteron, dbutanol and carbon) were detected with an almost 4$\pi$ solid angle covering calorimeter comprising of Crystal Ball and TAPS detectors along with the charged particle identifier plastic scintillators. The analysis results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged $\rho$ mesons. Furthermore, the results with unpolarized target have been compared to the available previous data sets while the polarized results have been compared with the recent MAID model prediction

Search for the production of Dark Matter in hadronic mono-top signatures with the CMS experiment

A search for the production of Dark Matter in hadronic mono-top signatures using data recorded by the CMS experiment in the years from 2016 to 2018 is presented. First, the analysis strategy is defined relying on the existence of large missing transverse momentum and a large-radius jet. The underlying theoretical model is then studied in order to validate the analysis strategy. Consequently, the modeling of the production of single vector bosons in association with additional jets is studied in detail because of its importance regarding the background model of this analysis. Corrections based on available state-of-the-art theoretical calculations are derived in order to improve the modeling of the aforementioned processes and these corrections are compared to alternative corrections based on Monte Carlo simulation. Next, the data analysis and its technical details are explained. Then, a statistical model is built estimating the major background processes utilizing data from control regions. Finally, a statistical hypothesis test combined with parameter estimation is performed in order to search for possible signal contributions in data. No significant signal contributions were found. Therefore, parameter ranges of the used theoretical signal model were excluded

Observation of B⁰s - B⁻⁰s oscillations and the development and application of same-side-kaon flavor tagging

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 201-209).The search for flavor oscillations in the neutral Bs - B meson system constitutes a flagship analysis of the Tevatron proton-anti-proton collider physics program and an important probe for effects due to new physics beyond the Standard Model of particles and interactions. In particular, the precise measurement of a process such as Boscillations sets a strong constraint on the parameters of quark-flavor mixing in the Standard Model. This dissertation reports the analysis which, for the first time, observed B- Bs oscillations, using data collected with the CDF detector. The sub-percent precision of the measurement is also noteworthy. The data sample used for this analysis includes fully and partially reconstructed Bdecays: ... The focus of this thesis is the algorithm of same-side-kaon tagging which provides _-0 a large fraction of the flavor-tagging power available to this analysis of B- B8 oscillations. Flavor tagging consists in assessing whether a B, meson is creates as a B_--0 or a B, state, and constitutes an important ingredient in the analysis presented in this document. The algorithm which is here described combines particle identification information and kinematic characteristics of the Bevent in an artificial neural network to provide improved tagging power E'2 of about 4.0 - 4.8%, depending on the data sample to which the algorithm is applied. The search for B1 oscillations is performed using an amplitude method based on a frequency scanning procedure. Applying a neural network-based combination of lepton, kaon and jet charge opposite-side tagging algorithms, with a total tagging power of ED2 = 1.8%, and the same-side-kaon tagging algorithm to a data sample of 1 fb-1, a signal of B- B_ oscillations with a significance greater than 5 standard deviations is found ...by Alberto Belloni.Ph.D

Search for CP Violation in B0s to J/psi Phi decay at CDF

The CDF experiment, which uses proton-antiproton collisions at sqrt{s}=1.9 TeV produced at the Fermilab Tevatron, is unique in its ability to observe all flavors of B hadrons and measure their properties. Among them, CP violation is of fundamental interest. In the B+ and B0 systems, measurements of CP violation parameters performed essentially at B factories have borne out the predictions of CKM model. Little is known, experimentally,about CP violation in the B0s system. The standard model predicts very little CP violation there, thus any nonzero measurement could be an indication of New Physics. In this thesis, I will report on the very first flavor-tagged analysis of approximately 2000 B0s -> Jpsi Phi decaysreconstructed in a 1.35 fb-1 data sample collected at CDF. This channel is sensitive not only to the width difference Delta-Gamma in the B0ssystem but also to the CP violation parameter beta_s. The final result we obtain is a confidence region in the two dimensional space of beta_sand Delta-Gamma. Assuming the standard model predictions of beta_s and Delta-Gamma, the probability is 15%, corresponding to 1.5 Gaussian standard deviations

Minimally-supervised Methods for Arabic Named Entity Recognition

Named Entity Recognition (NER) has attracted much attention over the past twenty years, as a main task of Information Extraction. The current dominant techniques for addressing NER are supervised methods that can achieve high performance, but require new manually annotated data for every new domain and/or genre change. Our work focuses on approaches that make it possible to tackle new domains with minimal human intervention to identify Named Entities (NEs) in Arabic text. Specifically, we investigate two minimally-supervised methods: semi-supervised learning and distant learning. Our semi-supervised algorithm for identifying NEs does not require annotated training data or gazetteers. It only requires, for each NE type, a seed list of a few instances to initiate the learning process. Novel aspects of our algorithm include (i) a new way to produce and generalise the extraction patterns (ii) a new filtering criterion to remove noisy patterns (iii) a comparison of two ranking measures for determining the most reliable candidate NEs. Next, we present our methodology to exploit Wikipedia structure to automatically develop an Arabic NE annotated corpus. A novel mechanism is introduced, based on the high coverage of Wikipedia, in order to address two challenges particular to tagging NEs in Arabic text: rich morphology and the absence of capitalisation. Neither technique has yet achieved performance levels comparable to those of supervised methods. Semi-supervised algorithms tend to have high precision but comparatively low recall, whereas distant learning tends to achieve higher recall but lower precision. Therefore, we present a novel approach to Arabic NER using a combination of semi-supervised and distant learning techniques. We used a variety of classifier combination schemes, including the Bayesian Classifier Combination (BCC) procedure, recently proposed for sentiment analysis. According to our results, the BCC model leads to an increase in performance of 8 percentage points over the best minimally-supervised classifier

Study of single top quarks in association with vector bosons

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University Londo

A measurement of top quark production at √s = 13TeV with LHCb data

The LHCb experiment provides unique detector coverage of the highest energy proton-proton interactions ever produced. Designed to study b-& c-hadron physics at the LHC, the detector is fully instrumented in the forward region, 2.0 < η < 4.5, with excellent tracking, vertex resolution and particle identification. The increased centre of mass energy in RunII gives rise to 3-fold increased inclusive top cross-section over RunI at the LHC, corresponding to a 10-fold increase within the LHCb acceptance. The top quark is the heaviest fundamental particle and is expected to play a special role in new physics scenarios. Higher order interference mechanisms, sensitive to physics beyond the reach of current colliders, result in a charge asymmetry in the relative angular distributions of tt pairs. The LHCb acceptance offers greater sensitivity to AttC due to reduced dilution from gluon-gluon fusion. Top quarks are identified through the presence of a high pT muon and b-jet in the final state. Forward production was first observed with RunI data at LHCb in this channel. Top pairs may be identified with an additional opposite-sign lepton or b-jet. The increase in available statistics with RunII, as well as improved signal to background ratio, enables differential measurements of heavy flavour tagged W+jet yields in muon pseudorapidity. New running conditions necessitated re-optimisation of jet input selection for reconstruction as well as renewal of heavy flavour tagging algorithms, achieved using deep learning techniques. Together these provide the first full RunII top cross-section in the μ +b channel at LHCb and the first top asymmetry measurement in the forward region. Each use data corresponding to an integrated luminosity of 5.4fb−1 (5% systematic). σ(t) [13 TeV] = 0.89 ± 0.06 (stat) ± 0.18 (syst) pb , σ(¯t) [13 TeV] = 0.66 ± 0.05 (stat) ± 0.17 (syst) pb . AtopC [13 TeV] = 0.14 ± 0.05 (stat) ± 0.05 (syst) . While the latter measurement was inconclusive with respect to the t ¯t asymmetry, the combined asymmetry was observed to 2.1σ above zero. Differential cross-sections were found to be within 1σ per bin of NLO standard model predictions. The precision of both sets of measurements are systematically limited, with largest contributions from heavy flavour yields (∼ 20%) and SV-tagging efficiencies (10%) despite at least partially cancelling in δAC