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Search for high mass dijet resonances with a new background prediction method in proton-proton collisions at 13 TeV
No full textA search for narrow and broad resonances with masses greater than 1.8 TeV decaying to a pair of jets is presented. The search uses proton-proton collision data at = 13 TeV collected at the LHC, corresponding to an integrated luminosity of 137 fb. The background arising from standard model processes is predicted with the fit method used in previous publications and with a new method. The dijet invariant mass spectrum is well described by both data-driven methods, and no significant evidence for the production of new particles is observed. Model independent upper limits are reported on the production cross sections of narrow resonances, and broad resonances with widths up to 55% of the resonance mass. Limits are presented on the masses of narrow resonances from various models: string resonances, scalar diquarks, axigluons, colorons, excited quarks, color-octet scalars, W′ and Z′ bosons, Randall-Sundrum gravitons, and dark matter mediators. The limits on narrow resonances are improved by 200 to 800 GeV relative to those reported in previous CMS dijet resonance searches. The limits on dark matter mediators are presented as a function of the resonance mass and width, and on the associated coupling strength as a function of the mediator mass. These limits exclude at 95% confidence level a dark matter mediator with a mass of 1.8 TeV and width 1% of its mass or higher, up to one with a mass of 4.8 TeV and a width 45% of its mass or higher.[graphic not available: see fulltext
Observation of Photoion Backward Emission in Photoionization of He and N
No full textWe experimentally investigate the effects of the linear photon momentum on the momentum distributions of photoions and photoelectrons generated in one-photon ionization in an energy range of 300 eV≤E≤40 keV. Our results show that for each ionization event the photon momentum is imparted onto the photoion, which is essentially the system’s center of mass. Nevertheless, the mean value of the ion momentum distribution along the light propagation direction is backward-directed by −3/5 times the photon momentum. These results experimentally confirm a 90-year-old prediction
Measurement of CKM matrix elements in single top quark -channel production in proton-proton collisions at 13 TeV
No full textThe first direct, model-independent measurement is presented of the modulus of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements , , and , in final states enriched in single top quark -channel events. The analysis uses proton-proton collision data from the LHC, collected during 2016 by the CMS experiment, at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb. Processes directly sensitive to these matrix elements are considered at both the production and decay vertices of the top quark. In the standard model hypothesis of CKM unitarity, a lower limit of 0.970 is measured at the 95% confidence level. Several theories beyond the standard model are considered, and by releasing all constraints among the involved parameters, the values 0.988 0.024, and 0.06 0.06, where the uncertainties include both statistical and systematic components, are measured
Dipole subtraction vs. phase space slicing in NLO NRQCD heavy-quarkonium production calculations
No full textWe compare two approaches to evaluate cross sections of heavy-quarkonium production at next-to-leading order in nonrelativistic QCD involving S - and P -wave Fock states: the customary approach based on phase space slicing and the approach based on dipole subtraction recently elaborated by us. We find reasonable agreement between the numerical results of the two implementations, but the dipole subtraction implementation outperforms the phase space slicing one both with regard to accuracy and speed
Blazars at the Cosmic Dawn
No full textThe uncharted territory of the high-redshift () Universe holds the key to understand the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, i.e., blazars, we have carried out a multi-wavelength study of a large sample of radio-loud quasars beyond . Our sample consists of 9 -ray detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3−10 keV photon index ), including 15 with NuSTAR observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint γ-ray emitters with steep spectra. The high-redshift blazars host massive black holes and luminous accretion disks . Their broadband spectral energy distributions are found to be dominated by high-energy radiation indicating their jets to be among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other blazars, indicating faster moving jets. We conclude that the presented list of the high-redshift blazars may act as a reservoir for follow-up observations, e.g., with NuSTAR, to understand the evolution of relativistic jets at the dawn of the Universe
A calibration of the Belle II hadronic tag-side reconstruction algorithm with decays
No full textTag-side reconstruction is an important method for reconstructing meson decays with missing energy. The Belle II tag-side reconstruction algorithm, Full Event Interpretation, relies on a hierarchical reconstruction of meson decays with multivariate classification employed at each stage of reconstruction. Given the large numbers of classifiers employed and decay chains reconstructed, the performance of the algorithm on data and simulation differs significantly. Here, calibration factors are derived for hadronic tag-side decays by measuring a signal side decay, , in fb of Belle II data. For a very loose selection on the tag-side multivariate classifier, the calibration factors are and for tag-side and mesons, respectively
TMD densities at leading and higher order from the noParton Branching method
No full textWe present a new determination of Transverse Momentum Dependent (TMD) parton distributions obtained with the Parton Branching (PB) method at LO, NLO and NNLO. The PB TMDs are extracted from fits to precision DIS data using DGLAP splitting functions at leading and higher order. We extract both the collinear part and the transverse momentum dependent part of the parton densities.In addition the fit sensitivity to dynamical resolution scales on TMD evolution in different kinematical region of x and Q2 will be investigated
Charge-density-wave ordering in three-dimensional metallic compounds
No full textThe Charge-density-wave (CDW) is a static modulation of the density of conduction electrons which is accompanied by a periodic distortion of the lattice. Although CDW mechanisms have been established in one-dimensional (1D) and two-dimensional (2D) systems, the driving force behind the CDW remains an enigma for three-dimensional (3D) systems. This thesis reports on two 3D systems, CuV2S4 and Er2Ir3Si5, with the purpose of explaining the mechanism for the formation of the CDW. Detailed investigations are presented of phase transitions of the compounds CuV2S4 and Er2Ir3Si5, using physical property measurements of single-crystals and single-crystal X-ray diffraction (SXRD). Another compound, Ni{0.89}V{2.11}Se4 with Ni/V disorder is also presented in the thesis. Earlier studies report that CuV2S4 undergoes an incommensurate CDW phase transition at 90 K and a second phase transition at 50 K. Upon the analysis of the SXRD data below 90 K, we observe incommensurate superlattice reflections at positions q = (σ, σ, 0), with σ = 3/4+δ. Moreover, there is a distortion of the lattice, where the symmetry lowers from cubic Fd-3m to orthorhombic Imm2, which is in agreement with the previous work. Below 50 K, the symmetry remained orthorhombic Imm2, however, we found the nature of the 50 K phase transition to be a lock-in transition towards a threefold superstructure. The lock-in transition occurs only on annealed crystals. As-grown (without annealing) crystals, on other hand, suffer from lattice defects, and as a result, they do not undergo the 50 K phase transition. Instead, the σ component of the modulation wave vector q decreases and passes the rational value of 3/4, but never reaches 2/3. From the analysis of the SXRD data, we have established a superspace model for the crystal structure of the CDW phase suggesting that the formation of extended 3D clusters of Vanadium atoms is at the origin of the CDW. At room temperature, R2Ir3Si5 (R = Lu, Er, Ho) is orthorhombic Ibam. A previous study by Electron diffraction (ED) of Lu2Ir3Si5 revealed the presence of incommensurate superlattice reflections at q = (-σ, 2σ, σ), with σ = 0.23~0.25, associated with a CDW phase transition below 140 K. From studies of the physical properties (2 to 300 K) of a single-crystal of Er2Ir3Si5 we have concluded the CDW in the material is a first-order phase transition. The analysis of the SXRD data below 150 K, shows the presence of incommensurate superlattice reflections at positions q = (1/4-δ, 1/2-δ, 1/4-δ) accompanied by a strong monoclinic distortion of the lattice. However, we find that triclinic symmetry I-1 provides a better fit to the model compared to monoclinic symmetry. Our analysis of the crystal structure shows that the CDW resides on the zigzag chains of Iridium atoms. What makes this CDW unusual is that, firstly, it is an incommensurate first-order transition accompanied by a monoclinic lattice distortion, and secondly, from the magnetic susceptibility measurements, we observe that there is a strong coupling between the CDW and magnetism, as the Er^{3+} moments are influenced by the CDW. We also show that in the high-quality single-crystal, the magnetic ordering of the compound is suppressed to at least 0.1 K. However, previous studies report that in a polycrystal of Er2Ir3Si5 the antiferromagnetic ordering is observed around 2.1 K. This seems to suggest that disorder in the polycrystal brings back the antiferromagnetism at the expense of the CDW transition. According to the literature, polycrystalline NiV2Se4 is reported to be a CDW system at 165 K. We sought to investigate the CDW in the material, however, the attempts to synthesize single crystals of NiV2Se4 led to Ni deficient material with Ni/V site disorder, resulting in Ni{0.89}V{2.11}Se4. By studying temperature-dependent structural and bulk properties of Ni{0.89}V{2.11}Se4, we report a possible Non-Fermi-liquid (NFL) to a Fermi-liquid (FL) transition at ambient pressure. The electrical resistivity shows metallic behavior with a broad anomaly around 150-200 K. ρ(T) is found to exhibit an anomalous T^{3/2} dependence which is a strong indication of NFL, and below 15 K it exhibits a T^2 dependence down to 1.5 K, meaning that the FL behaviour is recovered below 15 K. From the analysis of the SXRD data at 100 K, we observed no superlattice reflections and no change to the structure as it remained monoclinic I2/m, indicating the absence of a CDW phase transition. The presence of magnetic fluctuations and quenched disorder on the Ni/V sites could be the cause of NFL to FL transition, given that stoichiometric NiV2Se4 is claimed to be a non-magnetic CDW system. Synthesis of a stoichiometric NiV2Se4 without the disorder is necessary to investigate the possibility of a CDW phase transition, and it is being undertaken
Exclusive Decays with Hadronic Full Event Interpretation Tagging in 34.6 fb of Belle II Data
No full textWe present the results of the re-discovery of the decay in 34.6 fb of Belle II data using hadronic -tagging via the Full Event Interpretation algorithm. We observe 21 signal events on a background of 155 in a fit to the distribution of the square of the missing mass, , with a significance of 5.69, and determine a total branching fraction of (1.58 0.43 0.07)