Search results for " CLUSTER"
showing 10 items of 2162 documents
Top mass reconstruction in ATLAS
2011
The top-quark mass is a fundamental parameter of the Standard Model. After the discovery of the top quark, the measurements of its properties were of substantial interest. Within the framework of the SM, the top-quark mass can be used in combination with other electroweak precision measurements to constrain the mass of the yet unobserved Higgs boson.\nIn the new era of the Large Hadron Collider (LHC), the first top quarks have been produced in Europe in proton-proton collisions at a center-of-mass energy of 7~TeV. The top-quark mass measurement of ATLAS in the so called lepton+jets channel with 35~pb$^{-1}$ integrated luminosity will be presented. In this early data-taking period the larges…
Constraining heavy colored resonances from top-antitop quark events
2009
Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2 sigma. In this letter, we explore the possibility of reconciling the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.
Search for scalar top quark pair production in natural gauge mediated supersymmetry models with the ATLAS detector in pp collisions at s=7 TeV
2012
The results of a search for pair production of the lighter scalar partners of top quarks () in 2.05 fb−1 of pp collisions at TeV using the ATLAS experiment at the LHC are reported. Scalar top quar ...
Highlights of top quark cross-section measurements at ATLAS
2017
The highlights of the measurements of top quark production in proton-proton collisions at the Large Hadron Collider with the ATLAS detector are presented. The inclusive measurements of the top-pair production cross section have reached high precision and are compared to the best available theoretical calculations. The differential cross section measurements, including results using boosted top quarks, probe our understanding of top-pair production in the TeV regime. The results are compared to Monte Carlo generators implementing LO and NLO matrix elements matched with parton showers. Measurements of the single top quark production cross section are presented in the t -channel and s -channel…
Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum ins=7 TeVppCollisions U…
2012
A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at root s = 7 TeV. The measurement is based on 4.7 fb(-1) of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.
Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system
2021
AbstractCo-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show …
Multi-Object Spectroscopy of Open Clusters with FLAMES: Preliminary GTO Results
2006
We report on preliminary results of VLT/FLAMES observations of the old open clusters NGC 2506, Mel 66 and Cr 261, obtained as part of our Guaranteed Time on this instrument. We focus in particular on the very old cluster Cr 261, one of the oldest open clusters in the Galaxy. We compare the derived Li abundances with those of other old clusters, and we discuss briefly Li depletion on the main-sequence from the age of the Hyades to ∼8 Gyr. 1 The GTO Program on Open Clusters With the advent of the multi-object spectrograph FLAMES at the VLT [13], the study of open clusters has received a great boost due both to the larger telescope area and to the multiplexing capability offered by the new ins…
The energy transfer to the luminescence centers in PbWO4
1998
Abstract The luminescence spectra, rise and decay kinetics and the yield of luminescence in undoped PbWO 4 crystals were studied after pulsed electron beam irradiation. The luminescence intensity rise observed after irradiation pulse showed two mechanisms—excitonic relaxation and electron–hole recombination—were involved in the formation of the excited states of the blue luminescence centers. It is proposed that the excited states of WO 3 and WO 2− 4 luminescence centers were formed from some intermediate metastable state.
Electronic structure of terpene derivatives
1998
Abstract He I photoelectron spectra of terpene derivatives and their preparative intermediates have been measured. The changes of the ionization potentials are discussed in relation to the corresponding variations of the electronic structure. Especially, the effect of methyl and oxygen substitution has been studied.
Time-resolved luminescence and absorption in CdWO4
1998
Abstract The luminescence and short-lived absorption are studied in CdWO 4 single crystals under pulsed laser beam as well as pulsed electron beam excitation. The luminescence spectrum and decay kinetics for CdWO 4 powder are studied. The short-lived absorption in single crystals arises from electron transitions from the luminescence center excited state to the conduction band. From luminescence and short-lived absorption spectra the energy depths of luminescence center excited and ground states are estimated.