39 research outputs found
Top quark pair production cross-section results at LHC in final states with tau or no leptons
ATLAS and CMS measured the top quark pair production inclusive cross section
using proton-proton collision data collected at 7 TeV c.m. energy at the LHC
during the year 2011 in several channels. This article presents the
measurements of the cross section using selections of top quark pair production
events with one hadronically decaying {\tau} lepton or no leptons at all.Comment: Proceedings of the 5th International Workshop on Top Quark Physics,
September 16-21, 2012, Winchester, U.
Study of Systematic Uncertainties of Single Top Production at ATLAS
Sytematic uncertainties to the single top production cross section
measurement at the ATLAS experiment has been studied. Different sources of
systematic uncertainties such as detector luminosity, jet energy calibration,
SM background normalization, PDF parameterization and others have been
considered. Large scale Monte-Carlo events simulation has been performed to
estimate the contribution of each source in the overall uncertainty. The study
was done for cut based analysis as well as for multivariate analysis of the
single top measurements in ATLAS. The total systematic uncertainties of the
single top cross-section measurements in its three production channels have
been estimated at 1 and 10 integrated
luminosity of the LHC.Comment: Proceedings of the International Workshop on Top Quark Physics, 18-24
May 2008, La Biodola, Isola D'Elba, Ital
Measurement of with NA48/2 at CERN
The exclusive branching ratio of the radiative decay is measured using data collected by the NA48/2 experiment at CERN in 2003-2004. The measurement is performed in the phase-space region of the mass of the electron-positron pair, . This is the most accurate measurement of the exclusive . The result, is compatible with the theoretical value, 8.51 × 10(−)(8), calculated using the Chiral Perturbation Theory framework at next-to-leading order
Single-top production t-channel cross section measurement in the electron+jets final state at ATLAS with of data
The cross section of the Standard Model electroweak production of a single top quark in the t-channel has been measured using the LHC proton-proton collision data at TeV, of integrated luminosity, recorded by the ATLAS detector during the year 2010. The measurement has been based on a selection of the collision events with an electron and one b-tagged hadronic jet in the central region of the detector and one extra jet in the forward region of the detector. These requirements are dictated by the topology of the final state particles in the t-channel process. They helped to optimize an expected fraction of the t-channel process, according to a study based on Monte-Carlo simulation, in the selected events and suppress the contribution of the background processes. The main background processes such as production of hadronic jets via the strong interaction and production of a single W boson with associated hadronic jets are measured by means of data driven methods developed in this work. The measured cross section of single top quark production in the t-channel process is pb. The measured upper limit on the cross section is pb at the confidence level. The results are in agreement with the latest theoretical prediction of the t-channel cross section of the Standard Model production of a single top quark calculated at NNLO, pb, considering GeV
Search for heavy neutral lepton production in decays
A search for heavy neutral lepton production in decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the to level are established on the elements of the extended neutrino mixing matrix () for heavy neutral lepton mass in the range . This improves on the results from previous production searches in decays, setting more stringent limits and extending the mass range.A search for heavy neutral lepton production in K+ decays using a data sample collected with a minimum bias trigger by the NA62 experiment at CERN in 2015 is reported. Upper limits at the 10−7 to 10−6 level are established on the elements of the extended neutrino mixing matrix |Ue4|2 and |Uμ4|2 for heavy neutral lepton mass in the ranges 170–448 MeV/ c2 and 250–373 MeV/ c2 , respectively. This improves on the previous limits from HNL production searches over the whole mass range considered for |Ue4|2 , and above 300 MeV/ c2 for |Uμ4|2
First search for using the decay-in-flight technique
International audienceThe NA62 experiment at the CERN SPS reports the first search for K+→π+νν¯ using the decay-in-flight technique, based on a sample of 1.21×1011 K+ decays collected in 2016. The single event sensitivity is 3.15×10−10 , corresponding to 0.267 Standard Model events. One signal candidate is observed while the expected background is 0.152 events. This leads to an upper limit of 14×10−10 on the K+→π+νν¯ branching ratio at 95% CL
Measurement of the very rare decay
The NA62 experiment reports the branching ratio measurement BR at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare decay, observed with a significance of 3.4. The experiment achieves a single event sensitivity of , corresponding to 10.0 events assuming the Standard Model branching ratio of . This measurement is also used to set limits on BR(), where is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample
Search for decays to invisible particles
The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay where is a particle escaping detection with mass in the range GeV/ and rest lifetime greater than 100 ps. Model- dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs.The NA62 experiment at the CERN SPS reports a study of a sample of tagged mesons from , searching for the decay of the to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model-independent upper limit on the branching ratio for the decay , where is a particle escaping detection with mass in the range 0.110-0.155 GeV and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson