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Selected results of department 22

Measurement of the inclusive jet cross section in proton-antiproton collisions at √s=1.96 TeV

In order to investigate properties of matter at the smallest distances, we need to initiate, according to Heisenberg principle of uncertainty, processes with the largest possible changes in momentum. Before LHC, the best place to study such processes was collider Tevatron in Fermilab. There, the protons were collided with antiprotons at center of mass energy of √s=1.96 TeV, which was at that time the largest energy available at laboratory.Protons interact with antiprotons mostly through strong interaction. The whole text »

Construction of the detection apparatus ATLAS for experimenting at LHC

Our laboratory played an important role in construction of substantial parts of the apparatus, in particular

  • pixel detector designed for the meaurement of decays of short-lived particles;
  • hadron calorimeter TileCal for the measurement of energy of neutral hadrons and high-energy particle showers.

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Measurement of the top quark pair production charge asymmetry in proton-proton collisions at √s = 7 TeV in ATLAS experiment

Measurement of top quark pair production charge asymmetry serves as an important test of Standard Model of particle physics (SM). The charge asymmetry observed in recent measurements from Tevatron was greater than predictions with regard to SM. This paper presents a measurement of the top quark pair production charge asymmetry AC using proton-proton collisions at a centre-of-mass energy √s = 7 TeV collected by the ATLAS detector at the LHC. The whole text »

Measurement of the Higgs boson mass from the H→γγ and H→ZZ∗→4ℓ channels with the ATLAS detector using 25 fb−1 of pp collision data

An improved measurement of the mass of the Higgs boson is derived from a combined fit to the reconstructed invariant mass spectra of the decay channels H→γγ and H→ZZ*→4ℓ. The analysis uses the pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at center-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 25  fb−1. The measured value of the Higgs boson mass is mH = 125.36 ± 0.37(stat) ± 0.18(syst)  GeV.

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Evidence for the spin-0 nature of the Higgs boson using ATLAS data

New data obtained by experiment ATLAS enabled detailed investigation of properties of new particle discovered in last year. Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on proton–proton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin–parity JP = 0+ hypothesis is compared with alternative hypotheses using the Higgs boson decays H→γγ, H→ZZ*→4ℓ (image 1) and H→WW*→ℓνℓν, as well as the combination of these channels. The whole text »

Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC

A search for the Standard Model Higgs boson in proton-proton collisions with the ATLAS detector at the LHC is presented. In the datasets collected at √s = 7 TeV in 2011 and at √s = 8 TeV in 2012 the decay channels H→ZZ(∗)→4ℓ, H→γγ and H→WW(∗)→eνμν have been investigated. Clear evidence for the production of a neutral boson with a measured mass of 126.0 ± 0.4 (stat) ± 0.4 (sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, is compatible with the production and decay of the Standard Model Higgs boson. The whole text »

Precise measurement of the top-quark mass from lepton+jets events at D0

D0 experiment has conducted new, more precise, measurements of the mass of top quark where the final system of top and anti-top quark decayal consists odf one lepton and jets. Measurements was performed in proton-antiproton collisions at the Tevatron Collider with center-of-mass energy 1,96 TeV. Resulting measured value mt=176,01±1,64 GeV is one of the most precise measurements of the mass of top quark in a separate terminal channel. The whole text »

Selected results of the DELPHI experiment at LEP collider at CERN

The experimental activities of the Department are currently concentrated on the ATLAS experiment at the LHC collider at CERN. LHC started to provide sizable amounts of experimental data at highest energies ever only during the present year 2010. The collider is still under development, its parameters being tuned. The amount of collected data will increase with the optimization of the LHC performance. Discoveries reached by LHC experiments can thus be expected only in the next few years. Significant results reached by the Department members are thus connected with the previous era of CERN experiments – the DELPHI experiment at the electron-positron collider LEP.

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