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 sqrt(s) =7 TeV using the ATLAS experiment at the LHC are reported. Scalar top quarks are searched for in events with two same flavour opposite-sign leptons (electrons or muons) with invariant mass consistent with the Z boson mass, large missing transverse momentum and jets in the final state. At least one of the jets is identified as originating from a b-quark. No excess over Standard Model expectations is found. The results are interpreted in the framework of R-parity conserving, gauge mediated Supersymmetry breaking `natural' scenarios, where the neutralino is the next-to-lightest supersymmetric particle. Scalar top quark masses up to 310 GeV are excluded for the lightest neutralino mass between 115 GeV and 230 GeV at 95% confidence level, reaching an exclusion of the scalar top quark mass of 330 GeV for the lightest neutralino mass of 190 GeV. Scalar top quark masses below 240 GeV are excluded for all values of the lightest neutralino mass above the Z boson mass.
The missing ET distribution from the combined EE and MUMU data for SR1. Tabulated are the observed Data rates and the Standard Model predictions as well as the distributions expected for two signal scenarios, both with an STOP mass of 250 GeV, and NEUTRALINO1 masses of 100 GeV and 220 GeV respectively.
The number of b-tagged jets for SR1 for the combined EE and MUMU channels. Tabulated are the observed Data rates and the Standard Model predictions as well as the distributions expected for two signal scenarios, both with an STOP mass of 250 GeV, and NEUTRALINO1 masses of 100 GeV and 220 GeV respectively.
The distrubution of leading jet pT for SR1 for the combined EE and MUMU channels. Tabulated are the observed Data rates and the Standard Model predictions as well as the distributions expected for two signal scenarios, both with an STOP mass of 250 GeV, and NEUTRALINO1 masses of 100 GeV and 220 GeV respectively. The last pT bin includes the number of overflow events for both data abd SM expectation.
This paper describes a measurement of the W boson transverse momentum distribution using ATLAS pp collision data from the 2010 run of the LHC at sqrt(s) = 7 TeV, corresponding to an integrated luminosity of about 31 pb^-1. Events from both W -> e nu and W -> mu nu are used, and the transverse momentum of the W candidates is measured through the energy deposition in the calorimeter from the recoil of the W. The resulting distributions are unfolded to obtain the normalized differential cross sections as a function of the W boson transverse momentum. We present results for pTW < 300 GeV in the electron and muon channels as well as for their combination, and compare the combined results to the predictions of perturbative QCD and a selection of event generators.
The normalized, differential cross secton measured in the W to Electron decay channel for the three different PT definitions, Born, Dressed and Bare.
The normalized, differential cross secton measured in the W to Muon decay channel for the three different PT definitions, Born, Dressed and Bare.
The normalized, differential cross secton from the Muon and Electron decay channel Combined for the Born-level PT definition.
We have searched for resonances in the reaction e+e−→hadrons, γγ, μμ, and ee, in the energy range 39.79<s<45.52 GeV, using the Mark J detector at PETRA. We obtain stringent upper limits on the production of toponium and particles postulated to explain Z0→leptonpair+γ events observed at the CERN p―p collider. We also set limits on the mass and coupling constant of excited electrons.
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DATA ARE CORRECTED FOR TWO-PHOTON AND TAU PRODUCTION EFFECTS, ACCEPTANCE AND QED RADIATIVE EFFECTS UP TO ORDER ALPHA**3. THERE IS ALSO A 6 PCT NORMALISATION ERROR NOT INCLUDED. THE OVERALL AVERAGE VALUE OF R FROM THIS DATA IS 3.88 +- 0.04 +- 0.22.
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SEE PRL 55, 665 FOR MOST RECENT VALUES OF THE MU+ MU- CROSS SECTIONS.
We use the reaction e+e−→hadrons, in the Mark J detector at the DESY electron-positron collider PETRA, to determine the hadronic cross section up to 46.78 GeV. The production of a top quark with a charge equal to (2/3) is excluded up to 46.6 GeV with 95% C.L. The observed rise in the cross section at higher energies is consistent with the electroweak prediction for a Z0 mass of 93 GeV. We describe some unusual muon inclusive events.
Errors are statistical only.
Energy scan of R.
Inclusive muon cross section.
The results of a high-statistics study of inclusive muon spectra at PETRA are reported. Improved mass limits have been obtained for heavy quarks, heavy leptons, and charged Higgs particles. It is shown that the fragmentation properties of b quarks and c quarks are different, with the mean fragmentation variables 〈zb〉=0.75±0.03±0.06, 〈zc〉=0.46±0.02±0.05 and the average semileptonic branching ratio for the B and C hadrons R(B)=(10.5±1.5±1.3)%, R(C)=(11.5±1.0±1.7)%.
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We use the reaction e+e−→μ+μ−, in the Mark J detector at the DESY high-energy e+e− collider PETRA, to test the standard electroweak theory and find good agreement. We also set limits on the parameters of several extended gauge theories.
CROSS SECTION MEASUREMENT RELATIVE TO PREDICTED QED CROSS SECTION.
FORWARD-BACKWARD ASYMMETRY. THE SYSTEMATIC ERROR IN THE ASYMMETRY IS <0.5 PCT.
ANGULAR DISTRIBUTIONS NOT GIVEN IN PAPER. SUPPLIED BY E.DEFFUR.
The measurement of the nonelectromagnetic forward-backward charge asymmetry in the reaction e+e−→μ+μ− at s∼34.6 GeV and in the angular region 0<|cosθ|<0.8 is reported. With a systematic error less than 1%, we observe an asymmetry of (-8.1±2.1)%. This is in agreement with the standard electroweak theory prediction of (-7.6±0.6)%. The weak-current coupling constants are also reported.
SEE PRL 55, 665 FOR DISTRIBUTIONS AT 34.6 GEV AND ABOVE.
SEE PRL 55, 665 FOR CROSS SECTION VALUES AND FORWARD BACKWARD ASYMMETRY.
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We have measured both the rates and the forward-backward asymmetry of ℓ + ℓ − from Z 0 →ℓ + ℓ − (where ℓ= μ , τ ) with the L3 detector. We obtained Γ ℓℓ =88±4±3 MeV and the vector neutral current coupling constant, g v =0.00±0.07 and the axial vector neutral current coupling constant, g A =−0.515±0.015.
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