The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the mass of its isospin partner, the bottom quark. It decays almost 100% of the time to a W boson and a ...bottom quark. Using top-antitop pairs at the Tevatron proton-antiproton collider, the CDF and D0 Collaborations have measured the top quark's mass in different final states for integrated luminosities of up to 5.8 fb super(-1). This paper reports on a combination of these measurements that results in a more precise value of the mass than any individual decay channel can provide. It describes the treatment of the systematic uncertainties and their correlations. The mass value determined is 173.18 + or - 0.56(stat) + or - 0.75(syst) GeV or 173.18 + or - 0.94 GeV, which has a precision of + or -0.54%, making this the most precise determination of the top-quark mass.
We report a measurement of the bottom-strange meson mixing phase β(s) using the time evolution of B(s)(0)→J/ψ(→μ(+)μ(-))φ(→K(+)K(-)) decays in which the quark-flavor content of the bottom-strange ...meson is identified at production. This measurement uses the full data set of proton-antiproton collisions at √s=1.96 TeV collected by the Collider Detector experiment at the Fermilab Tevatron, corresponding to 9.6 fb(-1) of integrated luminosity. We report confidence regions in the two-dimensional space of β(s) and the B(s)(0) decay-width difference ΔΓ(s) and measure β(s)∈-π/2,-1.51∪-0.06,0.30∪1.26,π/2 at the 68% confidence level, in agreement with the standard model expectation. Assuming the standard model value of β(s), we also determine ΔΓ(s)=0.068±0.026(stat)±0.009(syst) ps(-1) and the mean B(s)(0) lifetime τ(s)=1.528±0.019(stat)±0.009(syst) ps, which are consistent and competitive with determinations by other experiments.
The dependence of the rate of proton-proton interactions on the centre-of-mass collision energy, √s, is of fundamental importance for both hadron collider physics and particle astrophysics. The ...dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton-proton interaction cross-section at a centre-of-mass energy, √s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3 ± 2.1 mb is measured for ξ > 5×10⁻⁶, where ξ is calculated from the invariant mass, M(X), of hadrons selected using the largest rapidity gap in the event. For diffractive events, this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV.
Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of ...17 nb
−1
recorded at the Large Hadron Collider. The anti-
k
t
algorithm is used to identify jets, with two jet resolution parameters,
R
=0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable
χ
. The results are compared to expectations based on next-to-leading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.
The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have ...been fully operational since 2007 and the detector has successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems’ precision is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.
This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from √s=7 TeV proton-proton collisions at the ...LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A(0)=0 GeV, tanβ=3, and μ>0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.
The jet fragmentation function and transverse profile for jets with 25 GeV<
p
T jet
<500 GeV and |
η
jet
|<1.2 produced in proton–proton collisions with a center-of-mass energy of 7 TeV are ...presented. The measurement is performed using data with an integrated luminosity of 36 pb
−1
. Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.
A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated ...luminosity of 315 nb⁻¹ collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% C.L. the q* mass interval 0.30<m(q*)<1.26 TeV, extending the reach of previous experiments.
A
bstract
This paper presents measurements of the polarization of
W
bosons in top quark decays, derived from
events with missing transverse momentum, one charged lepton and at least four jets, or two ...charged leptons and at least two jets. Data from
pp
collisions at a centre-of-mass energy of 7 TeV were collected with the ATLAS experiment at the LHC and correspond to an integrated luminosity of 1.04 fb
−1
. The measured fractions of longitudinally, left- and right-handed polarization are
F
0
= 0
.
67 ± 0
.
07,
F
L
= 0
.
32 ± 0
.
04 and
F
R
= 0
.
01 ± 0
.
05, in agreement with the Standard Model predictions. As the polarization of the
W
bosons in top quark decays is sensitive to the
Wtb
vertex Lorentz structure and couplings, the measurements were used to set limits on anomalous contributions to the
Wtb
couplings.
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