Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
CHI distribution for mass bin 340 to 520 GeV.
CHI distribution for mass bin 520 to 800 GeV.
CHI distribution for mass bin 800 to 1200 GeV.
Transverse mass spectra of protons emitted in Au+Au collisions at beam energies of 6, 8, and 10.8 GeV/nucleon have been measured as a function of collision centrality over a rapidity range 0.5<ylab<1.5. The spectra are well reproduced by Boltzmann distributions over the measured transverse mass region, which allows for extrapolation of the data to derive the rapidity density and apparent temperature of the emitting source. The shapes of the rapidity distributions suggest significant transparency or substantial longitudinal expansion in even the most central collisions at all three beam energies. The data are analyzed within a simple thermal source plus longitudinal expansion model.
The inverse slope, mean transverse mass and rapidity density values for centrality 0 to 5 PCT for 6 GeV/nucleon collisions. Statistical errors only.
The inverse slope, mean transverse mass and rapidity density values for centrality 5 to 12 PCT for 6 GeV/nucleon collisions. Statistical errors only.
The inverse slope, mean transverse mass and rapidity density values for centrality 12 to 23 PCT for 6 GeV/nucleon collisions. Statistical errors only.
Mid-rapidity spectra and yields of K$^-$ and K$^+$ have been measured for Au+Au collisions at 4, 6, 8, and 10.7 AGeV. The K$^-$ yield increases faster with beam energy than for K$^+$ and hence the K$^-$/K$^+$ ratio increases with beam energy. This ratio is studied as a function of both $\sqrt{s}$ and $\sqrt{s}$-$\sqrt{s_{th}}$ which allows the direct comparison of the kaon yields with respect to the production threshold in p+p reactions. For equal $\sqrt{s}$ - $\sqrt{s_{th}}$ the measured ratio K$^-$/K$^+$=0.2 at energies above threshold in contrast to the K$^-$/K$^+$ ratio of near unity observed at energies below threshold. The use of the K$^-$/K$^+$ ratio to test the predicted changes of kaon properties in dense nuclear matter is discussed.
Only statistical errors are presented.
Only statistical errors are presented.
Only statistical errors are presented.
Positive pion and kaon production from Au+Au reactions have been measured as a function of beam energy over the range 2.0-10.7~AGeV. Both the kaon and the pion production cross-sections at mid-rapidity are observed to increase steadily with beam kinetic energy. The ratio of K$^+$ to $\pi^+$ mid-rapidity yields increases from 0.0271$\pm0.0015\pm0.0014$ at 2.0~AGeV to 0.202$\pm0.005\pm0.010$ at 10.7~AGeV and is larger than the K$^+$/$\pi^+$ ratio from p+p reactions over the same beam energy region. There is no indication of an onset of any new production mechanism in heavy-ion reactions in this energy range beyond rescattering of hadrons.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). A single exponential function in MT was fit simultaneously to the two kaonspectra at each beam energy D2(N)/D(MT)/D(YRAP)/2/PI/MT=D(N)/D(YRAP)/2/PI/T/(T+ M(KAON))/EXP((MT-M(KAON))/T). The fits reproduce the spectra well with two free parameters, the inverse slope parameter T and the rapidity density, D(N)/D(YRAP)in that rapidity slice. The mid-rapidity range for 2, 4, 6, 8 AGeV is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV the width is ABS((YRAP-Ynn)/Ynn) < 0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only. The 1.96, 4. and 10.74 GeV are E866 data, another - E917 data.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). A single exponential function in MT was fit simultaneously to the two kaonspectra at each beam energy D2(N)/D(MT)/D(YRAP)/2/PI/MT=D(N)/D(YRAP)/2/PI/T/(T+ M(KAON))/EXP((MT-M(KAON))/T). The fits reproduce the spectra well with two free parameters, the inverse slope parameter T and the rapidity density, D(N)/D(YRAP)in that rapidity slice. The mid-rapidity range for 2, 4, 6, 8 AGeV is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV the width is ABS((YRAP-Ynn)/Ynn) < 0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only. The 1.96, 4. and 10.74 GeV are E866 data, another - E917 data.
The centrality selection at each beam energy is the most central 5% of the total interaction cross-section (SIG(C=interaction) = 6.8b). The spectra were fit with a scaled exponential, D2(N)/D(YRAP)/D(MT)/2/PI/MT=D(N)/D(YRAP)/2/PI/(T**(2-L))/GAMMA(2-L,M(PION)/T)/MT**L/EXP(MT/T), where GAMMA(2-L,M(PION)/T), the complementary incomplete gamma function, is introduced in the normalization so that D(N)/D(YRAP) is a fitted parameter (and other free parameters are L and T). The mid-rapidity range for 2, 4 (E866 data), 6, 8 AGeV (E917 data) beam energy is ABS((YRAP-Ynn)/Ynn) < 0.25, for 10.7 AGeV (E917 data) the width is ABS((YRAP-Ynn)/Ynn) <0.125, where Ynn is mid-rapidity in the laboratory frame. The errors are statistical only.
Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.
Charged particle sphericity distribution.
Charged particle aplanarity distribution.
Charged particle Thrust distribution.
We present the general properties of multihadron final states produced by e+e− annihilation at center-of-mass energies from 52 to 57 GeV in the AMY detector at the KEK collider TRISTAN. Global shape, inclusive charged-particle, and particle-flow distributions are presented. Our measurements are compared with QCD+fragmentation models that use either leading-logarithmic parton-shower evolution or QCD matrix elements at the parton level, and either string or cluster fragmentation for hadronization.
Rapidity distribution with respect to the Thrust axis.
Charged particle X distribution.
Charged particle PL distribution.
Forum