We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Forward-Backward Asymmetries of e+ e- production from the 1995 data in the fiducial volume THETA from 44 to 136 degrees and including an acollinearity cut of PSI < 25 degrees. The errors are statistical only and there is an additional correlated absolute error of 0.0025 to be added. The right most column is the s-channel contribution in the full solid angle.
We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies. The distributions of event shape variables and the energy dependence of their mean values are measured from 30GeV to 189GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbative component. We obtain a universal value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong coupling constant at each of the selected energies. The measurements demonstrate the running of alpha_s as expected in QCD with a value of alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).
The strong coupling constant, ALPHA-s, as determined from the combined event shape variables as a function of c.m. energy. The values for c.m. energy belowthe Z0 mass were determined only for four event shape variables.
We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected
Results from 1990 data. Additional systematic uncertainty of 0.004.. Both leptons inside the angle range 44 to 136 degrees with acollinearity cut of <25 degrees.
In this Report, QCD results obtained from a study of hadronic event structure in high energy e^+e^- interactions with the L3 detector are presented. The operation of the LEP collider at many different collision energies from 91 GeV to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, \alpha_s, from hadronic event shapes and the study of effects of soft gluon coherence through charged particle multiplicity and momentum distributions.
Differential distributions for event thrust.
A three-dimensional (3D) correlation function obtained from mid-rapidity, low pT pion pairs in central Au+Au collisions at sqrt(s_NN)=200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). Model comparisons to these distensions indicate a proper breakup time \tau_0 ~ 9 fm/c and a mean proper emission duration \Delta\tau ~ 2 fm/c, leading to sizable emission time differences (<|\Delta \tau_LCM |> ~ 12 fm/c), partly due to resonance decays. They also suggest an outside-in 'burning' of the emission source reminiscent of many hydrodynamical models.
Source function comparison between Therminator calculation and image for $S(r_x)$ in PCMS.
Source function comparison between Therminator calculation and image for $S(r_x)$ in PCMS.
We have measured the differential production cross sections as a function of scaled momentum x_p=2p/E_cm of the identified hadron species pi+, K+, K0, K*0, phi, p, Lambda0, and of the corresponding antihadron species in inclusive hadronic Z0 decays, as well as separately for Z0 decays into light (u, d, s), c and b flavors. Clear flavor dependences are observed, consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results were used to test the QCD predictions of Gribov and Lipatov, the predictions of QCD in the Modified Leading Logarithm Approximation with the ansatz of Local Parton-Hadron Duality, and the predictions of three fragmentation models. Ratios of production of different hadron species were also measured as a function of x_p and were used to study the suppression of strange meson, strange and non-strange baryon, and vector meson production in the jet fragmentation process. The light-flavor results provide improved tests of the above predictions, as they remove the contribution of heavy hadron production and decay from that of the rest of the fragmentation process. In addition we have compared hadron and antihadron production as a function of x_p in light quark (as opposed to antiquark) jets. Differences are observed at high x_p, providing direct evidence that higher-momentum hadrons are more likely to contain a primary quark or antiquark. The differences for pseudoscalar and vector kaons provide new measurements of strangeness suppression for high-x_p fragmentation products.
Measured differential cross section for phi meson production per Z0 decay into light, charm and bottom quarks separately. The errors given are the sum in quadrature of the statistical errors and those systematic errors arising from theunfolding procedure. Systematic errors common to the three flavours are not inc luded.
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.
Unfolded values of the the mean multiplicity and dispersion of the multiplicity distributions integrated over the rapidity region -1.5 to 1.5.
A search for vectorlike quarks is presented, which targets their decay into a $Z$ boson and a third-generation Standard Model quark. In the case of a vectorlike quark $T$ ($B$) with charge $+2/3e$ ($-1/3e$), the decay searched for is $T \rightarrow Zt$ ($B \rightarrow Zb$). Data for this analysis were taken during 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 13$ TeV. The final state used is characterized by the presence of $b$-tagged jets, as well as a $Z$ boson with high transverse momentum, which is reconstructed from a pair of opposite-sign same-flavor leptons. Pair and single production of vectorlike quarks are both taken into account and are each searched for using optimized dileptonic exclusive and trileptonic inclusive event selections. In these selections, the high scalar sum of jet transverse momenta, the presence of high-transverse-momentum large-radius jets, as well as - in the case of the single-production selections - the presence of forward jets are used. No significant excess over the background-only hypothesis is found and exclusion limits at 95% confidence level allow masses of vectorlike quarks of $m_T > 1030$ GeV ($m_T > 1210$ GeV) and $m_B > 1010$ GeV ($m_B > 1140$ GeV) in the singlet (doublet) model. In the case of 100% branching ratio for $T\rightarrow Zt$ ($B\rightarrow Zb$), the limits are $m_T > 1340$ GeV ($m_B > 1220$ GeV). Limits at 95% confidence level are also set on the coupling to Standard Model quarks for given vectorlike quark masses.
Signal efficiencies in $\%$ in the PP $2\ell$ $0-1$J channel in the 0-large-$R$ jet SR. Uncertainties are statistical only.
This paper presents measurements of $t\bar{t}$ production in association with additional $b$-jets in $pp$ collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb$^{-1}$. Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets $t\bar{t}$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of $t\bar{t}$ final states with three and four $b$-jets as well as differential cross-sections as a function of global event properties and properties of $b$-jet pairs. The measured inclusive fiducial cross-sections generally exceed the $t\bar{t}b\bar{b}$ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.
Relative differential cross section as a function of invariant mass of two closest b-jets in deltaR in lepton+jets channel
Relative differential cross section as a function of invariant mass of two closest b-jets in deltaR in lepton+jets channel
A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV recorded in 2015-2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined.
Endcap Muon RoI Cluster trigger efficiencies (in %) for baryogenesis $\chi \rightarrow \tau\tau\nu$ benchmark samples ($m_{h}=125$ GeV). The trigger efficiency is defined as the fraction of LLPs selected by the Muon RoI Cluster trigger as a function of the LLP decay position. The trigger is efficient for hadronic decays of LLPs that occur anywhere from the outer regions of the HCal to the middle station of the MS. These efficiencies are obtained from the subset of events with only a single LLP decay in the muon spectrometer in order to ensure that the result of the trigger is due to a single burst of MS activity. The uncertainties shown are statistical only. The relative differences in efficiencies of the benchmark samples are a result of the different kinematics.
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