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At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer ( vdM ) method are affected by the mutual electromagnetic interaction of the two beams. The colliding bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic- β effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the vdM regime, the beam–beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic- β corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam–beam effects on the vdM -based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam–beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute pp -luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam–beam-related systematic uncertainty on beam–beam corrections to absolute luminosity calibrations by the van der Meer method.

The production rates of \\({\\mathrm{D}}^{*\\pm}\\), \\({\\mathrm{D}}_{\\rm{s}}^{* \\pm}\\), \\({\\mathrm{D}}^{\\pm}\\), \\({\\mathrm{D}}^0 / \\bar{{\\mathrm{D}}}^0\\), \\({\\mathrm{D}}_{\\rm{s}}^{\\pm}\\), and \\(\\Lambda_{\\rm c}^{+}/{\\bar{\\Lambda}}_{\\rm c}^{-}\\) in \\({\\rm Z} \\rightarrow {\\mathrm c} \\bar{{\\mathrm c}}\\) decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the \\({\\mathrm{D}}^{*\\pm}\\) is well described as the sum of three contributions: charm hadronisation, b hadron decays and gluon splitting into a pair of heavy quarks. The probability for a c quark to hadronise into a \\({\\mathrm{D}}^{*+}\\) is found to be \\(f({\\mathrm c} \\to{\\mathrm{D}}^{*+}) = 0.233 \\pm 0.010 \\mathrm{(stat.)} \\pm 0.011\\mathrm{(syst.)}\\). The average fraction of the beam energy carried by \\({\\mathrm{D}}^{*\\pm}\\) mesons in \\({\\rm Z} \\to{\\rm c \\bar c}\\) events is measured to be \\({\\langle X_E ({\\mathrm{D}}^{*\\pm}) \\rangle}_{{\\mathrm c} \\bar{{\\mathrm c}}} =0.4878 \\pm 0.0046 \\mathrm{(stat.)} \\pm 0.0061 \\mathrm{(syst.)}.\\) The \\({\\mathrm{D}}^{*\\pm}\\) energy and the hemisphere mass imbalance distributions are simultaneously used to measure the fraction of hadronic Z decays in which a gluon splits to a \\({\\mathrm c} \\bar{{\\mathrm c}}\\) pair: \\(\\bar{n}_{\\mathrm{g} \\to{\\mathrm c}\\bar{{\\mathrm c}}} = (3.23 \\pm 0.48 \\mathrm{(stat.)} \\pm 0.53 \\mathrm{(syst.)})\\%.\\) The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be \\(P_V = 0.595\\pm0.045\\). The fractional decay width of the Z into \\({\\mathrm c}\\bar{{\\mathrm c}}\\) pairs is determined from the sum of the production rates for various weakly decaying charmed states to be \\({\\rm R_c} =0.1738 \\pm 0.0047{\\rm (stat.)} \\pm 0.0116 {\\rm (syst.)}.\\)

Inclusive branching ratios involving b to tau transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio b -> tau nu X and the semi-inclusive branching ratio b -> tau nu D*+/- X are measured to be (2.43 +/- 0.20 +/- 0.25)% and (0.88 +/- 0.31 +/- 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions b -> tau nu and b -> s nu nubar are set to 8.3 10**-4 and 6.4 10**-4 at the 90\\%~C.L. These results allow a 90\\% C.L. lower limit of 0.40 (GeV/c**2)**-1 to be set on the tan(beta)/mH+/- ratio, in the framework of type-II two-Higgs-doublet models.

At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (vdM) method are affected by the mutual electromagnetic interaction of the two beams. The colliding bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-\\(\\beta\\) effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the vdM regime, the beam-beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-\\(\\beta\\) corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam-beam effects on the vdM-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam-beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute pp-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam-beam-related systematic uncertainty on beam-beam corrections to absolute luminosity calibrations by the van der Meer method.

The measurement of missing transverse momentum in the ATLAS detector, described in this paper, makes use of the full event reconstruction and a calibration based on reconstructed physics objects. The performance of the missing transverse momentum reconstruction is evaluated using data collected in pp collisions at a centre-of-mass energy of 7 TeV in 2010. Minimum bias events and events with jets of hadrons are used from data samples corresponding to an integrated luminosity of about 0.3 [nb.sup.-1] and 600 [nb.sup.-1] respectively, together with events containing a Z boson decaying to two leptons (electrons or muons) or a W boson decaying to a lepton (electron or muon) and a neutrino, from a data sample corresponding to an integrated luminosity of about 36 [pb.sup.-1]. An estimate of the systematic uncertainty on the missing transverse momentum scale is presented.

We present studies of W and Z bosons with associated high energy photons produced in pp collisions at sqrt(s)=7 TeV. The analysis uses 35 pb-1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high pT leptons (electrons or muons) and a photon with ET>15 GeV separated from the lepton(s) by a distance Delta_R(l,gamma)>0.7 in eta-phi space. A total of 95 (97) pp->e nu gamma + X (pp->mu nu gamma + X) and 25 (23) pp->e+ e- gamma + X (pp->mu+ mu- gamma + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(alpha alpha_s) contributions.

Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons in sqrt{s}=7 TeV proton-proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical sign or opposite sign electric charges are described. In a data sample corresponding to an integrated luminosity of 35 pb-1 collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed on the squark mass between 450 and 690 GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy considered.

The polarisation of \\(\\tau\\)'s produced in Z decay is measured using 160 pb\\(^{-1}\\) of data accumulated at LEP by the ALEPH detector between 1990 and 1995. The variation of the polarisation with polar angle yields the two parameters \\({\\cal A}_e = 0.1504 \\pm 0.0068 \\) and \\({\\cal A}_{\\tau} = 0.1451 \\pm 0.0059\\) which are consistent with the hypothesis of e-\\(\\tau\\) universality. Assuming universality, the value \\({\\cal A}_{e\\mbox{-}\\tau} = 0.1474 \\pm 0.0045\\) is obtained from which the effective weak mixing angle \\(\\sin^2{\\theta_{\\mathrm{W}}^{\\mathrm{eff}}} =0.23147 \\pm 0.00057 \\) is derived.

The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the Aleph detector at LEP. The data are consistent with lepton universality. The resonance parameters are measured to be \\(M_{\\rm Z}=(91.1885 \\pm 0.0031){\\rm GeV}/c^2\\), \\(\\Gamma_{\\rm Z}= (2.4951 \\pm 0.0043)\\) GeV, \\(\\sigma^0_{\\rm had}=(41.559 \\pm 0.058)\\) nb and, combining the three lepton flavours, \\(R_{\\ell}= 20.725\\pm 0.039\\). The corresponding number of light neutrino species is \\(N_{\\nu}=2.983\\pm0.013\\) and the strong coupling constant is \\(\\alpha_s(M_{\\rm Z}) = 0.114\\pm{0.004} \\pm 0.002_{\\rm{QCD}} +\\,0.005\\,\\log_{10}\\left[\\frac{M_{\\rm H}}{150\\,{\\rm GeV}/c^2}\\right]\\,\\). The lepton pair forward-backward asymmetry is measured to be \\({\\rm A}_{\\rm FB}^{0, \\ell}=0.0173 \\pm 0.0016\\) from which the effective weak mixing angle is derived: \\(\\sin^2\\theta_{\\rm eff}^{\\rm lept} = 0.23089\\pm 0.00089\\). The measurement of the leptonic width \\(\\Gamma_{\\ell\\ell}=84.02\\pm0.15\\) MeV leads to a determination of the effective \\(\\rho\\) parameter \\(\\rho_{\\rm eff}^{\\rm lept} = 1.0064 \\pm 0.0018\\). The data support the Standard Model and favour a light Higgs.

Data from \\({\\rm e^+e^-}\\) annihilation into hadrons, taken with the ALEPH detector at the Z resonance, are analyzed. The four-jet rate is studied as a function of the resolution parameter and compared to next-to-leading order calculations combined with resummation of large logarithms. Angular correlations in four-jet events are measured and compared to next-to-leading order QCD predictions. With these observables two different measurements are performed. In a first analysis the strong coupling constant is measured from the four-jet rate yielding \\(\\alpha_s(M_{\\mathrm Z}) = 0.1170 \\pm 0.0001 ({\\rm stat}) \\pm 0.0013 ({\\rm sys})\\) . In a second measurement the strong coupling constant and the QCD colour factors are determined simultaneously from a fit to the four-jet rate and the four-jet angular correlations, giving \\(\\alpha_s(M_{\\rm Z}) = 0.119 \\pm 0.006 ({\\rm stat}) \\pm 0.026 ({\\rm sys})\\)\\(C_{\\rm A} = 2.93 \\pm 0.14 ({\\rm stat}) \\pm 0.58 ({\\rm sys})\\)\\(C_{\\rm F} = 1.35 \\pm 0.07 ({\\rm stat}) \\pm 0.26 ({\\rm sys})\\) in good agreement with the expectation from QCD.