5,103 research outputs found

    Analysis and discussion of the recent W mass measurements

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    The ATLAS and CDF measurements of the W mass are compared discussing some similarities and differences in the quoted systematic uncertainties.Comment: Talk given at the 52nd Rencontres de Moriond Electroweak Interactions and Unified Theories (2017

    LHC Results - Highlights

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    The LHC has delivered already 10/fb of proton proton collisions at a centre- of-mass energy of 7-8 TeV. With this data set, ATLAS and CMS have discovered a new boson at a mass of about 125 GeV and have searched for new physics at the TeV scale.Comment: 13 pages, Lecture given at the 2012 European School of High-Energy Physics, Anjou, France, 6-9 June 201

    About the rapidity and helicity distributions of the W bosons produced at LHC

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    WW bosons are produced at LHC from a forward-backward symmetric initial state. Their decay to a charged lepton and a neutrino has a strong spin analysing power. The combination of these effects results in characteristic distributions of the pseudorapidity of the leptons decaying from W+W^+ and W‚ąíW^- of different helicity. This observation may open the possibility to measure precisely the W+W^+ and W‚ąíW^- rapidity distributions for the two transverse polarisation states of WW bosons produced at small transverse momentum.Comment: 8 pages, 5 figure

    A critical point in the distribution of lepton energies from the decay of a spin-1 resonance

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    We consider a spin-11 resonance produced with an arbitrary spectrum of velocities and decaying into a pair of massless leptons, and we study the probability density function of the energy of the leptons in the laboratory frame. A special case is represented by the production of WW bosons in proton-proton collisions, for which the energy of the charged lepton from the decaying WW can be measured with sufficient accuracy for a high-precision measurement of MWM_W. We find that half of the resonance mass is a special value of the lepton energy, since the probability density function at this point is in general not analytic for a narrow-width resonance. In particular, the higher-order derivatives of the density function are likely to develop singularities, such as cusps or poles. A finite width of the resonance restores the regularity, for example by smearing cusps and poles into local stationary points. The quest for such points offers a handle to estimate the resonance mass with much reduced dependence on the underlying production and decay dynamics of the resonance.Comment: Revised version, 24 pages, 7 figure

    Study the effect of beam energy spread and detector resolution on the search for Higgs boson decays to invisible particles at a future e+^+e‚ąí^- circular collider

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    We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular \epem collider (FCC-ee) in the process e+e‚ąí‚ÜíHZe^+e^-\to HZ with Z‚Üí‚Ąď+‚Ąď‚ąíZ\to \ell^+\ell^- (‚Ąď=e\ell=e or őľ\mu) using an integrated luminosity of 3.5 ab‚ąí1^{-1} at a center-of-mass energy s=240\sqrt{s}=240 GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. %Two different detector concepts are considered: a detector corresponding to the CMS reconstruction performances and the expected design of the ILC detector. The minimum branching ratio for a 5ŌÉ5\sigma observation after 3.5ab‚ąí1^{-1} of data taking is 1.7¬Ī0.1%(stat+syst)1.7\pm 0.1\%(stat+syst) . The branching ratio exclusion limit at 95\% CL is 0.63¬Ī0.22%((stat+syst))0.63 \pm 0.22\%((stat+syst)).Comment: 17 pages, submitted to EPJ

    Impact of the PDFs on the Z and W lineshapes at LHC

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    The parton distribution functions (PDFs) of the proton play a role in determining the lineshape of ZZ and WW bosons produced at the LHC. In particular, the mode of the gauge boson virtuality is shifted with respect to the pole due to the dependence of the partonic luminosity on the boson virtuality. The knowledge of this shift contributes to the systematic uncertainty for a direct measurement of the boson mass. A detailed study of the shift and of its systematic uncertainty due to the limited knowledge of the PDFs is obtained using a tree-level model of ZZ and WW boson production in proton-proton collisions at s=13\sqrt{s}=13 TeV. A Monte Carlo simulation is further used to validate the tree-level model and study the dependence of the shift on the transverse momentum of the gauge bosons. The tree-level calculation is found to provide a good description of the shift. The systematic uncertainty on the lineshape due to the PDFs is estimated to be below one MeV in the phase-space relevant for a future high-precision mass measurement of the gauge boson masses at the LHC

    Understanding the TeV Scale through LHC Data, Dark Matter and Other Experiments

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    The workshop focused on new data from the LHC after the completion of its initial 7 TeV run, providing an opportunity to interpret the results and to plan for the future 14 TeV run. Particular attention was paid to the first serious indications for the discovery of a Higgs boson at a mass of 125 GeV. In addition to hearing from LHC experimentalists, attention was also given to input from experimenters at the Tevatron, as well as to the direct and indirect detection of dark matter, flavor physics, and other related searches. The main characteristic of the workshop was the close collaboration and intensive debate between theorists and experimentalists. The workshop also hosted a conference, jointly with the Johns Hopkins Series, on October 16/19, 2012

    Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

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    A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure

    Precise measurement of the W-boson mass with the CDF II detector

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    We have measured the W-boson mass MW using data corresponding to 2.2/fb of integrated luminosity collected in proton-antiproton collisions at 1.96 TeV with the CDF II detector at the Fermilab Tevatron collider. Samples consisting of 470126 W->enu candidates and 624708 W->munu candidates yield the measurement MW = 80387 +- 12 (stat) +- 15 (syst) = 80387 +- 19 MeV. This is the most precise measurement of the W-boson mass to date and significantly exceeds the precision of all previous measurements combined
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