CDF Logo Combined Limit for Searches for Chargino Neutralino Production in Multilepton Channels
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This Web page describes the combination of the results of the different analyses looking for SuperSymmetry in the multilepton channels. The analyses included in the combination are all the blessed results of
  • ee+e/mu, emu+e/mu (high-pt triggers)
  • mumu+e/mu, mue+e/mu (high-pt triggers)
  • ee+track (low-pt triggers)
  • mm+e/mu (low-pt triggers)
  • like sign dilepton ee,em,mm (high-pt triggers)
    to obtain a limit on the mass of the chargino and on the cross section times branching ratio for ppbar into chargino neutralino into three leptons.


    MORE DETAILS ON THE METHOD

    All analyses are performed as counting experiments, and the backgrounds are evaluated using a combination of data and Monte Carlo samples.
    When combining the analyeses to obtain a combined limit, all the analyses are treated as exclusive channels. This means particular care is taken into avoiding a event is counted in two different analyses. If an event is selected by two or more different analyses, we assign the event to the analysis with the highest Signal/Sqrt(Background) and remove it from the other analysis(es).
    For each analysis we then obtain an inclusive acceptance (which corresponds to the number of events expected for that analysis when run in its blessed configuration) and and exclusive acceptance, which is the nuber of events expected for that analysis ONLY, which is the acceptance in number of events brought by that analysis specifically which would have not been selected by the other analyses. The same ratio is used to scale the inclusive backgrounds.
    We combine the analyses using a frequentist approach described in hep-ex/9902006. To extract the limit we use a set of Monte Carlo samples generated using Pythia 6.216(6.3) and Isajet 7.51 or Softsusy 2.0.7 in three different scenarios:

  • standard mSUGRA:
    this is the standard mSUGRA "out of the box" from Pythia, with tanbeta=3, A0=0, mu>0 and values of M_0 = 60 with M_1/2 ranging between 162 and 230 GeV/c^2. The expected limit in this scenario is on the mass of the chargino of 122 GeV/c^2, corresponding on sigma times Br of 0.42 pb. We have also extracted the limit by using only the six channels of the two high-pt trilepton analyses and the plots and limits are shown below.
  • MSSM with no slepton mixing:
    in this scenario the slepton mixing has been turned off by setting the diagonal terms of the mixing matrix to zero in Softsusy. This enhances the branching ratios of chargino and neutralino in electrons and muons. In this scenario using all analyses combined we observe a limit on the chargino mass(sigma times branching ratio) of 129 GeV/c^2 (0.25 pb) and are sensitive to masses(sigma times Br) of 157 GeV/c^2(0.1 pb). We have also extracted the limit by using only the six channels of the two high-pt trilepton analyses and the plots and limits are shown below.
  • MSSM with W/Z decay:
    in this MSSM scenario we have kept tanbeta=3, A0=0, mu>0, and set artificially the relationships between the masses M(chargino-1) = M(neutralino-2) = 2M(neutralino-0), with neutralino-0 LSP, and the branching ratios chargino-1 into lepton, neutrino, LSP equal to the Branching ratio of the W into lepton+neutrino, and the Br(neutralino-2 into l+l-)=Br(Z^0 into l+l-).
    Below are the plots we blessed for the combination. Please refer to the single analyses web-pages for the plots relative to a particular analysis.

    Blessed Plots and Tables:

    Table with the summary of the analyses which enter in the combination (in pdf format):
  • Trileptons: EPS GIF
  • LS Dileptons: EPS GIF
  • Table with the systematic uncertainties and their correlations among channels.
  • Trileptons: PDF or GIF
  • LS Dileptons: PDF or GIF

  • NO SLEPTON MIXING - ALL
    Combined limit for all analyses as reported in CDF Note 8610 for the MSSM scenario with tanbeta=3, mu>0, M0=70, M_1/2 ranging between 162-240 GeV/c2 and NO SLEPTON MIXING. GIF or EPS

    NO SLEPTON MIXING - High-Pt Trileptons
    Combined limit for high-Pt trilepton analyses as reported in CDF Note 8610 for the MSSM scenario with tanbeta=3, mu>0, M0=70, M_1/2 ranging between 162-240 GeV/c2 and NO SLEPTON MIXING. GIF or EPS

    MSUGRA - ALL
    Combined limit for all analyses as reported in CDF Note 8610 for the mSugra scenario with tanbeta=3, mu>0, M0=60, M_1/2 ranging between 162-230 GeV/c2. All the default mSugra relations are kept as given from the model. The curves have been smoothed to avoid discontinuities due to poor statistics. GIF or EPS

    MSUGRA - High-Pt Trileptons
    Combined limit for high-pt trilepton analyses as reported in CDF Note 8610 for the mSugra scenario with tanbeta=3, mu>0, M0=60, M_1/2 ranging between 162-230 GeV/c2. All the default mSugra relations are kept as given from the model. GIF or EPS

    MSUGRA - ee+track only
    Combined limit for ee+track analysis only as reported in CDF Note 8610 for the mSugra scenario with tanbeta=3, mu>0, M0=60, M_1/2 ranging between 162-230 GeV/c2. All the default mSugra relations are kept as given from the model. GIF or EPS

    MSSM with W/Z decays - ALL
    Combined limit for all analyses as reported in CDF Note 8610 for an MSSM scenario with tanbeta=3, mu>0, where we have artificially set the masses of the lightest chargino equal to the mass of the second to lightest neutralino equal to twice the mass of the lightest neutralino (LSP), and the Branching ratio of the lightest chargino(second to lightest neutralino) into leptons equal to the BR of the W(Z) boson into leptons. GIF or EPS

    MSSM with W/Z decays - High-Pt Trileptons
    Combined limit for high-pt trilepton analyses as reported in CDF Note 8610 for an MSSM scenario with tanbeta=3, mu>0, where we have artificially set the masses of the lightest chargino equal to the mass of the second to lightest neutralino equal to twice the mass of the lightest neutralino (LSP), and the Branching ratio of the lightest chargino(second to lightest neutralino) into leptons equal to the BR of the W(Z) boson into leptons. GIF or EPS

    The following plots are the projections of the limit we could obtain on the three models we have explored with luminosities variable between 2 and 16 fb-1. For this "BASIC" projection in the calculation of the limit we have only scaled the acceptance and the background by the luminosity and assumed the uncertainties and signal/background ratio stayed the same.

    NO SLEPTON MIXING - ALL - BASIC PROJECTION
    Combined limit for all analyses as reported in CDF Note 8610 for the MSSM scenario with tanbeta=3, mu>0, M0=70, M_1/2 ranging between 162-240 GeV/c2 and NO SLEPTON MIXING. Plotted are also the expected limits for the luminosities of 2,4,8 and 16 fb-1, calculated using the same exact assumptions as the blessed result, but scaling up the signal and background by the indicated luminosities. GIF or EPS

    MSUGRA - ALL - BASIC PROJECTION
    Combined limit for all analyses as reported in CDF Note 8610 for the MSUGRA scenario with tanbeta=3, mu>0, M0=70, M_1/2 ranging between 162-230 GeV/c2. All the default mSugra relations are kept as given from the model. The observed limit curve has been smoothed to avoid discontinuities due to poor statistics. Plotted are also the expected limits for the luminosities of 2,4,8 and 16 fb-1, calculated using the same exact assumptions as the blessed result, but scaling up the signal and background by the indicated luminosities. GIF or EPS

    MSSM with W/Z decays - ALL - BASIC PROJECTION
    Combined limit for all analyses as reported in CDF Note 8610 for an MSSM scenario with tanbeta=3, mu>0, where we have artificially set the masses of the lightest chargino equal to the mass of the second to lightest neutralino equal to twice the mass of the lightest neutralino (LSP), and the Branching ratio of the lightest chargino(second to lightest neutralino) into leptons equal to the BR of the W(Z) boson into leptons. Plotted are also the expected limits for the luminosities of 2,4,8 and 16 fb-1, calculated using the same exact assumptions as the blessed result, but scaling up the signal and background by the indicated luminosities. GIF or EPS

    The following plots are provided as support for people who want to give more detailed talks about the combination and the limit itself.
    Branching ratio of chargino-neutralino into three leptons in the NO SLEPTON MIXING scenario EPS or GIF
    Branching ratio of chargino into leptons in the NO SLEPTON MIXING scenario EPS or GIF
    Branching ratio of neutralino into leptons in the NO SLEPTON MIXING scenario EPS or GIF
    Branching ratio of chargino-neutralino into three leptons in the mSUGRA scenario EPS or GIF
    Branching ratio of chargino into leptons in the mSUGRA scenario EPS or GIF
    Branching ratio of neutralino into leptons in the mSUGRA scenario EPS or GIF
    Difference between selectron and chargino masses as a function of M_1/2 in the MSSM with no slepton mixing scenario EPS or GIF
    Difference between selectron and chargino masses as a function of M_1/2 in the mSUGRA scenario EPS or GIF
    Difference between selectron and chargino masses as a function of M_1/2 in the MSSM with W/Z decays scenario EPS or GIF
    Acceptance for trilepton vs. ls-dilepton analyses as a function of the chargino mass for the Susy Monte Carlo samples generated in the MSSM scenario without slepton mixing.The curves have been smoothed to avoid discontinuities due to poor statistics. EPS or GIF
    Acceptance for trilepton vs. ls-dilepton analyses as a function of the chargino mass for the Susy Monte Carlo samples generated in the mSUGRA scenario. The curves have been smoothed to avoid discontinuities due to poor statistics. EPS or GIF
    Acceptance for trilepton vs. ls-dilepton analyses as a function of the chargino mass for the Susy Monte Carlo samples generated in the MSSM with W/Z decays scenario. The curves have been smoothed to avoid discontinuities due to poor statistics. EPS or GIF
    Acceptance for high-pt trilepton analyses as a function of the chargino mass for the three scenarios considered in the combination. The curves have been smoothed to avoid discontinuities due to poor statistics. EPS or GIF


    This web-page was last updated Dec 21st, 2006 by Giulia Manca.
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