Squark/Gluino Analysis
IFAE-Barcelona
IFAE-Barcelona


Authors

Monica D'Onofrio (donofrio@fnal.gov)

Gianluca De Lorenzo (gdl@fnal.gov)

Mario Martinez (mmp@fnal.gov)



CDF, FNAL,
P.0. Box 500, M.S. 318
Batavia, Illinois 60510
USA


Search for Squark/Gluino Production in MET+jets Final State
(2.0 fb-1 analysis)


We are reporting on the search for squarks and gluinos in proton-antiproton collisions with a center-of-mass energy of 1.96 TeV at the Tevatron, based on 2.0 fb-1 of data collected by the CDF detector in Run II. Events with multiple jets of hadrons and large missing transverse energy in the final state are studied within the framework of minimal supergravity and assuming R-parity conservation.
In mSUGRA, all supersymmetric particles except the neutralino are unstable and therefore will decay into their SM counterparts right after being produced. This cascade will result in a final state consisting on several jets, which come from squarks and/or gluinos, plus missing transverse energy coming from the neutralinos which leave CDF undetected. If squarks are significantely lighter than gluinos, they will tend to decay producing a dijet topology with missing transverse energy carried away by the two neutralinos. If gluinos are lighter than squarks, their pair production and decay will lead to topologies containing a large number of jets and Missing Transverse Energy.
The analysis is then optimized for events with at least two, three and four jets and missing transverse energy (MET) signature. Events are required to have:

  • MET > 70 GeV + cleanup cuts
  • At least two/three/four jets with ET > 25 GeV and |&eta|<2.0
  • At least one jet central |&eta| < 1.1
  • Jet EM Fraction < 0.9
  • Δφ (MET-jet)> 0.7 (first two/three leading jets).
    • In case of 2-jets region, if a third jet is in the event, Δφ (MET-3rd jet)> 0.2
    • In case of 4-jets region, Δφ (MET-4th jet)> 0.3
    No reconstructed Z from tracks and no isolated tracks with Δφ (MET-track)< 0.7


MET distribution after different requirements ( eps ) [1.4 fb-1 shown as example].

Three different set of cuts are defined to increase sensitivity in different zones with increasing gluino mass. The thresholds for the transverse energy (ET) of the jets, the MET and the scalar sum of the ET of the two main jets (HT2) or three main jets (HT) are quoted below:


  • Region 4-jets:  ET1 > 95 GeV ;  ET2 > 55 GeV ;  ET3 > 55 GeV ;  ET4 > 25 GeV ; MET > 90 GeV ;  HT > 280 GeV
  • Region 3-jets:  ET1 > 140 GeV ; ET2 > 100 GeV ; ET3 > 25 GeV ; MET > 120 GeV ; HT > 330 GeV
  • Region 2-jets:  ET1 > 165 GeV ;  ET2 > 100 GeV ; MET > 180 GeV ;  HT(2-jets) > 330 GeV

No excess with respect to Standard Model predictions is observed.

Table of number of events in data vs SM expectations after final cuts. (also in pdf ). Systematic uncertainties on the background include 6 % uncertainty on the luminosity.

In a mSUGRA scenario with A0=0, &mu<0 and tan(&beta)=5, we exclude masses up to about 392 GeV/c2 at 95% C.L. in the region where gluino and squark masses are similar, gluino masses up to 280 GeV/c2 for every squark mass, and gluino masses up to 423 GeV/c2 for squark masses below 378 GeV/c2.


  • EXCLUSION PLANES (*)

    • Exclusion Plane (Gluino Mass vs Squark Mass) gif & eps
      Exclusion Plane for squark and gluino masses at 95 % C.L: The blue region was excluded by the UA1 experiment. The light-green region was excluded by the UA2 experiment. The dark-green region was excluded by the CDF and D0 experiments after Run I. The brown region was excluded by the LEP experiment. In the black hashed region there is no mSUGRA solution. The dark-red region shows the area excluded by the current analysis with 2.0 fb-1 of CDF Run II data. The dashed black line shows the expected limit.

    • Exclusion Plane (m0 vs m1/2) gif & eps
      Regions excluded by this analysis at the 95 % C.L. in the (m0,m1/2) plane, in the framework of mSUGRA assuming R-parity conservation, tan(&beta)=5, A0=0 and &mu<0. In the dark-grey region there is no mSUGRA solution. The light-grey region indicates the region where m(stau) < m(neutralino). The beige and green regions are excluded by LEP2 chargino and slepton searches, respectively. The nearly horizonthal black lines are the iso-mass curves for gluinos corresponding to masses of 150, 300, 450 and 600 GeV/c2. The other lines are iso-mass curves for squarks, corresponding to masses of 150, 300, 450 and 600 GeV/c2. The dark-red line shows the exclusion limit set by the current analysis with 2.0 fb-1 of CDF Run II data. The dashed black line shows the expected limit.


    (*) The PDF and the renormalization scale uncertainties on the theoretical cross section are included in the limit calculation.


  • PROSPINO CROSS SECTIONS VS OBSERVED/EXPECTED 95% C.L. LIMITS (*)

    • Cross section as a function of Squark Mass (Gluino Mass about 230 GeV/c2) gif & eps
      PROSPINO NLO Cross section as a function of the squark mass for a gluino mass of 230 GeV/c2. The yellow band denotes the systematic uncertainty on the theoretical predictions. Solid and dashes lines denote the observed and expected 95 % C.L.

    • Cross section as a function of Gluino Mass (Squark Mass = Gluino Mass) gif & eps
      PROSPINO NLO Cross section as a function of the gluino mass. The yellow band denotes the systematic uncertainty on the theoretical predictions. Solid and dashes lines denote the observed and expected 95 % C.L.

    • Cross section as a function of Gluino Mass (Squark Mass = 460 GeV/c2) gif & eps
      PROSPINO NLO Cross section as a function of the gluino mass for a squark mass about 460 GeV/c2. The yellow band denotes the systematic uncertainty on the theoretical predictions. Solid and dashes lines denote the observed and expected 95 % C.L.

    (*) The PDF and the renormalization scale uncertainties on the theoretical cross section are NOT included in the limit calculation.


  • MISSING ET AND HT DISTRIBUTIONS WITH FINAL CUTS (N-1 plots)

    • Missing ET distribution for analysis cuts 4-jets region: gif & eps
      Missing Et Distribution for the 4-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on MET is placed.

      Missing ET distribution for analysis cuts 4-jets region: stacked background contributions gif & eps


    • Missing ET distribution for analysis cuts 3-jets region: gif & eps
      Missing ET Distribution for the 3-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on MET is placed.

      Missing ET distribution for analysis cuts 3-jets region: stacked background contributions gif & eps


    • Missing ET distribution for analysis cuts 2-jets region: gif & eps
      Missing Et Distribution for the 2-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on MET is placed.

      Missing ET distribution for analysis cuts 2-jets region: stacked background contributions gif & eps


    • HT distribution for analysis cuts 4-jets region: gif & eps
      HT Distribution for the 4-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on HT is placed.

      HT distribution for analysis cuts 4-jets region: stacked background contributions gif & eps


    • HT distribution for analysis cuts 3-jets region: gif & eps
      HT Distribution for the 3-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on HT is placed.

      HT distribution for analysis cuts 3-jets region: stacked background contributions gif & eps


    • HT distribution for analysis cuts 2-jets region : gif & eps
      HT Distribution for the 2-jets region. All selection criteria have been applied except the one on the variable that is represented. The data is compared to SM predictions (separated also in QCD and non-QCD backgrounds). The band presents the total systematic uncertainty on the background prediction. For illustrations, the signal for a typical mSUGRA point is shown. The arrow indicates where the cut on HT is placed.

      HT distribution for analysis cuts 2-jets region: stacked background contributions gif & eps




    List of expected SM background contributions after final cuts (also in pdf ). Systematic uncertainties on each background contribution include 6 % uncertainty on the luminosity.


  • CONTROL REGIONS DEFINED USING REVERSED CUTS

    Events are required to have at least one jet with azimuthal direction aligned to the direction of the MET (QCD dominated region)
    • 4-jets region:
      • MET Distribution when Δφ (MET-jet) < 0.7 at least for one of the three leading jets, or Δφ (MET-4th jet) < 0.3 (gif & eps) ;
      • HT Distribution when Δφ (MET-jet) < 0.7 at least for one of the three leading jets, or Δφ (MET-4th jet) < 0.3 (gif & eps) ;
    • 3-jets region:
      • MET Distribution when Δφ (MET-jet) < 0.7 at least for one of the three leading jets (gif & eps) ;
      • HT Distribution when Δφ (MET-jet) < 0.7 at least for one of the three leading jets (gif & eps) ;
    • 2-jets region:
      • MET Distribution when Δφ (MET-jet) < 0.7 at least for one of the two leading jets, or Δφ (MET-3rd jet) < 0.2 (gif & eps) ;
      • HT Distribution when Δφ (MET-jet) < 0.7 at least for one of the two leading jets, or Δφ (MET-3rd jet) < 0.2 (gif & eps) ;


    Events are required to have at least one jet with electromagnetic fraction larger than 0.9 (selects electrons, EWK/TOP dominated region)
    • 4-jets region:
      • MET Distribution when Jet EM Fraction is > 0.9 (at least for one of the four leading jets) (gif & eps) ;
      • HT Distribution when Jet EM Fraction is > 0.9 (at least for one of the four leading jets) (gif & eps) ;
    • 3-jets region:
      • MET Distribution when Jet EM Fraction is > 0.9 (at least for one of the three leading jets) (gif & eps) ;
      • HT Distribution when Jet EM Fraction is > 0.9 (at least for one of the three leading jets) (gif & eps) ;
    • 2-jets region:
      • MET Distribution when Jet EM Fraction is > 0.9 (at least for one of the two leading jets) (gif & eps) ;
      • HT Distribution when Jet EM Fraction is > 0.9 (at least for one of the two leading jets) (gif & eps) ;


    Events are required to have at least one isolated track pointing in the direction of the MET, or two isolated tracks with invariant mass within the Z boson mass range. (selects electrons and muons, EWK/TOP dominated region)
    • 4-jets region:
      • MET Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;
      • HT Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;
    • 3-jets region:
      • MET Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;
      • HT Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;
    • 2-jets region:
      • MET Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;
      • HT Distribution when there is at least one isolated track with Δφ (track-MET) < 0.7, or two isolated tracks with invariant mass within the range [76-106] GeV/c2. (gif & eps) ;


  • ADDITIONAL CONTROL REGIONS DEFINED for 2-jets selection

    Events are required to have passed all selection cuts for 2-jets region, but the ones on MET and HT. The arrow in each distribution indicates the cut on each quantity. The region below the cut is considered control region.
    • MET Distribution (gif & eps) ;
    • HT Distribution (gif & eps) ;

  • DETAILS ON RELATIVE CONTRIBUTION AND SIGNAL-to-BACKGROUND OPTIMIZATION

    • Different relative contributions of the signal production processes before the cuts as a function of gluino mass and at constant squark mass (460 GeV/c2). (gif & eps)
    • Different relative contributions of the signal production processes before the cuts as a function of gluino mass for the diagonal. (gif & eps)

    • S/sqrt(B) for the different selection criteria are presented at constant squark mass (460 GeV/c2) in the squark/gluino mass plane. (gif & eps)
    • S/sqrt(B) for the different selection criteria are presented along the diagonal in the squark/gluino mass plane. (gif & eps)

    • Signal efficiencies for the different selection criteria are presented at constant squark mass (460 GeV/c2) in the squark/gluino mass plane. Systematic uncertainties on the signal efficiencies related to PDF and the choice of renormalization and factorization scales are superimposed. (gif & eps)
    • Signal efficiencies for the different selection criteria are presented along the diagonal in the squark/gluino mass plane. Systematic uncertainties on the signal efficiencies related to PDF and the choice of renormalization and factorization scales are superimposed. (gif & eps)

    • Different relative contributions of the signal production processes after selection cuts as a function of gluino mass and at constant squark mass (460 GeV/c2). (gif & eps)
    • Different relative contributions of the signal production processes after selection cuts as a function of gluino mass for the diagonal. (gif & eps)

  •             Monica D'Onofrio (donofrio@fnal.gov)