Search for Resonances in the Dilepton Mass Distribution in pp Collisions at sqrt(s) = 7 TeV

Abstract

A search for narrow, high-mass resonances decaying to electron or muon pairs has been performed using pp collision data collected at √s = 7 TeV by the CMS experiment in 2011. The data sample corresponds to an integrated luminosity of approximately 5 fb- The event yields observed in the signal regions are consistent with predictions of the standard model backgrounds, and upper limits on the cross section times branching fraction for a resonance decaying to dileptons are extracted from a shape analysis of the dilepton invariant mass distribution. The resulting mass limits at 95\% confidence level are 2330 GeV for the Z' in the Sequential Standard Model, 2000 GeV for the superstring-inspired Z'ψ resonance, 890 (540) GeV for the Stueckelberg extension Z'st with the mass parameter ε=0.06 (0.04), and 2140 (1810) GeV for Kaluza--Klein gravitons with the coupling parameter k/Mpl of 0.10 (0.05). These limits are the most stringent to date.

Approved Plots from EXO-11-019 contained in paper (click on plot to get .pdf)

Figure Abbreviated Caption
muon mass spectra Figure 1 :The observed opposite-sign e±μ dilepton invariant mass spectrum (data points). The filled red histogram shows the contribution to the spectrum from ttbar and other sources of prompt leptons (tW, diboson production, Z→ττ), as derived from simulations. The background where at least one of the reconstructed objects is not a real lepton is shown in yellow and estimated from the data using the same-sign e±μ± spectrum.
muon mass spectra Figure 2a. The invariant mass spectrum of μ+μ- events. The points with error bars represent the data. The uncertainties on the data points are statistical only. The histograms represent the expectations from SM processes: Z/γ*, ttbar, other sources of prompt leptons (tW, diboson production, Z→ττ), and the multi-jet backgrounds. Multijet backgrounds contain at least one jet that has been misreconstructed as a lepton.
electron mass spectra Figure 2b. The invariant mass spectrum of ee events. The points with error bars represent the data. The uncertainties on the data points are statistical only. The histograms represent the expectations from SM processes: Z/γ*, ttbar, other sources of prompt leptons (tW, diboson production, Z→ττ), and the multi-jet backgrounds. Multijet backgrounds contain at least one jet that has been misreconstructed as a lepton.
 integral muon mass spectra Figure 3a. The cumulative distribution of the invariant mass spectrum of μ+μ- events. The points with error bars represent the data; the histograms represent the expectations from SM processes.
integral electron mass spectra Figure 3b. The cumulative distribution of the invariant mass spectrum of ee events. The points with error bars represent the data; the histograms represent the expectations from SM processes.
data-fit / fit for muons Figure 4a. The relative difference between the data and the fitted parametrization of the simulated background, where the latter is normalized to the data, is shown in a variety of mass bins for the muon channel. The binning was chosen so that there is a minimum prediction of 10 events in each bin and a minimum bin size of 20 GeV was required. The horizontal error bars simply represent the bin width and should not be intepreted as an uncertainty.
data-fit /fit for electrons Figure 4b. The relative difference between the data and the fitted parametrization of the simulated background, where the latter is normalized to the data, is shown in a variety of mass bins for the muon channel. The binning was chosen so that there is a minimum prediction of 10 events in each bin and a minimum bin size of 20 GeV was required. The horizontal error bars simply represent the bin width and should not be intepreted as an uncertainty.
Z' limits muon channel Figure 5a. Upper limits as a function of resonance mass M, on the production ratio Rσ of cross section times branching fraction into lepton pairs for Z'SSM, Z'ψ, and GKK production to the same quantity for Z bosons. The limits shown are from the μ+μ- final state. Shaded green and yellow bands correspond to the 68% and 95% quantiles for the expected limits. The predicted cross section ratios are shown as bands, with widths indicating the theoretical uncertainties. The differences in the widths reflect the different uncertainties on the k-factors used
Z' limits electron channel Figure 5a. Upper limits as a function of resonance mass M, on the production ratio Rσ of cross section times branching fraction into lepton pairs for Z'SSM, Z'ψ, and GKK production to the same quantity for Z bosons. The limits shown are from the ee final state. Shaded green and yellow bands correspond to the 68% and 95% quantiles for the expected limits. The predicted cross section ratios are shown as bands, with widths indicating the theoretical uncertainties. The differences in the widths reflect the different uncertainties on the k-factors used
Z' limits Figure 5a. Upper limits as a function of resonance mass M, on the production ratio Rσ of cross section times branching fraction into lepton pairs for Z'SSM, Z'ψ, and GKK production to the same quantity for Z bosons. The limits shown are from the combined dilepton result. Shaded green and yellow bands correspond to the 68% and 95% quantiles for the expected limits. The predicted cross section ratios are shown as bands, with widths indicating the theoretical uncertainties. The differences in the widths reflect the different uncertainties on the k-factors used
limits in the cu-cd plane Figure 6. 95% C.L. upper limits on the Z' cross sections for given masses are equivalent to excluded regions in the (cd, cu) plane which are bounded by the thin black lines in the figure. They are compared with the predicted values of (cd, cu) in three classes of models. The colours on curves correspond to different mixing angles of the generators defined in each model. For any point on a model curve, the mass limit corresponding to that value of (cd, cu) is given by the intersecting experimental contour.

High Mass Dimuon Event Displays

Object selection in the event displays:

  • Only muon tracks having StandAlone part are shown (have an independently reconstructed track part in the Muon detector)
  • Tracker tracks with pT > 2 GeV
  • ECAL and HCAL deposits > 0.2 GeV

Figure Abbreviated Caption
1379 GeV event rho-phi Event display of an event with an invariant mass of 1379 GeV in the ρ-φ plane of the detector.
1379 GeV event rho-z Event display of an event with an invariant mass of 1379 GeV in the ρ-z plane of the detector.
1256 GeV event rho-phi Event display of an event with an invariant mass of 1256 GeV in the ρ-φ plane of the detector.
1256 GeV event rho-z Event display of an event with an invariant mass of 1256 GeV in the ρ-z plane of the detector.
1107 GeV event rho-phi Event display of an event with an invariant mass of 1107 GeV in the ρ-φ plane of the detector.
1107 GeV event rho-z Event display of an event with an invariant mass of 1107 GeV in the ρ-z plane of the detector.
1089 GeV event rho-phi Event display of an event with an invariant mass of 1089 GeV in the ρ-φ plane of the detector.
1089 GeV event rho-z Event display of an event with an invariant mass of 1089 GeV in the ρ-z plane of the detector.

High Mass Dielectron Event Displays

Figure Abbreviated Caption
1309GeV event rho-phi plane Event display of an event with an invariant mass of 1309GeV in the ρ-φ plane of the detector. The minimum track Pt is 2GeV.
1309GeV event rho-z plane Event display of an event with an invariant mass of 1309GeV in the ρ-z plane of the detector. The minimum track Pt is 2GeV.
1121GeV event rho-phi plane Event display of an event with an invariant mass of 1121GeV in the ρ-φ plane of the detector. The minimum track Pt is 2GeV.
1121GeV event rho-z plane Event display of an event with an invariant mass of 1121GeV in the ρ-z plane of the detector. The minimum track Pt is 2GeV.
1075GeV event rho-phi plane Event display of an event with an invariant mass of 1075GeV in the ρ-φ plane of the detector. The minimum track Pt is 2GeV.
1075GeV event rho-z plane Event display of an event with an invariant mass of 1075GeV in the ρ-z plane of the detector. The minimum track Pt is 2GeV.
Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng 1075gev_rhophi.png r1 manage 58.5 K 2012-03-01 - 18:57 ThomasReis 1075GeV event display rho-phi
PNGpng 1075gev_rhophi_logo.png r1 manage 100.7 K 2012-03-06 - 13:34 ThomasReis 1075GeV event display rho-phi with CMS logo
PNGpng 1075gev_rhoz.png r1 manage 24.1 K 2012-03-01 - 18:58 ThomasReis 1075GeV event display rho-z
PNGpng 1075gev_rhoz_logo.png r1 manage 60.3 K 2012-03-06 - 13:35 ThomasReis 1075GeV event display rho-z with CMS logo
PNGpng 1121gev_rhophi.png r1 manage 57.9 K 2012-03-01 - 18:56 ThomasReis 1121GeV event display rho-phi
PNGpng 1121gev_rhophi_logo.png r1 manage 99.9 K 2012-03-06 - 13:35 ThomasReis 1121GeV event display rho-phi with CMS logo
PNGpng 1121gev_rhoz.png r1 manage 21.8 K 2012-03-01 - 18:56 ThomasReis 1121GeV event display rho-z
PNGpng 1121gev_rhoz_logo.png r1 manage 56.5 K 2012-03-06 - 13:36 ThomasReis 1121GeV event display rho-z with CMS logo
PNGpng 1309gev_rhophi.png r1 manage 57.3 K 2012-03-01 - 18:55 ThomasReis 1309GeV event display rho-phi
PNGpng 1309gev_rhophi_logo.png r1 manage 99.2 K 2012-03-06 - 13:36 ThomasReis 1309GeV event display rho-phi with CMS logo
PNGpng 1309gev_rhoz.png r1 manage 21.3 K 2012-03-01 - 18:55 ThomasReis 1309GeV event display rho-z
PNGpng 1309gev_rhoz_logo.png r1 manage 56.4 K 2012-03-06 - 13:37 ThomasReis 1309GeV event display rho-z with CMS logo
PDFpdf Data_MC_4_7fb_NormDiff_250_En_350_EE_Eta4.pdf r1 manage 20.4 K 2012-03-06 - 16:46 SherifElgammal Distribution of normalized difference in endcaps
PNGpng Data_MC_4_7fb_NormDiff_250_En_350_EE_Eta4.png r1 manage 20.5 K 2012-03-06 - 17:17 SherifElgammal  
PDFpdf Data_MC_4_7fb_NormDiff_En_over_150_EB_Eta4.pdf r1 manage 20.8 K 2012-03-05 - 09:26 SherifElgammal Distribution of normalized difference in barrel
PNGpng Data_MC_4_7fb_NormDiff_En_over_150_EB_Eta4.png r1 manage 20.8 K 2012-03-06 - 17:16 SherifElgammal  
GIFgif dataOverFitEles5000pb.gif r1 manage 43.1 K 2012-06-11 - 15:59 SamHarper figure 4 (bottom)
PDFpdf dataOverFitEles5000pb.pdf r1 manage 16.4 K 2012-06-11 - 16:00 SamHarper figure 4 (bottom)
GIFgif dataOverFitMuons5300pb.gif r1 manage 43.6 K 2012-06-11 - 16:28 SamHarper figure 4 (top)
PDFpdf dataOverFitMuons5300pb.pdf r1 manage 16.6 K 2012-06-11 - 16:29 SamHarper figure 4 (bottom)
GIFgif diEleIntMassHist4700LogX.gif r2 r1 manage 12.8 K 2012-03-07 - 15:09 SamHarper  
PDFpdf diEleIntMassHist4700LogX.pdf r2 r1 manage 25.4 K 2012-03-07 - 15:09 SamHarper  
GIFgif diEleIntMassHist4700pb.gif r2 r1 manage 14.8 K 2012-03-07 - 16:09 SamHarper di-electron integral mass hist di-electron integral mass hist
PDFpdf diEleIntMassHist4700pb.pdf r2 r1 manage 33.5 K 2012-03-07 - 16:09 SamHarper di-electron integral mass hist
GIFgif diEleIntMassSpectra5000pbLogX.gif r1 manage 44.0 K 2012-06-11 - 16:29 SamHarper figure 3 (right)
PDFpdf diEleIntMassSpectra5000pbLogX.pdf r1 manage 25.3 K 2012-06-11 - 16:29 SamHarper figure 3 (right)
PDFpdf diEleMassHist4700LogX.pdf r2 r1 manage 25.2 K 2012-03-07 - 15:10 SamHarper  
GIFgif diEleMassHist4700pb.gif r2 r1 manage 19.8 K 2012-03-07 - 16:09 SamHarper di-ele mass spectrum
PDFpdf diEleMassHist4700pb.pdf r2 r1 manage 29.5 K 2012-03-07 - 16:09 SamHarper di-ele mass spectrum
GIFgif diEleMassHist4700pbLogX.gif r2 r1 manage 16.1 K 2012-03-07 - 15:10 SamHarper  
GIFgif diEleMassSpectra5000pbLogX.gif r1 manage 47.8 K 2012-06-11 - 16:30 SamHarper figure 2 (right)
PDFpdf diEleMassSpectra5000pbLogX.pdf r1 manage 21.5 K 2012-06-11 - 16:30 SamHarper figure 2 (right)
GIFgif diMuIntMassHist5000pb.gif r1 manage 47.7 K 2012-03-01 - 16:09 SamHarper di-muon integral mass spectrum
PDFpdf diMuIntMassHist5000pb.pdf r2 r1 manage 24.9 K 2012-03-07 - 15:12 SamHarper di-muon integral mass spectrum
GIFgif diMuIntMassHist5000pbLogX.gif r2 r1 manage 12.6 K 2012-03-07 - 15:11 SamHarper  
PDFpdf diMuIntMassHist5000pbLogX.pdf r2 r1 manage 24.9 K 2012-03-07 - 15:14 SamHarper  
GIFgif diMuIntMassSpectra5300pbLogX.gif r1 manage 41.5 K 2012-06-11 - 16:30 SamHarper figure 3 (left)
PDFpdf diMuIntMassSpectra5300pbLogX.pdf r1 manage 24.8 K 2012-06-11 - 16:30 SamHarper figure 3 (left)
GIFgif diMuMassHist5000pb.gif r1 manage 64.3 K 2012-03-01 - 16:09 SamHarper di muon mass spectrum
PDFpdf diMuMassHist5000pb.pdf r1 manage 28.6 K 2012-03-01 - 15:07 SamHarper di muon mass spectrum
GIFgif diMuMassHist5000pbLogX.gif r2 r1 manage 17.2 K 2012-03-07 - 15:12 SamHarper  
PDFpdf diMuMassHist5000pbLogX.pdf r2 r1 manage 24.6 K 2012-03-07 - 15:13 SamHarper  
GIFgif diMuMassSpectra5300pbLogX.gif r1 manage 46.6 K 2012-06-11 - 16:31 SamHarper figure 2 (left)
PDFpdf diMuMassSpectra5300pbLogX.pdf r1 manage 18.3 K 2012-06-11 - 16:31 SamHarper figure 2 (left)
PDFpdf dielectronResolutionCorrected_4_7fb_EBEB_EBEE_public.pdf r1 manage 15.9 K 2012-03-02 - 02:50 VladlenTimciuc di-electron mass resolution for EBEB & EBEE (pdf)
PNGpng dielectronResolutionCorrected_4_7fb_EBEB_EBEE_public.png r1 manage 18.2 K 2012-03-02 - 02:49 VladlenTimciuc di-electron mass resolution for EBEB & EBEE
PDFpdf dielectronResolutionCorrected_4_7fb_EBEB_public.pdf r1 manage 16.0 K 2012-03-02 - 02:52 VladlenTimciuc di-electron mass resolution for EBEB (pdf)
PNGpng dielectronResolutionCorrected_4_7fb_EBEB_public.png r1 manage 17.1 K 2012-03-02 - 02:51 VladlenTimciuc di-electron mass resolution for EBEB
PDFpdf dielectronResolutionCorrected_4_7fb_EBEE_public.pdf r1 manage 15.9 K 2012-03-02 - 02:54 VladlenTimciuc di-electron mass resolution for EBEE (pdf)
PNGpng dielectronResolutionCorrected_4_7fb_EBEE_public.png r1 manage 17.5 K 2012-03-02 - 02:53 VladlenTimciuc di-electron mass resolution for EBEE
PNGpng dimuon-mass1089-RhoPhi.png r1 manage 80.7 K 2012-03-06 - 12:36 AlexanderLanyov Dimuon 1089 GeV event display rho-phi
PNGpng dimuon-mass1089-RhoZ.png r1 manage 58.7 K 2012-03-06 - 12:36 AlexanderLanyov Dimuon 1089 GeV event display rho-z
PNGpng dimuon-mass1107-RhoPhi.png r1 manage 79.7 K 2012-03-06 - 12:37 AlexanderLanyov Dimuon 1107 GeV event display rho-phi
PNGpng dimuon-mass1107-RhoZ.png r1 manage 57.4 K 2012-03-06 - 12:38 AlexanderLanyov Dimuon 1107 GeV event display rho-z
PNGpng dimuon-mass1256-RhoPhi.png r1 manage 81.0 K 2012-03-06 - 12:38 AlexanderLanyov Dimuon 1256 GeV event display rho-phi
PNGpng dimuon-mass1256-RhoZ.png r1 manage 58.5 K 2012-03-06 - 12:38 AlexanderLanyov Dimuon 1256 GeV event display rho-z
PNGpng dimuon-mass1379-RhoPhi.png r1 manage 89.6 K 2012-03-06 - 12:39 AlexanderLanyov Dimuon 1379 GeV event display rho-phi
PNGpng dimuon-mass1379-RhoZ.png r1 manage 57.9 K 2012-03-06 - 12:39 AlexanderLanyov Dimuon 1379 GeV event display rho-z
GIFgif eleMuMassSpectra4700pb.gif r2 r1 manage 67.8 K 2012-03-07 - 11:36 SamHarper e-mu mass spectra
PDFpdf eleMuMassSpectra4700pb.pdf r1 manage 23.3 K 2012-03-07 - 11:37 SamHarper e-mu mass spectra e-mu mass spectra e-mu mass spectra
GIFgif eleMuMassSpectra5000pb.gif r1 manage 50.8 K 2012-06-11 - 16:31 SamHarper figure 1
PDFpdf eleMuMassSpectra5000pb.pdf r1 manage 35.1 K 2012-06-11 - 16:31 SamHarper figure 1
PDFpdf emuPlotLS_prelim.pdf r1 manage 20.7 K 2012-03-02 - 15:58 ThomasReis e-mu invariant mass like-sign
PNGpng emuPlotLS_prelim.png r1 manage 45.4 K 2012-03-02 - 16:06 ThomasReis e-mu invariant mass like-sign
PDFpdf emuPlotOS_prelim.pdf r1 manage 23.3 K 2012-03-02 - 15:59 ThomasReis e-mu invariant mass opposite-sign
PNGpng emuPlotOS_prelim.png r1 manage 52.1 K 2012-03-02 - 16:06 ThomasReis e-mu invariant mass opposite-sign
PDFpdf emuPlot_prelim.pdf r1 manage 23.4 K 2012-03-02 - 15:59 ThomasReis e-mu invariant mass
PNGpng emuPlot_prelim.png r1 manage 49.1 K 2012-03-02 - 16:05 ThomasReis e-mu invariant mass
GIFgif limitsCUCD5000pb.gif r1 manage 66.4 K 2012-06-11 - 16:32 SamHarper figure 6
PDFpdf limitsCUCD5000pb.pdf r1 manage 9.0 K 2012-06-11 - 16:32 SamHarper figure 6
GIFgif plot_lhc_ll_4p7fb_cteq6l1_ALL_cms.gif r1 manage 55.2 K 2012-03-01 - 16:09 SamHarper  
GIFgif plot_lhc_ll_4p7fb_cteq6l1_stueck_cms.gif r1 manage 31.4 K 2012-03-01 - 16:09 SamHarper cu cd limit plot
PDFpdf plot_lhc_ll_4p7fb_cteq6l1_stueck_cms.pdf r1 manage 23.5 K 2012-03-01 - 15:07 SamHarper cu cd limit plot
PNGpng tev-167807-428-553377913_RhoPhi.png r1 manage 40.1 K 2012-03-02 - 19:15 AlexanderLanyov Dimuon 1107 GeV event display rho-phi
PNGpng tev-167807-428-553377913_RhoZ.png r1 manage 17.4 K 2012-03-02 - 19:16 AlexanderLanyov Dimuon 1107 GeV event display rho-z
PNGpng tev-171178-112-117297088-RhoPhi.png r1 manage 45.0 K 2012-03-02 - 19:36 AlexanderLanyov Dimuon 1089 GeV event display rho-phi
PNGpng tev-171178-112-117297088-RhoZ.png r1 manage 18.9 K 2012-03-02 - 19:36 AlexanderLanyov Dimuon 1089 GeV event display rho-z
PNGpng tev-177053_751646878_506_RhoPhi.png r1 manage 72.4 K 2012-03-01 - 19:59 AlexanderLanyov Dimuon 1256 GeV event display rho-phi
PNGpng tev-177053_751646878_506_RhoZ.png r1 manage 16.1 K 2012-03-01 - 20:08 AlexanderLanyov Dimuon 1256 GeV event display rho-z
PNGpng tev-179547_505584390_319_RhoPhi.png r1 manage 78.9 K 2012-03-01 - 20:09 AlexanderLanyov Dimuon 1379 GeV event display rho-phi
PNGpng tev-179547_505584390_319_RhoZ.png r1 manage 16.5 K 2012-03-01 - 20:10 AlexanderLanyov Dimuon 1379 GeV event display rho-z
GIFgif zprimeLimits_dielectron_4700pb.gif r1 manage 78.8 K 2012-03-01 - 16:10 SamHarper Z' limits in electron channel
PDFpdf zprimeLimits_dielectron_4700pb.pdf r1 manage 56.4 K 2012-03-01 - 15:09 SamHarper Z' limits in electron channel
GIFgif zprimeLimits_dielectron_5000pb.gif r1 manage 81.4 K 2012-06-11 - 16:32 SamHarper figure 5
PDFpdf zprimeLimits_dielectron_5000pb.pdf r1 manage 48.1 K 2012-06-11 - 16:32 SamHarper figure 5
GIFgif zprimeLimits_dilepton_5000pb.gif r2 r1 manage 85.3 K 2012-06-11 - 16:32 SamHarper figure 5
PDFpdf zprimeLimits_dilepton_5000pb.pdf r2 r1 manage 50.6 K 2012-06-11 - 16:32 SamHarper figure 5
GIFgif zprimeLimits_dimuon_5000pb.gif r2 r1 manage 56.1 K 2012-03-02 - 10:58 SamHarper Z' limits in muon channel
PDFpdf zprimeLimits_dimuon_5000pb.pdf r1 manage 59.2 K 2012-03-01 - 16:12 SamHarper Z' limits in muon channel
GIFgif zprimeLimits_dimuon_5300pb.gif r1 manage 81.6 K 2012-06-11 - 16:32 SamHarper figure 5
PDFpdf zprimeLimits_dimuon_5300pb.pdf r1 manage 51.1 K 2012-06-11 - 16:32 SamHarper figure 5
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