CDF Logo Model-Independent search for high-mass narrow resonances in the dielectron channel at CDF Exotics Logo
Based on 2.5 fb-1 of ppbar collision data collected with the Collider Detector at Fermilab II detector at the Fermilab Tevatron at sqrt(s)=1.96 TeV, we report on a search for high-mass resonances in the e+e- channel. The most significant region of excess of data over background occurs for an e+e- invariant mass window of 240 GeV/c2, and is 3.8 standard deviations above the standard model prediction. The probability of observing a background fluctuation with significance (S/&sigmaB) equal to or greater than 3.8 anywhere in the mass range of 150-1,000 GeV/c2 is about 0.6%, corresponding to a 2.5 &sigma significance. The upper limits on &sigma&Gamma(X->ee) at 95% confidence level, where the X's are spin-1 or spin-2 particles, exclude the standard model coupling Z' and the Randall-Sundrum graviton for k/MPl=0.1 with masses below 966 and 850 GeV/c2, respectively.

Plots and Tables

Invariant mass distribution
Invariant mass distribution of dielectron data compared to the expected backgrounds, shown on a log scale. Red dots with error bars are data. The blue shaded region is ``Other SM'' background, the green region is ``QCD'' background, and the white region is "Drell-Yan" background. The inset shows the same for the 240 GeV/c2 region using a linear scale. EPS or GIF.
(data-prediction)/uncertainty as function of dielectron mass. EPS or GIF.
Event Display
Typical dielectron event display. COT View (EPS or GIF). CAL View (EPS or GIF).
Resonances Search
The dielectron resonances search in the high-mass range of 150-1,000 GeV/c2 is performed with an unbinned likelihood ratio (&lambda) with a floating mass. The most significant deviation between data and the SM prediction, which is the maximum -2log&lambda is 14.38 at 241.3 GeV/c2. The S/&sigmaB corresponding to the region of maximum -2log&lambda is calculated by counting the number of observed events and estimated backgrounds and it is 3.8. EPS or GIF.
To estimate the probability of observing an excess equal to or greater than the maximum observed excess anywhere in the search range of 150-1,000 GeV/c2, we run 100,000 background only simulated events. The maximum -2log&lambda anywhere in the search range is recorded in each simulated event. The probability of observing an equal or greater excess anywhere in the 150-1,000 GeV/c2 mass range is defined as the fraction of simulated events with an equal to or greater than maximum -2log&lambda that shown in real data, which is 14.38 in this analysis and it is found to be 0.6%. The 0.6% probability stands for a 2.5 &sigma significance. EPS or GIF.
Limits (Spin-1, SM-like and E6Z's)
SM-like Z' with mass below 966 GeV/c2 is excluded.
Z' Model Z'SM Z'&psi Z'&chi Z'&eta Z'I Z'sq Z'N
Exp. Limit (GeV/c2) 965 849 860 932 757 791 834
Obs. Limit (GeV/c2) 966 853 864 933 737 800 840
EPS or GIF.
Limits (Spin-2, Randall-Sundrum gravitons)
RS graviton with mass below 850 GeV/c2 for k/MPl=0.1 is excluded. EPS or GIF.
k/MPl vs. RS mass. EPS or GIF.