This is public page of the Oxford High Mass Di-Electron Analysis using the CDF II detector
Authors: Joel Goldstein, Sam Harper and Peter Renton
The analysis is an 820pb inclusive search for X->ee where X has a mass between 150 GeV and 950 GeV. Both the central (|eta|<1.1) and plug (1.2<|eta|<3.0) detectors were used and events were required to either be central-central or central-plug. The selection cuts used can be found here. Some plots are especially suitable for summarizing the analysis results, these are marked as such.
spin-1 acceptance x efficiency: .gif .eps
spin-2 acceptance x efficiency: .gif .eps
log plots 50-500 GeV:
integral plots 50-500 GeV:
Speakers: be aware that the probability in these probability spectra is the probability for the bkg to fluctuate to the level of the data or higher. It is calculated using Poisson statistics. This calculation is performed in a mass window equal to the resolution of a narrow Z' at that mass point. By narrow, I mean that the detector resolution dominates the width. Now given that we are searching from 150-950 (only up to 550 GeV is shown because there are no data events past 500 and all you get is a flat line at 1), the 2E-3 probability that is observed happens somewhere in the mass spectrum in 19% of pseudo-experiments. The 3 sigma line corresponds to the probability where that probability or lower occurs in just 0.3% of the pseudo-experiments. Systematics are incorporated into the plot by taking the average of the probabilities of all possible background expectations weighted by a Gaussian with mean = bkg expectation and sigma = bkg error.
probability spectrum: .gif .eps
typical pseudo-experiment: .gif .eps
typical pseudo-experiment with 250 GeV Z' with sigma.Br = 0.1pb .gif .eps
Spin-1 (Z')
Expected spin-1 limits (no systematic errors) :
Expected spin-1 limits (with systematic errors) :
SM-like Z' limits (best for conferences) : with mass limits on
SM-like Z' : exclude Mz < 850 GeV
Spin-2 (RS Graviton)
Speakers: Please be aware that σ.Br(G->ee) is defined as σ.Br(G->ee) in the mass window of +/- 10% of the resonance mass, eg for a 500 GeV graviton, the limit is on the σ.Br(G->ee) from 450-550 GeV. This is the default option in HERWIG due to concerns about the accuracy of cross-section far away from the resonance (the cross-section violates unitary for one). Also the quoted limits are for k/Mpl = 0.1. If k/Mpl=0.01 is chosen, the limits will be slightly lower at low masses and higher at high masses due to the narrower width.
|
k/Mpl |
Excluded Graviton Mass (GeV) |
| 0.01 | 230 |
| 0.025 | 431 |
| 0.05 | 629 |
| 0.07 | 700 |
| 0.1 | 764 |
limit plots with model lines overlaid
comparison of limits with and without systematic errors
comparison of the limits from each channel
The highest mass event found was a central-central event with mass = 491GeV : COT CAL
The systematic uncertainties were taken to be the following. PDF errors are not shown as cannot be easily expressed as a single number. The PDF error was obtained by reweighting the Monte Carlo with the fluctuated eigenvectors of the CTEQ PDF.
The Randall-Sundrum Graviton branching ratio to photons is twice that of leptons. As such the di-photon analysis done by T. Berry (University of Liverpool, UK), R Culbertson (Fermilab) and S-M Wynne (University of Liverpool, UK) was combined with the di-electron analysis to produce stronger limits on RS Graviton production.
|
k/Mpl |
Excluded Graviton Mass (GeV) |
| 0.01 | 242 |
| 0.025 | 568 |
| 0.05 | 750 |
| 0.07 | 810 |
| 0.1 | 875 |
