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Authors Julien Donini, Tommaso Dorigo, Mia Tosi University of Padova and INFN Kenichi Hatakeyama Rockefeller University Christopher Neu, Daniel Whiteson University of Pennsilvania Shawn Kwang, Melvin Shochet University of Chicago Tomonobu Tomura University of Tsukuba |
We present a measurement of the energy scale of b-jets using the Z → bbbar signal based on 584 pb-1 of CDF Run II data.
We extract a signal of 5674 ± 448(stat.) Z → bbbar decays in low-radiation central dijet events.
We measure, using an unbinned likelihood technique, a b-jet energy scale factor of
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Kinematical distributions (data) Jet Et distributions for the two leading jets in experimental data before and after event selection (two leading jets with Et > 22 GeV and |η|<1.0). |
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Kinematical distributions (data and MC) Additional kinematical characteristics of double tagged data. Left: Et of third jet for data (red histogram) and Z→bb MC (blue histogram). Right: azimuthal difference (ΔΦ) between the leading two jets for data and MC. |
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Optimization of kinematical cuts Expected uncertainty on the jet energy scale factor returned by pseudo-experiments as a function of the cut on third jet Et (left plot) or the ΔΦ azimuthal angle between the two leading used to select the signal region (right plot). |
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Signal PDF Dijet mass probability density function for Z→bb MC signal for 20 different values of scale factor, ranging from 0.9 to 1.09. |
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Background template Data-driven background dijet mass distribution (red dots) fit with a parameterization (black line). |
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Test of fitting procedure (1) Pull mean (left plot) and pull sigma (right plot) on fitted b-jet energy scale factor as a function of the input scale factor. |
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Test of fitting procedure (2) Pull mean (left plot) and pull sigma (right plot) on number of events of fitted signal as a function of the input scale factor. |
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Sideband fits Result of fit to the dijet mass sideband regions (mjj<60 GeV || mjj>120 GeV) of selected data with different background models. Fit Χ2 is shown as a function of the kinematical variables (ΔΦ between leading two jets and Et of third jet) that define each different background models. |
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Final result Result of constrained unbinned likelihood fit performed to double tagged dijets data (blue points). A 4630 ± 727 Gaussian constraint on fitted number of events of signal is applied. The data-driven background shape and Monte-Carlo signal p.d.f are shown respectively in green and red. The fit returns 5674 ± 448 events of signal and a b-JES of 0.974 ± 0.011. The inset on the upper right shows the data minus background distribution (blue points) and the signal shape (in red) normalized to the fitted number of events of signal. |
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Additional plots Result of constrained likelihood fit performed on a smaller 50-200 GeV dijet mass window (left plot). Result of unconstrained fit (right plot). |
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| Statistics of analyzed data |
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Signal acceptance Breakdown of all sources of uncertainty on the expexted number of signal events. |
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MC acceptance Fraction of expected Z→bb, Z→cc and W→cs events in signal region and background regions, for double tagged events (++) and taggable events (00). |
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Systematic uncertainties Systematic uncertainies on fitted b-jet energy scale and number of events of signal. |
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Other systematics Other sources of systematic uncertainies. |
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