Search for production of an Upsilon(1S) meson in association with a W or Z boson using the full 1.96 TeV proton anti-proton collision data set at CDF

Abstract

Production of the Upsilon(1S) meson in association with a vector boson is a rare process in the standard model with a cross section predicted to be below the sensitivity of the Tevatron. Observation of this process could signify contributions not described by the standard model or reveal limitations with the current non-relativistic quantum-chromodynamic models used to calculate the cross section. We perform a search for this process using the full Run II data set collected by the CDF II detector corresponding to an integrated luminosity of 9.4/fb. The search considers the Upsilon(1S) to di-muon decay and the decay of the W and Z bosons into muons and electrons. In these purely leptonic decay channels, we observe one Upsilon(1S)W candidate with an expected background of 1.2 +/- 0.5 events, and one Upsilon(1S)Z candidate with an expected background of 0.1 +/- 0.1 events. Both observations are consistent with the predicted background contributions. The resulting upper limits on the cross section for Upsilon(1S)+W/Z production are the most sensitive reported from a single experiment and place restrictions on potential contributions from non-standard-model physics.

Figures (5)

• Figure 1: Dimuon invariant-mass spectrum in CDF II data from events contained within the low-$p_T$ dimuon-triggered sample. Shown are the defined $\Upsilon$ signal region and the sideband regions used for background determination.
• Figure 2: Missing-transverse-energy distributions predicted for signal $\Upsilon + (W \rightarrow \ell\nu)$ events. The distributions are shown for events that satisfy all other event requirements. The scale of the vertical axis is arbitrary.
• Figure 3: Transverse-mass distributions predicted for signal $\Upsilon + (W \rightarrow \ell\nu)$ events. The distributions are shown for events that satisfy all other event requirements. The scale of the vertical axis is arbitrary.
• Figure 4: Dilepton invariant-mass distribution predicted for signal $\Upsilon + (Z \rightarrow \ell\ell)$ events. The distribution is shown for events that satisfy all other event requirements. The scale of the vertical axis is arbitrary.
• Figure 5: Event display of the observed $\Upsilon Z$ candidate, showing the muon candidates identified from the $\Upsilon$ and $Z$ decays. The view is in the transverse ($r - \phi$) plane of the detector, where the inner core is the silicon vertex tracker, and the larger circle is the outer radius of the drift chamber where the tracks of charged particle with $p_T > 1.5\,{\rm GeV}/c$ are shown. The height of the surrounding pink and blue "towers" is roughly proportional to the energy deposits in the electromagnetic and hadronic compartments of the calorimeter, from which the $\hbox{$E\hbox{/}_{T}$}$ magnitude and direction (red arrow) is computed. Measurement-hits in the muon chambers are shown in the outermost box-shaped structure.