CDF Logo Search for vector bosons produced in association with Upsilons
using the full CDF dataset

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The production of the Upsilon (1S) meson in association with a vector boson is a rare process with a standard model cross section predicted to be outside the range of sensitivity at the Tevatron. Observation of this process could signify problems with the current non-relativistic QCD models used for the cross section calculation, or it might signify a contribution from new physics models. We perform a first search for this process using the full 9.7 fb-1 of Run 2 data collected by CDF, using the Υ → μμ decay together with the charged lepton decay modes of the W and Z bosons. In these purely leptonic decay channels, we observe one Υ + W candidate over an expected background of 1.2 ± 0.5 events, and one Υ + Z candidate over an expected background of 0.1 ± 0.1 events. Having not seen evidence for Υ + W/Z production we calculate cross section limits at 1.96 TeV. These are the best cross section limits for this process, and also provide a guide to limits on new physics processes producing an Υ + W/Z.


Data and signal MC samples

We use the high-pT electron triggered dataset and high-pT muon triggered dataset for the main analysis. We also use the upsilon trigger dataset for the estimation of the fake W/Z background. The signal MC is generated using MadGraph + Pythia.

Event Selection

Events are required to have an upsilon candidate: two opposite-charged low-pT (< 15 GeV) muons, 7 GeV/c² < dimuon mass < 13 GeV/c². The dimuon mass spectra of the upsilon trigger dataset are shown below.

.png .eps .pdf

The selection cuts of Υ + W are
  • An upsilon 1S candidate (9.25 GeV/c² < dimuon mass < 9.65 GeV/c²)
  • Exactly one additional high-pT (> 20 GeV) isolated electron or muon
  • The high-pT lepton is triggerable
  • Missing ET > 20 GeV
  • Transverse mass of W candidate in the range 50 - 90 GeV/c²
The missing ET and transverse mass distributions for Υ + W, W → lν are shown below.

.png .eps .pdf 
.png .eps .pdf 

The selection cuts of Υ + Z are
  • An upsilon 1S candidate
  • Exactly two additional high-pT (> 15 GeV) isolated electrons or muons
  • One of the high-pT leptons is triggerable with pT > 20 GeV
  • Opposite charge
  • Dilepton mass in the range 76 - 106 GeV/c²
The dilepton mass distributions for Υ + Z, Z → ll are shown below.

.png .eps .pdf 

Background estimation

The fake Υ + real W/Z background is estimated using the sideband regions of the dimuon mass spectra. The real Υ + fake W/Z is estimated using jet candidates that satisfy relaxed lepton identification criteria.

Systematic uncertainties

The systematic uncertainties of the signal acceptance are shown in the table below.

.png .tex

Expected and observed events

We observe one Υ + W candidate over an expected background of 1.2 ± 0.5 events, and one Υ + Z candidate over an expected background of 0.1 ± 0.1 events.

.png .tex

Event Display

The event display of the Υ + Z candidate is shown below.

.png .pdf


We set 95% C.L. cross section limits.

.png .tex

Supporting Documents:

  • More details are provided in the public note

    General Remarks:

  • Please contact us if you have any questions

     Updated by Chen Zhou
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    Last updated: Dec 4 2013.